Rat GHRF caused calcium- and dose-dependent stimulation of SRIF release in static 1-h incubations. SRIF release was stimulated by GHRF in a concentration range of 1-100 nM. However, the extended dose-response curve was biphasic in nature, with a significantly lower SRIF response in the presence of 1 μm GHRF vs. 100 nM GHRF. SRIF release, stimulated by another secretagogue (10 μm veratridine), was not affected by the presence or absence of 1 μm GHRF, suggesting the lack of toxic impairment of hypothalamic cell function by GHRF at this concentration.