Effects of GABA receptor agonists on [3H]dopamine release from median eminence and pituitary neurointermediate lobe.

The effects of GABAA and GABAB receptor agonists were examined on stimulus-induced release of [3H]dopamine ([3H]DA) from a synaptosomal preparation of median eminence (ME) and pituitary neurointermediate lobe (NI). Muscimol was found to inhibit [3H]DA release from ME in a bicuculline-sensitive, strychnine-insensitive manner, but had no effect in NI. Homocarnosine also inhibited [3H]DA release from ME. Baclofen had no effect in either area. These results demonstrate an interaction between two putative prolactin release inhibitory factors, DA and GABA, at the site of secretion into hypophysial portal blood.