Endothelin-1 and the release of neurohypophysial hormones under dehydration or haemorrhage

Abstract

Rats, euhydrated or dehydrated for 2 days, were given intracerebroventricularly (i.c.v.) endothelin-l (ET-1), once daily in a dose of 10 ng. In euhydrated rats treatment with ET-1 was followed by a decrease in the content of vasopressin (VP) and oxytocin (OT) in the neurointermediate lobe (NL); simultaneously, the plasma concentrations of VP and OT increased. In animals deprived of water for 48 h, plasma concentrations of both VP and OT were increased whereas their content in the NL decreased; if ET-1 was administered during dehydration, however, these effects were markedly attenuated. Under urethane anaesthesia, neither the plasma concentration nor the NL content of both VP and OT were affected by i.c.v. injection of 10 ng ET-1. On haemorrhage (1 ml per 100 g body weight) the plasma levels of both VP and OT were increased. The OT content in the NL was then decreased but no changes in the VP content in the NL were seen on haemorrhage. In haemorrhaged rats prior treatment with ET-1 decreased the VP content in the NL and increased the VP concentration in the plasma when compared with rats haemorrhaged but not treated with ET-1. Simultaneously, the decrease in the neurohypophysial OT content as brought about by bleeding was inhibited and the plasma OT level was distinctly diminished when compared with animals haemorrhaged but not injected with ET-1. These results suggest that ET-1 may have a regulatory role in neurohypophysial function, the regulatory events being possibly modified by afferentation of osmoreceptor origin and also by changes of the central input from arterial pressoreceptors as well as from atrial stretch receptors.