The effect of galanin on growth hormone-releasing factor and somatostatin release from median eminence fragments in vitro.

Galanin has been reported to stimulate secretion of GH in humans and rats. Thus, to investigate whether the effect of galanin on GH release is the result of either a stimulation of GH-releasing factor (GRF) and/or an inhibition of somatostatin (SRIF) release, we have evaluated the action of galanin on the release of SRIF and GRF from median eminence (ME) fragments in vitro. The MEs from adult male rats were incubated in Krebs-Ringer bicarbonate-glucose buffer, pH 7.4, at 37 degrees C, in an atmosphere of 95% O2, 5% CO2 with constant shaking for 30 min. Medium was discarded and replaced by medium containing various concentrations of galanin (10(-10)-10(-7) M). Galanin stimulated SRIF and GRF release in a dose-related manner. This effect was significant at concentrations varying from 10(-8) to 10(-7) M. To determine the mechanism by which galanin stimulated SRIF and GRF release, MEs were incubated with pimozide (dopaminergic blocker), phentolamine (alpha-adrenergic blocker) or naloxone (opioid blocker), at concentrations of 10(-6) M, and the effect of galanin was then evaluated. Phentolamine and naloxone did not alter the stimulatory effect of galanin, but when galanin was tested with pimozide, the galanin-induced release of SRIF and GRF was blocked. To determine whether the effect of galanin is mediated through D-1 and/or D-2 dopamine receptors, selective antagonists of D-1 (SCH 23390) and D-2 receptors (domperidone) were used (10(-7) M) in the presence of galanin (10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)