Octreotide-induced drinking, vasopressin, and pressure responses: role of central angiotensin and ACh

The involvement of central angiotensinergic and cholinergic mechanisms in t he effects of the intracerebroventricularly injected somatostatin analog oc treotide (Oct) on drinking, blood pressure, and vasopressin secretion in th e rat was investigated. Intracerebroventricular Oct elicited prompt drinkin g lasting for 10 min. Water consumption depended on the dose of Oct (0.01, 0.1, and 0.4 mu g). The drinking response to Oct was inhibited by pretreatm ents with the intracerebroventricularly injected angiotensin-converting enz yme inhibitor captopril, the AT(1)/AT(2) angiotensin receptor antagonist sa ralasin, the selective AT(1) receptor antagonist losartan, or the muscarini c cholinergic receptor antagonist atropine. The dipsogenic effect of Oct wa s not altered by prior subcutaneous injection of naloxone. Oct stimulated v asopressin secretion and enhanced blood pressure. These responses were also blocked by pretreatments with captopril or atropine. Previous reports indi cate that the central angiotensinergic and cholinergic mechanisms stimulate drinking and vasopressin secretion independently. We suggest that somatost atin acting on sst2 or sst5 receptors modulates central angiotensinergic an d cholinergic mechanisms involved in the regulation of fluid balance.