bluuebunny/crossref_metadata_2025 huggingface dataset:
Blockade of fatty acid oxidation mimics phase II-phase III transition in a fasting bird, the king penguin
Authors: Bernard Servane F. , Mioskowski Eliane , Groscolas René
Published: March 2015

This study tests the hypothesis that the metabolic and endocrine shift characterizing the phase II-phase III transition during prolonged fasting is related to a decrease in fatty acid (FA) oxidation. Changes in plasma concentrations of various metabolites and hormones and in lipolytic fluxes, as determined by continuous infusion of [2-3H]glycerol and [1-14C]palmitate, were examined in vivo in spontaneously fasting king penguins in the phase II status (large fat stores, protein sparing) before, during, and after treatment with mercaptoacetate (MA), an inhibitor of FA oxidation. MA induced a 7-fold decrease in plasma β-hydroxybutyrate and a 2- to 2.5-fold increase in plasma nonesterified fatty acids (NEFA), glycerol, and triacylglycerols. MA also stimulated lipolytic fluxes, increasing the rate of appearance of NEFA and glycerol by 60–90%. This stimulation might be partly mediated by a doubling of circulating glucagon, with plasma insulin remaining unchanged. Plasma glucose level was unaffected by MA treatment. Plasma uric acid increased 4-fold, indicating a marked acceleration of body protein breakdown, possibly mediated by a 2.5-fold increase in circulating corticosterone. Strong similarities between these changes and those observed at the phase II-phase III transition in fasting penguins support the view that entrance into phase III, and especially the end of protein sparing, is related to decreased FA oxidation, rather than reduced NEFA availability. MA could be therefore a useful tool for understanding mechanisms underlying the phase II-phase III transition in spontaneously fasting birds and the associated stimulation of feeding behavior.
Pregnancy and acute baroreflex resetting in conscious rabbits
Authors: Brooks Virginia L. , Clow Kathy A. , O'Hagan Kathleen P.
Published: March 2015

To test the hypothesis that acute resetting of baroreflex control of heart rate (HR) is enhanced during pregnancy, we determined whether the rightward shift in the baroreflex relationship between arterial pressure and HR after arterial pressure is raised [∼25 mmHg for 30 min, due to infusion of phenylephrine (PE) or methoxamine (Meth)] is greater in late pregnant compared with nonpregnant conscious rabbits. Baroreflex function was assessed by monitoring HR responses to both stepwise steady-state changes ( n = 14) and rapid ramp changes ( n = 10) in arterial pressure. Pregnancy decreased reflex gain, increased reflex minimum HR, and shifted the curves to a lower pressure level, when either the steady-state or ramp method was used (all changes, P < 0.05). When PE was used to increase pressure, resetting of steady-state curves was observed both before and during pregnancy, but the magnitude of the resetting was less in the pregnant rabbits. Further inspection of the data revealed that the size of the shift in pregnant rabbits was inversely related to the dose of PE. Because the pressure rise was the same in all experiments, PE appears to nonspecifically counteract acute resetting. When Meth was used instead to increase pressure, resetting of steady-state curves was similar in pregnant and nonpregnant rabbits and was unrelated to dose. Similarly, when reflex curves were generated using the ramp method, and either Meth or low doses of PE were used to increase pressure, no differences in the degree of resetting were observed between pregnant and nonpregnant rabbits. In summary, high doses of PE counteract acute resetting of baroreflex control of HR. More importantly, while baroreflex function is depressed, the ability of the baroreflex to reset appears to be preserved during pregnancy.
Glucocorticoids, thyroid hormones, and iodothyronine deiodinases in embryonic saltwater crocodiles
Authors: Shepherdley Caroline A. , Daniels Christopher B. , Orgeig Sandra , Richardson Samantha J. , Evans Barbara K. , Darras Veerle M.
Published: March 2015

We investigated the relationship between glucocorticoids, thyroid hormones, and outer ring and inner ring deiodinases (ORD and IRD) during embryonic development in the saltwater crocodile ( Crocodylus porosus). We treated the embryos with the synthetic glucocorticoid dexamethasone (Dex), 3,3′,5-triiodothyronine (T3), and a combination of these two hormones (Dex + T3). The effects of these treatments were specific in different tissues and at different stages of development and also brought about changes in plasma concentrations of free thyroid hormones and corticosterone. Administration of Dex to crocodile eggs resulted in a decrease in 3,3′,5,5′-tetraiodothyronine (T4) ORD activities in liver and kidney microsomes, and a decrease in the high- K m rT3 ORD activity in kidney microsomes, on day 60 of incubation. Dex treatment increased the T4 ORD activity in liver microsomes, but not kidney microsomes, on day 75 of incubation. Dex administration decreased T3 IRD activity in liver microsomes. However, this decrease did not change plasma-free T3 concentrations, which suggests that free thyroid hormone levels are likely to be tightly regulated during development.
Mineralocorticoids act centrally to regulate blood-borne tumor necrosis factor-α in normal rats
Authors: Francis Joseph , Beltz Terry , Johnson Alan Kim , Felder Robert B.
Published: March 2015

Excessive mineralocorticoid receptor (MR) stimulation induces neurohumoral excitation and cardiac and vascular fibrosis. In heart failure (HF) rats, with excessive neurohumoral drive, central infusion of the MR antagonist spironolactone (SL) decreases blood-borne TNF-α. This study aimed to determine whether DOCA, a precursor of aldosterone, acts centrally to stimulate TNF-α production in normal rats. DOCA (5 mg sc daily for 8 days) induced a progressive increase in TNF-α beginning on day 3 and increased tissue TNF-α in hypothalamus, pituitary, and heart but not in other brain and peripheral tissues harvested on day 9. A continuous intracerebroventricular infusion of SL (100 ng/h) blocked the plasma TNF-α response. Oral SL (1 mg/kg) blocked the plasma and tissue TNF-α responses. Thus DOCA increases TNF-α in brain, heart, and blood in normal rats. Activation of brain MR appears to account for the increase in plasma TNF-α. These findings have important implications for the understanding of pathophysiological states (e.g., HF, hypertension) characterized by high circulating levels of aldosterone.
Diuretic response to acute hypertension is blunted during angiotensin II clamp
Authors: Leong Patrick K. K. , Zhang Yibin , Yang Li E. , Holstein-Rathlou Niels-Henrik , McDonough Alicia A.
Published: March 2015

Acute hypertension inhibits proximal tubule (PT) fluid reabsorption. The resultant increase in end proximal flow rate provides the error signal to mediate tubuloglomerular feedback autoregulation of renal blood flow and glomerular filtration rate and suppresses renal renin secretion. To test whether the suppression of the renin-angiotensin system during acute hypertension affects the magnitude of the inhibition of PT fluid and sodium reabsorption, plasma ANG II levels were clamped by infusion of the angiotensin-converting enzyme (ACE) inhibitor captopril (12 μg/min) and ANG II after pretreatment with the bradykinin B2 receptor blocker HOE-140 (100 μg/kg bolus). Because ACE also degrades bradykinin, HOE-140 was included to block effect of accumulating vasodilatory bradykinins during captopril infusion. HOE-140 increased the sensitivity of arterial blood pressure to ANG II: after captopril infusion without HOE-140, 20 ng · kg−1 · min−1 ANG II had no pressor effect, whereas with HOE-140, 20 ng · kg−1 · min−1 ANG II increased blood pressure from 104 ± 4 to 140 ± 6 mmHg. ANG II infused at 2 ng · kg−1 · min−1 had no pressor effect after captopril and HOE-140 infusion (“ANG II clamp”). When blood pressure was acutely increased 50–60 mmHg by arterial constriction without ANG II clamp, urine output and endogenous lithium clearance increased 4.0- and 6.7-fold, respectively. With ANG II clamp, the effects of acute hypertension were reduced 50%: urine output and endogenous lithium clearance increased two- and threefold, respectively. We conclude that HOE-140, an inhibitor of the B2 receptor, potentiates the sensitivity of arterial pressure to ANG II and that clamping systemic ANG II levels during acute hypertension blunts the magnitude of the pressure diuretic response.
Why is V˙o 2 max after altitude acclimatization still reduced despite normalization of arterial O2 content?
Authors: Calbet J. A. L. , Boushel R. , Rådegran G. , Søndergaard H. , Wagner P. D. , Saltin B.
Published: March 2015

Acute hypoxia (AH) reduces maximal O2 consumption (V˙o 2 max), but after acclimatization, and despite increases in both hemoglobin concentration and arterial O2 saturation that can normalize arterial O2 concentration ([O2]),V˙o 2 max remains low. To determine why, seven lowlanders were studied at V˙o 2 max(cycle ergometry) at sea level (SL), after 9–10 wk at 5,260 m [chronic hypoxia (CH)], and 6 mo later at SL in AH (Fi O2 = 0.105) equivalent to 5,260 m. Pulmonary and leg indexes of O2 transport were measured in each condition. Both cardiac output and leg blood flow were reduced by ∼15% in both AH and CH ( P < 0.05). At maximal exercise, arterial [O2] in AH was 31% lower than at SL ( P < 0.05), whereas in CH it was the same as at SL due to both polycythemia and hyperventilation. O2extraction by the legs, however, remained at SL values in both AH and CH. Although at both SL and in AH, 76% of the cardiac output perfused the legs, in CH the legs received only 67%. PulmonaryV˙o 2 max (4.1 ± 0.3 l/min at SL) fell to 2.2 ± 0.1 l/min in AH ( P < 0.05) and was only 2.4 ± 0.2 l/min in CH ( P < 0.05). These data suggest that the failure to recoverV˙o 2 max after acclimatization despite normalization of arterial [O2] is explained by two circulatory effects of altitude: 1) failure of cardiac output to normalize and 2) preferential redistribution of cardiac output to nonexercising tissues. Oxygen transport from blood to muscle mitochondria, on the other hand, appears unaffected by CH.
Desmin cytoskeletal modifications after a bout of eccentric exercise in the rat
Authors: Barash Ilona A. , Peters David , Fridén Jan , Lutz Gordon J. , Lieber Richard L.
Published: March 2015

Desmin content and immunohistochemical appearance were measured in tibialis anterior muscles of rats subjected to a single bout of 30 eccentric contractions (ECs). Ankle torque was measured before EC and at various recovery times, after which immunohistochemical and immunoblot analyses were performed. Torque decreased by ∼50% immediately after EC and fully recovered 168 h later ( P < 0.001). Loss of desmin staining was maximal 12 h after EC and recovered by 72 h. Immunoblots unexpectedly demonstrated a significant increase in the desmin-to-actin ratio by 72 h after EC ( P < 0.01) and was still increasing after 168 h ( P < 0.0001). These data demonstrate a relatively rapid qualitative loss of desmin immunostaining immediately after a single EC bout but a tremendous quantitative increase in desmin content 72–168 h later. This dynamic restructuring of the muscle's intermediate filament system may be involved in the mechanism of EC-induced muscle injury and may provide a structural explanation for the protective effects observed in muscle after a single EC bout.
Extracellular signal-regulated kinase and phosphoinositol-3 kinase mediate IGF-1 induced proliferation of fetal sheep cardiomyocytes
Authors: Sundgren Nathan C. , Giraud George D. , Schultz Jess M. , Lasarev Michael R. , Stork Philip J. S. , Thornburg Kent L.
Published: March 2015

Growth of the fetal heart involves cardiomyocyte enlargement, division, and maturation. Insulin-like growth factor-1 (IGF-1) is implicated in many aspects of growth and is likely to be important in developmental heart growth. IGF-1 stimulates the IGF-1 receptor (IGF1R) and downstream signaling pathways, including extracellular signal-regulated kinase (ERK) and phosphoinositol-3 kinase (PI3K). We hypothesized that IGF-1 stimulates cardiomyocyte proliferation and enlargement through stimulation of the ERK cascade and stimulates cardiomyocyte differentiation through the PI3K cascade. In vivo administration of Long R3 IGF-1 (LR3 IGF-1) did not stimulate cardiomyocyte hypertrophy but led to a decreased percentage of cells that were binucleated in vivo. In culture, LR3 IGF-1 increased myocyte bromodeoxyuridine (BrdU) uptake by three- to five-fold. The blockade of either ERK or PI3K signaling (by UO-126 or LY-294002, respectively) completely abolished BrdU uptake stimulated by LR3 IGF-1. LR3 IGF-1 did not increase footprint area, but as expected, phenylephrine stimulated an increase in binucleated cardiomyocyte size. We conclude that 1) IGF-1 through IGF1R stimulates cardiomyocyte division in vivo; hyperplastic growth is the most likely explanation of IGF-1 stimulated heart growth in vivo; 2) IGF-1 through IGF1R does not stimulate binucleation in vitro or in vivo; 3) IGF-1 through IGF1R does not stimulate hypertrophy either in vivo or in vitro; and 4) IGF-1 through IGF1R requires both ERK and PI3K signaling for proliferation of near-term fetal sheep cardiomyocytes in vitro.
Reduced central leptin sensitivity in rats with diet-induced obesity
Authors: Levin Barry E. , Dunn-Meynell Ambrose A.
Published: March 2015

On low-fat chow diet, rats prone to diet-induced obesity (DIO) have increased arcuate nucleus neuropeptide Y (NPY) expression but similar leptin levels compared with diet-resistant (DR) rats (19). Here, body weight and leptin levels rose in DIO rats, and they defended their higher body weight after only 1 wk on a 31% fat high-energy (HE) diet. However, DIO NPY expression did not fall to DR levels until 4 wk when plasma leptin was 168% of DR levels. When switched to chow, DIO rats lost carcass fat (18). By 10 wk, leptin levels fell to 148% and NPY expression again rose to 150% of DR levels. During 4 wk of food restriction, DIO leptin fell by ∼50% while NPY increased by 30%. While both returned to control levels by 8 wk, DIO rats still regained all lost weight when fed ad libitum. Finally, the anorexic effect of intracerebroventricular leptin (10 μg) was inversely correlated with subsequent 3-wk weight gain on HE diet. Thus NPY expression and food intake are less sensitive to the leptin's suppressive effects in DIO rats. While this may predispose them to develop DIO, it does not fully explain their defense of a higher body weight on HE diet.
Effects of fetal behavioral states on renal sympathetic nerve activity and arterial pressure of unanesthetized fetal sheep
Authors: Lumbers Eugenie R. , Yu Ze-Yan , Crawford Edward N.
Published: March 2015

Fetal behavior, renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), and heart rate (HR) were studied 1-3 days after surgery in seven fetal sheep (aged 127-136 days). Five behavioral states were defined from chart recordings of electrocortical (electrocorticographic; ECoG) activity and eye, limb, and breathing movements. Most records were of high-voltage ECoG (HV) or low-voltage (LV) ECoG with breathing (LVB); 6.7 ± 1.7% were LV ECoG with no breathing (LV0). RSNA was lower in LV0 ( P < 0.001) and greater in LVB than in HV ( P < 0.05). MAP was lower in both LV states than in HV and when the fetuses went from LV to HV ( P < 0.001 to P < 0.03). HR was highest in HV ( P < 0.001). In HV and LVB and when the fetus went from LV to HV, MAP and HR were inversely related ( P = 0.012-0.003). In LVB and from LV to HV there were direct relationships between MAP and RSNA ( P = 0.0014, P = 0.08), and when the fetus went from LV to HV there was also an inverse relationship between HR and RSNA ( P = 0.02). Thus fetal RSNA, MAP, and HR are affected by behavioral state as is fetal cardiovascular control. The increase in RSNA during fetal breathing showed that there was an altered level of fetal RSNA associated with fetal breathing activity.
Effects of truncated angiotensins in humans after double blockade of the renin system
Authors: Plovsing Ronni R. , Wamberg Christian , Sandgaard Niels C. F. , Simonsen Jane A. , Holstein-Rathlou Niels-Henrik , Høilund-Carlsen Poul Flemming , Bie Peter
Published: March 2015

Angiotensins different from ANG II exhibit biological activities, possibly mediated via receptors other than ANG II receptors. We studied the effects of 3-h infusions of ANG III, ANG-(1-7), and ANG IV in doses equimolar to physiological amounts of ANG II (3 pmol · kg-1 · min-1), in six men on low-sodium diet (30 mmol/day). The subjects were acutely pretreated with canrenoate and captopril to inhibit aldosterone actions and ANG II synthesis, respectively. ANG II infusion increased plasma angiotensin immunoreactivity to 53 ± 6 pg/ml (+490%), plasma aldosterone to 342 ± 38 pg/ml (+109%), and blood pressure by 27%. Glomerular filtration rate decreased by 16%. Concomitantly, clearance of endogenous lithium fell by 66%, and fractional proximal reabsorption of sodium increased from 77 to 92%; absolute proximal reabsorption rate of sodium remained constant. ANG II decreased sodium excretion by 70%, potassium excretion by 50%, and urine flow by 80%, whereas urine osmolality increased. ANG III also increased plasma aldosterone markedly (+45%), however, without measurable changes in angiotensin immunoreactivity, glomerular filtration rate, or renal excretion rates. During vehicle infusion, plasma renin activity decreased markedly (∼700 to ∼200 mIU/l); only ANG II enhanced this decrease. ANG-(1-7) and ANG IV did not change any of the measured variables persistently. It is concluded that 1) ANG III and ANG IV are cleared much faster from plasma than ANG II, 2) ANG II causes hypofiltration, urinary concentration, and sodium and potassium retention at constant plasma concentrations of vasopressin and atrial natriuretic peptide, and 3) a very small increase in the concentration of ANG III, undetectable by usual techniques, may increase aldosterone secretion substantially.
5-Aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR) stimulates myocardial glycogenolysis by allosteric mechanisms
Authors: Longnus Sarah L. , Wambolt Richard B. , Parsons Hannah L. , Brownsey Roger W. , Allard Michael F.
Published: March 2015

We tested the hypothesis that activation of AMP-activated protein kinase (AMPK) promotes myocardial glycogenolysis by decreasing glycogen synthase (GS) and/or increasing glycogen phosphorylase (GP) activities. Isolated working hearts from halothane-anesthetized male Sprague-Dawley rats perfused in the absence or presence of 0.8 or 1.2 mM 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR), an adenosine analog and cell-permeable activator of AMPK, were studied. Glycogen degradation was increased by AICAR, while glycogen synthesis was not affected. AICAR increased myocardial 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranotide (ZMP), the active intracellular form of AICAR, but did not alter the activity of GS and GP measured in tissue homogenates or the content of glucose-6-phosphate and adenine nucleotides in freeze-clamped tissue. Importantly, the calculated intracellular concentration of ZMP achieved in this study was similar to the Kmvalue of ZMP for GP determined in homogenates of myocardial tissue. We conclude that the data are consistent with allosteric activation of GP by ZMP being responsible for the glycogenolysis caused by AICAR in the intact rat heart.
Responses to human CGRP, ADM, and PAMP in human thymic arteries
Authors: Champion Hunter C. , Bivalacqua Trinity J. , Pierce Robert L. , Murphy William A. , Coy David H. , Hyman Albert L. , Kadowitz Philip J.
Published: March 2015

Responses to human CGRP, adrenomedullin (ADM), and proadrenomedullin NH2-terminal 20 peptide (PAMP) were studied in small human thymic arteries. CGRP, ADM, and PAMP produced concentration-dependent vasodilator responses in arteries preconstricted with the thromboxane mimic U-46619. Responses to ADM and PAMP were attenuated, whereas responses to CGRP were not altered by endothelial denudation. Inhibitors of nitric oxide synthase and guanylyl cyclase attenuated responses to ADM and PAMP but not to CGRP. The CGRP1 receptor antagonist CGRP(8–37) attenuated responses to CGRP and ADM but not to PAMP. Responses to CGRP were reduced by SQ-22536 and Rp-cAMPS, inhibitors of adenylyl cyclase and PKA. These data suggest that responses to CGRP and ADM are mediated by CGRP(8–37)-sensitive receptors and that the endothelial ADM receptor induces vasodilation by a nitric oxide-guanylyl cyclase mechanism, whereas a smooth muscle CGRP receptor signals by a cAMP-dependent mechanism. A different endothelial receptor recognizes PAMP and signals by a nitric oxide-dependent mechanism.
Cardiovascular effects of leptin and orexins
Authors: Shirasaka Tetsuro , Takasaki Mayumi , Kannan Hiroshi
Published: March 2015

Leptin, the product of the obgene, is a satiety factor secreted mainly in adipose tissue and is part of a signaling mechanism regulating the content of body fat. It acts on leptin receptors, most of which are located in the hypothalamus, a region of the brain known to control body homeostasis. The fastest and strongest hypothalamic response to leptin in ob/ob mice occurs in the paraventricular nucleus, which is involved in neuroendocrine and autonomic functions. On the other hand, orexins (orexin-A and -B) or hypocretins (hypocretin-1 and -2) were recently discovered in the hypothalamus, in which a number of neuropeptides are known to stimulate or suppress food intake. These substances are considered important for the regulation of appetite and energy homeostasis. Orexins were initially thought to function in the hypothalamic regulation of feeding behavior, but orexin-containing fibers and their receptors are also distributed in parts of the brain closely associated with the regulation of cardiovascular and autonomic functions. Functional studies have shown that these peptides are involved in cardiovascular and sympathetic regulation. The objective of this article is to summarize evidence on the effects of leptin and orexins on cardiovascular function in vivo and in vitro and to discuss the pathophysiological relevance of these peptides and possible interactions.
Brain angiotensinergic mediation of enhanced water consumption in lactating rats
Authors: Speth Robert C. , Smith M. Susan , Grove Kevin L.
Published: March 2015

The mechanism by which lactating rats increase fluid consumption to meet the demands of milk production is unknown. Because ANG II is the most potent dipsogenic stimulus known, this study examined whether angiotensinergic signaling plays a role in enhanced drinking in lactating rats. ANG II administered intracerebroventricularly caused a significantly greater dipsogenic response in lactating rats than in control rats, suggesting that dipsogenic responsivity to ANG II is enhanced in the brains of lactating rats. The angiotensin type 1 (AT1) ANG II receptor subtype antagonist SKF-108566, also given intracerebroventricularly, caused a significant reduction in water consumption in lactating rats, whereas it did not significantly affect water intake in control rats. In contrast, stimulation of drinking by the muscarinic agonist carbachol, also administered intracerebroventricularly, did not differ between lactating and control rats. Inhibition of drinking by the muscarinic antagonist atropine also did not differ significantly between lactating and control rats. These results suggest that the increased drinking in lactating rats involves an increased responsivity to ANG II in neurons that mediate dipsogenesis, as well as an enhancement in the amount of angiotensinergic input to these ANG II-responsive neurons.
Parathyroid hormone-related protein induction in focal stroke: a neuroprotective vascular peptide
Authors: Funk Janet L. , Migliati Elton , Chen Guanjie , Wei Hongbing , Wilson Jonathan , Downey Katherine J. , Mullarky Paul J. , Coull Bruce M. , McDonagh Paul F. , Ritter Leslie S.
Published: March 2015

Parathyroid hormone-related protein (PTHrP) is a multifunctional peptide that enhances blood flow in non-central nervous system (CNS) vascular beds by causing vasodilation. PTHrP expression is induced in non-CNS organs in response to ischemia. Experiments were therefore undertaken to determine whether PTHrP can be induced in brain in response to ischemic injury and whether PTHrP can act locally as a vasodilator in the cerebral vasculature, an effect that could be neuroprotective in the setting of stroke. PTHrP expression was examined by Northern analysis and immunohistochemical staining in male Sprague-Dawley rats subjected to permanent middle cerebral artery occlusion (MCAO). Vasodilatory effects of superfused PTHrP(1–34) on pial arterioles were determined by intravital fluorescence microscopy. Effects of PTHrP(1–34) peptide administration on MCAO infarction size reduction were assessed. PTHrP expression was induced in the ischemic hemisphere as early as 4 h after MCAO and remained elevated for up to 24 h. Increased immunoreactive PTHrP at sites of ischemic tissue injury was located in the cerebral microvessels. Superfusion with PTHrP(1–34) peptide for up to 25 min increased pial arteriolar diameter by 30% in normal animals. In animals with permanent MCAO, PTHrP(1–34) peptide treatment significantly decreased cortical infarct size (−47%). In summary, PTHrP expression increases at sites of ischemic brain injury in the cerebrovasculature. This local increase in PTHrP could be an adaptive response that enhances blood flow to the ischemic brain, thus limiting cell injury.
Role of nitric oxide and cyclooxygenase-2 in regulating the renal hemodynamic response to norepinephrine
Authors: López Ruth , Llinás María T. , Roig Francisco , Salazar F. Javier
Published: March 2015

We have reported that the renal hemodynamic effects of norepinephrine (NE) are modulated by cyclooxygenase-2 (COX-2)-derived metabolites. Our main objective was to examine whether there is an interaction between nitric oxide (NO) and COX-2 in modulating the renal hemodynamic effects of NE. NE was infused at three doses to anesthetized dogs pretreated with vehicle ( n = 8), a selective COX-2 inhibitor (nimesulide) ( n = 6), an NO synthesis inhibitor [ N G-nitro-l-arginine methyl ester;l-NAME] ( n = 8), or with nimesulide andl-NAME ( n = 5). During NE infusion, PGE2 excretion increased (125%) in the control group and did not change in the l-NAME-treated dogs. The simultaneous inhibition of NO and COX-2 potentiated to a greater extent the NE-induced renal vasoconstriction than inhibition of either NO or COX-2. The NE-induced renal vasoconstriction during NO and COX-2 inhibition was reduced ( P < 0.05) by infusing an AT1 receptor antagonist ( n = 6). These results suggest that there is an interaction between NO and COX-2 in protecting the renal vasculature from the NE effects and that angiotensin II partly mediates the NE-induced renal vasoconstriction when NO synthesis and COX-2 activity are reduced.
Food hoarding is increased by food deprivation and decreased by leptin treatment in Syrian hamsters
Authors: Buckley Carolyn A. , Schneider Jill E.
Published: March 2015

Compensatory increases in food intake are commonly observed after a period of food deprivation in many species, including laboratory rats and mice. Thus it is interesting that Syrian hamsters fail to increase food intake after a period of food deprivation, despite a fall in plasma leptin concentrations similar to those seen in food-deprived rats and mice. In previous laboratory studies, food-deprived Syrian hamsters increased the amount of food hoarded. We hypothesized that leptin treatment during food deprivation would attenuate food-deprivation-induced increases in hoarding. Baseline levels of hoarding were bimodally distributed, with no hamsters showing intermediate levels of hoarding. Both high (HH) and low hoarding (LH) hamsters were included in each experimental group. Fifty-six male hamsters were either food deprived or given ad libitum access to food for 48 h. One-half of each group received intraperitoneal injections of leptin (4 mg/kg) or vehicle every 12 h during the food-deprivation period. Within the HH group, the hoarding score increased significantly in food-deprived but not fed hamsters ( P < 0.05). Leptin treatment significantly decreased hoarding in the food-deprived HH hamsters ( P < 0.05). The LH hamsters did not increase hoarding regardless of whether they were food deprived or had ad libitum access to food. These results are consistent with the idea that HH hamsters respond to energetic challenges at least in part by changing their hoarding behavior and that leptin might be one factor that mediates this response.
Decreased susceptibility of cardiac function to hypoxia-reoxygenation in renin-angiotensinogen transgenic rats
Authors: Wagner Kay-Dietrich , Essmann Vanja , Mydlak Karsten , Wirth Manfred , Gmehling Gunnar , Bohlender Jürgen , Stauss Harald M. , Günther Joachim , Schimke Ingolf , Scholz Holger
Published: March 2015

We tested the hypothesis that the renin-angiotensin system (RAS) protects the contractile function of the myocardium against the damaging effect of hypoxia-reoxygenation. For this purpose, the contractility of isolated papillary muscles from wild-type (WT) rats and from rats expressing human renin and angiotensinogen as transgenes (TGR) was compared. After 15 min of hypoxia, peak force (PF) was decreased to 24 ± 5% of the normoxic values in TGR ( n = 10) and to 18 ± 1% in WT rats ( n = 12). PF and relaxation rates recovered completely in TGR but not in WT rats during 45 min of reoxygenation. Improved contractility of the papillary muscles from TGR during hypoxia-reoxygenation correlated with increased glutathione peroxidase activities and creatine kinase (CK)-MB and CK-BB isoenzyme levels. On the other hand, inhibition of the RAS with ramipril (1 mg/kg body wt for 3 wk) in WT animals resulted in deterioration of the contractile function of the papillary muscles during reoxygenation compared with untreated rats. These findings suggest that activation of the RAS protects contractile function of the cardiac muscle against hypoxia-reoxygenation, possibly through changes in CK isoenzymes and enhanced antioxidant capacity.
Role of oxidative stress in angiotensin-induced hypertension
Authors: Reckelhoff Jane F. , Romero J. Carlos
Published: March 2015

Infusion of ANG II at a rate not sufficient to evoke an immediate vasoconstrictor response, produces a slow increase in blood pressure. Circulating levels of ANG II may be within ranges found in normotensive individuals, although inappropriately high with respect to sodium intake. When ANG II levels are dissociated from sodium levels, oxidative stress (OXST) occurs, which can increase blood pressure by several mechanisms. These include inadequate production or reduction of bioavailability of nitric oxide, alterations in metabolism of arachidonic acid, resulting in an increase in vasoconstrictors and decrease in vasodilators, and upregulation of endothelin. This cascade of events appears to be linked, because ANG II hypertension can be blocked by inhibition of any factor located distally, blockade of ANG II, OXST, or endothelin. Such characteristics are shared by other models of hypertension, such as essential hypertension, hypertension induced by reduction in renal mass, and renovascular hypertension. Thus these findings are clinically important because they reveal 1) uncoupling between ANG II and sodium, which can trigger pathological conditions; 2) the various OXST mechanisms that may be involved in hypertension; and 3) therapeutic interventions for hypertension developed with the knowledge of the cascade involving OXST.
Effects of rearing temperature on sympathoadrenal activity in young adult rats
Authors: Young James B. , Weiss Jeffrey , Boufath Nadine
Published: March 2015

Animals reared at 18°C exhibit enhanced innervation of brown adipose tissue (BAT) and greater cold tolerance as adults, yet gain more weight when fed an enriched diet compared with rats reared at 30°C. To explore this paradox, sympathoadrenal activity was examined using techniques of [3H]norepinephrine ([3H]NE) turnover and urinary catecholamine excretion in male and female rats reared until 2 mo of age at 18 or 30°C. Gene expression in BAT was also analyzed for several sympathetically related proteins. Although [3H]NE turnover in heart did not differ between groups, [3H]NE turnover in BAT was consistently elevated in the 18°C-reared animals, even 2 mo after removal from the cool environment. Gene expression for uncoupling proteins 1 and 3, GLUT-4, leptin, and the α1A-adrenergic receptor was more abundant in BAT and the increase in epinephrine excretion with fasting suppressed in 18°C-reared animals. These studies demonstrate that obesity consequent to exposure to 18°C in early life occurs despite tonic elevation of sympathetic input to BAT. Diminished adrenal epinephrine responsiveness to fasting may play a contributory role.
Respiratory changes induced by kainic acid lesions in rostral ventral respiratory group of rabbits
Authors: Mutolo Donatella , Bongianni Fulvia , Carfì Marco , Pantaleo Tito
Published: March 2015

The role played by the Bötzinger complex (BötC), the pre-Bötzinger complex (pre-BötC), and the more rostral extent of the inspiratory portion of the ventral respiratory group (iVRG) in the genesis of the eupneic pattern of breathing was investigated in anesthetized, vagotomized, paralyzed, and artificially ventilated rabbits by means of kainic acid (KA, 4.7 mM) microinjections (20–30 nl). Unilateral KA microinjections into all of the investigated VRG subregions caused increases in respiratory frequency associated with moderate decreases in peak phrenic amplitude in the BötC and pre-BötC regions. Bilateral KA microinjections into either the BötC or pre-BötC transiently eliminated respiratory rhythmicity and caused the appearance of tonic phrenic activity (“tonic apnea”), whereas injections into the rostral iVRG completely suppressed inspiratory activity. Rhythmic activity resumed as low-amplitude, high-frequency oscillations and displayed a progressive, although incomplete, recovery. Combined bilateral KA microinjections (BötC and pre-BötC) caused persistent (>3 h) tonic apnea. Results show that all of the investigated VRG subregions exert a potent control on both the intensity and frequency of inspiratory activity, thus suggesting that these areas play a major role in the genesis of the eupneic pattern of breathing.
Adenovirus-mediated human prostasin gene delivery is linked to increased aldosterone production and hypertension in rats
Authors: Wang Cindy , Chao Julie , Chao Lee
Published: March 2015

Prostasin has been demonstrated to be an activator of epithelial sodium channels in cultured renal and bronchial epithelial cells. In this study, we evaluated the effects of adenovirus-mediated gene transfer of human prostasin on blood pressure regulation and sodium reabsorption in Wistar rats. Expression of human prostasin mRNA was identified in rat adrenal gland, liver, kidney, heart, lung, and aorta, and immunoreactive human prostasin was detected in the circulation and urine of rats receiving prostasin gene transfer. A single injection of adenovirus carrying the prostasin gene caused prolonged increases in blood pressure for 3–4 wk. Blood pressure increase was accompanied by elevated plasma aldosterone levels and reduced plasma renin activity. The increase in blood pressure and plasma aldosterone levels as well as the reduction of plasma renin activity correlated with the expression of human prostasin transgene. Elevated plasma aldosterone levels were detected at 3 days after gene transfer before the development of hypertension, indicating that stimulation of mineralocorticoid production is the primary target of prostasin. Prostasin gene transfer significantly reduced urinary K+excretion but increased urinary Na+and kallikrein excretion. Elevated renal kallikrein levels promote natriuresis, which may lead to sodium escape and prevent further increases of blood pressure after prostasin gene transfer. In summary, these results suggest that prostasin participates in blood pressure and electrolyte homeostasis by regulating the renin-angiotensin-aldosterone and kallikrein-kinin systems.
Ca2+/calmodulin-dependent and cAMP-dependent kinases in induction of c-fosin human mesangial cells
Authors: Zeng Hong , Liu Ying , Templeton Douglas M.
Published: March 2015

Mesangial cell proliferation is an early event in several progressive renal diseases. When mesangial cells in culture are rendered quiescent by serum starvation and subsequently stimulated to proliferate, induction of c- fos is an early indicator of entry into the cell cycle. Several heparin-sensitive signals transduce these events. We have examined the potential roles of CaMK and PKA. Selective stimulation of CaMK with Ca2+ionophores and of PKA with forskolin or dibutyryl cAMP both result in induction of c- fos mRNA. CaMK but not PKA signaling is suppressed by low concentrations of heparin. Cross talk between the pathways has been demonstrated in some cells, with evidence of CaMK phosphorylating cAMP response element binding protein (CREB) at an inhibitory site and PKA suppressing CaMK-dependent signaling. However, in the present study, both pathways phosphorylated CREB on Ser133and induced c- fosin an additive manner. Serum, ionomycin, and forskolin all caused a rapid decline in cyclin D1 levels, but only serum effected a subsequent increase, indicative of cell cycle progression. We conclude that, in human mesangial cells, CaMK and PKA can both contribute to cell cycle entry, and, although induction of c- fos by CaMK requires active PKA, neither pathway antagonizes or synergizes c- fosinduction by the other.
Aldosterone interaction with epidermal growth factor receptor signaling in MDCK cells
Authors: Gekle Michael , Freudinger Ruth , Mildenberger Sigrid , Silbernagl Stefan
Published: March 2015

Epidermal growth factor (EGF) regulates cell proliferation, differentiation, and ion transport by using extracellular signal-regulated kinase (ERK)1/2 as a downstream signal. Furthermore, the EGF-receptor (EGF-R) is involved in signaling by G protein-coupled receptors, growth hormone, and cytokines by means of transactivation. It has been suggested that steroids interact with peptide hormones, in part, by rapid, potentially nongenomic, mechanisms. Previously, we have shown that aldosterone modulates Na+/H+exchange in Madin-Darby canine kidney (MDCK) cells by means of ERK1/2 in a way similar to growth factors. Here, we tested the hypothesis that aldosterone uses the EGF-R as a heterologous signal transducer in MDCK cells. Nanomolar concentrations of aldosterone induce a rapid increase in ERK1/2 phosphorylation, cellular Ca2+concentration, and Na+/H+exchange activity similar to increases induced by EGF. Furthermore, aldosterone induced a rapid increase in EGF-R-Tyr phosphorylation, and inhibition of EGF-R kinase abolished aldosterone-induced signaling. Inhibition of ERK1/2 phosphorylation reduced the Ca2+response, whereas prevention of Ca2+influx did not abolish ERK1/2 phosphorylation. Our data show that aldosterone uses the EGF-R-ERK1/2 signaling cascade to elicit its rapid effects in MDCK cells.
Confocal imaging of organic anion transport in intact rat choroid plexus
Authors: Breen Christopher M. , Sykes Destiny B. , Fricker Gert , Miller David S.
Published: March 2015

We used confocal microscopy and quantitative image analysis to follow the movement of the fluorescent organic anion fluorescein (FL) from bath to cell and cell to blood vessel in intact rat lateral choroid plexus. FL accumulation in epithelial cells and underlying vessels was rapid, concentrative, and reduced by other organic anions. At steady state, cell fluorescence exceeded bath fluorescence by a factor of 3–5, and vessel fluorescence exceeded cell fluorescence by a factor of ∼2. In cells, FL distributed between diffuse and punctate compartments. Cell and vessel accumulation of FL decreased when metabolism was inhibited by KCN, when bath Na+ was reduced from 130 to 26 mM, and when the Na+ gradient was collapsed with ouabain. Cell and vessel accumulation increased by >50% when 1–10 μM glutarate was added to the bath. Finally, transport of FL and carboxyfluorescein (generated intracellularly from carboxyfluorescein diacetate) from cell to blood vessel was greatly diminished when medium K+ concentration ([K+]) was increased 10-fold. These results 1) validate a new approach to the study of choroid plexus function, and 2) indicate a two-step mechanism for transepithelial organic anion transport: indirect coupling of uptake to Na+ at the apical membrane and electrical potential-driven efflux at the basolateral membrane.
Localization of human equilibrative nucleoside transporters, hENT1 and hENT2, in renal epithelial cells
Authors: Mangravite Lara M. , Xiao Guangqing , Giacomini Kathleen M.
Published: March 2015

Nucleoside transporters are important in the disposition of nucleosides and nucleoside analogs in the kidney. Two human equilibrative nucleoside transporters have been cloned and characterized, hENT1 and hENT2. The primary goal of this study was to localize these transporters in polarized renal epithelia. hENT1 and hENT2 were tagged with green fluorescence protein, stably expressed in renal epithelial cells, and localized by immunofluorescence and functional analysis. Our data demonstrated that both transporters are expressed on the basolateral membrane. hENT1 is also present on the apical membrane. Additionally, we examined the importance to basolateral targeting of two COOH-terminal targeting motifs: a RXXV motif for hENT1 and a dileucine repeat for hENT2. Neither motif appeared to affect targeting, but the dileucine repeat was implicated in surface expression of hENT2. In addition, a splice variant of hENT2 was identified that is predicted to result in a 156-residue COOH-terminal truncation. This variant had a tissue distribution similar to wild-type hENT2 but was retained intracellularly. These data suggest that hENT1 and hENT2 on the basolateral membrane function with concentrative nucleoside transporters on the apical membrane to mediate active reabsorption of nucleosides within the kidney.
Role of the cytoskeleton in mediating effect of vasopressin and herbimycin A on secretory K channels in CCD
Authors: Wei Yuan , Wang Wen-Hui
Published: March 2015

We have previously demonstrated that inhibiting protein tyrosine kinase (PTK) and stimulating protein kinase A (PKA) increase the activity of the small-conductance K (SK) channel in the cortical collecting duct (CCD) of rat kidneys (Cassola AC, Giebisch G, and Wang WH. Am J Physiol Renal Fluid Electrolyte Physiol 264: F502–F509, 1993; Wang WH, Lerea KM, Chan M, and Giebisch G. Am J Physiol Renal Physiol 278: F165–F171, 2000). In the present study, we used the patch-clamp technique to study the role of the cytoskeleton in mediating the effect of herbimycin A, an inhibitor of PTK, and vasopressin on the SK channels in the CCD. The addition of colchicine, an inhibitor of microtubule assembly, or taxol, an agent that blocks microtubule reconstruction, had no significant effect on channel activity. However, colchicine and taxol treatment completely abolished the stimulatory effect of herbimycin A on the SK channels in the CCD. Removal of the microtubule inhibitors restored the stimulatory effect of herbimycin A. In contrast, treatment of the tubules with either taxol or colchicine did not block the stimulatory effect of vasopressin on the SK channels. Moreover, the effect of herbimycin A on the SK channels was also absent in the CCDs treated with either cytochalasin D or phalloidin. In contrast, the stimulatory effect of vasopressin was still observed in the tubules treated with phalloidin. However, cytochalasin D treatment abolished the effect of vasopressin on the SK channels. Finally, the effects of vasopressin and herbimycin A are additive because inhibiting PTK can still increase the channel activity in CCD that has been challenged by vasopressin. We conclude that an intact cytoskeleton is required for the effect on the SK channels of inhibiting PTK and that the SK channels that are activated by inhibiting PTK were differently regulated from those stimulated by vasopressin.
New approaches to genetic manipulation of mice: tissue-specific expression of ACE
Authors: Cole Justin M. , Xiao Hong , Adams Jonathan W. , Disher Kevin M. , Zhao Hui , Bernstein Kenneth E.
Published: March 2015

The renin-angiotensin system (RAS) plays a central role in body physiology, controlling blood pressure and blood electrolyte composition. ACE.1 (null) mice are null for all expression of angiotensin-converting enzyme (ACE). These mice have low blood pressure, the inability to concentrate urine, and a maldevelopment of the kidney. In contrast, ACE.2 (tissue null) mice produce one-third normal plasma ACE but no tissue ACE. They also have low blood pressure and cannot concentrate urine, but they have normal indices of renal function. These mice, while very informative, show that the null approach to creating knockout mice has intrinsic limitations given the many different physiological systems that no longer operate in an animal without a functioning RAS. To investigate the fine control of body physiology by the RAS, we developed a novel promoter swapping approach to generate a more selective tissue knockout of ACE expression. We used this to create ACE.3 (liver ACE) mice that selectively express ACE in the liver but lack all ACE within the vasculature. Evaluation of these mice shows that endothelial expression of ACE is not required for blood pressure control or normal renal function. Targeted homologous recombination has the power to create new strains of mice expressing the RAS in selected subsets of tissues. Not only will these new genetic models be useful for studying blood pressure regulation but also they show great promise for the investigation of the function of the RAS in complicated disease models.
Effects of fatty acids on mitochondrial β-oxidation enzyme gene expression in renal cell lines
Authors: Ouali Fetta , Djouadi Fatima , Bastin Jean
Published: March 2015

Regulatory effects of fatty acids on gene expression of medium-chain acyl-CoA dehydrogenase (MCAD), a mitochondrial β-oxidation enzyme, were investigated in rabbit kidney cell lines derived from proximal tubule (RC.SV1), thick ascending limb of Henle's loop (RC.SV2), or collecting duct (RC.SV3). Exposure to long-chain fatty acids led to significant increases (2-fold) in MCAD mRNA abundance in RC.SV1 and RC.SV2 cells; kinetics and dose-response studies established that maximal MCAD gene stimulation was reached 4 h after addition of 50 μM oleate (C18:1) in the culture medium. These effects of fatty acids were totally abolished in the presence of 1 μg/ml actinomycin D, a transcription inhibitor. Staining of cellular lipids revealed that fatty acid-induced gene stimulation could occur in the absence of cellular fatty acid accumulation. Altogether, these data indicate that small changes in cellular fatty acid flux can have direct short-term effects on fatty acid oxidation enzyme gene expression in renal cells, and this might take part in the regulation of cellular fatty acid homeostasis in response to changes in tubular fluid composition.