The release of oxytocin and vasopressin in the neurointermediate lobe of the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto rat (WKY)

The release of arginine-vasopressin (AVP) and oxytocin (OT) from the rat neurointermediate lobe (NIL) of the pituitary was studied in vitro in the male spontaneously hypertensive rat (SHR) and the Wistar-Kyoto rat (WKY). The basal and stimulated (50 mM KCl; a submaximal dose) release of AVP were significantly higher in the SHR than in the WKY. No corresponding strain difference was seen in OT release. In the WKY, depolarisation released more OT than AVP. The GABA-A agonist muscimol attenuated the KCl induced release of both peptides. The findings indicate that a lower dose of muscimol is required to inhibit the AVP than the OT release. It is concluded that the strain difference in AVP release does not apply to OT terminals, which indicates a difference in mechanisms regulating the AVP and OT release at the NIL level.