Effects of hormones on protein and amino acid metabolism in mammary-gland explants of mice

Abstract

The effects of insulin [I] cortisol [F] and prolactin [PRL] on amino acid uptake and protein biosynthesis were determined in mammary-gland explants from mid-pregnant mice. I stimulated [3H]leucine incorporation into protein within 15 min of adding insulin to the incubation medium. I also had a rapid stimulatory effect on the rate of aminoiso[14C]butyric acid uptake, but it had no effect on the intracellular accumulation of [3H]leucine. F inhibited the rate of [3H]leucine incorporation into protein during the initial 4 h of incubation, but it had no effect at subsequent times. [3H]Leucine uptake was unaffected by F, but amino[14C]isobutyric acid uptake was inhibited after a 4 h exposure period to this hormone. PRL stimulated the rate of [3H]leucine incorporation into protein when tissues were exposed to this hormone for 4 h or more; up to 4 h, no effect of PRL was detected. At all times tested, PRL had no effect on the uptake of either amino[14C]isobutyric acid or [3H]leucine. Incubation with actimomycin D abolished the prolactin stimulation of protein biosynthesis, but this antibiotic did not affect the I response. A distinct difference in the mechanism of action of these hormones on protein biosynthesis in the mammary gland is thus apparent.