Effect of angiotensin II and eledoisin on cholinergic neurons in rat hippocampus

Angiotensin II and eledoisin modulate drinking behaviour in rats that is mediated by monoaminergic and cholinergic neurons. In the present study we have shown that combined intracerebroventricular injections of either 0.1 or 1.0 microgram doses of angiotensin and eledoisin resulted in a decrease of about 25-35% in activities of choline acetyltransferase, ATP-citrate lyase in the hippocampus. In addition, 1 microgram quantities of these peptides depressed activity of carnitine acetyltransferase but did not alter activity of acetylcholinesterase. On the other hand, the application of 0.1 microgram of angiotensin caused no change in activity of monoamine oxidase A, while 1.0 microgram dose brought about its 67% activation. Eledoisin abolished this effect of angiotensin II. These data provide evidence that angiotensin II and eledoisin evoke non related adaptive changes in cholinergic and monoaminergic neurons of the hippocampus.

Differential effects of angiotensin II and eledoisin on monoamine oxidase A and B activities in rat brain

Intracerebroventricular injections of angiotensin II caused 108, 62, and 54% increases in monoamine oxidase A activities in rat hippocampus, hypothalamus, and striatum, respectively. These activatory effects were abolished by simultaneous injections of eledoisin. No significant changes of monoamine oxidase B activities were found under the same experimental conditions. Neither angiotensin II nor elodoisin changed substrate/inhibitor affinities of both isoenzymes. These data indicate that angiotensin II and tachykinin transmitter systems may exert opposite, long-term regulatory effects on monoaminergic neurons in rat brain.

Suppression of drinking but not feeding by central eledoisin and physalaemin in the rat

The tachykinins, eledoisin and physalaemin, given by intracerebroventricular (i.c.v.) injection have been shown to be potent antidipsogenic agents in rats. To evaluate their selectivity of action on rat ingestive behaviors, we compared their effects following i.c.v. injection on the intake of water, of milk containing 3.5 or 15% fat, and of solid food. The two tachykinins inhibited water intake induced by i.c.v. angiotensin II or by cellular dehydration, but did not reduce the intake of 15% fat milk or of solid food. The intake of 3.5% fat milk was inhibited only by the highest dose (1000 ng/rat) of eledoisin which also increased grooming and locomotion. The present findings suggest that in adult rats central eledoisin and physalaemin exert a selective suppressive effect on drinking behavior without affecting feeding.

Drinking and feeding inhibition by ICV pulse injection or infusion of bombesin, ranatensin and litorin to rats

The effects on ingestive behavior of the naturally occurring bombesin-like peptides ranatensin and litorin were studied in comparison to those of bombesin by intracerebroventricular pulse injection or by continuous infusion in the rat. Ranatensin and litorin, like bombesin, proved to inhibit drinking and feeding behavior. Marked differences, however, were observed in their effects. In particular our results indicate that these peptides possess different selectivity of action on drinking elicited by different dipsogenic stimuli and different potency and effectiveness in inhibiting food intake induced by food deprivation. Moreover, the effects of the three peptides were markedly affected also by the modality of administration (pulse injection or continuous infusion). On the basis of these results it seems possible to hypothesize that the endogenous bombesin-like peptides may differently affect rat ingestive behavior according to their structure and to the rate and modality of their release in the brain.

Drinking stimulation by a new angiotensin, crinia-angiotensin II, in rats and pigeons

The effects of crinia-angiotensin II on water intake and arterial blood pressure were investigated in conscious rats and pigeons. Injected by intravenous route to rats and pigeons, crinia-angiotensin II produced a hypertensive response practically identical to that induced by intravenous angiotensin II. Injected by intracerebroventricular route crinia-angiotensin II proved to be as active as angiotensin II in eliciting water intake in pigeons, while being less effective in rats. These findings, while demonstrating that naturally occurring angiotensins may be as active as angiotensin II itself in eliciting drinking, suggest that different molecular requirements must be satisfied to activate the angiotensin receptors for drinking in rats and pigeons.

Dual effect of naloxone on drinking behaviour of rats

Naloxone, administered to rats subcutaneously or by i.c.v. route, produces a dose-dependent inhibition of water intake elicited by angiotensin II or water deprivation. However, doses of the drug which do not affect drinking inhibit the antidipsic effect of subcutaneous morphine. The larger is the dose of morphine, the larger is the antimorphinic effect evoked by naloxone. These data would suggest that, at least in respect to the effects of narcotics on water intake, naloxone is a partial agonist of the nalorphine type, but the slopes of naloxone and of morphine dose-response regression lines are not in keeping with this hypothesis. Thus, the mechanism of the anti-morphic effect elicited by naloxone on drinking behaviour remains to be clarified.

Dipsogenic effect of angiotensin II, bombesin and tachykinins in the duck

The effect on drinking behaviour of intracerebroventricular injections of angiotensin II, bombesin, eledoisin and substance P was studied in the duck. While substance P was almost completely ineffective, angiotensin II, bombesin and eledoisin elicited a clear dipsogenic response which was dose-dependent and apparently specific. Angiotensin II was about 10 times more potent than bombesin and far more potent than eledoisin. These results confirm once more the wide phylogenetic distribution of the dipsogenic response to angiotensin II. Furthermore, they show that bombesin and eledoisin, which potently inhibit water intake in the rat, exert in the duck a dipsogenic effect strictly parallel to that elicited in the pigeon. On the basis of the animal species so far tested it is possible to hypothesize that bombesin and tachykinins stimulate water intake in birds, while inhibiting drinking in mammals.

Effect of subcutaneous injections of carbuterol on renin release and water intake in the rat

The effect on renin release and water intake of subcutaneous injections of the beta-adrenergic agonist carbuterol has been studied in the rat. Carbuterol, as well as isoprenaline, elicited a clear dipsogenic effect, dose-dependent, apparently mediated by stimulation of the renin-angiotensin system. The dipsogenic potency of carbuterol, in comparison to that of isoprenaline, was weaker; the ratio of dipsogenic potency between the two substances proved to be very similar to that of their relative vasodepressor activities. These findings appear to be consistent with the hypothesis that beta 2-adrenergic receptors of vascular type are involved in renin release and water intake stimulation.

Modifications of drinking behaviour and of arterial blood pressure induced by tachykinins in rats and pigeons

Intracerebroventricular injections of the naturally occurring tachykinins eledoisin, physalaemin and substance P elicit a powerful antidipsogenic effect in the rat, while in the pigeon they potently stimulate water intake. The aim of this paper was to study in conscious rats and pigeons the vascular effect of these peptides and to compare this effect to the one elicited on water intake. The results of these experiments demonstrate that there is no direct relationship between the two effects. Our findings suggest that the effect of these peptides on water intake might be specific on CNS and not related to their vascular activity.

[Lacrimatory effect of eledoisin in dogs]

Eledoisin, administered to dogs by conjunctival route, potently stimulated lacrimal secretion. The effect did not depend on activation of adrenergic, histaminergic or 5-hydroxytryptaminergic receptor and was only in part due to stimulation of cholinergic receptors.

[Effect of eledoisin on the process of corneal repair in rabbits]

Eledoisin cured corneal lesions produced in the rabbit by cocaine but failed to heal those produced by sodium hydroxide. The effect was probably due to accelerated epithelial proliferation.

Antidipsogenic effect of intracranial injections of substance P in rats

1. The effect on water intake of intracranial injections of Substance P was studied in the rat. 2. Substance P strongly inhibited drinking elicited by Angiotensin II, Carbachol water deprivation or sodium chloride load, in that order. 3. The peptide was particularly effective when water intake was induced by injections of Angiotensin II into the preoptic area. In these experiments, drinking was inhibited by doses of Substance P as low as 1 ng. 4. The results suggest that in the rat Substance P may play a role in the brain in the regulation of water intake, acting as a thirst inhibitor.