Vasopressin(4-9) fragment activates V1a-type vasopressin receptor in rat supraoptic neurones

THE effect of vasopressin fragment 4-9 (AVP((4-9))) was investigated on freshly dissociated rat supraoptic neurones by measuring changes in intracellular calcium concentration ([Ca2+](i)) using fura-2 microspectrofluorimetry. In 60% of neurones responding to vasopressin, AVP((4-9)) induced a transient rise in [Ca2+](i) that was dose-dependent in the concentration range 10 nM to 1 mu M AVP((4-9)) and strongly decreased in Ca2+-free buffer (84% inhibition). This [Ca2+](i) response was completely and reversibly abolished by SR 49059 (10 nM), a specific V-1a receptor antagonist, but not by SR 121463A, a specific V-2 receptor antagonist. Our results demonstrate the presence of functional receptors activated by AVP(4-9) On vasopressin-sensitive neurones that possess the apparent pharmacological profile of the V-1a-type vasopressin receptor. NeuroReport 10:1735-1739 (C) 1999 Lippincott Williams & Wilkins.