EFFECT OF PROLACTIN ON ALPHA-AMINOISOBUTYRIC-ACID UPTAKE IN MOUSE MAMMARY-GLAND EXPLANTS

Studies were carried out to characterize the effect of prolactin (PRL) on amino acid uptake into mammary gland explants derived from 12- to 14-day pregnant mice. PRL approximately doubles the rate of uptake of alpha-aminoisobutyrate (AIB), arginine, and hydroxyproline but has no effect on the intracellular accumulation of unincorporated leucine. PRL increases the apparent maximum velocity of AIB uptake from 0.16 to 0.43 nmol.l intracellular water-1.min-1. No effect of PRL, however, on the apparent Michaelis constant (0.75 mM) of AIB uptake was observed. The onset of the PRL stimulation of AIB uptake occurs 4-5 h after PRL addition to the cultured mammary tissues. The lowest stimulatory concentration of PRL on AIB uptake is 5-10 ng/ml, and a maximum response is achieved with 75 ng/ml. The action of PRL on AIB uptake requires both ongoing RNA and protein synthesis, since puromycin (50-mu-g/ml), cycloheximide (5-mu-g/ml), and actinomycin D (1-mu-g/ml) abolished the PRL response.