Somatostatin centrally inhibits vasopressin secretion during haemorrhage

Somatostatin is a hypothalamic inhibiting factor which has been reported to be involved in the regulation of the secretion of several anterior pituitary hormones. To determine if somatostatin plays a role in the control of vasopressin secretion from the posterior pituitary, we examined the effects of intracerebroventricular infusion of somatostatin-14 and a super-active analogue, cyclo-(N-Me-Ala-Tyr-D-Trp-Lys-Val-Phe), on the concentration of plasma vasopressin in response to haemorrhage in conscious sheep. Haemorrhage (15 ml/kg over 15 min) elevated plasma vasopressin. Treatment with either somatostatin-14 or the analogue inhibited the elevation of plasma vasopressin induced by haemorrhage. The inhibition may result from an effect of somatostatin on neurotransmitter afferent inputs to the hypothalamus which trigger vasopressin release during haemorrhage. Our study demonstrates for the first time that somatostatin administered centrally inhibits vasopressin secretion during haemorrhage in the conscious animal.