The Role of Catecholamines in the Release of Anterior Pituitary Prolactin<i>in Vitro</i>

Abstract

Rat hypothalamic extracts, dopamine (DA), norepinephrine (NE), and epinephrine (EP), were incubated with rat pituitary tissue in medium 199. In all cases rat hypothalamic extracts significantly inhibited pituitary prolactin (PRL) release in vitro. When the hypothalamic extracts were subjected to preincubation with a rat brain monoamine oxidase enzyme preparation (MAO) or ot aluminum oxide (alumina) catecholamine adsorption, the hypothalamic extracts lost their ability to inhibit PRL release in vitro Pepsin pretreatment did not impair the inhibition of PRL release by hypothalamic extracts and iproniazid 10 μg/ml of medium blocked the effect of MAO on the hypothalamic extracts. The DA and NE content of MAO treated and untreated hypothalamic extracts was measured by a fluorometric technique. The catecholamine containing acid eluate from the alumina adsorption procedure was able to inhibit PRL release to the same degree as untreated hypothalamic extracts. Dopamine (5.26 × 10−9 to 5.26 × 10−7M) and NE (2.42 × 10−8 to 4.85 × 10−7M) significantly inhibited prolactin release while smaller amounts were ineffective. Higher concentrations of EP (6.0 × 10−8 to 3.0 × 10−7M) significantly inhibited PRL release. These results show that DA and NE at amounts less than those found in the hypothalamus can directly act on the rat anterior pituitary to inhibit PRL release. The results further indicate that the PRL inhibitory activity of hypothalamic extracts can be totally accounted for by the amount of endogenous catecholamines in the hypothalamus. (Endocrinology95: 1202, 1974)