INFUSION OF DOPAMINE AT LOW CONCENTRATIONS STIMULATES THE RELEASE OF PROLACTIN FROM ALPHA-METHYL-P-TYROSINE-TREATED RATS

Prolactin (PRL) secretion from the anterior pituitary gland is inhibit ed by dopamine (DA) released into the hypophysial portal vasculature f rom neurons in the hypothalamus. We have shown previously that DA also stimulates PRL secretion in vitro. Here we report that DA has a dual effect on PRL release in vivo. Injection of rats with alpha-methyl-p-t yrosine (200 mg/kg, ip) induced an immediate 35-fold enhancement of PR L secretion which reached a plateau by 90 min after injection on diest rus 1. When DA was infused intravenously at varying doses beginning at 90 min after alpha-methyl-p-tyrosine, differing effects on PRL secret ion were observed. These effects were dose dependent: higher doses of DA (1000 ng/kg/min) inhibited and lower doses (10 ng/kg/min) stimulate d PRL secretion. These data suggest that DA may be an important stimul ator of PRL secretion in vivo.