Release of somatostatin and thyrotropin-releasing hormone from rat hypothalamic fragments in vitro.

Abstract

The release of somatostatin (SRIF) and TRH from hypothalami of adult male rats was studied in vitro. Quartered hypothalamic fragment were incubated in a physiological buffer for three successive 20-min periods, which served as preincubation, control, and test periods, respectively. SRIF and TRH were measured by RIA. Serial dilutions of medium immunoreactivity were parallel to those of synthetic SRIF and TRH standards, and the elution volumes of SRIF and TRH immunoreactivity on Sephadex G-25 were identical to those of the respective synthetic peptides. Recovery of synthetic SRIF and TRH from the incubation medium was virtually complete. SRIF and TRH release were increased by membrane depolarization induced by 60 mm K+ or veratridine (10-5 m), and the effect was Ca++ dependent. Dibutyryl cAMP increased the release of TRH but not that of SRIF. Dopaminergic agents (dopamine, l-dopa, and bromocriptine) increased the release of both SRIF and TRH, and the effects of dopamine were blocked by haloperidol, a dopami...