beta-(-4 Chlorophenyl) GABA (baclofen) inhibits prolactin and thyrotropin release by acting on the rat brain

Baclofen, a GABA B agonist, inhibits prolactin release due to different kinds of stress. In the present study its effect was evaluated in several endocrine experimental situations to explore the specificity of this effect, as well as the site of action of the drug. Baclofen significantly inhibited prolactin and thyrotropin outputs induced by 25 min of suckling, without altering milk ejection or LH secretion. The effect was also tested in median eminence-lesioned rats and in in vitro incubations. Baclofen did not modify prolactin levels in rats in which brain control of the pituitary secretion was eliminated by destruction of the median eminence, and it did not inhibit prolactin or thyrotropin secretion from incubated hemipituitaries. It is postulated that baclofen inhibits prolactin and thyrotropin secretion by acting on GABA B receptors related to the brain control of pituitary secretion.