The effects of neuropeptides on the release of immunoreactive somatostatin (SRIF) from the rat hypothalamus were examined in vitro using a perifusion system. Twelve hypothalamic halves of male rats were placed on a Sephadex G-25 column and continuously eluted with Krebs-Ringer bicarbonate buffer, poH 7.4, at 37 C. A high potassium concentration (56 mM) stimulated SRIF release in a calcium-dependent manner. The infusion of glucagon (10(-7), 5 x 10(-7), and 10(-6) M) resulted in a dose-related increase in the release of SRIF. Neurotensin (10(-6) M) also stimulated SRIF release, whereas vasoactive intestinal polypeptide (10(-7) and 10(-6) M) inhibited SRIF release. SRIF release was not affected by cholecystokinin-octapeptide (10(-6) M), cholecystokinin-tetrapeptide (10(-6) M), or tRH (10(-6) M). These findings suggest that SRIF release from the rat hypothalamus is influenced by glucagon, neurotensin, and vasoactive intestinal polypeptide.