On the mechanisms of kappa-opioid-induced diuresis

In conscious saline loaded rats, the kappa-opioid agonists tifluadom, U50488, and ethylketocyclazocine, given subcutaneously, induced a characteristic diuresis which could be antagonized by naloxone. Bilateral adrenal demedullation significantly reduced adrenal gland catecholamine content and plasma adrenaline levels, but did not significantly affect plasma corticosterone levels, indicating that the adrenal cortex remained both intact and functional. Seven days following bilateral adrenal demedullation, the subcutaneous administration of the kappa-agonists no longer induced diuresis. However, demedullation did not affect the diuretic response to frusemide or clonidine, nor did it affect the antidiuretic response induced by the mu-opioid agonists morphine and buprenorphine. Adrenal catecholamines do not appear to be involved in kappa-opioid-induced diuresis, since pretreatment with propranolol, prazosin and idazoxan did not affect the diuretic response in intact animals. The results indicate a link between the adrenal medulla and kappa-opioid-induced diuresis and suggest that a peripheral mechanism may also be involved in mediating this effect.     

Kappa-opioid-induced changes in renal water and electrolyte management and endocrine secretion.

1. Subcutaneous injection of the kappa-opioid agonist U50,488 into conscious, saline-loaded rats was associated with a diuresis, antinatriuresis and antikaliuresis which lasted for up to 3 h. Plasma renin activity and corticosterone levels were elevated but plasma vasopressin (AVP) and aldosterone levels were unaltered in similarly treated rats. 2. U50,488 administration to adrenal demeddulated rats was not associated with a diuresis but produced an antinatriuresis, though sodium excretion rates were higher in demedullated than in sham-operated animals. Plasma AVP and corticosterone levels were not affected by demeddulation or subsequent U50,488 treatment. Sham-operated, U50-488-treated rats showed the expected increase in plasma corticosterone levels. 3. U50,488 administration resulted in an antidiuresis and an antinatriuresis in AVP-deficient Brattleboro DI rats. 4. When coupled with fasting stress U50,488 administration resulted in similar but attenuated renal responses compared with those observed in unfasted rats. Basal plasma corticosterone levels were elevated in fasted animals and were further increased by U50,488. 5. Both water and electrolyte handling by the kidney are altered by U50,488. The diuretic effects of U50,488 were reversed by adrenal demedullation and in the absence of endogenous AVP, but the antinatriuretic actions were not altered, suggesting that the effects upon renal water and electrolyte excretion may be mediated by separate mechanisms.     

Cardiovascular responses to kappa opioid agonists in intact and adrenal demedullated rats

The effects of three kappa opioid agonists namely, bremazocine, tifluadom and U-50,488H were studied on blood pressure and heart rate in urethane-anesthetized normal and bilateral adrenal demedullated rats. Bremazocine (0.2, 0.4 and 0.6 mg/kg i.v.) produced a dose-dependent decrease in heart rate, while only 0.4 mg/kg bremazocine produced marked hypotension. The effect appeared to be long lasting because even at 60 min following drug administration the decreases in both heart rate and blood pressure continued. Bilateral adrenal demedullation did not change bremazocine-induced fall in blood pressure but the bradycardia was partially blocked. Tifluadom (0.1-0.4 mg/kg i.v.) produced an initial arrest of heart beat followed by bradycardia which recovered in about 60 min. Except for a very transient fall soon after drug administration no significant effect was observed on blood pressure. In adrenal demedullated rats, tifluadom induced initial arrest of heart was not affected but the subsequent bradycardia was blocked. U-50,488H (0.2, 0.4 and 0.6 mg/kg i.v.) produced dose-dependent bradycardia and hypotension both of which were blocked following bilateral adrenal demedullation. Naltrexone methylbromide (MRZ 2663 BR), a quaternary opioid antagonist, injected 5 min prior to U-50,488H, blocked its cardiovascular effects. The results suggest that kappa opioid agonists given i.v. depress cardiovascular system and these effects are mediated through the adrenal medulla and peripheral opioid receptors. The differential effects of kappa opioid agonists on blood pressure and heart rate suggest that either the three kappa agents interact differentially at the kappa opioid receptors or the subtypes of receptors for the kappa opioid exist.     

Importance of the sympathetic nervous system in the development of renal hypertension in the rat

1. Chemical sympathectomy with 6-hydroxydopamine (6-OHDA) prevented the development of renal hypertension in 80% of weanling male rats of the C.F. strain.2. Adult male rats treated with 6-OHDA developed hypertension on bilateral clamping of the renal arteries.3. Demedullation of the adrenal glands followed by 6-OHDA treatment in adult rats prevented the development of hypertension in 75% of them.4. Weanling rats treated with 6-OHDA did not have any measurable catecholamines in their hearts up to 72-78 days after treatment.5. Unlike the weanling rats, the hearts of adult rats (demedullated or with intact medulla) showed significant refilling (40-50%) of catecholamine stores 60 days after 6-OHDA treatment.6. It is concluded that the functional sympathetic nervous system is important in the development of renal hypertension in the rat.     

Kappa-opioid-receptor agonists modulate the renal excretion of water and electrolytes in anaesthetized rats.

1. Subcutaneous injection of the kappa-opioid agonists U50,488 (10 mg kg-1) and tifluadom (3.5 mg kg-1) into Inactin-anaesthetized, saline-infused rats was associated with a diuresis, antinatriuresis and antikaliuresis which lasted for up to 2 h. A high (5 mg kg-1), but not low (0.1 mg kg-1), dose of naloxone blocked the renal effects of U50,488. 2. U50,488 administration in anaesthetized, vasopressin-deficient Brattleboro DI rats was associated with an attenuated diuresis, though the antinatriuretic response remained intact. 3. The diuretic action of U50,488 was associated with an increase in glomerular filtration rate while fractional fluid reabsorption remained steady. In contrast, fractional sodium and potassium reabsorption were increased. 4. These data suggest that kappa-opioid agonists alter renal handling of both water and electrolytes. This appears to be mediated by two separate mechanisms: increased fluid loss largely reflects altered glomerular events while the fall in electrolyte excretion results from altered tubular handling.     

Effects of U-50488H and U-50488H withdrawal on c-fos expression in the rat paraventricular nucleus. Correlation with c-fos in brainstem catecholaminergic neurons

1. In the present work, we have studied the expression of Fos during acute and chronic administration of the kappa-opioid receptor agonist U-50488H and after U-5088H withdrawal in the rat hypothalamic paraventricular nucleus (PVN). Fos production was also studied in brainstem regions that innervate the PVN: the A(2) cell group of the nucleus of solitary tract (NTS-A(2)) and the A(1) cell group of the ventrolateral medulla (VLM-A(1)), combined with immunostaining for tyrosine hydroxylase (TH) for immunohistochemical identification of active neurons after acute U-50488H administration. 2. For acute experiments, male rats were treated with saline i.p. for 4 days. On day 5, rats were given saline or U-50488H (15 mg x kg(-1), i.p.). Other groups of rats were rendered tolerant/dependent on U-50488H by injecting the drug twice daily (15 mg x kg(-1), i.p.) for 4 days. Control animals received saline i.p. on the same time schedule. On day 5, rats were treated with vehicle i.p., with U-50488H (15 mg x kg(-1)) or with the selective kappa opioid-receptor antagonist nor-binaltorphimine (Nor-BNI, 5 mg x kg(-1), i.p.). 3. Using immunohistochemical staining of Fos, present results indicate that acute administration of U-50488H produced an increase in Fos expression in the PVN and in the noradrenergic A(1) and A(2) cell groups. Moreover, when double-label immunohistochemistry was used to identify Fos and catecholaminergic-positive neurons in the brainstem, it was found that catecholaminergic-positive neurons in the NTS and VLM showed a significant increase in Fos expression in response to acute U-50488H injection. Chronic application of U-50488H leads to the development of tolerance towards their effects on Fos expression in the PVN as well as in the NTS and VLM. However, administration of Nor-BNI to U-50488H-dependent rats did not induce any changes in Fos immunoreactivity in the PVN or in the brainstem. 4. These findings demonstrate that acute activation of kappa-opioid receptors results in different altered patterns of immediate-early gene expression in the PVN, which occurs concurrently with an increased activity of their inputs from the brainstem. Interestingly in contrast to morphine withdrawal, present results demonstrate that rats withdrawn from U-50488H did show no changes in Fos-immunoreactivity in the PVN, NTS or VLM, indicating the absence of dependence on the kappa-agonist under the present experimental conditions.     

Peripheral kappa-opioid modulation of the formalin response: an electrophysiological study in the rat

The activity of single dorsal horn nociceptive neurones was recorded in the spinal cord of halothane anaesthetized rats. S.c. injection of a 5% formalin solution into the receptive field of these neurones resulted in two peaks of neuronal firing over a period of 60 min. Prior administration of the kappa-opioid receptor agonist U50488H directly into the site of formalin injection caused a dose-dependent decrease in the size of both the first and second peaks of the response which was naloxone reversible. Injection of U50488H into the contralateral paw had no effect on either peak of the formalin response. Injection of the top dose (100 micrograms) of U50488H had no effect on the electrically evoked A beta- or C-fibre responses of the neurone. Neither morphine nor Tyr-D-Ser(Otbu)-Gly-Phe-Leu-Thr (DSTBULET), administered into the receptive field, had any significant effect on either peak of the formalin response. Plasma extravasation in the skin, measured using Evans blue, produced by the formalin injection was not blocked by U50488H. Thus, whilst the spinal responses of this peripheral model of inflammation can be inhibited by peripheral kappa-opioid activation, but not mu- or delta-, plasma extravasation associated with this inflammation is not reduced.     

Roles of KATP channels in delayed cardioprotection and intracellular Ca(2+) in the rat heart as revealed by kappa-opioid receptor stimulation with U50488H

The effect of preconditioning with U50488 H (UP), a selective kappa-opioid receptor (kappa-OR) agonist, on infarct size and intracellular Ca2+ ([Ca2+]i) in the heart subjected to ischaemic insults were studied and evaluated. U50488 H administered intravenously reduced the infarct size 18-48 h after administration in isolated hearts subjected to regional ischaemia/reperfusion (I/R). The effect was dose dependent. A peak effect was reached at 10 mg x kg-1 U50488 H and at 24 h after administration. The effect of 10 mg x kg-1 U50488 H at 24 h after administration was abolished by nor-binaltorphimine (nor-BNI), a selective kappa-OR antagonist, indicating the effect was kappa-OR mediated. The infarct reducing effect of U50488 H was attenuated when a selective blocker of mitochondrial (5-hydroxydecanoic acid, 5-HD) or sarcolemmal (HRM-1098) ATP-sensitive potassium channel (KATP) was coadministered with U50488 H 24 h before ischaemia or when 5-HD was administered just before ischaemia. U50488 H also attenuated the elevation in [Ca2+]i and reduction in electrically induced [Ca2+]i transient in cardiomyocytes subjected to ischaemic insults. The effects were reversed by blockade of KATP channel, which abolished the protective effect of preconditioning with U50488 H. The results indicated that mitochondrial KATP channel serves as both a trigger and a mediator, while sarcolemmal KATP channel as a trigger only, of delayed cardioprotection of kappa-OR stimulation. The effects of these channels may result from prevention/attenuation of [Ca2+]i overload induced by ischaemic insults.     

Effects of guanethidine on the blood pressure response to splanchnic nerve stimulation in the rat: Role of the adrenal medulla

1. Splanchnic nerve stimulation provokes a larger increase in blood pressure in intact rats than in rats previously demedullated by means of expression of the adrenals in situ and adrenalectomy followed by adrenocortical grafting.

2. Rats pretreated with guanethidine showed an attenuated albeit prolonged hypertensive response to splanchnic stimulation. Similar effects were exerted by guanethidine in rats demedullated by expression. In rats demedullated by grafting, smaller doses of guanethidine induced a more substantial depression of the blood pressure response without increasing its duration.

3. It is concluded that inhibition of the peripheral sympathetic endings induced by guanethidine was partially compensated by the enhancement of the cardiovascular effects of the mediators released by the adrenal medulla and that demedullation by expression did not completely eliminate chromaffin tissue.

     

Evidence that the kappa agonist U50488H has non-opioid actions

The antagonism of the antinociceptive effects of various kappa-opioid agonists has been studied in the mouse abdominal constriction test. Naloxone produced a much smaller degree of antagonism of U50488H than it did of two other kappa-agonists, U69593 and tifluadom. The kappa-selective antagonist, norbinaltorphimine, also failed to shift the dose-response curve to U50488H in this test, despite producing considerable antagonism of the U50488H effect in the rotarod test and of U69593 in both experimental situations. These results are suggestive of a non-opioid component to the action of U50488H in the abdominal constriction test. At high concentrations, U50488H, but not U69593, also showed non-opioid effects in reducing contractile activity in the field-stimulated isolated guinea-pig ileum, as demonstrated by the profile of antagonism seen with beta-chlornaltrexamine and naloxone. These results suggest that U69593, rather than U50488H, may be the kappa-agonist of choice to use, particularly in in-vivo experiments.     

Spinal kappa-opioid receptor-mediated antinociception is stimulus-specific

The intrathecal injection of a variety of selective kappa-opioid receptor ligands did not result in significant inhibition of thermal nociceptive tail flick responses in rats. In contrast, these compounds dose dependently inhibited pressure nociceptive responses. Cross-tolerance studies revealed that the kappa-opioid receptor ligands tifluadom, U-50488H and dynorphin-(1-17) act upon a receptor distinguishable from the receptor through which morphine exerts its inhibition of mechanical nociceptive responses. The less selective kappa-opiate receptor ligands bremazocine and ethylketocyclazocine (EKC), however, blocked both tail flick and tail pressure nociceptive responses and their effect showed marked cross-tolerance to morphine in the tail flick nociceptive test, but not for the pressure nociceptive responses. We suggest that EKC and bremazocine act upon the spinal kappa-opioid receptor to block mechanical nociceptive responses but that the analgesic effect of EKC and bremazocine on thermal nociceptive responses is probably mediated via spinal micron- and/or delta-, and delta-opioid receptors, respectively.     

Mechanisms of hyperglycemic response to chlorpromazine administered into lateral ventricle in rats. II. Secretion of epinephrine from adrenal medulla

An injection of chlorpromazine(CPZ) into the lateral ventricle caused hyperglycemia in intact rats, but not in adrenal-demedullated rats. However, the hyperglycemic response to CPZ was not blocked by hypophysectomy or pretreatment with dexamethasone. Beta-adrenergic blocking and ganglionic blocking both prevented CPZ-induced hyperglycemia. Furthermore, injection of CPZ did not potentiate the hyperglycemic response to exogenous epinephrine in demedullated rats. From these results, it is suggested that CPZ causes hyperglycemia mainly by the release of epinephrine from adrenal medulla stimulated by impulses from the central nervous system.     

Dissociable effects of the κ-opioid receptor agonists bremazocine, U69593, and U50488H on locomotor activity and long-term behavioral sensitization induced by amphetamine and cocaine

RATIONALE: Mesolimbic dopaminergic neurotransmission plays a critical role in the locomotor effects of psychostimulant drugs, but a general involvement in the induction of long-term psychostimulant sensitization is questionable. By influencing dopaminergic neurotransmission, opioid drugs can alter the behavioral effects of psychostimulants. OBJECTIVES: The effects of the kappa-opioid receptor agonists bremazocine, U69593, and U50488H on the locomotor stimulant and the long-term sensitizing effects of amphetamine and cocaine were investigated in rats. Unlike U69593 and U50488H, bremazocine is also an antagonist at mu- and delta-opioid receptors, as well as an agonist at a subtype of delta-opioid receptors inhibiting dopamine D1 receptor-stimulated adenylate cyclase. METHODS: Bremazocine, U69593, and U50488H were administered prior to amphetamine and cocaine, and locomotor activity was measured. In separate studies, the opioids were co-administered with amphetamine and cocaine for 5 days, and locomotor sensitization was assessed 3 weeks post-treatment. RESULTS: Bremazocine and U69593 attenuated the psychomotor stimulant effects of amphetamine and cocaine. U50488H attenuated the locomotor effect of cocaine and biphasically affected amphetamine-induced locomotion, i.e., suppression followed by stimulation. Bremazocine prevented the development of amphetamine-induced but not cocaine-induced long-term sensitization. Neither U69593 nor U50448H affected the induction of long-term amphetamine or cocaine sensitization. CONCLUSIONS: In agreement with previous studies, the present data suggest that differential mechanisms underlie the acute stimulant versus the long-term sensitizing effects of psychostimulants, and the induction of long-term sensitization by amphetamine versus cocaine. Stimulation of kappa-opioid receptors does not seem to block the induction of long-term psychostimulant sensitization. Thus, bremazocine is likely to block the induction of amphetamine sensitization through a non-kappa-opioid receptor mechanism. We suggest that this effect of bremazocine is the result of its unique agonist action at a subtype of delta-opioid receptors, thereby acting as a functional dopamine D1 receptor antagonist. This would be consistent with the literature showing that the induction of long-term amphetamine sensitization depends on the activation of dopamine D1 receptors. In addition, the present data are in keeping with studies showing that dopamine neurotransmission is not critical for the induction of long-term cocaine sensitization.     

Renin-angiotensin mediation of adrenal catecholamine secretion induced by hypoglycaemia in the cat

1 The mechanism involved in catecholamine (CA) release from the cat adrenal gland in response to insulin hypoglycaemia was studied. In intact cats, hypoglycaemia induced an 11 fold increase in adrenomedullary CA secretion. 2 Acute bilateral nephrectomy nearly abolished the increased CA release from the adrenal gland during hypoglycaemia. 3 Infusion of Sar1-Ileu8-Angiotensin II (AII), a competitive AII antagonist, suppressed the adrenomedullary response to the insulin-induced hypoglycaemia. After termination of the antagonist infusion CA secretion from the adrenal medulla increased rapidly, reaching the same level as in insulin-treated cats. 4 Infusion of rabbit anti-angiotensin I antibodies suppressed CA release from the adrenal gland of hypoglycaemic cats. This effect was more prolonged than that of Sar1-Ileu8-AII. 5 These results indicate that CA release from the adrenal medulla of the cat in response to insulin-induced hypoglycaemia, is mediated through the renal reninangiotensin system. Since hypoglycaemia causes sympathetic stimulation through a central mechanism, angiotensin may act through the central nervous system.     

Bedeutung der Nebennierenkatecholamine für die reflektorische kardiovasculÄre Gegenregulation bei renal hypertonischen Ratten

Summary The antihypertensive effects of oxprenolol, an adrenoceptive betareceptor blocking agent, hydralazine or a combination of both compounds were compared in intact and adrenal demedullated rats. Blood pressure in the conscious animal was measured according to the method of Gerold, et al., and in the anaesthetized rat according to the method of Byrom and Wilson.Although oxprenolol had no influence on blood pressure in the intact rat, an antihypertensive effect was seen in conscious or anaesthetized, demedullated animals. The antihypertensive effect of hydralazine was more pronounced in conscious, intact rats than in conscious, demedullated rats, while its effect was similar in anaesthetized, intact or demedullated rats.An antagonism of the effect of hydralazine by oxprenolol was seen in intact, but not in demedullated animals. In the conscious, demedullated animal oxprenolol enhanced the antihypertensive effect of hydralazine.It can be concluded that adrenal catecholamines play a major role in reflex adjustment to a fall in blood pressure and that this effect can be enhanced by adrenergic beta-receptor blockade.

     

Influence of adrenal demedullation on stress-related behaviour in Wistar rats

The influence of adrenal demedullation on stress-related behaviour (chronic immobilization) was investigated in respect to the following parameters and physiological processes: number of animals surviving the exposure, blood pressure behaviour, endogenous opioid system, pain sensitivity, endogenous level of substance P (SP) in pituitary and hypothalamus. The results showed that chronic immobilization stress and adrenal demedullation induce the same direction of alterations of physiological processes and parameters. This fact suggests the involvement of common regulatory mechanisms both in demedullation and chronic stress. An important process in this respect may be the induction of functional insufficiency of the adrenal medulla especially concerning the adrenal peptidergic mechanisms. Contrary to the sham operated rats the demedullated animals showed differences in their stress-related behaviour of parameters of adaptive regulatory processes. In rats with demedullation either no additional stress-related alterations of parameters in relation to the general adaptation processes were induced or the demedullation-induced alterations were antagonized partially or completely by chronic immobilization.     

Effects of opioid agonists on urine production in neonatal rats

The modulatory effects of opioids on urine production in adult rats have been well-documented. We report here the first investigation of the effects of these agents on urination in neonatal rats. The kappa-agonists U50,488H (1,10 mg kg-1) and (+)-tifluadom (10 mg kg-1) produced an increase in urine output in 10-day old pups whereas the (-)-isomer of tifluadom was ineffective in this model. The diuretic effects of the highest dose of U50,488H were attenuated by a 10 but not a 1 mg kg-1 dose of the opioid antagonist naltrexone. These findings suggest that kappa-agonists, as in adult animals, produce diuresis in neonates by activity at kappa-opioid receptors and also confirm the stereoselective nature of the response. The increase in urination produced by U50,488H (10 mg kg-1) was also reduced by the alpha-adrenoceptor antagonist phentolamine (1 mg kg -1), an observation which supports the hypothesis that kappa-agonists--in addition to their well-established inhibitory effects on the release of antidiuretic hormone--may increase urination via an adrenergic mechanism at the level of the adrenal medulla. The mu-opioid agonist morphine (0.1-10 mg kg-1), in contrast to its observed effects in older animals, did not produce antidiuresis in either normally-hydrated or water-loaded 10-day old rat pups. The results of this study therefore show that the stimulatory effects of kappa-agonists on urine production appear to be fully-functional at 10-days but the inhibitory effects of opioids on urination lag behind in development.     

Noradrenaline content of the heart of the adrenal-demedullated rat

1. The noradrenaline (NA) concentration in the "heart" (atria and right ventricle) of male rats was estimated at different periods following adrenal demedullation. For 1-3 weeks after the operation there was, in all rats, a reduction in NA content of the tissue, whereas, after somewhat longer intervals, the concentrations had returned to normal in some but not in all animals, so that the range of values was very wide.2. In order to be able to test the effect of 2-aminotetralin on the cardiac NA of animals deprived of their medulla but having normal initial NA concentrations, an interval of 6-8 months was allowed to elapse between operation and injection of the drug; at this time the effect of the drug on cardiac NA was the same in intact and demedullated animals. There is thus no reason to attribute to the adrenal medulla any supporting role in the resynthesis of cardiac NA during periods of increased sympathetic activity.3. The time course of the pronounced fall in cardiac NA after adrenal demedullation resembles the time course of sodium retention shown by Gaunt, Renzi, Gisoldi & Howie (1967) to follow this operation. It is therefore suggested that it is the change in electrolyte metabolism which is responsible for the abnormality of NA storage; both phenomena occur in demedullated but not in adrenalectomized animals.     

Effect of opiates on transmitter release from visualized hypogastric boutons innervating the rat pelvic ganglia.

1. The effect of opiates on neurotransmission between visualized hypogastric nerve boutons and postganglionic cell bodies has been examined using extracellular recording of nerve bouton impulses (NBIs) and excitatory postsynaptic currents (e.p.s.cs). 2. Morphine (10 to 40 microM) did not affect neurotransmission in the ganglia. Dynorphin-A (4 microM) and U50488H (1 microM) decreased quantal transmitter release and naloxone (10 microM) reversed these effects. 3. Morphine (10 microM), dynorphin-A (4 microM) and U50488H (1 microM) did not affect either the time course or consistency with which the NBI was recorded. 4. Dynorphin-A (1 to 4 microM) and U50488H (1 microM) decreased the average amplitude of e.p.s.cs by increasing the number of failures to release quanta from single or small groups of 2 to 4 boutons during continuous nerve stimulation at 0.1 Hz. 5. The decrease in quantal release induced by dynorphin-A and U50488H in 0.2 to 0.5 mM [Ca2+]zero was readily reversed by increasing the extracellular calcium ion concentration to 1 mM. 6. It was concluded that kappa-opioid receptors are located on the boutons of the hypogastric nerve and when activated by kappa-opioid receptor agonists reduce quantal release without affecting the NBI.     

Lack of effect of perinatal lead exposure on kappa-opioid receptor function

The effects of lead exposure have been studied upon the behavioural and diuretic responses to the kappa-opioid receptor agonist U-50488H in neonatal rats. Lead was administered in the maternal drinking water (100, 300 and 1000 ppm) from conception to postnatal day 14. The hyperactivity, wall climbing behaviours and diuretic effects of U-50488H (0.1-30 mg/kg, i.p.) in 5- and 20-day-old rat pups were unaffected at all 3 lead dose levels. Lead treatment per se produced a decrease in activity at 20 days. These results contrast with our previously reported disruption of mu- and delta-opioid receptor systems following perinatal lead exposure and suggest that the toxic effects of this metal may be confined to particular types of opioid receptor.