Water intake in rats subjected to hypothalamic immunoneutralization of angiotensin II, atrial natriuretic peptide, vasopressin, or oxytocin.

To investigate the influence of various peptides on control of dehydration-induced drinking, water intake elicited by overnight water deprivation was analyzed in groups of male rats after intracerebroventricular (third ventricle, icv) injection of 2 microliters of normal rabbit serum or an equal volume of antiserum directed against angiotensin II (Ab-AII), atrial natriuretic peptide, vasopressin, or oxytocin. There was no difference in water intake after normal rabbit serum and antiserum injections when water was offered immediately after icv injections. Water intake was greatly reduced by Ab-AII when water was offered 1 hr and 3 hr after icv injection. The other antisera were partially effective only when water was offered 3 hr after icv injection. The dipsogenic effect of icv injection of AII in normally hydrated rats was reduced only by icv injection of Ab-AII 3 hr before and not by the other antisera. Ab-AII injected icv had no effect on the drinking that occurred just before and after the onset of darkness and that was associated with eating (prandial drinking). The results indicate that AII is primarily responsible for dehydration-induced drinking, and the other peptides may play a permissive role since their antisera were partially effective, with longer latencies after antiserum injection, which is perhaps the result of gradual diffusion to effective sites within the hypothalamus. In contrast, endogenous AII appears to play little, if any, role in prandial drinking.

The involvement of oxytocin in ovulation and in the outputs of cyclo-oxygenase and 5-lipoxygenase products from isolated rat ovaries.

The effects on ovulation of a specific anti-oxytocin rabbit serum (anti-OT) (50.0 microliters) given by intrabursal injection into the right ovaries of etherized adult female rats at proestrus, were explored by counting the number of ovulated ova present within the right oviducts. Left ovaries were not treated and served as control ovaries. Control rats were treated with male normal rabbit serum (NRS) (50.0 microliters) given by intrabursal injections into the right ovaries of animals at proestrus. Ovulation was induced by injection of human chorionic gonadotrophin (hCG). Anti-OT administered into the right ovarian bursae of proestrous rat ovaries evoked a significant 51% inhibition of ovulation in comparison with that observed in control non-injected left ovaries (p less than 0.01). Also, when the ovulation of right ovaries injected with anti-OT was compared with that of left ovaries injected with NRS, the number of ovulated ova in the right side was significantly smaller (30%) than on the contralateral side (p less than 0.02). However, in rats pre-treated with hCG the intrabursal injection of oxytocin (OT) (50.0 mU/ml) into right and left ovaries failed to alter the number of ovulated ova compared with that of rats receiving intrabursal injections of saline. The basal control and the OT-evoked synthesis and release of endogenous prostaglandin E2 (PGE2) and PGF2 alpha were explored in ovaries isolated from prepuberal rats injected with pregnant mare's serum gonadotrophin (PMSG), two days prior to sacrifice. OT augmented the basal release of PGF2 alpha but did not influence that of PGE2. Moreover, the conversion of exogenous 14C-arachidonic acid (14C-AA) into different prostanoids and into 5-HETE, in the presence and in the absence of added OT (50.0 mU/ml), was studied in rat ovaries isolated in proestrus. The challenge with OT augmented the basal synthesis and release of PGF2 alpha and of 5-HETE from 14C-AA, but failed to influence the formation of products generated via the cyclo-oxygenase pathway, namely 6-keto-PGF1 alpha, PGE2 and thromboxane B2 (TXB2). Therefore, the present results suggest that ovarian OT may play a role in the ovulatory process, via generation of PGF2 alpha to enhance contractions of ovarian smooth muscle and of 5-HETE to promote follicular collagenolysis.