Effect of an antidiuretic hormone on the aldosterone level in the blood plasma of rats with chronic water load and limited sodium intake

The concentration of aldosterone in blood plasma of rats with chronic water and restricted sodium chloride intake substantially rose after subcutaneous injection of the antidiuretic hormone pituitrin in physiological doses. No simultaneous increase in blood corticosterone was seen. The production of hormones by rat adrenals remained unchanged. The results of experiments made with ACTH alone or combined with pituitrin permitted the conclusion that the increase in aldosterone concentration was not linked with a possible stimulation of endogenous ACTH secretion. The augmentation of aldosterone concentration in the peripheral blood of rats with chronic water intake induced by pituitrin is likely to be due to a decrease in metabolic clearance of the hormone.     

Role of liver nerves and adrenal medulla in glucose turnover of running rats

Sympathetic control of glucose turnover was studied in rats running 35 min at 21 m X min-1 on the level. The rats were surgically liver denervated, adrenodemedullated, or sham operated. Glucose turnover was measured by primed constant infusion of [3-3H]glucose. At rest, the three groups had identical turnover rates and concentrations of glucose in plasma. During running, glucose production always rose rapidly to steady levels. The increase was not influenced by liver denervation but was halved by adrenodemedullation. Similarly, hepatic glycogen depletion was identical in denervated and control rats but reduced after adrenodemedullation. Early in exercise, glucose uptake rose identically in all groups and, in adrenodemedullated rats, matched glucose production. Accordingly, plasma glucose concentration increased in liver-denervated and control rats but was constant in adrenodemedullated rats. Compensatory changes in hormone or substrate levels explaining the lack of effect of liver denervation were not found. In rats with intact adrenals, the plasma epinephrine concentration was increased after 2.5 min of running. It is concluded that, in rats carrying out exercise of moderate intensity and duration, hepatic glycogenolysis and glucose production are not influenced by the autonomic liver nerves but are enhanced by circulating epinephrine.     

Catecholamines in the tissues and blood of rats after administration of acetaldehyde and ethanol

Acetaldehyde alone and in combination with acute and chronic ethanol intoxication has been studied for its effect on the concentration of epinephrine and norepinephrine in different brain areas, in the heart muscle, in adrenals and blood plasma of rats. Acetaldehyde is shown to enhance the epinephrine and norepinephrine levels in the brain areas which are non-specific for neuromediation of the mentioned catecholamines. The joint administration of acetaldehyde and ethanol increased the epinephrine concentration in adrenals probably due to the effect of acetaldehyde. On the contrary, the norepinephrine concentration in the heart decreased because of the action of ethanol. The authors' data show that acetaldehyde becomes an inductor of the mechanisms of hormone-mediator dissociation, thus altering the functions of vegetative-adrenal system. The results of the investigation support the hypothesis that acetaldehyde plays a significant role among pathogenic factors of ethanol intoxication, since it changes in a special way the catecholamine concentration in the brain and in peripheral tissues.     

The circadian rhythm of the adrenal glucocorticoid function in female rats selected for the reaction of the estrous cycle to constant illumination

Studies have been made of the circadian rhythms of a glucorticoid hormone, corticosterone, in the adrenals and blood serum in female Wistar rats from two substrains selected for high (ESTH) and low (ESTL) ability to develop permanent oestrus under constant illumination. Significant changes in parameters of the circadian rhythm of the hormone were observed in animals of the 26th generation of selection. Total alleviation of corticosterone rhythm in the blood was on observed in ESTL rats, while in ESTH animals maximum level of the hormone in the blood was shifted to the dark time. Comparison of a high corticosterone content of the adrenals in ESTL rats with a low concentration in the blood plasma indicates the increase in metabolic clearance of the hormone in animals from this strain. It is suggested that the decreased corticosteroid production in the adrenals of ESTH rats facilitates the development of permanent oestrus under constant illumination.     

Effect of dipeptide vilon on emotional stress resistance in rats

Effects of synthetic thymomimetic vilon on open field behaviour, immediate early gene c-Fos expression in paraventricular hypothalamus properties of organs sensitive to emotional stress, and characteristics of albumin in the blood plasma in male Wistar rats, were investigated and are discussed in the article. It is shown that intraperitoneal vilon injection rises the resistance against emotional stress according to prognostic indexes open field behaviour. Vilon administration also inhibits hypertrophy of the adrenals, involution of the thymus, and elevates concentration of albumin in the blood plasma. The number of Fos-immunoreactive neurons in the paraventricular hypothalamus was lower after vilon administration especially in rats resistant against emotional stress.     

Atrial natriuretic factor (ANF) inhibits the growth and the secretory activity of rat adrenal zona glomerulosa in vivo

A prolonged infusion with ANF induced atrophy of zona glomerulosa cells of rat adrenals and lowering of plasma concentration of aldosterone, without provoking significant changes in PRA. It also notably reduced the rise in the aldosterone plasma level caused by the acute stimulation with angiotensin II. Zona fasciculata cells and the blood concentration of corticosterone did not display any significant change. These findings are interpreted to indicate that ANF exerts an inhibitory effect on the growth and secretory activity of rat zona glomerulosa.     

Steroid production by quartered and capsular rat adrenal gland in response to haemorrhage.

60 min after rapid bleeding (1.5--2.0 per cent of b. w.) both aldosterone and corticosterone production rate by quartered rat adrenals were found to be elevated. However, no difference was observed in the rate of aldosterone and corticosterone production by capsular adrenals of sham operated and hypovolaemic rats. Corticosterone production rate by decapsulated adrenals was much more higher after haemorrhage than in the control group. The same alterations could be observed incubating adrenal tissue with ACTH (0.3 mug per ml). Steroid production rate by quartered adrenals of sodium deficient rats was not affected by high in vitro concentration of angiotensin II (2.5 mug per ml). It is concluded that the effect of acute blood loss on corticosteroid biosynthesis of the rat is mediated by ACTH alone.     

Comparative Studies on the Orcadian Rhythm of Corticosterone Lipid and Cholesterol Levels in Adrenals and Blood of Rats

The time-dependent relationship of corticosterone, lipids and cholesterol over a 48-hr period was studied in the adrenals and blood of rats. In addition an attempt was made to determine whether there was a reciprocal dependence among these compounds and also a correlation between corticosterone and cholesterol in the adrenals and blood.

Corticosterone and cholesterol exhibit a circadian rhythm in the adrenals and blood. The same is true for lipids in the serum. A reciprocal dependence between the compounds in the adrenals and blood could not be demonstrated. Only the time-dependent processes of the corticosterone content in the adrenals and plasma are well correlated with each other. High levels of these steroids in the adrenals are associated with high levels of these steroids in the plasma and vice versa.

An inverse correlation between corticosterone and cholesterol exists in the adrenals and in blood. Maximal levels of corticosterone correspond to minimal levels of cholesterol and vice versa.     

Comparative Studies on the Orcadian Rhythm of Corticosterone Lipid and Cholesterol Levels in Adrenals and Blood of Rats

The time-dependent relationship of corticosterone, lipids and cholesterol over a 48-hr period was studied in the adrenals and blood of rats. In addition an attempt was made to determine whether there was a reciprocal dependence among these compounds and also a correlation between corticosterone and cholesterol in the adrenals and blood.

Corticosterone and cholesterol exhibit a circadian rhythm in the adrenals and blood. The same is true for lipids in the serum. A reciprocal dependence between the compounds in the adrenals and blood could not be demonstrated. Only the time-dependent processes of the corticosterone content in the adrenals and plasma are well correlated with each other. High levels of these steroids in the adrenals are associated with high levels of these steroids in the plasma and vice versa.

An inverse correlation between corticosterone and cholesterol exists in the adrenals and in blood. Maximal levels of corticosterone correspond to minimal levels of cholesterol and vice versa.     

Evidence that an extrahypothalamic pituitary corticotropin-releasing hormone (CRH)/adrenocorticotropin (ACTH) system controls adrenal growth and secretion in rats

Within two weeks, hypophysectomy induced in rats a striking decrease in the level of circulating ACTH (the concentration of which was at the limit of sensitivity of our assay system), coupled with a net reduction in the plasma corticosterone concentration and an evident adrenal atrophy. Zona fasciculata, the main producer of glucocorticoids, was decreased in volume, due to a lowering in both the number and average volume of its parenchymal cells. Subcutaneous ACTH infusion (0.1 pmol·min^-1), administered during the last week following hypophysectomy, restored the normal blood level of ACTH and completely reversed all effects of hypophysectomy on the adrenals. Subcutaneous infusion for one week with -helical-CRH or corticotropin-inhibiting peptide (1 nmol·min^-1), which are competitive inhibitors of CRH and ACTH, evoked a further significant lowering of plasma corticosterone concentration and markedly enhanced adrenal atrophy in hypophysectomized rats. These findings strongly suggest that an extrahypothalamic pituitary CRH/ACTH system may be involved in the maintenance of the growth and steroidogenic secretory activity of the rat adrenal cortex.     

Social isolation increases the response of peripheral benzodiazepine receptors in the rat

Social isolation of rats for 30 days immediately after weaning reduces the cerebrocortical and plasma concentrations of progesterone, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG), and 3alpha,5alpha-tetrahydrodeoxycorticosterone (3alpha,5alpha-TH DOC). The percentage increases in the brain and plasma concentrations of these neuroactive steroids apparent 30 min after intraperitoneal injection of the peripheral benzodiazepine receptor (PBR) ligand CB 34 (25 mg/kg) have now been shown to be markedly greater in isolated rats than in group-housed controls. The CB 34-induced increase in the abundance of 3alpha,5alpha-TH PROG was more pronounced in the brain than in the plasma of isolated rats. Analysis of [3H]PK 11195 binding to membranes prepared from the cerebral cortex, adrenals, or testis revealed no significant difference in either the maximal number of binding sites for this PBR ligand or its dissociation constant between isolated and group-housed animals. Social isolation also induced a small but significant decrease in the plasma concentration of adrenocorticotropic hormone. Moreover, CB 34 increased the plasma concentration of this hormone to a greater extent in isolated rats than in group-housed animals. The persistent decrease in the concentrations of neuroactive steroids induced by social isolation might thus be due to an adaptive decrease in the activity either of the hypothalamic-pituitary-adrenal axis or of PBRs during the prolonged stress, reflecting a defense mechanism to limit glucocorticoid production. The larger increase in neuroactive steroid concentrations induced by CB 34 and the enhanced pituitary response to this compound in isolated rats indicate that this mild stressor increases the response of PBRs.     

Reciprocal humoral regulation of endocrine noradrenaline sources in perinatal development of rats

The goal of the present study was to verify our hypothesis of humoral interaction between the norepinephrine secreting organs in the perinatal period of ontogenesis that is aimed at the sustaining of physiologically active concentration of norepinephrine in blood. The objects of the study were the transitory organs, such as brain, organ of Zuckerkandl, and adrenals, the permanent endocrine organ of rats that releases norepinephrine into the bloodstream. To reach this goal, we assessed the adrenal secretory activity (norepinephrine level) and activity of the Zuckerkandl’s organ under the conditions of destructed noradrenergic neurons of brain caused by (1) their selective death induced by introduction of a hybrid molecular complex, which consisted of antibodies against dopamine-β-hydroxylase (DBH) conjugated with saporin cytotoxin (anti-DBH-saporin) into the lateral brain ventricles of neonatal rats; and (2) microsurgical in utero destruction of embryo’s brain (in utero encephalectomy). It was observed that 72 h after either pharmacological or microsurgical norepinephrine synthesis deprivation in the newborn rat’s brain, the level of norepinephrine was increased in adrenals and, conversely, decreased in the Zuckerkandl’s organ. Therefore, the experiments with models of chronical inhibition of norepinephrine synthesis in prenatal and early postnatal rat’s brain revealed changes in the secretory activity of peripheral norepinephrine sources. This, apparently, favors the sustaining of physiologically active norepinephrine level in the bloodstream.     

Influence of right atrial stretch on plasma renin activity in the conscious rat

Rats were prepared with inflatable balloons at the superior vena cava - right atrium junction. After recovery 1 week later, when blood was taken from conscious, normovolaemic animals plasma renin activity was found not to be influenced by right atrial stretch. Plasma renin activity was then measured in rats in which an extracellular fluid deficit had been produced by peritoneal dialysis against a hyperoncotic, isotonic solution. Although basal plasma renin activity was elevated (6.8 +/- 0.9 from 1.5 +/- 0.2 ng X mL X h, n = 19), no depression was observed in the experimental group after 15 or 90 min of balloon inflation. In rats pretreated with isoprenaline (10 micrograms/kg body wt.) plasma renin activity was also increased over basal levels, but again balloon inflation caused no reduction in plasma renin activity. It would appear that right atrial stretch has little, if any, influence on renin release in the conscious rat.     

Effect of selection for behavior on the pituitary-adrenal function of norway ratsRattus norvegicus in postnatal ontogeny

The activity of the pituitary-adrenal system was studied in the Norway rats selected for both maintenance and elimination of the aggressive behavior towards man in the postnatal ontogeny. The selection of the wild rats for domesticated behavior was shown to result in changes of the pituitary-adrenal system formation in the postnatal ontogeny, which is indicated by differences in the dynamics of the adrenals weight as well as of corticosterone content in the blood plasma and in the adrenals both at rest and under stress conditions between the domesticated and aggressive rats.     

Involvement of nitric oxide in nickel-induced hyperglycemia in rats.

Nitric oxide is an important bioactive signaling molecule that mediates a variety of normal physiological functions which, if altered, could contribute to the genesis of many pathological conditions, including diabetes. In the present study we have shown the involvement of NO in nickel-induced hyperglycemia in male albino rats. Administration of nickel chloride (25 to 100 micromol/kg; ip) to overnight-fasted rats resulted in significant dose and time-dependent increase in plasma glucose, attaining maximum level at 1 h posttreatment and thereafter decreasing to normal levels by 4 h. The involvement of NO in nickel-induced hyperglycemia was evident by the observation that pretreatment of rats with NG-monomethyl-l-arginine (10 to 50 micromol/kg; ip), an inhibitor of nitric oxide synthase (NOS), significantly attenuated the nickel-mediated increase in the plasma glucose levels in a dose-dependent fashion. The activity of Ca(2+)-dependent NOS (constitutive form, c-NOS) was found to be significantly elevated in adrenals (5.5-fold) and brain (1.4-fold) at 1 and 2 h posttreatment, attaining normal levels by 4 h. In contrast, the activity of c-NOS in pancreas was significantly decreased (2.8-fold) with a concomitant increase (11.6-fold) in inducible NOS (i-NOS) at the same time interval. As observed by immunoblot analysis, a significant increase in i-NOS protein expression in the pancreas was observed at 1 and 2 h posttreatment. This was associated with a significant elevation in cGMP levels in adrenals, brain, and pancreas, possibly via the stimulation of cytosolic guanylate cyclase. This elevation in cGMP was abolished by low concentration of hemoglobin. These effects were associated with the accumulation of nickel in the target tissues. Taken together, our data suggest that nickel causes a significant increase in the levels of (i) cGMP and c-NOS in adrenals and brain and (ii) i-NOS in pancreas. These events may be responsible for modulating the release of insulin from pancreas finally leading to hyperglycemic condition in rats.     

Small Rises in Plasma Choline Reverse the Negative Arteriovenous Difference of Brain Choline

The concentrations of free choline in blood plasma from a peripheral artery and from the transverse sinus, in the CSF, and in total brain homogenate, have been measured in untreated rats and in rats after acute intraperitoneal administration of choline chloride. In untreated rats, the arteriovenous difference of brain choline was related to the arterial choline level. At low arterial blood levels (less than 10 microM) as observed under fasting conditions, the arteriovenous difference was negative (about -2 microM), indicating a net release of choline from the brain of about 1.6 nmol/g/min. In rats with spontaneously high arterial blood levels (greater than 15 microM), the arteriovenous difference was positive, implying a marked net uptake of choline by the brain (3.1 nmol/g/min). The CSF choline concentration, which reflects changes in the extracellular choline concentration, also increased with increasing plasma levels and closely paralleled the gradually rising net uptake. Acute administration of 6, 20, or 60 mg of choline chloride/kg caused, in a dose-dependent manner, a sharp rise of the arterial blood levels and the CSF choline, and reversed the arteriovenous difference of choline to markedly positive values. The total free choline in the brain rose only initially and to a quantitatively negligible extent. Thus, the amount of choline taken up by the brain within 30 min was stored almost completely in a metabolized form and was sufficient to sustain the release of choline from the brain as long as the plasma level remained low. We conclude that the extracellular choline concentration of the brain closely parallels fluctuations in the plasma level of choline.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of atrial natriuretic peptide on acid-base balance in rats with chronic renal failure

We explored the effects of 12-hour infusion of atrial natriuretic peptide (alpha-rANP:rat, 1-28) on arterial acid-base balance, using 5/6 nephrectomized rats with chronic renal failure. Before the infusion, nephrectomized rats had a higher mean arterial blood pressure, greater urine volume, and lower creatinine clearance than the normal controls, but they did not show a significant difference in arterial hydrogen ion concentration (pH), plasma bicarbonate concentration (HCO3-), partial pressure of carbon dioxide (PCO2), plasma base excess (BE), or plasma ANP concentration. alpha-rANP infusion produced a continuous blood pressure reduction in both nephrectomized and control rats. Urine volume and urinary sodium and potassium excretion tended to increase at 2-hour infusion, but not at 12-hour infusion. In the controls alpha-rANP significantly increased pH from 7.47 to 7.50, and decreased PCO2 by 14%. In contrast, in nephrectomized rats alpha-rANP significantly decreased pH from 7.48 to 7.44, HCO3- by 13%, and BE from -0.07 to -3.22 meq/l. Rats with chronic renal failure had greater reduction in HCO3- than the controls (p less than 0.05). There was no difference in plasma ANP level between the two groups. Thus, it is indicated that the long-term infusion of alpha-rANP reduces pH in rats with chronic renal failure, thereby adversely affecting the acid-base balance.     

Effect of infusing the branched-chain amino acids on concentrations of amino acids in plasma and brain and on brain catecholamines after total hepatectomy in the rat

In totally hepatectomized rats supported by infusion of glucose, the concentrations of many amino acids in plasma and brain rose progressively over time, while the brain levels of norepinephrine decreased. Infusion of a solution containing glucose, leucine, isoleucine, and valine after hepatectomy greatly reduced the accumulation of other essential amino acids in plasma and brain. However, the decrease in brain norepinephrine content was not significantly affected by this infusion, suggesting that high brain concentrations of monoamine precursor amino acids are not the primary cause of norepinephrine depletion after hepatectomy.     

Different activation of ACTH and corticosterone release in response to various stressors in rats

The aim of this study was to investigate the reaction of the hypothalamo-pituitary-adrenocortical (HPA) system to various stressors (fasting, crowding, cold and heat) by measuring blood ACTH and corticosterone (CORT) concentration as well as the cholesterol (CHOL) content in the adrenals. To examine the effects of stress termination, the rats were returned and kept under control conditions for the same period as that of stress duration (supposed recovery period). According to our results HPA system was activated by all the stressors applied. Heat seems to be the strongest stressor since the exposure of animals to a high ambient temperature resulted in the greatest rise of plasma ACTH concentration as well as CORT synthesis and secretion. These values remained elevated after the stress termination i.e. after the rats had been returned to room temperature. Fasting seems to be the weakest stressor given because it causes the smallest increase in blood ACTH and CORT concentrations. Moreover, in refed rats the HPA function was fully recovered. In conclusion, the various stressors applied seem to induce a different response of the HPA system as judged by quantitative changes in ACTH and CORT release.     

Effect of the stress of unilateral adrenalectomy on the depletion of individual cholesteryl esters in the rat adrenal

Normal rats were subjected to unilateral adrenalectomy and were killed 3 hr later. The concentration and composition of the cholesteryl esters in adrenals removed at operation and after death were compared. The esterified cholesterol concentration was lower in the adrenals obtained 3 hr after surgery. Cholesteryl arachidonate decreased in concentration significantly more than any other ester, followed in order of magnitude by linoleate and oleate. The cholesteryl ester concentration of adrenals removed from sham-operated rats 3 hr after surgery was also greatly reduced. On the basis of comparison with other work on the hydrolysis of cholesteryl esters by adrenal homogenates, it is concluded that the apparent selectivity in depletion of cholesteryl esters is due to differences in their rates of hydrolysis.