Studies on the kinetics of dopamine-regulated prolactin secretion.

The regulation of prolactin (PRL) release by dopamine has been studied using short-term dissociated rat pituitary cell cultures. Concentrations of dopamine between 10(-12) and 10(-10) M stimulate PRL release, whereas concentrations between 10(-9) and 10(-7) M inhibit. By studying the kinetics of PRL release it was found that (1) the rate of PRL release increases only after a post-stimulus delay of 20 min, and (2) the response is phasic, stimulatory intervals being separated by intervals in which the rate of PRL release falls below the level of basal release. Inhibition of PRL release by dopamine occurs within 10 min after adding dopamine and is maintained tonically for a least 2 h. Cells treated with non-specific secretogogue (57 mM K+) during the inhibitory phases of dopamine-regulated release, are stimulated to secrete significant amounts of hormone.