Benzodiazepine- and barbiturate-interactions with GABAA receptor responses on lactotrophs.

Modulation of the biphasic effect of muscimol on prolactin secretion by benzodiazepines and secobarbital was investigated, using an in vitro superfusion system. The stimulatory effect of low concentrations of muscimol was potentiated by both classes of drugs, and the effect of benzodiazepines appeared to be mediated by central-type benzodiazepine receptors. Neither benzodiazepines nor secobarbital affected the inhibitory response to muscimol. Clonazepam reduced the potency of bicuculline methiodide as an antagonist of the stimulatory effect, but did not alter the potency of picrotoxinin. These results demonstrate a selective potentiation of one component of the GABAA receptor effect on lactotrophs by benzodiazepines and barbiturates and provide evidence for a functional effect of these drugs at a site without the CNS.