CHANGES IN MEDIOBASAL HYPOTHALAMIC DOPAMINE AND GABA RELEASE - A POSSIBLE MECHANISM UNDERLYING TAURINE-INDUCED PROLACTIN SECRETION

Taurine (Tau), a putative inhibitory amino acid neurotransmitter, has been shown to stimulate prolactin (PRL) release. Using ovariectomized, estrogen-replaced adult rats we investigated initially the effect of this amino acid, injected by different routes, on PRL secretion in viv o. Tau (100-500 mg/kg) had no effect on PRL release when given i.p.; 1 5 min after i.c.v. injection of Tau (3 mu moles), a significant increa se in serum PRL levels was observed (78 +/- 9 ng/ml over basal levels, p < 0.01 vs. controls). In vitro (cultured anterior pituitary cells) PRL release was not affected by a 5 h incubation with Tau (10(-3)-10(- 8) M). Basal dopamine (DA) or gamma-aminobutyric acid (GABA) output fr om superfused mediobasal hypothalamic fragments (MBH) was not affected by Tau (10(-3) M or 10(-5) M). However, during stimulation with KCl ( 50 mM), Tau (10(-3) M) significantly lowered DA release, and increased GABA output. It is concluded that Tau acts at a central level to incr ease PRL secretion, most probably by modulating the hypothalamic relea se of neurotransmitters controlling lactotroph function.