bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of sympathetic responses at birth in sheep by lesion of the paraventricular nucleus
Authors: Segar Jeffrey L. , Ellsbury Dan L. , Smith Oliva M.
Published: March 2015

Birth is characterized by a surge in sympathetic outflow, heart rate (HR), mean arterial blood pressure (MABP) and circulating catecholamines. The paraventricular nucleus (PVN) of the hypothalamus is an important central regulatory site of sympathetic activity, but its role in the regulation of sympathoexcitation at birth is unknown. To test the hypothesis that the PVN regulates sympathetic activity at birth, experiments were performed in chronically instrumented near-term (137- to 142-day gestation, term 145 days) sheep before and after delivery by cesarean section. Stereotaxic guided electrolytic lesioning of the PVN ( n= 6) or sham lesioning ( n = 6) was performed 48 h before study. At 30 min after birth, renal sympathetic nerve activity (RSNA) increased 128 ± 26% above fetal values in the sham-lesioned animals ( P < 0.05). In contrast, at a similar time point, RSNA decreased to 52 ± 12% of the fetal value in the PVN-lesioned animals. Lesioning of the PVN did not affect the usual postnatal increases in MABP and epinephrine levels although HR failed to rise above fetal values. ANG II but not arginine vasopressin or norepinephrine levels increased in PVN-lesioned animals after birth, whereas all three hormones increased ( P < 0.05) in sham-lesioned animals. Fetal and newborn HR baroreflex responses were similar in both groups. However, the usual postnatal attenuation of baroreflex-mediated inhibition of RSNA was blunted in the PVN-lesioned group. The results of this study demonstrate that ablation of the PVN abolishes sympathoexcitation with birth at near-term gestation. The PVN may play a critical role in physiological adaptation at birth.
Crocodile transthyretin: structure, function, and evolution
Authors: Prapunpoj Porntip , Richardson Samantha J. , Schreiber Gerhard
Published: March 2015

Structure and function were studied for Crocodylus porosustransthyretin (crocTTR), an important intermediate in TTR evolution. The cDNA for crocTTR mRNA was cloned and sequenced and the amino acid sequence of crocTTR was deduced. In contrast to mammalian TTRs, but similar to avian and lizard TTRs, the subunit of crocTTR had a long and hydrophobic NH2-terminal region. Different from the situation in mammals, triiodothyronine (T3) was bound by crocTTR with higher affinity than thyroxine (T4). Recombinant crocTTR and a chimeric construct, with the NH2-terminal region of crocTTR being replaced by that of Xenopus laevis TTR, were synthesized in the yeast Pichia pastoris. Analysis of the affinity of the chimeric TTRs showed that the NH2-terminal region modulates T4and T3binding characteristics of TTR. The structural differences of the NH2-terminal regions of reptilian and amphibian TTRs were caused by a shift in splice sites at the 5′ end of exon 2. The comparison of crocodile and other vertebrate TTRs shows that TTR evolution is an example for positive Darwinian evolution and identifies its molecular mechanism.
Hypothermia and recovery from respiratory arrest in a neonatal rat in vitro brain stem preparation
Authors: Mellen Nicholas M. , Milsom William K. , Feldman Jack L.
Published: March 2015

This study was designed to examine the possibility that respiratory arrest during hypothermia occurs at the level of premotor or motor neurons rather than at the level of the central rhythm generator itself. Specifically, we sought to determine the consequences of hypothermic cooling until respiratory arrest, and subsequent rewarming, on neurons in the pre-Bötzinger Complex, as an indication of the output of the entire rhythmogenic network; and from cervical spinal (phrenic) ventral roots, as an indication of motor neuron output, in an in vitro neonatal rat brain stem-spinal cord preparation. We found that hypothermia led to a slowing of the respiratory rhythm with little or no decrease in the magnitude of phrenic motor output or the field potential of pre-Bötzinger Complex neurons. Ultimate arrest occurred abruptly and simultaneously in recordings from both sites, indicating that the arrest was due to failure of the central rhythm-generating network, primarily due to removal of a conditional excitation. On being rewarmed, the motor output recorded at both sites was usually fractionated, initially suggesting that changes occurred in network synchronization either during cooling or during reactivation following hypothermic arrest.
Arterial baroreflex function and cardiovascular variability: interactions and implications
Authors: Lanfranchi Paola A. , Somers Virend K
Published: March 2015

The arterial baroreflex contributes importantly to the short-term regulation of blood pressure and cardiovascular variability. A number of factors (including reflex, humoral, behavioral, and environmental) may influence gain and effectiveness of the baroreflex, as well as cardiovascular variability. Many central neural structures are also involved in the regulation of the cardiovascular system and contribute to the integrity of the baroreflex. Consequently, brain injuries or ischemia may induce baroreflex impairment and deranged cardiovascular variability. Baroreflex dysfunction and deranged cardiovascular variability are also common findings in cardiovascular disease. A blunted baroreflex gain and impaired heart rate variability are predictive of poor outcome in patients with heart failure and myocardial infarction and may represent an early index of autonomic activation in left ventricular dysfunction. The mechanisms mediating these relationships are not well understood and may in part be the result of cardiac structural changes and/or altered central neural processing of baroreflex signals.
Effects of fetal ovine adrenalectomy on sympathetic and baroreflex responses at birth
Authors: Segar Jeffrey L. , Van Natta Timothy , Smith Oliva J.
Published: March 2015

Studies were performed to test the hypothesis that the absence of adrenal glucocorticoids late in gestation alters sympathetic and baroreflex responses before and immediately after birth. Fetal sheep at 130–131 days gestation (term 145 days) were subjected to bilateral adrenalectomy before the normal prepartum increase in plasma cortisol levels. One group of fetuses ( n = 5) received physiological cortisol replacement with a continuous infusion of hydrocortisone (2 mg · day−1 · kg−1 for 10 days), whereas the other group received 0.9% NaCl vehicle ( n = 5). All animals underwent a second surgery 48 h before the study for placement of a renal nerve recording electrode. Heart rate (HR), mean arterial blood pressure (MABP), renal sympathetic nerve activity (RSNA), and baroreflex control of HR and RSNA were studied before and after cesarean section delivery. At the time of study (140–141 days gestation), fetal plasma cortisol concentration was undetectable in adrenalectomized (ADX) fetuses and 58 ± 9 ng/ml in animals receiving cortisol replacement (ADX + F). Fetal and newborn MABP was significantly greater in ADX + F relative to ADX animals. One hour after delivery, MABP increased 13 ± 3 mmHg and RSNA increased 91 ± 12% above fetal values in ADX + F (both P < 0.05) but remained unchanged in ADX lambs. The midpoint pressures of the fetal HR and RSNA baroreflex function curves were significantly greater in ADX + F (54 ± 3 and 56 ± 3 mmHg for HR and RSNA curves, respectively) than ADX fetuses (45 ± 2 and 46 ± 3 mmHg). After delivery, the baroreflex curves reset toward higher pressure in ADX + F but not ADX lambs. These results suggest that adrenal glucocorticoids contribute to cardiovascular regulation in the late-gestation fetus and newborn by modulating arterial baroreflex function and sympathetic activity.
Role of oxidative stress in age-related reduction of NO-cGMP-mediated vascular relaxation in SHR
Authors: Payne Jason A. , Reckelhoff Jane F. , Khalil Raouf A.
Published: March 2015

The incidence of hypertension increases during the late stages of aging; however, the vascular mechanisms involved are unclear. We investigated whether the late stages of aging are associated with impaired nitric oxide (NO)-mediated vascular relaxation and enhanced vascular contraction and whether oxidative stress plays a role in the age-related vascular changes. Aging (16 mo) male spontaneously hypertensive rats (SHR) nontreated or treated for 8 mo with the antioxidant tempol (1 mM in drinking water) or vitamin E (E; 5,000 IU/kg chow) and vitamin C (C; 100 mg · kg-1· day-1in drinking water) and adult (12 wk) male SHR were used. After the arterial pressure was measured, aortic strips were isolated from the rats for measurement of isometric contraction. The arterial pressure and phenylephrine (Phe)-induced vascular contraction were enhanced, and the ACh-induced vascular relaxation and nitrite/nitrate production were reduced in aging compared with adult rats. In aging rats, the arterial pressure was nontreated (188 ± 4), tempol-treated (161 ± 6), and E + C-treated (187 ± 1 mmHg). Phe (10-5M) caused an increase in active stress in nontreated aging rats (14.3 ± 1.0) that was significantly ( P < 0.05) reduced in tempol-treated (9.0 ± 0.7) and E + C-treated rats (9.8 ± 0.6 × 104N/m2). ACh produced a small relaxation of Phe contraction in nontreated aging rats that was enhanced ( P < 0.05) in tempol- and E + C-treated rats. l-NAME (10-4M), inhibitor of NO synthase, or ODQ (10-5M), inhibitor of cGMP production in smooth muscle, inhibited ACh relaxation and enhanced Phe contraction in tempol- and E + C-treated but not the nontreated aging rats. ACh-induced vascular nitrite/nitrate production was not different in nontreated, tempol- and E + C-treated aging rats. Relaxation of Phe contraction with sodium nitroprusside, an exogenous NO donor, was smaller in aging than adult rats but was not different between nontreated, tempol- and E + C-treated aging rats. Thus, during the late stages of aging in SHR rats, an age-related inhibition of a vascular relaxation pathway involving not only NO production by endothelial cells but also the bioavailability of NO and the smooth muscle response to NO is partially reversed during chronic treatment with the antioxidants tempol and vitamins E and C. The data suggest a role for oxidative stress in the reduction of vascular relaxation and thereby the promotion of vascular contraction and hypertension during the late stages of aging.
Autoregulation of renal medullary blood flow in rabbits
Authors: Eppel Gabriela A. , Bergström Göran , Anderson Warwick P. , Evans Roger G.
Published: March 2015

We examined the extent of renal medullary blood flow (MBF) autoregulation in pentobarbital-anesthetized rabbits. Two methods for altering renal arterial pressure (RAP) were compared: the conventional method of graded suprarenal aortic occlusion and an extracorporeal circuit that allows RAP to be increased above systemic arterial pressure. Changes in MBF were estimated by laser-Doppler flowmetry, which appears to predominantly reflect erythrocyte velocity, rather than flow, in the kidney. We compared responses using a dual-fiber needle probe held in place by a micromanipulator, with responses from a single-fiber probe anchored to the renal capsule, to test whether RAP-induced changes in kidney volume confound medullary laser-Doppler flux (MLDF) measurements. MLDF responses were similar for both probe types and both methods for altering RAP. MLDF changed little as RAP was altered from 50 to ≥170 mmHg (24 ± 22% change). Within the same RAP range, RBF increased by 296 ± 48%. Urine flow and sodium excretion also increased with increasing RAP. Thus pressure diuresis/natriuresis proceeds in the absence of measurable increases in medullary erythrocyte velocity estimated by laser-Doppler flowmetry. These data do not, however, exclude the possibility that MBF is increased with increasing RAP in this model, because vasa recta recruitment may occur.
Synergistic effects of nitric oxide and prostaglandins on renal escape from vasopressin-induced antidiuresis
Authors: Murase Takashi , Tian Ying , Fang Xiao Ying , Verbalis Joseph G.
Published: March 2015

Recent results from our laboratories indicate that renal escape from AVP-induced antidiuresis is accompanied by marked downregulation of kidney aquaporin-2 (AQP2) and AVP V2 receptors. The present studies evaluated the effect of nitric oxide (NO) and PG synthesis blockade on escape from antidiuresis. dDAVP-infused rats were water loaded (WL) for 5 days. l-NAME, an NO synthesis inhibitor, or diclofenac, a cyclooxygenase inhibitor, was infused subcutaneously beginning 1 day before WL. As early as 2 days after WL, urine volume increased and urine osmolality decreased, indicating the onset of escape. Endogenous NO synthesis, measured as urinary NO2+ NO3excretion, was significantly increased in the WL group compared with the non-WL controls during all 5 days of WL. l-NAME (20 mg · kg−1· day−1) markedly decreased urine volume on days 4 and 5of WL, indicating inhibition of the escape phenomenon. Kidney AQP2 protein was significantly increased by this dose ofl-NAME as well. A lower dose of l-NAME (10 mg · kg−1· day−1) or diclofenac (2.5 mg · kg−1· day−1) did not significantly affect the escape phenomenon by itself, but the combination of l-NAME and diclofenac showed a marked inhibitory effect on the escape phenomenon, which was also accompanied by a significant increase in kidney AQP2 expression. These results therefore suggest that renal NO and PG both play important roles in escape from AVP-induced antidiuresis by acting synergistically to downregulate kidney AQP2 expression.
Diaphragm contractile dysfunction in MyoD gene-inactivated mice
Authors: Staib Jessica L. , Swoap Steven J. , Powers Scott K.
Published: March 2015

MyoD is one of four myogenic regulatory factors found exclusively in skeletal muscle. In an effort to better understand the role that MyoD plays in determining muscle contractile properties, we examined the effects of MyoD deletion on both diaphragmatic contractile properties and myosin heavy chain (MHC) phenotype. Regions of the costal diaphragm from wild-type and MyoD knockout [ MyoD (−/−)] adult male BALB/c mice ( n = 8/group) were removed, and in vitro diaphragmatic contractile properties were measured. Diaphragmatic contractile measurements revealed that MyoD (−/−) animals exhibited a significant ( P < 0.05) downward shift in the force-frequency relationship, a decrement in maximal specific tension (Po; −33%), a decline in maximal shortening velocity (Vmax; −37%), and concomitant decrease in peak power output (−47%). Determination of MHC isoforms in the diaphragm via gel electrophoresis revealed that MyoD elimination resulted in a fast-to-slow shift ( P < 0.05) in the MHC phenotype toward MHC types IIA and IIX in MyoD (−/−) animals. These data indicate that MyoD deletion results in a decrease in diaphragmatic submaximal force generation and Po, along with decrements in both Vmaxand peak power output. Hence, MyoD plays an important role in determining diaphragmatic contractile properties.
Joint pituitary-hypothalamic and intrahypothalamic autofeedback construct of pulsatile growth hormone secretion
Authors: Farhy Leon S. , Veldhuis Johannes D.
Published: March 2015

Growth hormone (GH) secretion is vividly pulsatile in all mammalian species studied. In a simplified model, self-renewable GH pulsatility can be reproduced by assuming individual, reversible, time-delayed, and threshold-sensitive hypothalamic outflow of GH-releasing hormone (GHRH) and GH release-inhibiting hormone (somatostatin; SRIF). However, this basic concept fails to explicate an array of new experimental observations. Accordingly, here we formulate and implement a novel fourfold ensemble construct, wherein 1) systemic GH pulses stimulate long-latency, concentration-dependent secretion of periventricular-nuclear SRIF, thereby initially quenching and then releasing multiphasic GH volleys (recurrent every 3-3.5 h); 2) SRIF delivered to the anterior pituitary gland competitively antagonizes exocytotic release, but not synthesis, of GH during intervolley intervals; 3) arcuate-nucleus GHRH pulses drive the synthesis and accumulation of GH in saturable somatotrope stores; and 4) a purely intrahypothalamic mechanism sustains high-frequency GH pulses (intervals of 30-60 min) within a volley, assuming short-latency reciprocal coupling between GHRH and SRIF neurons (stimulatory direction) and SRIF and GHRH neurons (inhibitory direction). This two-oscillator formulation explicates (but does not prove) 1) the GHRH-sensitizing action of prior SRIF exposure; 2) a three-site (intrahypothalamic, hypothalamo-pituitary, and somatotrope GH store dependent) mechanism driving rebound-like GH secretion after SRIF withdrawal in the male; 3) an obligatory role for pituitary GH stores in representing rebound GH release in the female; 4) greater irregularity of SRIF than GH release profiles; and 5) a basis for the paradoxical GH-inhibiting action of centrally delivered GHRH.
Expression of dopaminergic receptors in the hypothalamus of lean and obese Zucker rats and food intake
Authors: Fetissov Sergueï O. , Meguid Michael M. , Sato Tomoi , Zhang Li-Hua
Published: March 2015

As revealed by previous microdialysis studies, basal and food intake-accompanied dopamine release significantly differs in the hypothalamus of obese vs. lean Zucker rats. In the present study, we determined whether dopaminergic receptors are also compromised in obesity. Dopaminergic D1and D2 receptor mRNA expression was studied in the ventromedial hypothalamus (VMH), lateral hypothalamic area (LHA), and the adenohypophysis (AH) of obese and lean Zucker rats using RT-PCR technique. In obese Zucker rats, we found an upregulation of D1 receptor mRNA in the VMH and AH and a downregulation in the LHA, whereas D2 receptor mRNA was downregulated in both the VMH and LHA, but not changed in the AH, compared with lean rats. Also, an increase of D1 receptor staining was seen in the paraventricular nucleus of obese rats by immunohistochemistry. We selected the VMH to test if the observed changes in the dopamine receptor expression of obese rats induce behavioral sensitization to dopamine as expressed by hyperphagia. The overnight food-deprived rats received a single VMH injection (10 nmol) of sulpiride (D2receptor antagonist) or saline as control, then food was provided and 1-h food intake was measured. Food intake after sulpiride vs. saline injection was greater in obese rats but was not different in lean rats. Our data suggest that downregulation of D2 receptor in the hypothalamus at least in the VMH induces behavior sensitization for having large meals. Low D2 receptor expression may be causal for an exaggerated dopamine release observed in obese rats during food ingestion and for reduced satiety feedback effect of dopamine. High level of D1 receptor expression in the VMH and low in the LHA may also contribute to the specific feeding pattern in obese rats represented by large meal size and low meal number.
Simulated microgravity impairs aldosterone secretion in rats: possible involvement of adrenomedullin
Authors: Neri Giuliano , Bova Sergio , Malendowicz Ludwik K. , Mazzocchi Giuseppina , Nussdorfer Gastone G.
Published: March 2015

The prolonged exposure to microgravity (MG) or simulated MG (SMG) has been reported to cause hypotension, mainly due to reduced vascular contractility, and dysregulation of fluid and electrolyte balance. However, the mechanism(s) involved in these MG- or SMG-induced effects is not yet completely elucidated. Hence, we investigated in the rat the effect of prolonged (15 day) SMG, in the form of hindlimb unweighting, on the renin-angiotensin-aldosterone system (RAAS), as well as on atrial natriuretic peptide (ANP) and adrenomedullin (ADM), two hypotensive peptides that play a major role in the regulation of RAAS activity by inhibiting adrenal aldosterone secretion. SMG caused a mild hypotension in rats, associated with the blockade of body weight gain. Plasma aldosterone concentration and basal and agonist-stimulated in vitro aldosterone secretion from adrenal slices were decreased, and plasma renin activity was moderately increased. Neither Na+ and K+ serum concentrations nor ACTH and corticosterone blood levels were significantly affected. Plasma ANP concentration did not display significant alterations, while ADM blood concentration underwent a marked rise. The administration of the ADM-receptor antagonist ADM-(22–52) during the last 3 days of hindlimb unweighting reversed the SMG-induced hypotension and hypoaldosteronism. Collectively, these findings allow us to suggest that prolonged SMG impairs RAAS activity in rats, through a mechanism probably involving upregulation of the ADM system. Both hypoaldosteronism and increased ADM secretion may contribute to the development of hypotension during prolonged exposure to SMG.
48-h Hypoxic exposure results in endothelium-dependent systemic vascular smooth muscle cell hyperpolarization
Authors: Earley Scott , Naik Jay S. , Walker Benjimen R.
Published: March 2015

Chronic hypoxia (CH) results in reduced sensitivity to vasoconstrictors in conscious rats that persists upon restoration of normoxia. We hypothesized that this effect is due to endothelium-dependent hyperpolarization of vascular smooth muscle (VSM) cells after CH. VSM cell resting membrane potential was determined for superior mesenteric artery strips isolated from CH rats (Pb = 380 Torr for 48 h) and normoxic controls. VSM cells from CH rats studied under normoxia were hyperpolarized compared with controls. Resting vessel wall intracellular Ca2+ concentration ([Ca2+]i) and pressure-induced vasoconstriction were reduced in vessels isolated from CH rats compared with controls. Vasoconstriction and increases in vessel wall [Ca2+]i in response to the α1-adrenergic agonist phenylephrine (PE) were also blunted in resistance arteries from CH rats. Removal of the endothelium normalized resting membrane potential, resting vessel wall [Ca2+]i, pressure-induced vasoconstrictor responses, and PE-induced constrictor and Ca2+ responses between groups. Whereas VSM cell hyperpolarization persisted in the presence of nitric oxide synthase inhibition, heme oxygenase inhibition restored VSM cell resting membrane potential in vessels from CH rats to control levels. We conclude that endothelial derived CO accounts for persistent VSM cell hyperpolarization and vasoconstrictor hyporeactivity after CH.
Functional properties of human muscle fibers after short-term resistance exercise training
Authors: Widrick Jeffrey J. , Stelzer Julian E. , Shoepe Todd C. , Garner Dena P.
Published: March 2015

The aim of this study was to assess the relationships between human muscle fiber hypertrophy, protein isoform content, and maximal Ca2+-activated contractile function following a short-term period of resistance exercise training. Six male subjects (age 27 ± 2 yr) participated in a 12-wk progressive resistance exercise training program that increased voluntary lower limb extension strength by >60%. Single chemically skinned fibers were prepared from pre- and posttraining vastus lateralis muscle biopsies. Training increased the cross-sectional area (CSA) and peak Ca2+-activated force (Po) of fibers containing type I, IIa, or IIa/IIx myosin heavy chain by 30–40% without affecting fiber-specific force (Po/CSA) or unloaded shortening velocity (Vo). Absolute fiber peak power rose as a result of the increase in Po, whereas power normalized to fiber volume was unchanged. At the level of the cross bridge, the effects of short-term resistance training were quantitative (fiber hypertrophy and proportional increases in fiber Poand absolute power) rather than qualitative (no change in Po/CSA, Vo, or power/fiber volume).
Are developing β-adrenoceptors able to desensitize? Acute and chronic effects of β-agonists in neonatal heart and liver
Authors: Auman J. T. , Seidler F. J. , Tate C. A. , Slotkin T. A.
Published: March 2015

During fetal and neonatal development, β-adrenergic receptors (β-ARs) appear to be resistant to desensitization by β-agonist drugs. To determine the mechanisms underlying the regulatory differences between adults and neonates, we administered isoproterenol, a mixed β1/β2-AR agonist, and terbutaline, a β2-selective agonist. Effects were examined in the ensuing 4 h after a single injection, or after the last of four daily injections. We prepared cell membranes from heart (predominantly β1-ARs) and liver (predominantly β2-ARs) and assessed signal transduction in the adenylyl cyclase (AC) pathway. In the first few hours after a single administration of isoproterenol to adult rats, cardiac β-ARs showed activation of G proteins (elevated AC response to forskolin) and desensitization of β-AR-mediated responses; after the fourth injection, heterologous desensitization emerged, characterized by a loss of signaling mediated either through β-ARs or glucagon receptors. Terbutaline evoked an increase in the forskolin response but no desensitization of receptor-mediated responses. When we gave the same treatments to neonatal rats, we observed cardiac G protein activation, but there was neither homologous nor heterologous desensitization of β-ARs or glucagon receptors. In the adult liver, isoproterenol and terbutaline both failed to evoke desensitization, regardless of whether the drugs were given once or for 4 days. In neonates, however, acute or chronic treatment elicited homologous desensitization of β-AR-mediated AC signaling, while sensitizing the response to glucagon. These results show that neonatal β-ARs are inherently capable of desensitization in some, but not all, cell types; cellular responses can be maintained through heterologous sensitization of signaling proteins downstream from the receptor. Differences from adult patterns of response are highly tissue selective and are likely to depend on ontogenetic differences in subtypes of β-ARs and AC.
Investigations on the physiological controls of water and saline intake in C57BL/6 mice
Authors: Johnson Ralph F. , Beltz Terry G. , Thunhorst Robert L. , Johnson Alan Kim
Published: March 2015

To examine the behavioral and neural control of body fluid homeostasis, water and saline intake of C57BL/6 mice was monitored under ad libitum conditions, after treatments that induce water or salt intake, and after ablation of the periventricular tissue of the anteroventral third ventricle (AV3V). Mice have nocturnal drinking that is most prevalent after the offset and before the onset of lights. When given ad libitum choice, C57BL/6 mice show no preference for saline over water at concentrations up to 0.9% NaCl and a progressive aversion to saline above that concentration. Systemic hypertonic saline, isoproterenol, and polyethylene glycol treatments are dipsogenic; however, systemic ANG II is not. Intracerebroventricular injections of both hypertonic saline and ANG II are dipsogenic, and diuretic treatment followed by a short period of sodium deprivation induces salt intake. After ablation of the AV3V, mice can be nursed to recovery from initial adipsia and, similar to rats, show chronic deficits to dipsogenic treatments. Taken together, the data indicate that mechanisms controlling thirst in response to cellular dehydration in C57BL/6 mice are similar to rats, but there are differences in the efficacy of extracellular dehydration-related mechanisms, especially for systemic ANG II, controlling thirst and salt appetite.
Effects of litter size on sympathetic activity in young adult rats
Authors: Young James B.
Published: March 2015

Rearing animals in small litters induces a permanent increase in body weight and body fat. To determine whether changes in sympathoadrenal activity contribute to this effect, litter size was adjusted the day after birth and maintained until weaning at 21 days. Sympathetic nervous system (SNS) activity was measured in adult animals using [3H]norepinephrine ([3H]NE) turnover in peripheral tissues. Although litter size was without effect on [3H]NE turnover in chow-fed animals, acceleration of [3H]NE turnover by dietary sucrose was completely abolished in heart and attenuated in interscapular brown adipose tissue and kidney of rats reared in small litters. Body and epididymal fat-pad weights were heavier in rats reared in small litters; however, weight gain in response to dietary enrichment with sucrose did not differ as a function of litter size. Thus litter size alters dietary activation of the SNS, and this effect presumably reflects changes in central nervous system regulation.
Prostaglandins that increase renin production in response to ACE inhibition are not derived from cyclooxygenase-1
Authors: Cheng Hui-Fang , Wang Sue-Wan , Zhang Ming-Zhi , McKanna James A. , Breyer Richard , Harris Raymond C.
Published: March 2015

It is well known that nonselective, nonsteroidal anti-inflammatory drugs inhibit renal renin production. Our previous studies indicated that angiotensin-converting enzyme inhibitor (ACEI)-mediated renin increases were absent in rats treated with a cyclooxygenase (COX)-2-selective inhibitor and in COX-2 −/− mice. The current study examined further whether COX-1 is also involved in mediating ACEI-induced renin production. Because renin increases are mediated by cAMP, we also examined whether increased renin is mediated by the prostaglandin E2receptor EP2subtype, which is coupled to Gsand increases cAMP. Therefore, we investigated if genetic deletion of COX-1 or EP2prevents increased ACEI-induced renin expression. Age- and gender-matched wild-type (+/+) and homozygous null mice (−/−) were administered captopril for 7 days, and plasma and renal renin levels and renal renin mRNA expression were measured. There were no significant differences in the basal level of renal renin activity from plasma or renal tissue in COX-1 +/+ and −/− mice. Captopril administration increased renin equally [plasma renin activity (PRA): +/+ 9.3 ± 2.2 vs. 50.1 ± 10.9; −/− 13.7 ± 1.5 vs. 43.9 ± 6.6 ng ANG I · ml−1· h−1; renal renin concentration: +/+ 11.8 ± 1.7 vs. 35.3 ± 3.9; −/− 13.0 ± 3.0 vs. 27.8 ± 2.7 ng ANG I · mg protein−1· h−1; n = 6; P < 0.05 with or without captopril]. ACEI also increased renin mRNA expression (+/+ 2.4 ± 0.2; −/− 2.1 ± 0.2 fold control; n = 6–10; P < 0.05). Captopril led to similar increases in EP2−/− compared with +/+. The COX-2 inhibitor SC-58236 blocked ACEI-induced elevation in renal renin concentration in EP2null mice (+/+ 24.7 ± 1.7 vs. 9.8 ± 0.4; −/− 21.1 ± 3.2 vs. 9.3 ± 0.4 ng ANG I · mg protein−1· h−1; n = 5) as well as in COX-1 −/− mice (SC-58236-treated PRA: +/+ 7.3 ± 0.6; −/− 8.0 ± 0.9 ng ANG I · ml−1· h−1; renal renin: +/+ 9.1 ± 0.9; −/− 9.6 ± 0.5 ng ANG I · mg protein−1· h−1; n = 6–7; P < 0.05 compared with no treatment). Immunohistochemical analysis of renin expression confirmed the above results. This study provides definitive evidence that metabolites of COX-2 rather than COX-1 mediate ACEI-induced renin increases. The persistent response in EP2nulls suggests involvement of prostaglandin E2receptor subtype 4 and/or prostacyclin receptor (IP).
Regional responsiveness of renal perfusion to activation of the renal nerves
Authors: Guild Sarah-Jane , Eppel Gabriela A. , Malpas Simon C. , Rajapakse Niwanthi W. , Stewart Alistair , Evans Roger G.
Published: March 2015

We tested for regional differences in perfusion responses, within the renal medulla and cortex, to renal nerve stimulation in pentobarbital sodium-anesthetized rabbits. Laser-Doppler flux (LDF) was monitored at various depths below the cortical surface (1–15 mm). Basal cortical LDF (1–3 mm, ∼200–450 U) was greater than medullary LDF (5–15 mm, ∼70–160 U), but there were no statistically significant differences in basal LDF within these regions. The background LDF signal during aortic occlusion was similar in the cortex (2 mm, 31 U) and outer medulla (7 mm, 31 U), but slightly greater in the inner medulla (12 mm, 44 U). During electrical stimulation of the renal nerves (0.5–8 Hz), cortical LDF and total renal blood flow were similarly progressively reduced with increasing stimulus frequency. Medullary LDF (measured between 5 and 15 mm) was overall less responsive than cortical LDF. For example, 4-Hz stimulation reduced inner medullary LDF (9 mm) by 19 ± 6% but reduced cortical LDF (1 mm) by 54 ± 11%. However, medullary LDF responses to nerve stimulation were similar at all depths measured. Our results indicate that while the vascular elements controlling medullary perfusion are less sensitive to the effects of electrical stimulation of the renal nerves than are those controlling cortical perfusion, sensitivity within these vascular territories appears to be relatively homogeneous.
Serum but not myocardial TNF-α concentration is increased in pacing-induced heart failure in rabbits
Authors: Aker Stephanie , Belosjorow Sergej , Konietzka Ina , Duschin Alexej , Martin Claus , Heusch Gerd , Schulz Rainer
Published: March 2015

In animals and patients with severe heart failure (HF), the serum tumor necrosis factor-α (TNF-α) concentration is increased. It is, however, still controversial whether or not such increased serum TNF-α originates from the heart itself or is of peripheral origin secondary to gastrointestinal congestion and increased endotoxin concentration. We therefore now examined TNF-α in serum, myocardium, and liver of sham-operated and HF rabbits. In nine rabbits in which HF was induced by left ventricular (LV) pacing at 400 beats/min for 3 wk, LV end-diastolic diameter was increased and systolic shortening fraction (9.4 ± 1.0 vs. 28.5 ± 1.3%, echocardiography, P < 0.05) was reduced. Serum TNF-α was higher in HF than in sham-operated rabbits (240 ± 24 vs. 150 ± 22 U/ml, WEHI-cell assay, P < 0.05). In the heart, TNF-α was located mainly in the vascular endothelium (immunohistochemistry), and TNF-α protein (920 ± 160 vs. 900 ± 95 U/g) did not differ between groups. In the liver of HF rabbits, hepatocytes expressed TNF-α, and TNF-α protein was increased compared with sham-operated rabbits (2,390 ± 310 vs. 1,220 ± 135 U/g, P < 0.05) and correlated to the number of hepatic leukocytes ( r = 0.85) and serum TNF-α ( r = 0.69). The intestinal endotoxin concentration was 24.5 ± 1.2 vs. 17.0 ± 3.1 endotoxin units/g wet wt ( P < 0.05) in HF compared with sham-operated rabbits. In this HF model, serum but not myocardial TNF-α is increased. The increased serum TNF-α originates from peripheral sources.
High-fat diet prevents eating response and attenuates liver ATP decline in rats given 2,5-anhydro-d-mannitol
Authors: Friedman Mark I. , Koch James E. , Graczyk-Milbrandt Grazyna , Ulrich Patricia M. , Osbakken Mary D.
Published: March 2015

Administration of the fructose analog 2,5-anhydro-d-mannitol (2,5-AM) stimulates eating in rats fed a low-fat diet but not in those fed a high-fat diet that enhances fatty acid oxidation. The eating response to 2,5-AM treatment is apparently triggered by a decrease in liver ATP content. To assess whether feeding a high-fat diet prevents the eating response to 2,5-AM by attenuating the decrease in liver ATP, we examined the effects of the analog on food intake, liver ATP content, and hepatic phosphate metabolism [using in vivo31P-NMR spectroscopy (NMRS)]. Injection (intraperitoneal) of 300 mg/kg 2,5-AM increased food intake in rats fed a high-carbohydrate/low-fat diet, but not in those fed high-fat/low-carbohydrate (HF/LC) food. Liver ATP content decreased in all rats given 2,5-AM compared with saline, but it decreased about half as much in rats fed the HF/LC diet. NMRS on livers of anesthetized rats indicated that feeding the HF/LC diet attenuates the effects of 2,5-AM on liver ATP by reducing phosphate trapping. These results suggest that rats consuming a high-fat diet do not increase food intake after injection of 2,5-AM, because the analog is not sufficiently phosphorylated and therefore fails to decrease liver energy status below a level that generates a signal to eat.
Sinoaortic denervation abolishes pressure resetting for daily physical activity in rabbits
Authors: Nishida Yasuhiro , Chen Qing Hui , Zhou Ming-Sheng , Horiuchi Jouji
Published: March 2015

It has been speculated that if baroafferent signals are only related to the negative feedback control of arterial pressure (AP), then physical activity would increase the range of AP fluctuation in baroafferent-denervated animals. Mean AP (MAP), heart rate (HR), and cardiac output (CO) were measured for 24 h in free-moving conscious rabbits. On the basis of hydrostatic pressure and electromyogram, MAP data taken during periods of physical activity and rest were selected from the overall 24-h MAP data and then converted into histograms. During physical activity, the mode of MAP histogram increased in intact rabbits and was unchanged in sinoaortic-denervated (SAD) rabbits. Movement increased the mode of total peripheral resistance (TPR) but did not significantly change CO in intact rabbits. Conversely in SAD rabbits, movement slightly decreased TPR and slightly increased CO. These findings indicate that arterial baroafferent signals are required to shift MAP to a higher pressure level by an increase in TPR but not in CO during a moving phase. These results suggest that baroafferent signals may not only minimize the fluctuating range of MAP through negative feedback control but also be involved in actively resetting MAP toward a higher pressure level during daily physical activity.
Oxygen-limited thermal tolerance in Antarctic fish investigated by MRI and31P-MRS
Authors: Mark F. C. , Bock C. , Pörtner H. O.
Published: March 2015

The hypothesis of an oxygen-limited thermal tolerance was tested in the Antarctic teleost Pachycara brachycephalum. With the use of flow-through respirometry, in vivo31P-NMR spectroscopy, and MRI, we studied energy metabolism, intracellular pH (pHi), blood flow, and oxygenation between 0 and 13°C under normoxia (Po2: 20.3 to 21.3 kPa) and hyperoxia (Po2: 45 kPa). Hyperoxia reduced the metabolic increment and the rise in arterial blood flow observed under normoxia. The normoxic increase of blood flow leveled off beyond 7°C, indicating a cardiovascular capacity limitation. Ventilatory effort displayed an exponential rise in both groups. In the liver, blood oxygenation increased, whereas in white muscle it remained unaltered (normoxia) or declined (hyperoxia). In both groups, the slope of pHichanges followed the alpha-stat pattern below 6°C, whereas it decreased above. In conclusion, aerobic scope declines around 6°C under normoxia, marking the pejus temperature. By reducing circulatory costs, hyperoxia improves aerobic scope but is unable to shift the breakpoint in pH regulation or lethal limits. Hyperoxia appears beneficial at sublethal temperatures, but no longer beyond when cellular or molecular functions become disturbed.
Macrophages, not neutrophils, infiltrate skeletal muscle in mice deficient in P/E selectins after mechanical reloading
Authors: Frenette Jéroôme , Chbinou Nadia , Godbout Charles , Marsolais David , Frenette Paul S.
Published: March 2015

Our objective was to test the hypothesis that endothelial selectins, P and E selectins, are necessary for leukocyte migration after muscle injury from unloading/reloading. Mice hindlimbs were suspended for 10 days followed by reloading periods of 6 or 24 h after which the soleus muscle was dissected. Light microscopic observations showed that macrophages, but not neutrophils, were able to invade soleus muscles in mice deficient in P/E selectins (P/E-/-) during reloading periods. The recruitment efficiency of neutrophils after 6 and 24 h of reloading was minimal in P/E-/-mice relative to unloaded animals. The recruitment of macrophages in the soleus muscle was preserved in P/E-/-mice. The concentration of macrophages increased by 8.1-fold compared with unloaded muscles in double-mutant mice after 24 h of reloading. The accumulation of macrophages in reloaded muscles did not lead to fiber necrosis. Together, these findings indicate that macrophages can invade skeletal muscle through cellular mechanisms that do not involve P/E selectins during skeletal muscle reloading.
Brain vasopressin and sodium appetite
Authors: Flynn Francis W. , Kirchner Thomas R. , Clinton Margaret E.
Published: March 2015

Intraventricular injections of vasopressin (VP) and antagonists with varying degrees of specificity for the VP receptors were used to identify the action of endogenous brain VP on 0.3 M NaCl intake by sodium-deficient rats. Lateral ventricular injections of 100 ng and 1 μg VP caused barrel rotations and a dramatic decrease in NaCl intake by sodium-deficient rats and suppressed sucrose intake. Intraventricular injection of the V1/V2 receptor antagonist [d(CH2)5 1,O-Et-Tyr2,Val4, Arg8]VP and the V1 receptor antagonist [d(CH2)5 1,O-Me-Tyr2,Arg8]VP (MeT-AVP) significantly suppressed NaCl intake by sodium-deficient rats without causing motor disturbances. MeT-AVP had no effect on sucrose intake (0.1 M). In contrast, the selective V2 receptor antagonist had no significant effect on NaCl intake. Last, injections of 100 ng MeT-AVP decreased mean arterial blood pressure (MAP), whereas 100 ng VP elevated MAP and pretreatment with MeT-AVP blocked the pressor effect of VP. These results indicate that the effects produced by 100 ng MeT-AVP represent receptor antagonistic activity. These findings suggest that the effect of exogenous VP on salt intake is secondary to motor disruptions and that endogenous brain VP neurotransmission acting at V1 receptors plays a role in the arousal of salt appetite.
Muscle impairment occurs rapidly and precedes inflammatory cell accumulation after mechanical loading
Authors: Frenette Jérôme , St-Pierre Matthieu , Côté Claude H. , Mylona Eleni , Pizza Frank X.
Published: March 2015

Modified muscle use can result in muscle atrophy and impairment. We tested whether inflammatory cell concentrations correlate temporally with muscle impairment during modified loading periods. Rat hindlimbs were unloaded for 10 days followed by reloading. The density of neutrophils and ED1+ macrophages was significantly increased by 16.5- and 9.8-fold, respectively, after 1 day of reloading. ED2+macrophage concentration was not significantly increased until 3 days of reloading. Maximal isometric tetanic tension (Po; N/cm2) decreased during hindlimb suspension (HS), which was followed by a second drop in Poafter 2 h of reloading. This latter loss in muscle force was uncoupled with the significant elevation in muscle inflammatory cell concentrations. Experiments where HS soleus muscles were incubated with caffeine revealed that at least 40% of the Po decrement at 2 h could be associated with a loss of efficiency of the excitation-contraction (E-C) coupling process. These data suggest that an important mechanism for the early loss in force is the inability to activate the contractile machinery likely caused by a failure in the E-C coupling process during the reloading period.
Hypocretin release in normal and narcoleptic dogs after food and sleep deprivation, eating, and movement
Authors: Wu M.-F. , John J. , Maidment N. , Lam H. A. , Siegel J. M.
Published: March 2015

Hypocretins (orexins) are recently discovered hypothalamic neuropeptides that have been implicated in the etiology of narcolepsy. The normal behavioral functions of these peptides are unclear, although a role in feeding has been suggested. We measured hypocretin-1 (Hcrt-1) in the cerebrospinal fluid of dogs during a variety of behaviors. We found that 48 h without food (24 h beyond normal 24-h fasting period) produced no significant change in Hcrt-1 levels nor did feeding after the deprivation. In contrast, 24 h of sleep deprivation produced on average a 70% increase in Hcrt-1 level compared with baseline levels. The amount of increase was correlated with the level of motor activity during the sleep-deprivation procedure. A 2-h period of exercise in the same dogs produced a 57% increase in Hcrt-1 levels relative to quiet waking levels, with the magnitude of the increase being highly correlated with the level of motor activity. The strong correlation between motor activity and Hcrt-1 release may explain some of the previously reported behavioral, physiological, and pathological phenomena ascribed to the Hcrt system.
Angiotensin receptors contribute to blood pressure homeostasis in salt-depleted SHR
Authors: Nakamura Shigefumi , Averill David B. , Chappell Mark C. , Diz Debra I. , Brosnihan K. Bridget , Ferrario Carlos M.
Published: March 2015

This study evaluated the contribution of angiotensin peptides acting at various receptor subtypes to the arterial pressure and heart rate of adult 9-wk-old male conscious salt-depleted spontaneously hypertensive rats (SHR). Plasma ANG II and ANG I in salt-depleted SHR were elevated sevenfold compared with peptide levels measured in sodium-replete SHR, whereas plasma ANG-(1–7) was twofold greater in salt-depleted SHR compared with salt-replete SHR. Losartan (32.5 μmol/kg), PD-123319 (0.12 μmol · kg−1 · min−1), [d-Ala7]ANG-(1–7) (10 and 100 pmol/min), and a polyclonal ANG II antibody (0.08 mg/min) were infused intravenously alone or in combination. Combined blockade of AT2 and AT(1–7) receptors significantly increased the blood pressure of losartan-treated SHR (+15 ± 1 mmHg; P < 0.01); this change did not differ from the blood pressure elevation produced by the sole blockade of AT(1–7) receptors (15 ± 4 mmHg). On the other hand, sole blockade of AT2 receptors in losartan-treated SHR increased mean arterial pressure by 8 ± 1 mmHg ( P < 0.05 vs. 5% dextrose in water as vehicle), and this increase was less than the pressor response produced by blockade of AT(1–7) receptors alone or combined blockade of AT(1–7) and AT2 receptors. The ANG II antibody increased blood pressure to the greatest extent in salt-depleted SHR pretreated with only losartan (+11 ± 2 mmHg) and to the least extent in salt-depleted SHR previously treated with the combination of losartan, PD-123319, and [d-Ala7]ANG-(1–7) (+7 ± 1 mmHg; P < 0.01). Losartan significantly increased heart rate, whereas other combinations of receptor antagonists or the ANG II antibody did not alter heart rate. Our results demonstrate that ANG II and ANG-(1–7) act through non-AT1receptors to oppose the vasoconstrictor actions of ANG II in salt-depleted SHR. Combined blockade of AT2 and AT(1–7) receptors and ANG II neutralization by the ANG II antibody reversed as much as 67% of the blood pressure-lowering effect of losartan.
Disinhibition of female sexual behavior by a CRH receptor antagonist in Syrian hamsters
Authors: Jones Juli E. , Pick Rebecca R. , Davenport Matthew D. , Keene Alex C. , Corp Eric S. , Wade George N.
Published: March 2015

Several conditions that inhibit female sexual behavior are thought to be associated with altered corticotropin-releasing hormone (CRH) activity in the brain. The present experiments examined the hypothesis that endogenous CRH receptor signaling mediates the inhibition of estrous behavior by undernutrition and in other instances of sexual dysfunction. Intracerebroventricular (ICV) infusion of CRH or urocortin inhibited estrous behavior in ovariectomized steroid-primed hamsters. Conversely, ICV infusion of the CRH receptor antagonist astressin prevented the suppression of estrous behavior by food deprivation or by ICV administration of neuropeptide Y. Astressin treatment also induced sexual receptivity in nonresponders, animals that do not normally come into heat when treated with hormones, and this effect persisted in subsequent weekly tests in the absence of any further astressin treatment. Activation of the hypothalamo-pituitary-adrenocortical axis was neither necessary nor sufficient to inhibit estrous behavior, indicating that this phenomenon is due to other central actions of CRH receptor agonists. This is the first direct evidence that CRH receptor signaling may be a final common pathway by which undernutrition and other conditions inhibit female sexual behavior.