bluuebunny/crossref_metadata_2025 huggingface dataset:
Palmitate movement across red and white muscle membranes of rainbow trout
Authors: Richards Jeff G. , Bonen Arend , Heigenhauser George J. F. , Wood Chris M.
Published: January 2004

We examined the movement of [3H]palmitate across giant sarcolemmal vesicles prepared from red and white muscle of rainbow trout ( Oncorhynchus mykiss). Red and white muscle fatty acid carriers have similar affinities for palmitate (apparent Km= 26 ± 6 and 33 ± 8 nM, respectively); however, red muscle has a higher maximal uptake compared with white muscle ( Vmax= 476 ± 41 vs. 229 ± 23 pmol·mg protein-1·s-1, respectively). Phloretin (250 μM) inhibited palmitate influx in red and white muscle vesicles by ∼40%, HgCl2(2.5 mM) inhibited palmitate uptake by 20-30%, and the anion-exchange inhibitor DIDS (250 μM) inhibited palmitate influx in red and white muscle vesicles by ∼15 and 30%, respectively. Western blot analysis of red and white muscle vesicles did not detect a mammalian-type fatty acid transporter (FAT); however, preincubation of vesicles with sulfo- N-succinimidyloleate, a specific inhibitor of FAT in rats, reduced palmitate uptake in red and white muscle vesicles by ∼15 and 25%, respectively. A mammalian-type plasma membrane fatty acid-binding protein was identified in trout muscle using Western blotting, but the protein differed in size between red and white muscle. At low concentrations of free palmitate (2.5 nM), addition of high concentrations (111 μM total) of oleate (18:0) caused ∼50% reduction in palmitate uptake by red and white muscle vesicles, but high concentrations (100 μM) of octanoate (8:0) caused no inhibition of uptake. Five days of aerobic swimming at ∼2 body lengths/s and 9 days of chronic cortisol elevation in vivo, both of which stimulate lipid metabolism, had no effect on the rate of palmitate movement in red or white muscle vesicles.
Inactivation of the DMH selectively inhibits the ACTH and corticosterone responses to hypoglycemia
Authors: Evans Scott B. , Wilkinson Charles W. , Gronbeck Pam , Bennett Jennifer L. , Zavosh Aryana , Taborsky Gerald J. , Figlewicz Dianne P.
Published: January 2004

We have previously reported that repeated bouts of insulin-induced hypoglycemia (IIH) in the rat result in blunted activation of the paraventricular, arcuate, and dorsomedial hypothalamic (DMH) nuclei. Because DMH activation has been implicated in the sympathoadrenal and hypothalamic-pituitary-adrenal (HPA) responses to stressors, we hypothesized that its blunted activation may play a role in the impaired counterregulatory response that is also observed with repeated bouts of IIH. In the present study, we evaluated the role of normal DMH activation in the counterregulatory response to a single bout of IIH. Local infusion of lidocaine ( n = 8) to inactivate the DMH during a 2-h bout of IIH resulted in a significant overall decrease of the ACTH response and a delay of onset of the corticosterone response compared with vehicle-infused controls ( n = 9). We observed suppression of the ACTH response at time ( t) = 90 and 120 min (50 ± 12 and 63 ± 6%, respectively, of control levels) and early suppression of the corticosterone response at t = 30 min (59 ± 13% of the control level). The epinephrine, norepinephrine, and glucagon responses were not altered by DMH inactivation. Our finding suggests that DMH inactivation may play a specific role in decreasing the HPA axis response after repeated bouts of IIH.
Fluoxetine-induced changes in body weight and 5-HT1Areceptor-mediated hormone secretion in rats on a tryptophan-deficient diet
Authors: D'Souza D. N. , Zhang Y. , Garcia F. , Battaglia G. , Van de Kar L. D.
Published: January 2004

Tryptophan depleting protocols are commonly used to study the role of serotonin in mood disorders. The present study examined the impact of a tryptophan-deficient diet and fluoxetine on the serotonergic regulation of neuroendocrine function and body weight. We hypothesized that the regulation of postsynaptic 5-HT1Areceptors is dependent on the levels of 5-HT in the synapse. Rats on a control or a tryptophan-deficient diet received daily injections of saline or fluoxetine (5 or 10 mg·kg-1·day-1ip) from day 7 to day 21. The tryptophan-deficient diet produced a 41% reduction in the level of 5-HT but no change in the density of [3H]paroxetine-labeled 5-HT transporters. Treatment with fluoxetine inhibited the gain in weight in rats maintained on the control diet. The tryptophan-deficient diet produced a significant loss in body weight that was not significantly altered by treatment with fluoxetine. Treatment with fluoxetine produced a dose-dependent desensitization of hormone responses to injection of the 5-HT1Areceptor agonist (±)8-hydroxy-2-(di- n-propylamino)tetralin ((±)8-OH-DPAT). The tryptophan-deficient diet produced an increase in the basal levels of corticosterone but did not alter the basal levels of ACTH or oxytocin. Also, this diet inhibited the magnitude of 8-OH-DPAT-induced increase in plasma levels of ACTH and oxytocin but did not impair the ability of fluoxetine to desensitize the 5-HT1Areceptor-mediated increase in plasma hormones. These data suggest that a reserve of 5-HT enables fluoxetine to desensitize postsynaptic 5-HT1Areceptors in the hypothalamus. In conclusion, the profound physiological changes induced by tryptophan depletion may complicate the interpretation of studies using this experimental approach.
Regulation of hepatic glucose metabolism by leptin in pig and rat primary hepatocyte cultures
Authors: Raman Priya , Donkin Shawn S. , Spurlock Michael E.
Published: January 2004

Direct effects of leptin on gluconeogenesis in rat hepatocytes are equivocal, and model systems from other species have not been extensively explored in assessing the regulation of glucose metabolism by leptin. Therefore, the goal of the present study was to compare the effects of leptin on gluconeogenesis in pig and rat hepatocyte cultures as well as to investigate an underlying mechanism of action at the level of phospho enolpyruvate carboxykinase (PEPCK). In rat hepatocytes, leptin exposure (3 h, 50 and 100 nM) attenuated glucagon-stimulated hepatic gluconeogenesis by 35 and 38% ( P < 0.05), respectively. However, leptin did not produce any significant acute effect in pig hepatocytes. Leptin exposure for 24 h failed to produce any significant effect on gluconeogenesis in either rat or pig hepatocytes cultured in the presence of glucagon or dexamethasone. Mechanistically, there was a 25-35% decrease ( P < 0.05) in glucagon-induced PEPCK mRNA levels in rat but not pig hepatocytes cultured with leptin. This effect on PEPCK mRNA was not due to an alteration in the relative abundance of the leptin receptor or the ability of PEPCK to respond to cAMP. The nonuniformity of the effects of leptin on gluconeogenesis in pig and rat hepatocytes indicates differences in leptin action between species. Furthermore, the unique action of leptin in porcine hepatocytes points to the utility of this model system for biomedical research and also underscores the value of comparative studies.
Hemodynamic effects of blood loss during a passive response to a stressor in the conscious rabbit
Authors: Schadt James C. , Hasser Eileen M.
Published: January 2004

In the conscious rabbit, exposure to an air jet stressor increases arterial pressure, heart rate, and cardiac output. During hemorrhage, air jet exposure extends the blood loss necessary to produce hypotension. It is possible that this enhanced defense of arterial pressure is a general characteristic of stressors. However, some stressors such as oscillation (OSC), although they increase arterial pressure, do not change heart rate or cardiac output. The cardiovascular changes during OSC resemble those seen during freezing behavior. In the present study, our hypothesis was that, unlike air jet, OSC would not affect defense of arterial blood pressure during blood loss. Male New Zealand White rabbits were chronically prepared with arterial and venous catheters and Doppler flow probes. We removed venous blood until mean arterial pressure decreased to 40 mmHg. We repeated the experiment in each rabbit on separate days in the presence and absence (SHAM) of OSC. Compared with SHAM, OSC increased arterial pressure 14 ± 1 mmHg, central venous pressure 3.3 ± 0.4 mmHg, and hindquarter blood flow 34 ± 4% while decreasing mesenteric conductance 32 ± 3% and not changing heart rate or cardiac output. During normotensive hemorrhage, OSC enhanced hindquarter and renal vasoconstriction. Contrary to our hypothesis, OSC (23.5 ± 0.6 ml/kg) increased the blood loss necessary to produce hypotension compared with SHAM (16.8 ± 0.6 ml/kg). In nine rabbits, OSC prevented hypotension even after a blood loss of 27 ml/kg. Thus a stressful stimulus that resulted in cardiovascular changes similar to those seen during freezing behavior enhanced defense of arterial pressure during hemorrhage.
Divergent gonadotropin-gonadal dose-responsive coupling in healthy young and aging men
Authors: Keenan Daniel M. , Veldhuis Johannes D.
Published: January 2004

The present study extends a recent composite model of in vivo interglandular signaling to assess the impact of age on 1) nonequilibrium exchange among diffusible and protein-bound testosterone (Te); 2) elimination of total and free Te; 3) basal and pulsatile Te secretion (sec); 4) the implicit feedforward function mediating luteinizing hormone (LH) concentration (con) drive of instantaneous Te sec; and 5) possible stochastic variability of the predicted LH con-Te sec dose-response linkage. To this end, we measured LH and Te con every 10 min for 24 h in healthy young ( n = 13) and older men ( n = 13). Statistical comparisons of analytic estimates revealed that elderly subjects manifest 1) reduced maximal burstlike LH-stimulated Te sec (impaired stimulus efficacy); 2) depressed half-maximally LH-stimulated Te sec (lower Leydig-cell responsivity); 3) decreased pulsatile and total Te sec; 4) elevated basal Te sec; 5) a prolonged half-life of total but not free Te con; and 6) delayed time evolution of LH and Te sec bursts. In contradistinction, age did not influence estimated LH-pulse potency (ED50), steroidogenic sensitivity (slope term), or stochastic variability of LH-Te coupling. On the basis of these data, we postulate that aging in the human male alters specific dose-response attributes linking LH con and Te sec and disrupts the time waveform of LH and Te sec bursts.
Temperature dependence of the Ca2+-ATPase (SERCA2) in the ventricles of tuna and mackerel
Authors: Landeira-Fernandez Ana M. , Morrissette Jeffery M. , Blank Jason M. , Block Barbara A.
Published: January 2004

Recent physiological studies on the cardiovascular performance of tunas suggest that the elevated heart rates of these fish may rely on increased use of intracellular sarcoplasmic reticulum (SR) Ca2+stores. In this study, we compare the cellular cardiac performance in endothermic tunas (bluefin, albacore, yellowfin) and their ectothermic sister taxa (mackerel) in response to acute temperature change. The cardiac sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2) plays a major role during cardiac excitation-contraction (E-C) coupling, transporting Ca2+from the cytosol into the lumen of the SR and thus promoting the relaxation of the muscle. Measurements of oxalate-supported Ca2+uptake in SR-enriched ventricular vesicles indicated that tunas were capable of sustaining a rate of Ca2+uptake that was significantly higher than the mackerel. Among tunas, the cold-tolerant bluefin had the highest rates of SR Ca2+uptake and ATPase activity. The differences among Ca2+uptake and ATP hydrolysis rates do not seem to result from intrinsic differences between the SERCA2 present in the different tunas, as shown by their similar temperature sensitivities and similar values for activation energy. Western blots reveal that increased SERCA2 protein content is associated with the higher Ca2+uptake and ATPase activities seen in bluefin ventricles compared with albacore, yellowfin, and mackerel. We hypothesize that a key step in the evolution of high heart rate and high metabolic rate in tunas is increased activity of the SERCA2 enzyme. We also suggest that high levels of SERCA2 in bluefin tuna hearts may be important for retaining cardiac function at cold temperatures.
Skin surface cooling improves orthostatic tolerance in normothermic individuals
Authors: Durand S. , Cui J. , Williams K. D. , Crandall C. G.
Published: January 2004

Previous studies suggest that skin surface cooling (SSC) preserves orthostatic tolerance; however, this hypothesis has not been experimentally tested. Thus the purpose of this project was to identify whether SSC improves orthostatic tolerance in otherwise normothermic individuals. Eight subjects underwent two presyncope limited graded lower-body negative pressure (LBNP) tolerance tests. On different days, and randomly assigned, LBNP tolerance was assessed under control conditions and during SSC (perfused 16°C water through tube-lined suit worn by each subject). Orthostatic tolerance was significantly elevated in each individual due to SSC, as evidenced by a significant increase in a standardized cumulative stress index (normothermia 564 ± 58 mmHg·min; SSC 752 ± 58 mmHg·min; P < 0.05). At most levels of LBNP, blood pressure during the SSC tolerance test was significantly greater than during the control test. Furthermore, the reduction in cerebral blood flow velocity was attenuated during some of the early stages of LBNP for the SSC trial. Plasma norepinephrine concentrations were significantly higher during LBNP with SSC, suggesting that SSC may improve orthostatic tolerance through increased sympathetic activity. These data demonstrate that SSC is effective in improving orthostatic tolerance in otherwise normothermic individuals.
Anorectic actions of prolactin-releasing peptide are mediated by corticotropin-releasing hormone receptors
Authors: Lawrence Catherine B. , Liu Yong-Ling , Stock Michael J. , Luckman Simon M.
Published: January 2004

Prolactin-releasing peptide (PrRP) reduces food intake and body weight and modifies body temperature when administered centrally in rats, suggesting a role in energy homeostasis. However, the mediators of PrRP's actions are unknown. The present study, therefore, first examined the possible involvement of the anorectic neuropeptides corticotropin-releasing hormone (CRH) and the melanocortins (e.g., α-melanocyte-stimulating hormone) in PrRP's effects on food intake and core body temperature and, second, determined if PrRP affects energy expenditure by measuring oxygen consumption (V̇o2). Intracerebroventricular injection of PrRP (4 nmol) to 24-h-fasted male Sprague-Dawley rats decreased food intake and modified body temperature. Blockade of central CRH receptors by intracerebroventricular coadministration of the CRH receptor antagonist astressin (20 μg) reversed the PrRP-induced reduction in feeding. However, astressin's effect on PrRP-induced changes in body temperature was complicated because the antagonist itself caused a slight rise in body temperature. In contrast, intracerebroventricular coadministration of the melanocortin receptor-3/4 antagonist SHU-9119 (0.1 nmol) had no effect on any of PrRP's actions. Finally, intracerebroventricular injection of PrRP (4 nmol) caused a significantly greater V̇o2 over a 3-h test period compared with vehicle-treated rats. These results show that the anorectic actions of PrRP are mediated by central CRH receptors but not by melanocortin receptors-3/4 and that PrRP can modify V̇o2.
Dbh(-/-) mice are hypotensive, have altered circadian rhythms, and have abnormal responses to dieting and stress
Authors: Swoap Steven J. , Weinshenker David , Palmiter Richard D. , Garber Graham
Published: January 2004

We used mice deficient in dopamine β-hydroxylase [ Dbh(-/-)] and their littermate controls [ Dbh(+/-)] to examine the role of epinephrine (Epi) and norepinephrine (NE) in the maintenance of cardiovascular parameters during 7 days of caloric restriction and acute exposure to environmental stress. Cardiovascular parameters of the mice were monitored using blood pressure radiotelemeters at an ambient temperature of 29°C. Under normal conditions, Dbh(-/-) mice had a low heart rate, were severely hypotensive, and displayed an attenuated circadian blood pressure rhythm. Upon 50% caloric restriction, Dbh(+/-) mice exhibited decreases in heart rate and mean blood pressure. However, the blood pressures of Dbh(-/-) mice did not fall significantly in response to caloric restriction, and the bradycardia associated with caloric restriction was attenuated in these mice. In response to an open-field test, the blood pressure and heart rate of Dbh(+/-) mice increased substantially and rapidly, whereas Dbh(-/-) mice had blunted changes in blood pressures and no change in heart rate. These data suggest a primary role of Epi and NE in mediating the hypotension induced by dieting. Furthermore, Epi and NE play a smaller, but still significant, role in the bradycardia induced by caloric restriction. In contrast, Epi and NE are required for the tachycardia in an open field but are not required for the increase in blood pressure.
Late-gestation betamethasone enhances coronary artery responsiveness to angiotensin II in fetal sheep
Authors: Roghair Robert D. , Lamb Fred S. , Bedell Kurt A. , Smith Oliva M. , Scholz Thomas D. , Segar Jeffrey L.
Published: January 2004

Antenatal glucocorticoids are used to promote the maturation of fetuses at risk for preterm delivery. While perinatal glucocorticoid exposure has clear immediate benefits to cardiorespiratory function, there is emerging evidence of adverse long-term effects. To determine if antenatal betamethasone alters vascular reactivity, we examined isometric contraction of endothelium-intact coronary and mesenteric arteries isolated from twin fetal sheep at 121-124 days gestation (term being 145 days). One twin received betamethasone (10 μg/h iv) while the second twin received vehicle (0.9% NaCl) for 48 h immediately before the final physiological measurements and tissue harvesting. Fetuses that received betamethasone had higher mean arterial blood pressures than the saline-treated twin controls (53 ± 1 vs. 48 ± 1 mmHg, P < 0.05). Coronary vessels from betamethasone-treated fetuses exhibited enhanced peak responses to ANG II (72 ± 17 vs. 23 ± 6% of the maximal response to 120 mM KCl, P < 0.05). There was no significant difference in response of the coronary arteries to other vasoactive compounds [KCl, U-46619, sodium nitroprusside, 8-bromo-cGMP (8-BrcGMP), isoproterenol, and forskolin]. Contractile responses to ANG II were similar in betamethasone and control mesenteric arteries (48 ± 17 vs. 36 ± 12% of the maximal response to 10-6M U-46619). Western blot analysis revealed AT1receptor protein expression was increased by betamethasone in coronary but not in mesenteric arteries. These findings demonstrate that antenatal betamethasone exposure enhances coronary but not mesenteric artery vasoconstriction to ANG II by selectively upregulating coronary artery AT1receptor protein expression.
Sensory nerves contribute to insulin secretion by glucagon-like peptide-1 in mice
Authors: Ahrén Bo
Published: January 2004

It has been hypothesized that the potent insulinotropic action of the gut incretin hormone glucagon-like peptide-1 (GLP-1) is exerted not only through a direct action on the beta cells but may be partially dependent on sensory nerves. We therefore examined the influence of GLP-1 in mice rendered sensory denervated by neonatal administration of capsaicin performed at days 2 and 5 (50 mg/kg). Control mice were given vehicle. Results show that at 10-16 wk of age in control mice, intravenous GLP-1 at 0.1 or 10 nmol/kg augmented the insulin response to intravenous glucose (1 g/kg) in association with improved glucose elimination. In contrast, in capsaicin-pretreated mice, GLP-1 at 0.1 nmol/kg could not augment the insulin response to intravenous glucose and no effect on glucose elimination was observed. Nevertheless, at the high dose of 10 nmol/kg, GLP-1 augmented the insulin response to glucose in capsaicin-pretreated mice as efficiently as in control mice. The insulin response to GLP-1 from isolated islets was not affected by neonatal capsaicin, and, furthermore, the in vivo insulin response to glucose was augmented whereas that to arginine was not affected by capsaicin. It is concluded that GLP-1-induced insulin secretion at a low dose in mice is dependent on intact sensory nerves and therefore indirectly mediated and that this distinguishes GLP-1 from other examined insulin secretagogues.
Jejunal administration of linoleic acid increases activity of neurons in the paraventricular nucleus of the hypothalamus
Authors: Randich Alan , Chandler Paula C. , Mebane Hannah C. , Turnbach Meredith E. , Meller Stephen T. , Kelm Gary R. , Cox James E.
Published: January 2004

The present experiment examined whether neurons located in the paraventricular nucleus of the hypothalamus (PVN) respond to intestinal infusions of long-chain fatty acids. Single-unit recordings were made of neurons located in and adjacent to the PVN during jejunal administration of linoleic acid. Jejunal administration of linoleic acid increased single-unit activity of neurons located in the PVN but did not affect activity of neurons located in adjacent tissue outside the PVN. The largest increases in neuronal activity were observed in the anterior PVN (0.9-1.3 mm posterior to bregma) compared with the posterior PVN (1.8-2.1 mm posterior to bregma). Jejunal administration of saline failed to affect activity of neurons located either inside or outside the PVN. When the same neurons were subsequently tested for their response to intravenous administration of 2 μg/kg of CCK-8, excitatory responses were more frequently observed than inhibitory responses, but both types of responses were observed regardless of whether neurons were located inside or outside the PVN. In addition, there was no strong correlation between the magnitude of the neuronal response evoked by jejunal administration of linoleic acid compared with intravenous CCK-8. These data suggest that neurons located in the anterior PVN may play a role in the mediation of suppression of food intake produced by intestinal administration of lipids.
Neuroprotection by tempol in a model of iron-induced oxidative stress in acute ischemic stroke
Authors: Mehta Shyamal H. , Webb R. Clinton , Ergul Adviye , Tawak Amany , Dorrance Anne M.
Published: January 2004

Studies suggest iron exacerbates the damage caused by ischemic stroke. Our aim was to elucidate the effect of iron overload on infarct size after middle cerebral artery occlusion (MCAO) and to evaluate the efficacy of tempol, a superoxide dismutase mimetic, as a neuroprotective agent. Rats were administered iron ± tempol before MCAO; control rats received saline. The middle cerebral artery was occluded for 24 h, and the size of the resultant infarct was assessed and expressed as the percentage of the hemisphere infracted (%HI). Iron treatment increased infarct size compared with control (51.83 ± 3.55 vs. 27.56 ± 3.28%HI iron treated vs. control, P = 0.01); pretreatment with tempol reversed this (51.83 ± 3.55 vs. 26.09 ± 9.57%HI iron treated vs. iron + tempol treated, P = 0.02). We hypothesized that reactive oxygen species (ROS) were responsible for the iron-induced damage. We measured ROS generated by exogenous iron in brain and peripheral vasculature from rats that had not undergone MCAO. There was no increase in ROS production in the brain of iron-treated rats or in brain slices incubated with iron citrate. However, ROS generation in carotid arteries incubated with iron citrate was significantly increased. ROS generation from the brain was assessed after MCAO by dihydroethidine staining; there was a dramatic increase in the ROS generation by the brain in the iron-treated rats compared with control 30 min after MCAO. We propose that iron-induced ROS generation in the cerebral vasculature adds to oxidative stress during an ischemic episode after the disruption of the blood-brain barrier.
Roles of baroreflex and vestibulosympathetic reflex in controlling arterial blood pressure during gravitational stress in conscious rats
Authors: Gotoh Taro Miyahara , Fujiki Nobuhiro , Matsuda Tomoko , Gao Shuang , Morita Hironobu
Published: January 2004

Gravity acts on the circulatory system to decrease arterial blood pressure (AP) by causing blood redistribution and reduced venous return. To evaluate roles of the baroreflex and vestibulosympathetic reflex (VSR) in maintaining AP during gravitational stress, we measured AP, heart rate (HR), and renal sympathetic nerve activity (RSNA) in four groups of conscious rats, which were either intact or had vestibular lesions (VL), sinoaortic denervation (SAD), or VL plus SAD (VL + SAD). The rats were exposed to 3 G in dorsoventral axis by centrifugation for 3 min. In rats in which neither reflex was functional (VL + SAD group), RSNA did not change, but the AP showed a significant decrease (-8 ± 1 mmHg vs. baseline). In rats with a functional baroreflex, but no VSR (VL group), the AP did not change and there was a slight increase in RSNA (25 ± 10% vs. baseline). In rats with a functional VSR, but no baroreflex (SAD group), marked increases in both AP and RSNA were observed (AP 31 ± 6 mmHg and RSNA 87 ± 10% vs. baseline), showing that the VSR causes an increase in AP in response to gravitational stress; these marked increases were significantly attenuated by the baroreflex in the intact group (AP 9 ± 2 mmHg and RSNA 38 ± 7% vs. baseline). In conclusion, AP is controlled by the combination of the baroreflex and VSR. The VSR elicits a huge pressor response during gravitational stress, preventing hypotension due to blood redistribution. In intact rats, this AP increase is compensated by the baroreflex, resulting in only a slight increase in AP.
Serotonin receptor subtypes required for ventilatory long-term facilitation and its enhancement after chronic intermittent hypoxia in awake rats
Authors: McGuire Michelle , Zhang Yi , White David P. , Ling Liming
Published: January 2004

Respiratory long-term facilitation (LTF), a serotonin-dependent, persistent augmentation of respiratory activity after episodic hypoxia, is enhanced by pretreatment of chronic intermittent hypoxia (CIH; 5 min 11-12% O2-5 min air, 12 h/night for 7 nights). The present study examined the effects of methysergide (serotonin 5-HT1,2,5,6,7 receptor antagonist), ketanserin (5-HT2 antagonist), or clozapine (5-HT2,6,7 antagonist) on both ventilatory LTF and the CIH effect on ventilatory LTF in conscious male adult rats to determine which specific receptor subtype(s) is involved. In untreated rats (i.e., animals not exposed to CIH), LTF, induced by five episodes of 5-min poikilocapnic hypoxia (10% O2) separated by 5-min normoxic intervals, was measured twice by plethysmography. Thus the measurement was conducted 1-2 days before (as control) and ∼1 h after systemic injection of methysergide (1 mg/kg ip), ketanserin (1 mg/kg), or clozapine (1.5 mg/kg). Resting ventilation, metabolic rate, and hypoxic ventilatory response (HVR) were unchanged, but LTF (∼18% above baseline) was eliminated by each drug. In CIH-treated rats, LTF was also measured twice, before and ∼8 h after CIH. Vehicle, methysergide, ketanserin, or clozapine was injected ∼1 h before the second measurement. Neither resting ventilation nor metabolic rate was changed after CIH and/or any drug. HVR was unchanged after methysergide and ketanserin but reduced in four of seven clozapine rats. The CIH-enhanced LTF (∼28%) was abolished by methysergide and clozapine but only attenuated by ketanserin (to ∼10%). Collectively, these data suggest that ventilatory LTF requires 5-HT2 receptors and that the CIH effect on LTF requires non-5-HT2 serotonin receptors, probably 5-HT6 and/or 5-HT7 subtype(s).
Autologous fat transplants influence compensatory white adipose tissue mass increases after lipectomy
Authors: Lacy Eva L. , Bartness Timothy J.
Published: January 2004

Direct tests of the hypothesized total body fat regulatory system have been accomplished by partial surgical lipectomy. This usually results in the restoration of the lipid deficit through compensatory increases in nonexcised white adipose tissue (WAT) masses of ground squirrels, laboratory rats, and mice, as well as Siberian and Syrian hamsters. We challenged this hypothesized total body fat regulatory system by testing the response of Siberian hamsters to 1) lipid deficits [lipectomy; primarily bilateral epididymal WAT (EWAT) removal], 2) lipid surfeits (addition of donor EWAT with no lipectomy), 3) no net change in lipid [EWAT or inguinal WAT (IWAT) lipectomy with the excised fat replaced to a new location (autologous)], 4) lipectomy with the same pad (EWAT lipectomy only) added from a sibling (nonautologous), and 5) sham surgeries for each treatment. Food intake generally was not affected. Body mass was not affected across all treatments. Grafts ∼3 mo later had normal appearance both macro- and microscopically and were revascularized. The normal lipectomy-induced compensatory increases in nonexcised WAT masses surprisingly were exaggerated with autologous EWAT transplants, but not for autologous IWAT or nonautologous EWAT transplants. There was no compensatory decrease in native WAT masses with nonautologous EWAT additions. Collectively, only lipectomy triggered reparation of the lipid deficit, but the other manipulations did not, suggesting a system biased toward rectifying decreases in lipid or an inability of the hypothesized total body fat regulatory system to recognize WAT transplants.
Mice bearing Acads mutation display altered postingestive but not 5-s orosensory response to dietary fat
Authors: Smith Richards Brenda K. , Belton Brenda N. , York Barbara , Volaufova Julia
Published: January 2004

A previous survey of mouse inbred strains revealed a wide range in self-selected fat intake, from 26 to 83% of energy. The BALB/cByJ strain selected a lower percentage of fat intake (36%) than all other strains tested except for the CAST/Ei. BALB/cByJ mice are deficient in the short-chain acyl-CoA dehydrogenase (SCAD) enzyme due to a spontaneous mutation in Acads. We hypothesized that this deficiency would alter fat appetite and used three behavioral test paradigms to compare the response of BALB/cByKz. Acads -/- and BALB/cByKz. Acads +/+ mice to fat stimuli. First, during 10-day exposure to a macronutrient self-selection diet, Acads -/- mice consumed proportionately less fat and more carbohydrate than Acads +/+ mice, yet total energy intake was similar between strains. Next, in 48-h two-bottle preference tests, Acads +/+ mice displayed a preference for 50% corn oil, but Acads -/- mice did not. Finally, in brief-access taste tests employing successive 5-s presentations of corn oil in an ascending concentration series ending with 50%, there were no effects of strain on total licks, indicating that Acads does not alter acute orosensory response to this fat stimulus. With 15-s presentations, however, the Acads +/+ mice licked more of the 50% oil than Acads -/-, suggesting orosensory effects related to the increased exposure time. In contrast to corn oil, there were no strain differences in licking response to sucrose solution in either the two-bottle or brief-access taste tests. The observation that SCAD-deficient mice display altered postingestive responses to dietary fat provides further evidence for the metabolic control of feeding.
Impaired substance P release from renal sensory nerves in SHR involves a pertussis toxin-sensitive mechanism
Authors: Kopp Ulla C. , Cicha Michael Z.
Published: January 2004

Stretching the renal pelvic wall activates renal mechanosensory nerves by a PGE2-mediated release of substance P via activation of the cAMP-PKA pathway. Renal pelvic ANG II modulates the responsiveness of renal sensory nerves by suppressing the PGE2-mediated activation of adenylyl cyclase via a pertussis toxin (PTX)-sensitive mechanism. In SHR, activation of renal mechanosensory nerves is impaired. This is due to suppressed release of substance P in response to increased pelvic pressure. The present study was performed to investigate whether the PGE2-mediated release of substance P was suppressed in SHR vs. WKY and, if so, whether the impaired PGE2-mediated release of substance P was due to ANG II activating a PTX-sensitive mechanism. In an isolated renal pelvic wall preparation, PGE2, 0.14 μM, increased substance P release from 9 ± 3 to 22 ± 3 pg/min ( P < 0.01) in Wistar-Kyoto rats (WKY), but had no effect in spontaneously hypertensive rats (SHR). A tenfold higher concentration of PGE2, 1.4 μM, was required to increase substance P release in SHR, from 7 ± 1 to 22 ± 3 pg/min ( P < 0.01). In SHR, treating renal pelvises with losartan enhanced the release of substance P produced by subthreshold concentration of PGE2, 0.3 μM, from 16 ± 2 to 26 ± 3 pg/min ( P < 0.01). Likewise, treating renal pelvises with PTX enhanced the PGE2-mediated release of substance P from 10 ± 1 to 33 ± 3 pg/min ( P < 0.01) in SHR. In WKY, neither losartan nor PTX had an effect on the release of substance P produced by subthreshold concentrations of PGE2, 0.03 μM. In conclusion, the impaired responsiveness of renal sensory nerves in SHR involves endogenous ANG II suppressing the PGE2-mediated release of substance P via a PTX-sensitive mechanism.
What sets the long-term level of sympathetic nerve activity: is there a role for arterial baroreceptors?
Authors: Malpas Simon C.
Published: January 2004

Much of our knowledge of the influence of the sympathetic nervous system on the control of blood pressure is built on experimental approaches that focus very much on time scales <24 h. Although direct recordings of sympathetic nerve activity (SNA) over short time scales provide important information, it is difficult to place their relevance over the longer term where the development of chronic changes in blood pressure are likely to be a mixture of hormonal, renal, and neural influences. Recently new experimental approaches are now revealing a possible role for arterial baroreceptors in the chronic regulation of SNA. These studies reveal that chronic increases in blood pressure are associated with chronic changes in SNA that may be due to nonresetting of the blood pressure-SNA baroreflex relationship. This review discusses the implications of such information, highlighting new technologies for long-term recording of SNA that appear to hold much promise for revealing the role of SNA to the kidney for the long-term control of blood pressure.
Regulation of action potential duration under acute heat stress byIK,ATPandIK1in fish cardiac myocytes
Authors: Paajanen Vesa , Vornanen Matti
Published: January 2004

The mechanism underlying temperature-dependent shortening of action potential (AP) duration was examined in the fish ( Carassius carassius L.) heart ventricle. Acute temperature change from +5 to +18°C (heat stress) shortened AP duration from 2.8 ± 0.3 to 1.3 ± 0.1 s in intact ventricles. In 56% (18 of 32) of enzymatically isolated myocytes, heat stress also induced reversible opening of ATP-sensitive K+channels and increased their single-channel conductance from 37 ± 12 pS at +8°C to 51 ± 13 pS at +18°C (Q10= 1.38) ( P < 0.01; n = 12). The ATP-sensitive K+channels of the crucian carp ventricle were characterized by very low affinity to ATP both at +8°C [concentration of Tris-ATP that produces half-maximal inhibition of the channel ( K1/2)= 1.35 mM] and +18°C ( K1/2= 1.85 mM). Although acute heat stress induced ATP-sensitive K+current ( IK,ATP) in patch-clamped myocytes, similar heat stress did not cause any glibenclamide (10 μM)-sensitive changes in AP duration in multicellular ventricular preparations. Examination of APs and K+currents from the same myocytes by alternate recording under current-clamp and voltage-clamp modes revealed that changes in AP duration were closely correlated with temperature-specific changes in the voltage-dependent rectification of the background inward rectifier K+current IK1. In ∼15% of myocytes (4 out of 27), IK,ATP-dependent shortening of AP followed the IK1-induced AP shortening. Thus heat stress-induced shortening of AP duration in crucian carp ventricle is primarily dependent on IK1. IK,ATPis induced only in response to prolonged temperature elevation or perhaps in the presence of additional stressors.
Short-term CR decreases cardiac mitochondrial oxidant production but increases carbonyl content
Authors: Judge Sharon , Judge Andrew , Grune Tilman , Leeuwenburgh Christiaan
Published: January 2004

Lifelong caloric restriction (CR) reduces the rate of mitochondrial oxidant production and the accumulation of oxidized proteins and prevents some of the age-associated decline in 20S proteasome activity. However, few studies have investigated how rapidly the beneficial effects of CR take place. We investigated whether 2 mo of CR in 6-mo-old rats would be of sufficient duration to elicit these beneficial changes. Mitochondrial oxidant production was significantly diminished in the CR rats compared with the ad libitum-fed animals. Short-term CR also caused a significant decrease in mitochondrial superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities, but there were no differences in cytosolic SOD and GPX activities, whereas mitochondrial and cytosolic catalase (CAT) activity was increased with CR. However, protein carbonyl content was significantly elevated in both the mitochondrial and cytosolic fractions from CR rats. Of the three major 20S proteasome activities (chymotrypsin-like, trypsin-like, and peptidylglutamyl-peptide hydrolase), the peptidylglutamyl-peptide hydrolase activity was significantly elevated in the CR animals, possibly because of the fact that there were more oxidized proteins to be degraded. Although fewer oxidants were produced in the CR animals, it is possible that the ability to scavenge oxidants was transiently suppressed because of the reduction in mitochondrial antioxidant enzyme activities, which may explain the observed increases in carbonyl content.
Melanocortin receptors mediate the excitatory effects of blood-borne murine leptin on hypothalamic paraventricular neurons in rat
Authors: Zhang Zhi-Hua , Felder Robert B.
Published: January 2004

The central pathways and mediators involved in sympathoexcitatory responses to circulating leptin are not well understood, although the arcuate-paraventricular nucleus (ARC-PVN) pathway likely plays a critical role. In urethane-anesthetized rats, ipsilateral intracarotid artery (ICA) injection of murine leptin (100 μg/kg) activated most PVN neurons tested. These responses were reduced by intracerebroventricular injection of the melanocortin subtype 3 and 4 receptor (MC3/4-R) antagonist SHU-9119 (0.6 nmol). The MC3/4-R agonist MTII (0.6 nmol icv) activated PVN neurons. Some PVN neurons that were excited by ICA leptin were inhibited by local application of neuropeptide Y (NPY, 2.5 ng). ICA leptin (100 μg/kg) excited presympathetic rostral ventrolateral medulla neurons and renal sympathetic nerve activity without significant change in blood pressure or heart rate; these effects were mimicked by intracerebroventricular injection of MTII (0.6 nmol). These data provide in vivo electrophysiological evidence to support the hypothesis that circulating leptin activates the sympathetic nervous system by stimulating the release of α-melanocyte-stimulating hormone in the vicinity of PVN neurons that are inhibited by the orexogenic peptide NPY.
Excitatory amino acid receptors in the dorsomedial hypothalamus mediate prostaglandin-evoked thermogenesis in brown adipose tissue
Authors: Madden C. J. , Morrison S. F.
Published: January 2004

We determined whether the dorsomedial hypothalamus (DMH) plays a role in the thermogenic, metabolic, and cardiovascular effects evoked by centrally administered PGE2. Microinjection of PGE2 (170 pmol/60 nl) into the medial preoptic area of the hypothalamus in urethane-chloralose-anesthetized, artificially ventilated rats increased brown adipose tissue (BAT) sympathetic nerve activity (SNA; +207 ± 18% of control), BAT temperature (1.5 ± 0.2°C), expired CO2 (0.9 ± 0.1%), heart rate (HR; 106 ± 12 beats/min), and mean arterial pressure (22 ± 4 mmHg). Within 5 min of subsequent bilateral microinjections of the GABAA receptor agonist muscimol (120 pmol·60 nl-1·side-1) or the ionotropic excitatory amino acid antagonist kynurenate (6 nmol·60 nl-1·side-1) into the DMH, the PGE2-evoked increases were, respectively, attenuated by 91 ± 3% and 108 ± 7% for BAT SNA, by 73 ± 12% and 102 ± 28% for BAT temperature, by 100 ± 4% and 125 ± 21% for expired CO2, by 72 ± 11% and 70 ± 16% for HR, and by 84 ± 19% and 113 ± 16% for mean arterial pressure. Microinjections outside the DMH within the dorsal hypothalamic area adjacent to the mamillothalamic tracts or within the ventromedial hypothalamus were less effective for attenuating the PGE2-evoked thermogenic, metabolic, and cardiovascular responses. These results demonstrate that activation of excitatory amino acid receptors within the DMH is necessary for the thermogenic, metabolic, and cardiovascular responses evoked by microinjection of PGE2 into the medial preoptic area.
p38γ MAPK regulation of glucose transporter expression and glucose uptake in L6 myotubes and mouse skeletal muscle
Authors: Ho Richard C. , Alcazar Oscar , Fujii Nobuharu , Hirshman Michael F. , Goodyear Laurie J.
Published: January 2004

Skeletal muscle expresses at least three p38 MAPKs (α, β, γ). However, no studies have examined the potential regulation of glucose uptake by p38γ, the isoform predominantly expressed in skeletal muscle and highly regulated by exercise. L6 myotubes were transfected with empty vector (pCAGGS), activating MKK6 (MKK6CA), or p38γ-specific siRNA. MKK6CA-transfected cells had higher rates of basal 2-deoxy-d-[3H]glucose (2-DG) uptake ( P < 0.05) but lower rates of 2,4-dinitrophenol (DNP)-stimulated glucose uptake, an uncoupler of oxidative phosphorylation that operates through an insulin-independent mechanism ( P < 0.05). These effects were reversed when MKK6CA cells were cotransfected with p38γ-specific siRNA. To determine whether the p38γ isoform is involved in the regulation of contraction-stimulated glucose uptake in adult skeletal muscle, the tibialis anterior muscles of mice were injected with pCAGGS or wild-type p38γ (p38γWT) followed by intramuscular electroporation. Basal and contraction-stimulated 2-DG uptake in vivo was determined 14 days later. Overexpression of p38γWT resulted in higher basal rates of glucose uptake compared with pCAGGS ( P < 0.05). Muscles overexpressing p38γWT showed a trend for lower in situ contraction-mediated glucose uptake ( P = 0.08) and significantly lower total GLUT4 levels ( P < 0.05). These data suggest that p38γ increases basal glucose uptake and decreases DNP- and contraction-stimulated glucose uptake, partially by affecting levels of glucose transporter expression in skeletal muscle. These findings are consistent with the hypothesis that activation of stress kinases such as p38 are negative regulators of stimulated glucose uptake in peripheral tissues.
Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus)
Authors: Arnold Walter , Ruf Thomas , Reimoser Susanne , Tataruch Frieda , Onderscheka Kurt , Schober Franz
Published: January 2004

Herbivores of temperate and arctic zones are confronted during winter with harsh climatic conditions and nutritional shortness. It is still not fully understood how large ungulates cope with this twofold challenge. We found that red deer, similar to many other northern ungulates, show large seasonal fluctuations of metabolic rate, as indicated by heart rate, with a 60% reduction at the winter nadir compared with the summer peak. A previously unknown mechanism of energy conservation, i.e., nocturnal hypometabolism associated with peripheral cooling, contributed significantly to lower energy expenditure during winter. Predominantly during late winter night and early morning hours, subcutaneous temperature could decrease substantially. Importantly, during these episodes of peripheral cooling, heart rate was not maintained at a constant level, as to be expected from classical models of thermoregulation in the thermoneutral zone, but continuously decreased with subcutaneous temperature, both during locomotor activity and at rest. This indicates that the circadian minimum of basal metabolic rate and of the set-point of body temperature regulation varied and dropped to particularly low levels during late winter. Our results suggest, together with accumulating evidence from other species, that reducing endogenous heat production is not restricted to hibernators and daily heterotherms but is a common and well-regulated physiological response of endothermic organisms to energetically challenging situations. Whether the temperature of all tissues is affected, or the body shell only, may simply be a result of the duration and degree of hypometabolism and its interaction with body size-dependent heat loss.
α-Adrenergic vascular responsiveness to sympathetic nerve activity is intact after head-down bed rest in humans
Authors: Kamiya Atsunori , Michikami Daisaku , Iwase Satoshi , Hayano Junichiro , Kawada Toru , Sugimachi Masaru , Sunagawa Kenji
Published: January 2004

Space-flight and its ground-based simulation model, 6° head-down bed rest (HDBR), cause cardiovascular deconditioning in humans. Because sympathetic vasoconstriction plays a very important role in circulation, we examined whether HDBR impairs α-adrenergic vascular responsiveness to sympathetic nerve activity. We subjected eight healthy volunteers to 14 days of HDBR and before and after HDBR measured calf muscle sympathetic nerve activity (MSNA; microneurography) and calf blood flow (venous occlusion plethysmography) during sympathoexcitatory stimulation (rhythmic handgrip exercise). HDBR did not change the increase in total MSNA ( P = 0.97) or the decrease in calf vascular conductance ( P = 0.32) during exercise, but it did augment the increase in calf vascular resistance ( P = 0.0011). HDBR augmented the transduction gain from total MSNA into calf vascular resistance, assessed as the least squares linear regression slope of vascular resistance on total MSNA (0.05 ± 0.02 before HDBR, 0.20 ± 0.06 U·min-1·burst-1after HDBR, P = 0.0075), but did not change the transduction gain into calf vascular conductance ( P = 0.41). Our data indicate that α-adrenergic vascular responsiveness to sympathetic nerve activity is preserved in the supine position after HDBR in humans.
Hexosamines and TGF-β1use similar signaling pathways to mediate matrix protein synthesis in mesangial cells
Authors: Singh Lalit P. , Green Kenneith , Alexander Michelle , Bassly Shira , Crook Errol D.
Published: January 2004

Hyperglycemia-induced alterations in mesangial (MES) cell function and extracellular matrix (ECM) protein accumulation are seen in diabetic glomerulopathy. Transforming growth factor-β1(TGF-β1) mediates high-glucose-induced matrix production in the kidney. Recent studies demonstrated that some of the effects of high glucose on cellular metabolism are mediated by the hexosamine biosynthesis pathway (HBP) in which fructose-6-phosphate is converted to glucosamine (GlcN) 6-phosphate. We previously showed that the high-glucose-mediated fibronectin and laminin synthesis in MES cells is mediated by the HBP and that GlcN is more potent than glucose in inducing TGF-β1promoter luciferase activity. In this study, we investigated the hypothesis that the effects of glucose on MES matrix production occur via hexosamine regulation of TGF-β1. Culturing simian virus (SV)-40-transformed rat kidney MES cells in 25 mM glucose (HG) for 48 h increases cellular fibronectin and laminin levels about twofold on Western blots compared with low glucose (5 mM). GlcN (1.5 mM) or TGF-β1(2.5-5 ng/ml) for 24-48 h also increases ECM synthesis. However, the effects of HG or GlcN with TGF-β1are not additive. The presence of anti-TGF-β1antibodies (20 μg/ml) blocks both TGF-β1- and GlcN-induced fibronectin synthesis. TGF-β1increased ECM levels via PKA (laminin and fibronectin) and PKC (fibronectin) pathways. Similarly, TGF-β1and hexosamines led to nonadditive increases in phosphorylation of the cAMP responsive element binding transcription factor. These results suggest that the effects of excess glucose on MES ECM synthesis occur via HBP-mediated regulation of TGF-β1.