THE RELEASE OF OXYTOCIN AND VASOPRESSIN IN THE NEUROINTERMEDIATE LOBEOF THE SPONTANEOUSLY HYPERTENSIVE RAT (SHR) AND THE WISTAR-KYOTO RAT (WKY)

The release of arginine-vasopressin (AVP) and oxytocin (OT) from the r at 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) rel ease of AVP were significantly higher in the SHR than in the WKY. No c orresponding strain difference was seen in OT release. In the WKY, dep olarisation released more OT than AVP. The GABA-A agonist muscimol att enuated the KCl induced release of both peptides. The findings indicat e that a lower dose of muscimol is required to inhibit the AVP than th e OT release. It is concluded that the strain difference in AVP releas e does not apply to OT terminals, which indicates a difference in mech anisms regulating the AVP and OT release at the NIL level.