Effects of postnatal reserpine administration on sympatho-adrenal development in the rat

Reserpine (2.5 or 5 mg/kg, s.c.) was administered to neonatal rats and the adrenals were analyzed for catecholamines (CA), tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH) activities and for the ability of isolated storage vesicles to incorporate [³H]epinephrine. Four hr after reserpine administration, an acute depletion of CA was observed, and by 24 hr CA fell to 10–20 per cent of controls; recovery required 2 weeks. Pretreatment of neonates with chlorisondamine (10 mg/kg, s.c.) did not prevent acute (4 hr) CA depletion by reserpine, but did block the decline observed in adult rats, indicating that the acute depletion in neonates is not due to neurogenic stimulation via the splanchnic nerve. At no time after the administration of reserpine to neonates was a change in TH observed, and only a small increment in DBH activity was obtained. In contrast, adult rats given reserpine showed marked increases in both TH and DBH, and depletion of CA was less marked and of shorter duration. Administration of reserpine to rats of different ages demonstrated that an “adult” pattern of response (TH induction) was obtained only after 8 days of age. On the other hand, nicotine (10 mg/kg, s.c.) given to neonates did evoke TH induction, indicating that at birth the tissue is capable of induction if stimulated directly. Inhibition of [³H]epinephrine uptake by reserpine in vitro (10^?7M) was lower in vesicles from neonates than that observed in vesicles from adults, but drug administration in vivo produced marked inhibition in both adults and neonates by 4 hr. with recovery occurring by 4 days post-injection. These data show that the administration of reserpine to neonatal rats produces an acute depletion of CA which is not dependent on either blockade of vesicular uptake or on reflex actions of the drug, and which is not accompanied by TH induction. These differences from the adult may account for the more intense and longer-lasting effects of the drug in neonates. The lack of functional connections between the central nervous system and the neonatal adrenal medulla may be responsible for the immature response pattern.     

Effects of pinacidil on the sympatho-adrenal system in dogs.

1. The aim of the present work was to study the antihypertensive effect of pinacidil, a potassium channel opener, in sinoaortic denervated (SAD) conscious dogs and to investigate whether the involvement of the sympathetic nervous system induced by this vasodilator compound is only of baroceptor reflex origin. 2. Pinacidil (0.1, 0.2, 0.4 mg kg-1 i.v.) induced a dose-dependent decrease in blood pressure in normal as well as in SAD dogs. In contrast, the induced-tachycardia observed in normal dogs was not found in SAD animals. 3. Since pinacidil induced an increase in plasma catecholamines, free fatty acids, glucose, plasma renin activity and aldosterone in SAD dogs it is suggested that this sympathetic activation is independent of the baroreceptor reflex pathways. 4. The sympathetic activation is mainly of peripheral origin, since pinacidil (0.7 mg kg-1 i.v.) induced an increase in adrenaline release from the adrenal gland after section of the great splanchnic nerve in anaesthetized dogs. This increase is probably due to an effect that does not involve K+ channel opening. However, this effect of pinacidil was not observed during splanchnic nerve stimulation (in this case, the involvement of K+ channel opening is suggested).     

Effect of chronic administration of selective glucocorticoid receptor antagonists on the rat hypothalamic-pituitary-adrenocortical axis.

The effects of the selective glucocorticoid receptor (GR) antagonists ORG 34850, ORG 34116, and ORG 34517 on the rat hypothalamic-pituitary-adrenocortical (HPA) system were investigated. To assess the potency of the compounds to occupy GR in the brain and pituitary, we applied a single acute subcutaneous (s.c.) injection (10 mg/kg). ORG 34517 was most potent to occupy GR in the anterior pituitary and distinct brain areas, whereas all compounds were unable to occupy mineralocorticoid receptor (MR). Chronic administration of ORG 34850, ORG 34116, and ORG 34517 (20 mg/kg/day) for 1, 3, and 5 weeks resulted only in minor changes in brain GR levels. However, profound increases of hippocampal MR were observed virtually at all time points. Treatment with ORG 34850 and ORG 34116 elicited episodic increases in HPA axis activity, whereas ORG 34517 did not cause any changes in HPA activity. Thus, the GR antagonists exert distinct effects on the HPA axis, which may be pertinent for the proposed antidepressant activity of these compounds.     

Effects of acute and chronic administration of mu- and delta-opioid agonists on the hypothalamic-pituitary-adrenocortical (HPA) axis in the rat.

The control of hypothalamic-pituitary-adrenocortical (HPA) activity by opioids seems to involve stimulatory and inhibitory pathways. The purpose of the present study was to determine the acute and chronic effects of selective mu- and delta-opioid agonists, administered centrally (i.c.v.) on pituitary-adrenocortical activity in the rat. The mu-agonist DAGO ([D-Ala2,N-MePhe4,Gly-ol5]enkephalin; 0.75 nmol i.c.v.) and the delta-agonist DPDPE ([D-Pen2,5]enkephalin; 194 nmol i.c.v.) both stimulated corticosterone release when administered acutely. Chronic administration of DAGO and DPDPE resulted in the development of tolerance to their neuroendocrine effects. These data suggest that both mu- and delta-opioid receptors are involved in the regulation of HPA activity under physiological conditions and during opiate abuse.     

Effect of Cd administration on the pituitary-adrenal axis

The possibility that Cd administration could activate the pituitary-adrenal axis has been studied. It was found that acute administration of Cd strongly increased serum corticosterone levels. Adrenocortical activation correlated well with serum Cd levels, suggesting that adrenal activation was dependent on the presence of the metal in the blood. In addition, our data clearly demonstrate that increased corticosterone secretion caused by Cd was, at least in part, mediated by adrenocorticotropin release. Therefore, it appears that Cd might cause similar endocrine and metabolic changes as classical stress agents.     

Chronic central nicotinic blockade after a single administration of the bisquaternary ganglion-blocking drug chlorisondamine.

Drug-naive rats were tested for horizontal and vertical activity in photocell cages, for up to 80 min starting immediately after a subcutaneous injection of (-)-nicotine bitartrate or 0.9% w/v NaCl solution (saline). Nicotine (0.1 to 0.4 mg kg-1 base) depressed vertical activity and induced ataxia in the first 20 min, but increased both horizontal and vertical activity later in the session; these actions were dose-dependent. A single intraventricular (i.v.t.) injection of chlorisondamine Cl (2 microgram base), a quaternary ganglion-blocking drug, given one to two weeks before testing, blocked the ataxic and stimulant actions of nicotine. The antagonistic actions of chlorisondamine (0.2, 1.0, 5.0 micrograms i.v.t., single administration) were shown to be dose-dependent. The stimulant actions of nicotine were blocked in a dose-dependent way for the duration of the experiment (5 weeks); nicotine's depressant actions were completely blocked at two weeks but not at five weeks. A ganglion-blocking dose of chlorisondamine (0.1 mg kg-1), given subcutaneously (s.c.), failed to reduce the behavioural actions of nicotine, whereas a much higher systemic dose (10 mg kg-1 s.c.) was effective for at least five weeks. Chlorisondamine failed to alter the behavioural effects of (+)-amphetamine or apomorphine, while blocking those of nicotine. It is concluded that chlorisondamine antagonizes some of nicotine's central actions in a potent, long-lasting and pharmacologically selective way.     

Effects of repeated morphine administration on copulation and on the hypothalamic-pituitary-gonadal axis of male rats.

Adult male rats were administered morphine twice a day for 45 days and the effects of morphine on the copulation rate, the weight of various organs, and on the hypothalamic-pituitary-gonadal axis were examined. Morphine administered rats showed a loss of weight, hypertrophy of the adrenals, decreased weight of accessory sex organs, low sperm count, and decreased copulation rate. The contents of the luteinizing hormone releasing hormone in the hypothalamus and the luteinizing hormone in the pituitary remained unchanged. Serum luteinizing hormone and testosterone levels decreased, but serum follicle-stimulating hormone levels increased. These results suggest that morphine inhibits the hypothalamic-pituitary-gonadal axis and causes a diminution in the number of fertilizations of the partner females.     

Effects of chronic ethanol administration on plasma-membrane-bound glycosyltransferase activities

Physiological and membranous modifications induced by a 4-week ethanol administration in mouse liver plasma membrane were studied. Galactosyl- and glucosyltransferase activities were stimulated in the presence of dolichylphosphate alone or with phosphatidyl-choline. The galactosyltransferase activity was inhibited by chronic ethanol administration. These enzymes were modulated by different phospholipids. The phosphatidic acid was the most efficient activator. Ethanol provoked an inhibition of the galactosyltransferase activity whatever the phospholipid used, as well as an inhibition of the glucosyltransferase activity, chiefly in presence of phosphatidyl-inositol. The preincubation of control or treated mouse liver plasma membranes with liposomes loaded by dolichylphosphate and cholesterol greatly enhanced the enzymatic activities without removing the inhibition by ethanol treatment.     

Effects of prazosin on hemodynamics and sympatho-adrenal activity in hypertensive patients

We studied peripheral and central hemodynamics and plasma catecholamine levels in 12 previously untreated patients with essential hypertension before and during treatment with the alpha 1-adrenoceptor antagonist prazosin (9.8 +/- 1.1 mg/day for 3-6 weeks following dose titration) as a single drug. Prazosin did not alter intra-arterially recorded blood pressures in the group as a whole, in spite of adequate plasma levels (12.6 +/- 1.2 ng/ml). There were no changes in cardiac output, blood volume, systemic or forearm vascular resistance, or forearm venous tone at rest during treatment. The blood pressure response to prazosin was correlated to pretreatment systemic and forearm vascular resistances. Arterial adrenaline levels were unchanged, but noradrenaline levels increased from 1.30 +/- 0.10 to 1.85 +/- 0.20 nM (p less than 0.05). Both noradrenaline and blood pressure responses to isometric hand-grip exercise were delayed and reduced during treatment. The hemodynamic and plasma catecholamine responses to a cold pressor test and tilting (50% head-up during 10 min) were similar before and during treatment. Our results may be related to development of tolerance to the alpha-adrenoceptor blocking effect of prazosin during long-term treatment. The elevation of arterial noradrenaline levels suggests that increased sympathetic activity also may have opposed the hypotensive response to prazosin.     

Blunting by chronic phosphatidylserine administration of the stress-induced activation of the hypothalamo-pituitary-adrenal axis in healthy men

Summary The effect of chronic administration of phosphatidylserine derived from brain cortex on the neuroendocrine responses to physical stress has been examined in a placebo-controlled study in 9 healthy men.Phosphatidylserine 800 mg/d for 10 days significantly blunted the ACTH and cortisol responses to physical exercise (P=0.003 and P=0.03, respectively), without affecting the rise in plasma GH and PRL.Physical exercise significantly increased the plasma lactate concentration both after placebo and phosphatidylserine.The results suggest that chronic oral administration of phosphatidylserine may counteract stress-induced activation of the hypothalamo-pituitary-adrenal axis in man.     

Effects of chronic acetone administration on ethanol-inducible monooxygenase activities in the rat

Liver microsomal monooxygenase activities known to be ethanol-inducible were determined in female Sprague-Dawley rats after 2-week treatment with 1% (v/v) acetone. Daily acetone intake was in the order of 1.2 g/kg. The final body weight, liver weight and microsomal protein content of acetone-treated rats were identical to those of untreated controls. Microsomal NADPH-cytochrome c reductase activity was also unaffected, while cytochrome P-450 content was only increased 12-18%. Ethanol-inducible p-nitrophenol hydroxylation, aniline hydroxylation and 7-ethoxycoumarin O-deethylation activities were enhanced 5.3-, 4.4- and 2.6-fold, respectively, by chronic acetone treatment. The sex-dependent inducing effect of ethanol on benzphetamine N-demethylation activity in female rats was not observed however, after acetone. Addition of acetone in vitro had a stimulatory effect on aniline hydroxylation by microsomes from control and acetone-induced rats. Acetone, however, was found to be a competitive inhibitor of p-nitrophenol hydroxylation activity (apparent Ki = 1.8 mM), an observation suggesting that p-nitrophenol is a more selective substrate than aniline for rat liver ethanol- and acetone-inducible cytochrome P-450j. Interruption of the chronic acetone treatment for 24 hr resulted in the almost complete disappearance of its inducing affects, this treatment apparently reproducing only the rapidly reversible preferential inducing effects of chronic ethanol administration. This experimental model of induction by acetone in the rat, when compared to chronic ethanol administration, would thus permit a more selective look at the consequences of these common inducing effects in particular, with respect to drug metabolism and toxicity in vivo, and this, in the absence of the hepatotoxic effects of ethanol itself.     

Effects of chronic nicotine administration on the response and adaptation to stress

The effects of chronic nicotine administration (0.4 mg/kg for 40 days) and its withdrawal on the adrenocortical response to acute and repeated exposure to stress have been examined and related to changes in brain 5-hydroxyindole levels. No significant effects on the response to acute stress were observed. Repeated exposure to the stressful procedure resulted in complete adaptation of the adrenocortical response and the development of a significant (P<0.01) positive correlation between the plasma corticosterone and hippocampal 5-HT concentrations. In nicotine-treated rats, complete adaptation did not occur and the plasma corticosterone showed a significant (P<0.05) negative correlation with hippocampal 5-HT. Nicotine withdrawal was not associated with any reduction in plasma corticosterone, but did abolish its relationship with hippocampal 5-HT.     

Effects of chronic nicotine administration on the denervated rat adrenal medulla.

1 The effects of chronic nicotine administration (1 or 10 mg/kg, s.c., twice daily) were studied in intact and denervated rat adrenal glands to determine the relative roles of central input and direct actions on catecholamines. 2 Catecholamine depletion was obtained in the intact glands from 1-7 days of treatment with 10 mg/kg, with recovery by 14 days of treatment; catecholamines were not decreased in denervated adrenal glands. 3 Catecholamine depletion was accompanied by a decline in functional storage vesicles (determined by [3H]-adrenaline uptake per gland) in the intact side, while no change was seen in the denervated side; the proportion of newly synthesized vesicles increased markedly during 1-7 days of treatment with 10 mg/kg in the intact side, while a much smaller increase of shorter duration was seen in the denervated adrenal gland. 4 Chronic nicotine administration at either dose level induced tyrosine hydroxylase in both intact and denervated glands, but the increase occurred more slowly in the denervated glands. 5 Dopamine beta-hydroxylase levels increased similarly in both sides during treatment with nicotine (10 mg/kg). 6 These studies suggest that although long-term adrenal denervation eliminates the catecholamine depletion caused by chronic administration of nicotine, the mechanisms for induction of catecholamine synthesizing enzymes are still capable of responding to the drug.     

Effects of chronic dextromethorphan administration on the cellular immune responses in mice

We examined the chronic effect of dextromethorphan (DM) on the cellular immune responses in mice. T cell stimulator, phytohemagglutinin did not show significant effect on lymphocyte proliferation. Costimulator of T and B cell, pokeweed mitogen, and B cell stimulator, lipopolysaccharide exhibited DM-induced decreased lymphocyte proliferation. Significantly suppressed natural killer (NK) cell cytotoxicity was evidenced following 6 months DM exposure. These results suggest that chronic DM administration perturb B cell functioning and NK cell cytotoxicity. In addition, prenatal DM exposure did not potentiate the immunomodulation in postnatal effect induced by chronic DM.     

Effects of nicotine and chlorisondamine on cerebral glucose utilization in immobilized and freely-moving rats

Chlorisondamine blocks central nicotinic receptors for many weeks via an unknown mechanism. Intracerebroventricular administration of [(3)H]-chlorisondamine in rats results in an anatomically restricted and persistent intracellular accumulation of radioactivity. The initial aim of the present study was to test whether nicotinic receptor antagonism by chlorisondamine is also anatomically restricted. Male adult rats were pretreated several times with nicotine to avoid the disruptive effects of the drug seen in drug-na?ve animals. They then received chlorisondamine (10 microg i. c.v.) or saline, and local cerebral glucose utilization (LCGU) was measured 4 weeks later after acute nicotine (0.4 mg kg(-1) s.c.) or saline administration. During testing, rats were partially immobilized. Nicotine significantly increased LCGU in the anteroventral thalamus and in superior colliculus. Chlorisondamine completely blocked the first of these effects. Chlorisondamine significantly reduced LCGU in the lateral habenula, substantia nigra pars compacta, ventral tegmental area, and cerebellar granular layer. The second experiment was of similar design, but the rats were not pre-exposed to nicotine, and were tested whilst freely-moving. Acute nicotine significantly increased LCGU in anteroventral thalamus, superior colliculus, medial habenula and dorsal lateral geniculate. Overall, however, nicotine significantly decreased LCGU. Most or all of the central effects of nicotine on LCGU were reversed by chlorisondamine given 4 weeks beforehand. These findings suggest that chlorisondamine blocks nicotinic effects widely within the brain. They also indicate that in freely-moving rats, nicotine can reduce or stimulate cerebral glucose utilization, depending on the brain area. British Journal of Pharmacology (2000) 129, 147 - 155     

Effects of chronic administration of (+)-amphetamine on maze performance of the rat

1. The influence of (+)-amphetamine, given 1 min after each training session, on the performance of 124 rats in a Lashley III maze was measured every 48 hr.2. The first three injections of the drug significantly improved the learning ability of naive rats.3. With prolonged treatment, (+)-amphetamine strongly impaired the maze performance of these rats.4. The chronic administration of (+)-amphetamine to previously trained rats produced the same adverse effect.5. Amylobarbitone sodium given to previously trained rats 30 min before the training sessions completely blocked the adverse effect of (+)-amphetamine.6. (+)-Amphetamine did not produce impairment of performance when given chronically 30 min before training sessions, to previously trained rats.