Release of vasopressin within the rat suprachiasmatic nucleus: no effect of a V1/V2 antagonist.

The release of arginine vasopressin (AVP) within the suprachiasmatic nucleus (SCN) of anaesthetized male rats was monitored by microdialysis. Dialysis of the nucleus with 56 mM K+ solution (to 400%) as well as with 1 M NaCl-hypertonic medium (to 530%) triggered a significant increase in intra-SCN release of AVP (p < 0.01). To investigate whether endogenous AVP influences its own release, we administered in a second experiment the combined V1/V2 receptor antagonist d(CH2)5[D-Tyr(Et)2,Val4]AVP directly into the dialysed area. Compared with vehicle-treated controls, the antagonist had no effects on intranuclear release of AVP during basal or stimulated conditions. Thus, in contrast to recent observations in the supraoptic nucleus, we found no indications for autoregulatory mechanisms of AVP release within the SCN.