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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.

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.