Regulation In Rats Research Articles

Cholinergic Involvement in Vascular and Glucoregulatory Actions of Insulin in Rats

This study was designed to test the glucose metabolic and vasodilator actions of insulin in rats and its relation to cholinergic system-dependent mechanisms. The first group of rats had pulsed Doppler flow probes and intravascular catheters implanted to determine blood pressure, heart rate, and regional blood flows. Insulin sensitivity was assessed by the euglycemic-hyperinsulinemic clamp technique carried out in the absence or presence of atropine. The second group of rats was used to determine the cholinergic contribution to in vivo insulin-mediated glucose utilization in individual muscles. Glucose uptake was examined by using [(3)H]2-deoxy-D-glucose. Muscarinic cholinergic blockade was found to significantly (P = 0.002) reduce insulin sensitivity and to completely abrogate the renal (P = 0.008) and hindquarter (P = 0.02) vasodilator responses to euglycemic infusion of insulin. A significant reduction in insulin-stimulated in vivo glucose uptake was also noted in soleus (P = 0.006), quadriceps (P = 0.03), gastrocnemius (P = 0.02), and extensor digitorum longus (EDL) (P = 0.001) muscles, when insulin was infused at a rate of 4 mU . kg(-1) . min(-1), whereas at the rate of 16 mU . kg(-1) . min(-1), a significant reduction in glucose uptake was only observed in EDL (P = 0.03) and quadriceps (P = 0.01) muscles. Together, these results demonstrate a potential role for cholinergic involvement with physiological insulin actions in glucose clearance and blood flow regulation in rats.

Acute and Chronic Regulation of the Renal Na+/H+ Exchanger NHE3 in Rats with STZ-Induced Diabetes mellitus

Background: Early stages of diabetic nephropathy are characterized by alterations of glomerular filtration, increased tubular sodium and water reabsorption, and systemic volume expansion, which may be a major cause for the development of hypertension. As a significant fraction of renal salt and water transport is mediated by the proximal tubular Na⁺/H⁺ exchanger NHE3, we investigated its regulation in rats with STZ-induced diabetes mellitus. Methods: Male Sprague-Dawley rats were injected +/– streptozotocin (STZ, 60 mg/kg), and sacrificed after 2, 7 or 14 days. Renal cortical BBM vesicles were prepared to measure Na⁺/H⁺ exchange (NHE) activity and NHE3 protein abundance. Cortical NHE3 mRNA was extracted to perform Northern blot analysis. Pharmacological inhibitors were used in vivo and in vitro in order to identify isoform specificity conferring changes in NHE activity mediated by the diabetic milieu. Results: Compared to control rats, STZ rats were clearly hyperglycemic at all time points studied. NHE activity was significantly increased by 40 and 37% in diabetic rats after 7 and 14 days, respectively, but not after 2 days. The increase in Na⁺/H⁺ exchange activity was not inhibited by HOE-642 (3 µM). Administration of exogenous insulin to diabetic rats resulted in lower blood sugars, but not NHE activity. Moreover, serum glucose concentration did not correlate with NHE activity in any subgroup nor in all animals analyzed together. However, in STZ rats supplemented with exogenous insulin NHE activity was positively correlated with serum insulin concentrations (r = 0.86, p < 0.01). In vivo, the increase in NHE activity induced by STZ could be completely inhibited when rats were fed 6 ppm of HOE-642 with the diet over 14 days. The changes in Na⁺/H⁺ exchange activity were not paralleled by changes in NHE3 protein or mRNA abundance in diabetic rats at any of the time points investigated. Conclusions: These results suggest that proximal tubular Na/H exchange activity is modified in the early stage of diabetes mellitus.

Influence of early dietary experience on energy regulation in rats

The environmental mechanisms that have contributed to the rapid increases in overweight and obesity in the US over the past 25–30 years have yet to be fully specified. One hypothesis that has been forwarded is that increased consumption of calories in liquid form may be a contributing factor, since some studies support the idea that caloric compensation is less adequate for liquid calories compared to calories delivered in more solid form. Work from our laboratory using rats has examined the role that differences in diet viscosity may play in altering energy intake and body weight regulation. This work has suggested that when offered diets matched on caloric density, macronutrient and micronutrient composition, and differing only in viscosity, adult rats fail to compensate for calories delivered in low-viscosity form in short-term intake tests. Further, long-term consumption of low-viscosity diets leads to enhanced weight gain in adult rats. In the present studies, we examined whether short- or long-term exposure to varying relationships between viscosity and calories led to altered food intake or body weight regulation in juvenile rats. The results demonstrated that animals given either short- or long-term experience with direct relationships between viscosity and calories (high viscosity, high calorie meals and low viscosity, low calorie meals) did not differ in food intake or body weight gain compared to animals given short- or long-term experience with indirect relationships between viscosity and calories (high viscosity, low calorie meals and low viscosity, high calorie meals). When juvenile rats were given long-term (9 weeks) exposure to a single, high or low viscosity diet supplement, matched on caloric density and differing only in viscosity, there were no effects on body weight gain. However, analysis of body composition using DEXA demonstrated that animals consuming the low viscosity supplements had significantly greater body fat than animals that consumed either the high viscosity supplement or no dietary supplement at all. These differences in body fat persisted for at least 3 months following the cessation of dietary supplements; during this 3-month period, animals previously exposed to the low viscosity supplement also gained significantly more weight than animals previously exposed to the high viscosity supplement. Taken together, the results suggest that consuming calories in low viscosity form may contribute to poor intake regulation over the short-term and to increased adiposity over the long term. When animals experience these diets as juveniles, these effects may persist into adulthood.

Pharmacological Properties of N-095, a Drug Containing Red Ginseng, Polygala Root, Saffron, Antelope Horn and Aloe Wood

This study sought to establish a pharmacological profile for N-095, a crude drug containing red ginseng, polygala root, saffron, antelope horn and aloe wood. Our studies on rats and mice revealed a number of pharmacological properties of this novel drug. N-095 increased the forced swimming time in mice and prevented gastric ulcers in rats under restraint and water immersion stress conditions at 100 mg/kg or higher. It also prevented footpad swelling in rats treated with lambda-carrageenin and histamine-induced gastric ulcers in rats at 300 mg/kg or higher. Furthermore, N-095 augmented the sedative effect in mice induced by hexobarbital, which is characterized by a decreased spontaneous motor activity and a prolongation of sleeping time. N-095 also stimulated spontaneous contractility of the uterus in rats at 1000 mg/kg and 2000 mg/kg and prevented hemolysis of erythrocytes by heating. In contrast, N-095 had no effect on the respiratory or cardiovascular system or on water and electrolyte regulation in rats or mice. These results show that N-095 is a relatively safe drug for use as a nutrient or tonic.

Mechanical unloading improves intracellular Ca2+regulation in rats with doxorubicin-induced cardiomyopathy

We sought to assess whether mechanical unloading has beneficial effects on cardiomyocytes from doxorubicin-induced cardiomyopathy in rats. Mechanical unloading by a left ventricular assist device (LVAD) improves the cardiac function of terminal heart failure in humans. However, previous animal studies have failed to demonstrate beneficial effects of mechanical unloading in the myocardium. The effects of mechanical unloading by heterotopic abdominal heart transplantation were evaluated in the myocardium from doxorubicin-treated rats by analyzing the intracellular free calcium level ([Ca(2+)](i)) and the levels of intracellular Ca(2+)-regulatory proteins. In doxorubicin-treated rats, the duration of cell shortening and [Ca(2+)](i) transients in cardiomyocytes was prolonged (432 +/- 28.2% of control in 50% relaxation time; 184 +/- 10.5% of control in [Ca(2+)](i) 50% decay time). Such prolonged time courses significantly recovered after mechanical unloading (114 +/- 10.4% of control in 50% relaxation time; 114 +/- 5.8% of control in 50% decay time). These effects were accompanied by an increase in sarcoplasmic reticulum Ca(2+) ATPase (SERCA2a) protein levels (0.97 +/- 0.05 in unloaded hearts vs. 0.41+/- 0.09 in non-unloaded hearts). The levels of other intracellular Ca(2+)-regulatory proteins (phospholamban and ryanodine receptor) were not altered after mechanical unloading in doxorubicin-treated hearts. These parameters in unloaded hearts without doxorubicin treatment were similar to normal hearts. Mechanical unloading increases functional sarcoplasmic reticulum Ca(2+) ATPase and improves [Ca(2+)](i) handling and contractility in rats with doxorubicin-induced cardiomyopathy. These beneficial effects of mechanical unloading were not observed in normal hearts.

894. Targeting Adenovirus Mediated Gene Transfer to Chondrocytes In Vitro

Metabolically responsive insulin transgenes can be transduced into the livers of diabetic rodents and lead to normalization of randomly sampled blood glucose. Hepatocytes can only produce insulin through a constitutive pathway. Therefore, rapidly changing serum levels of insulin are not possible with this form of gene therapy for diabetes. However, blood glucose remains under better control than can be accounted for by the systemic levels of insulin produced by hepatocytes transduced by an adenoviral vector to express a metabolically sensitive transgene, Ad/(GlRE)3BP-1 2xFur. We hypothesize that intrahepatic carbohydrate metabolism is changed during hepatic insulin gene therapy to contribute to the mechanism of glucose regulation in rats treated with this form of gene therapy. We previously measured in vitro carbohydrate metabolism in primary hepatocytes transduced with Ad/(GlRE)3BP-1 2xFur showing decreased glycogen, decreased gluconeogenesis, and decreased glucose uptake. We now expand the observations to in vivo carbohydrate metabolism. Sprague-Dawley rats were made diabetic with streptozotocin then received Ad/(GlRE)3BP-1 2xFur (2 x 1010 PFU/kg), and compared to non-diabetic rats, diabetic controls, and diabetic rats treated with peripherally administered insulin. Blood glucose and carbohydrate-regulatory hormones were monitored. Glycogen was measured in a group of rats sacrificed during unrestrained feeding. Another group of rats underwent 24 hour fasts with administration of deuterium oxide near the end of the fast to measure pathways of hepatic glucose production by NMR spectroscopy to demonstrate different pathways of gluconeogenesis and glycogenolysis that are active depending on the sites of incorporation of deuterium onto carbon molecules of glucose produced in the liver. Blood glucose was similar in rats producing hepatic insulin and normal rats, with higher levels of glucagon and growth hormone in rats treated with gene therapy. Random levels of hepatic glycogen were highest in normal rats (34.2 + 6.4 mg/g of liver tissue), with less in rats producing insulin within the liver (26.0 + 9.0 mg/g), and lowest in diabetic rats (15.1 + 4.4 mg/g). Normal and gene therapy treated rats had similar blood glucose during the fast, with higher glucose in the diabetic controls. Plasma glucose was extracted and converted to mono-acetylated glucose for evaluation by NMR spectroscopy. The NMR spectra show different relative activity in pathways of hepatic glucose metabolism. Hepatic insulin gene therapy is associated with normalization of random and fasting blood glucose levels, but the mechanism of glucose regulation is different than normal animals due to changes in intrahepatic carbohydrate metabolism and counterregulatory hormones. Potential mechanisms are: (1) autocrine or paracrine activity of hepatic insulin, (2) unique counterregulatory hormone responses due to the anatomical site of hepatic insulin production, (3) changes in hepatic carbohydrate metabolism induced by intracellular insulin, and (4) changes in metabolic enzymes due to transcription factors used by the metabolically responsive transgene.

Leptin gene expression and serum leptin levels in zinc deficiency: implications for appetite regulation in rats.

Zinc deficiency in animals causes impaired growth and anorexia, and the mechanisms for these symptoms of zinc deficiency are not yet clear. We investigated whether circulating leptin levels and gene expression would be dysregulated under zinc deficiency and what would be the implications for appetite in rats. In study 1, 24 Sprague-Dawley rats were provided consecutively with three different dietary zinc intake levels: Zn-adequate (30 mg/kg of diet), Zn-depleted (1 mg/kg of diet), and Zn-replete (50 mg/kg of diet), for 1, 2, and 2 weeks, respectively. At the end of each dietary period, one-third of the rats were killed. In study 2, rats were assigned to one of the four Zn diet groups: Zn-adequate (30 mg/kg of diet), pair-fed (30 mg/kg of diet), Zn-deficient (1 mg/kg of diet), or Zn-sufficient (50 mg/kg of diet), and were fed for 4 weeks. Tissue Zn and serum leptin were measured, and leptin gene expression in adipose tissues (inguinal and abdominal) was determined by reverse transcription-polymerase chain reaction and northern blotting. Blood subfractions as plasma, red blood cells, and mononuclear cells and liver Zn level were decreased during the Zn-depletion period (P <.05). Serum leptin showed a tendency to increase during the Zn-depletion period and decreased back to the level of the Zn-repletion period. Leptin mRNA levels in inguinal adipocytes also increased during the Zn-depletion (P <.05) and Zn-deficient periods, which is consistent with the change in serum leptin. However, the decrease in leptin mRNA in abdominal adipocytes was not consistent with the increase in inguinal leptin levels and the change in serum leptin. Increased leptin levels in linguinal adipocytes is consistent with the expected physiological change of a decrease in appetite under Zn deficiency. However, before coming to any firm conclusion, further studies on adipose tissue-specific leptin expression, including the appetite-related neuropeptides, are necessary for clarifying the cause of lower appetite in zinc deficiency.

Reduced membrane-bound catechol-O-methyltransferase in the liver of spontaneously hypertensive rats.

We have previously reported that methylation of catecholamines by catechol-O-methyltransferase (COMT) was attenuated in spontaneously hypertensive rats (SHR) with acute hypotension as compared with that of Wistar-Kyoto (WKY) rats. Here we examined the soluble (S-) and membrane-bound (MB-) COMT activities and COMT protein in the liver, kidney, and erythrocytes in both strains. Both the activities and the amounts of MB-COMT in the liver were lower in SHR than in WKY rats, but no such trend was found in the kidney or erythrocytes. Nor was such a trend observed in any of these three tissues for S-COMT. These results indicate that liver MB-COMT may be a relevant factor in blood pressure regulation in rats.

Rostral ventrolateral medulla C1 neurons and cardiovascular regulation.

1. The rostral ventrolateral medulla (RVLM) is essential for the normal control of arterial pressure. This region of the brainstem is heterogeneous, and contains spinally projecting neurons that contain phenylethanolamine-N-methyltransferase (C1 neurons) and non-C1 neurons. 2. The availability of a toxin, a dopamine-beta-hydroxylase antibody conjugated to saporin, that can selectively destroy C1 neurons within the RVLM allows for the study of cardiovascular regulation in rats following depletion of the C1 neuronal population. 3. C1 neurons are not essential for the maintenance of resting blood pressure in anesthetized rats, but do contribute to many cardiovascular responses mediated through the RVLM. 4. The depressor response elicited by clonidine injected into the RVLM is dependent upon C1 neurons. 5. Studies in rats with selective toxin-induced destruction of RVLM C1 neurons demonstrate that C1 neurons contribute importantly to cardiovascular regulation.

IRL2500, A Selective ETB Antagonist for Endothelin-Induced Vasodilatation in the Pulmonary Vascular Bed in Rats

Introduction: Endothelins (ET-1 and ET-2) have vasoactive effects mediated by receptors (ETA & ETB). The objective of the present study was to determine the effect of endothelins and their antagonists on the pulmonary vascular bed in vivo. To accomplish this, we employed the unique rat model and studied the pulmonary vascular beds of intact-chest animal under conditions of constant pulmonary blood flow. Methods: Twenty-five rats were anesthetized with pentobarbital, and a specially designed balloon catheter was placed into rat's the pulmonary artery via the right jugular vein. The right lower lobe of the lung was perfused at constant flow (14 ± 0.6 ml/min) with blood removed from a cannulated carotid artery. The baseline pulmonary arterial pressure was 12.8 ± 1.1 mmHg. In order to demonstrate vasodilator responses to testing agents, the pulmonary arterial pressure was elevated to 34.8 ± 1.4 mmHg by continuous infusion of U46619, a thromboxane-like substance. The effect of various endothelin agonists and antagonists were then studied. Results: Intrapulmonary arterial injections of ET-1, IRL1620 (ETB agonist) and ET-3 produced dose-dependent vasodilator responses in the pulmonary vascular bed. At a dose of 1µg, ET-1, IRL1620 and ET-3 caused decreases in pulmonary arterial pressure of 8.1 ± 0.4 mmHg, 8.2 ± 0.3 mmHg and 7.9 ± 0.3 mmHg respectively (all significantly different from baseline, n=5, p<0.05). After pretreatment with IRL2500 (ETB antagonist, 10mg/kg, i.v.), the vasodilator responses to ET-1, IRL1620 and ET-3 at the same dose were 0.9 ± 0.1mmHg, 2.1 ± 0.3 mmHg and 1.8 ± 0.3 mmHg respectively (n=5, not significantly differ from the baseline). This data suggests that IRL2500 can block the vasodilator responses to ET-1, IRL1620 and ET-3 in the lung. Data from a different group of animal demonstrate that the vasodilator responses to ET-1, IRL1620 and ET-3 are not altered significantly by pretreatment with BQ123 (an ETA antagonist) (n=5) Conclusions: Using a new rat model, these results indicate that ET-1, IRL1620 and ET-3 dilate the pulmonary vascular bed by activation of the ETB receptor. The present data also suggest that IRL2500, as a specific ETB antagonist can be a useful pharmacological tool to study the pulmonary vascular regulation in rats. This new intact rat preparation appears to be valuable in carrying out cardiopulmonary studies in vivo.

Relationship between electroencephalogram slow-wave magnitude and heart rate variability during sleep in rats

To explore whether depth of sleep is related to changes in autonomic control in rats, continuous power-spectral analysis of electroencephalogram (EEG) and heart rate variability (HRV) was performed in unanesthetized rats during normal daytime sleep. Quiet sleep (QS) was associated with an increase in high-frequency power of HRV (0.6–2.4 Hz, HF) but a decrease in low-frequency power (0.06–0.6 Hz) to HF ratio (LF/HF) compared with awakening. During QS, LF/HF was significantly and negatively correlated with delta power of EEG (0.5–4.0 Hz), whereas mean R-R interval and HF were not. As in humans, cardiac sympathetic regulation in rats is negatively related to the depth of sleep during QS, although vagal regulation is not. Our methodology offers a parallel way of studying the interaction between cerebral cortical and autonomic functions in rats.

Forebrain-mediated adaptations to myocardial infarction in the rat.

Recent studies suggest that the forebrain contributes to the circulatory derangements leading to heart failure after myocardial injury. We tested that hypothesis by examining the effect of myocardial infarction (MI) or sham MI (MI-s) on neurohumoral regulation in rats with prior anteroventral (AV) third ventricle lesion (AV3V-x) or sham lesion (AV3V-s). AV3V-s/MI rats had higher sodium intake, lower urine volume, and lower urinary sodium excretion than AV3V-s/MI-s rats. AV3V-x/MI rats had lower sodium intake and higher urine volume than AV3V-s/MI or AV3V-s/MI-s rats and urinary sodium excretion comparable to AV3V-s/MI-s rats. AV3V-x had no effect on baseline plasma renin activity (PRA). One week after MI, PRA had increased in AV3V-s but decreased in AV3V-x rats. AV3V-x reduced renal sympathetic nerve activity in MI and MI-s rats. AV3V-x improved baroreflex function in MI rats but diminished it in MI-s rats. Survival beyond 2 wk was lower in the AV3V-x/MI rats than in all other groups. These results confirm a critical role for the forebrain in the neurohumoral adjustments to MI.

Involvement of purinergic signalling in central mechanisms of body temperature regulation in rats.

1. P2 purinoreceptors are present in hypothalamic and brainstem nuclei that are involved in the regulation of body temperature (T(b)). The role of ATP acting on these P2 receptors in thermoregulation was investigated by studying the effects of the stable ATP analogue alpha,beta-methyleneATP (alpha,beta-meATP) and P2 receptor antagonists suramin and pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on T(b) when injected intracerebroventricularly (i.c.v.) via a pre-implanted cannula in conscious rats at various ambient temperatures and during lipopolysaccharide (LPS)-induced fever. 2. Depending on ambient temperature, alpha,beta-meATP (0.2 micromol, i.c.v.) induced a fall in T(b) (-3.3 degrees C, P<0.05), no changes in T(b) when compared to pre-injection levels, or an increase in T(b) ( approximately 1.0 degrees C, P<0.05) in rats maintained at 10 degrees C, 25 degrees C and 30 degrees C ambient temperature, respectively. 3. Suramin (7 nmol, i.c.v.) induced a lasting (up to 6 h) increase in T(b) (on average 1.2 degrees C, P<0.05) in rats kept at 25 degrees C or 30 degrees C, but failed to induce any rise in T(b) in rats at 10 degrees C ambient temperature. An increase in T(b) was also observed in rats (25 degrees C ambient temperature) treated with PPADS (0.2 micromol, i.c.v.). 4. alpha,beta-meATP (0.2 micromol) injected i.c.v. or directly into the anterior hypothalamus caused a profound fall in T(b) (by 0.9 degrees C and 1.0 degrees C, respectively; P<0.05) during LPS (E.coli; 50 microg kg(-1))-induced fever in rats at 25 degrees C ambient temperature. Fever was initiated more rapidly in rats treated with suramin (7 nmol) or PPADS (70 nmol), however its late phase was unaffected. Suramin (7 nmol) and PPADS (70 nmol) injected at the time when fever was already developed (2.5 h after LPS injections) did not alter febrile T(b). 5. These data indicate that purinergic signalling may play a significant role in central mechanisms of T(b) regulation at various ambient temperatures and during fever.

Roles of the central prostaglandin EP3 receptors in cardiovascular regulation in rats

In this study, we examined the effects of an intracerebroventricular (i.c.v.) administration of prostaglandin E 2 (PGE 2) and of selective agonists for PGE 2 receptor subtypes, EP1, EP2, EP3 and EP4, on central cardiovascular regulation and renal sympathetic nerve activity (RSNA) in urethane-anesthetized rats. The central administration of PGE 2 (0.01–1.0 nmol) resulted in increases in blood pressure, heart rate (HR) and RSNA in a dose-dependent manner. Cardiovascular responses to PGE 2 (0.5 nmol, i.c.v.) were attenuated by pretreatment with ganglionic and adrenoceptor blocking agents, but not with SC-19220 (20 nmol, i.c.v.), an EP1 receptor antagonist. An i.c.v. administration of the EP3 agonist ONO-AE-248 (50.0 nmol) resulted in an increase in RSNA with pressor and tachycardia responses, while administration of the EP2 agonist ONO-AE1-259 and the EP4 agonist ONO-AE1-329 caused transient hypotension and slight increases in HR and RSNA. The administration of the selective EP1 agonist ONO-DI-004 showed no effect. These results suggest that the central PGE 2-induced activation of the sympathetic nerve activity with hypertension and tachycardia may depend on stimulation of the EP3 receptors in the central nervous system.

Changes in glucocorticoid and mineralocorticoid receptors of liver and kidney cytosols after pathologic stress and its regulation in rats.

As effectors, glucocorticoid and mineralocorticoid receptors play an important role in pathologic stress. This study was designed to observe the changes in glucocorticoid receptor of liver cytosols and mineralocorticoid receptor of kidney cytosols after pathologic stress in rats. Controlled laboratory study. Medical university. Male Wistar rats (weight range, 180-200 g). Rats received a low-degree or heavy-degree immersion scald that covered 10% or 35% total body surface area and were randomly divided to receive either tumor necrosis factor-alpha, interleukin-1beta polyclonal neutralizing antibody, alpha-melanocyte-stimulating hormone, KPV peptide (Ac-D-Lys-L-Pro-D-Val), or saline (control). The binding capacity and the apparent dissociation constant of the steroid-binding sites of normal, low-degree, and heavy-degree scalded rats were measured by radioligand-binding assay, with [3H]dexamethasone and aldosterone as the ligand, respectively. The binding capacity of glucocorticoid receptor in hepatic cytosols in rats 12 hrs after heavy-degree scald (208.45 +/- 30.78 fmol/mg of protein) was lower than that of the control group (306.71 +/- 27.96 fmol/mg of protein; p < .01). The binding capacity of glucocorticoid receptor in hepatic cytosols in rats 12 hrs after low-degree scald (296.64 +/- 16.06 fmol/mg of protein) was not significantly different compared with the control group (p > .05). There were two types of mineralocorticoid receptor in kidney cytosols in rats, and their binding capacity and apparent dissociation constant were not identical. The binding capacity of mineralocorticoid receptor in rats 12 hrs after heavy-degree scald (binding capacity 1, 22.40 +/- 5.40 fmol/mg of protein; binding capacity 2, 196.30 +/- 32.50 fmol/mg of protein) was lower than that of the control group (binding capacity 1, 41.60 +/- 7.20 fmol/mg of protein; binding capacity 2, 317.60 +/- 70.00 fmol/mg of protein; p < .01). The binding capacity of mineralocorticoid receptor in kidney cytosols in rats 12 hrs after low-degree scald (binding capacity 1, 41.40 +/- 5.00 fmol/mg of protein; binding capacity 2, 314.80 +/- 45.70 fmol/mg of protein) was not significantly different compared with the control group (p > .05). The injections of anti-rat tumor necrosis factor-alpha, interleukin-1beta polyclonal neutralizing antibody, alpha-melanocyte-stimulating hormone, and KPV peptide (Ac-D-Lys-L-Pro-D-Val) might prevent a reduction in the binding capacity of glucocorticoid receptor in hepatic cytosols and mineralocorticoid receptor in kidney cytosols in rats with heavy-degree scald in vivo. These studies suggest that the glucocorticoid receptor of hepatic cytosols and the mineralocorticoid receptor of renal cytosols decreased in rats with heavy-degree immersion scald and that the injections of anti-rat tumor necrosis factor-alpha, interleukin-1beta polyclonal neutralizing antibody, alpha-melanocyte-stimulating hormone, and KPV peptide might increase the level of glucocorticoid receptor and mineralocorticoid receptor in vivo.

Renal hypertension prevents run training modification of cardiomyocyte diastolic Ca2+ regulation in male rats.

The combined effects of endurance run training and renal hypertension on cytosolic Ca2+ concentration ([Ca2+]c) dynamics and Na+-dependent Ca2+ regulation in rat left ventricular cardiomyocytes were examined. Male Fischer 344 rats underwent stenosis of the left renal artery [hypertensive (Ht), n = 18] or a sham operation [normotensive (Nt), n = 20]. One-half of the rats from each group were treadmill trained for >16 wk. Cardiomyocyte fura 2 fluorescence ratio transients were recorded for 7 min during electrical pacing at 0.5 Hz, 2 mM extracellular Ca2+ concentration, and 29 degrees C. The rate of [Ca2+]c decline was not changed by run training in the Nt group but was reduced in the Ht group. At 7 min, cardiomyocytes were exposed to 10 mM caffeine in the absence of Na+ and Ca2+, which triggered sarcoplasmic reticular Ca2+ release and suppressed Ca2+ efflux via Na+/Ca2+ exchanger. External Na+ was then added, and Na+-dependent Ca2+ efflux rate was recorded. Treadmill training significantly enhanced Na+-dependent Ca2+ efflux rate under these conditions in the Nt group but not in the Ht group. These data provide evidence that renal hypertension prevents the normal run training-induced modifications in diastolic [Ca2+]c regulation mechanisms, including Na+/Ca2+ exchanger.

Liver gene regulation in rats following both 70 or 90% hepatectomy and endotoxin treatment.

The metabolic state effect of liver failure on liver gene regulation was evaluated in a rat model. Following 70 or 90% hepatectomy and lipopolysaccharide or vehicle treatment at intervals up to 24 h, the liver remnants were analyzed for mRNA levels for acute-phase, liver-specific and growth-related proteins. After 70% hepatectomy mRNA for alpha 1-acid glycoprotein, alpha 2-macroglobulin, thiostatin and fibrinogen, haptoglobin increased three- to sevenfold (P < 0.05), and mRNA for cyclin D and histone 3 increased seven- and 15-fold (P < 0.05), respectively. After lipopolysaccharide injection and 70% hepatectomy were done, mRNA for acute-phase proteins raised significantly (P < 0.05), more to five to 20-fold, while mRNA for growth-related proteins raised significantly (P < 0.05) less to three- to fourfold. After 90% hepatectomy, acute-phase protein mRNA increased five- to ninefold (P < 0.05) more than after 70% hepatectomy, while mRNA for histone 3 and cyclin D did not increase within 24 h, which indicates a delayed growth after 90% hepatectomy. In 90% of hepatectomized rats treated with lipopolysaccharide, acute-phase protein mRNA raised three- to sixfold (P < 0.05) less than after vehicle treatment. In endotoxemia from liver failure, the synthesis of acute-phase proteins is upregulated by gene regulation at the expense of that for regeneration, which may be an appropriate response for immediate survival. In severe liver failure, endotoxin may interfere with the appropriate gene regulation.

α-Helical-corticotropin-releasing hormone reverses anxiogenic effects of C-type natriuretic peptide in rats

Previously we have shown that atrial natriuretic peptide (ANP) has anxiolytic-like properties after intraperitoneal, intracerebroventricular and intraamygdala infusion in rats. Since C-type natriuretic peptide (CNP) exerts endocrine and behavioral effects opposing those of ANP, we characterized the behavioral properties of CNP after icv infusion in rats by their performance in the elevated plus maze with and without the corticotropin-releasing hormone (CRH) antagonist α-helical-CRH (α-CRH). Low CNP doses of 0.05 μg icv or 0.1 μg icv did not significantly influence the behavior of rats in the plus maze. At higher doses (0.5 μg, 2 μg, 5 μg icv) CNP had distinct anxiogenic properties. Our hypothesis that corticotropin-releasing hormone (CRH) is involved, which elicits anxiety-like behavior, was examined by icv coadministration of α-CRH, an antagonist at CRH-1 and CRH-2-receptors. Icv α-CRH alone had no intrinsic anxiolytic properties at a dose of 25 μg. The anxiogenic effects of 2 μg CNP icv seen in the plus maze were entirely blocked by α-CRH. Directly after exposition ACTH and corticosterone levels did not differ between the groups, but after 30 min ACTH levels were significantly higher in the CNP-treated group compared to α-CRH/CNP-treated animals. Corticosterone was found significantly lowered in the α-CRH/saline group compared to the CNP treated group but not compared to saline controls. Our data suggest opposing effects of CNP and ANP on anxiety-related behavior and neuroendocrine regulation in rats, which appear to be mediated via different receptor occupation and brain regions, and by a CRH-dependent mechanism.

Effects of Alcohol on Blood Pressure and Production of Vascular Aldosterone and Corticosterone

Aims: The aims of this study were to search for the role of alcohol in blood pressure regulation in rats and to investigate the effects of alcohol on the production of vascular aldosterone and corticosterone. Methods: Male Wistar rats received alcohol 0.7 g · kg^–1 · day^–1 (alcohol-treated group 1) or 1.4 g · kg^–1 · day^–1 (alcohol-treated group 2) or 2.1 g · kg^–1 · day^–1 (alcohol-treated group 3), orally, for 3 months, and blood pressure was monitored by a pressure transducer. Systolic blood pressure increased in Wistar rats treated with alcohol compared to control rats. Mesenteric artery perfusion ex vivo was performed and pressor responses to norepinephrine were determined. The pressor responses to norepinephrine in mesenteric arteries treated with alcohol were significantly increased. The perfusate from the mesenteric arteries was collected and applied to a Sep-Pak C 18 cartridge column for reverse-phase high-performance liquid chromatography and aldosterone and corticosterone levels were determined by radioimmunoassay, aldosterone was decreased but corticosterone was increased in the perfusate from arteries treated with alcohol. Results: Reverse transcriptase polymerase chain reaction showed that alcohol inhibited the expression of 11β-HSD2 and CYP11B2 mRNA in mesenteric arteries. Conclusions: These results reveal that alcohol is able to induce hypertension and provide evidence that alcohol inhibits the transcriptions of both 11β-HSD2 and CYP11B2 in the vasculature, leading to lower aldosterone and higher corticosterone production in vessels, and increased vasoconstrictor responses to norepinephrine.

Effect of dietary cardiac glycosides on blood pressure regulation in rats

To investigate the possible physiological significance of dietary cardiac glycosides in blood pressure regulation, the blood pressure of normal Sprague Dawley rats raised on a regular diet, which naturally contains large amounts of Na+-pump inhibitors, was compared with that of rats on a purified synthetic diet, which contains no Na+-pump specific inhibitors, and with that of rats on a synthetic diet supplemented with 10 µg·mL-1ouabain or 10 µg·mL-1convallatoxin in the drinking water. After 6 weeks on the synthetic diet, the systolic blood pressure in the synthetic diet group was significantly elevated (145 ± 5 vs. 128 ± 4 mmHg, P &lt; 0.05). At 10 weeks it reached a plateau (154 ± 3 vs. 122 ± 3 mmHg, P &lt; 0.05). Plasma renin activity and Na+level were significantly higher in animals fed synthetic diets than in the regular diet group (P &lt; 0.01). Administration of either losartan or lisinopril or a switch to a low salt synthetic diet (0.03% sodium) normalized the synthetic diet-induced high blood pressure. Supplementation of the synthetic diet with the cardiac glycosides delayed the onset of the increase in blood pressure for 4 weeks. Plasma aldosterone levels were approximately doubled in the cardiac glycoside-treated groups. Higher plasma Na+levels and hematocrit values present in the synthetic diet group were normalized by the glycoside supplements. These results suggest that supplemental dietary cardiac glycosides exert bidirectional effects on blood pressure regulation through actions that modulate extracellular fluid and electrolyte balance.Key words: cardiac glycosides, convallatoxin, ouabain, ouabain-like substance, purified synthetic diet, high blood pressure, renin-angiotensin system.