Changes in mediobasal hypothalamic dopamine and GABA release: A possible mechanism underlying taurine-induced prolactin secretion

Summary 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 vivo. Tau (100–500 mg/kg) had no effect on PRL release when given i.p.; 15 min after i.c.v. injection of Tau (3moles), a significant increase 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 from superfused mediobasal hypothalamic fragments (MBH) was not affected by Tau (10^–3 M or 10^–5 M). However, during stimulation with KCl (50mM), Tau (10^–3 M) significantly lowered DA release, and increased GABA output. It is concluded that Tau acts at a central level to increase PRL secretion, most probably by modulating the hypothalamic release of neurotransmitters controlling lactotroph function.