| Abstract: | The effects of insulin, cortisol and prolactin on amino acid uptake and protein biosynthesis were determined in mammary-gland explants from mid-pregnant mice. Insulin stimulated 3H]leucine incorporation into protein within 15 min of adding insulin to the incubation medium. Insulin also had a rapid stimulatory effect on the rate of aminoiso14C]butyric acid uptake, but it had no effect on the intracellular accumulation of 3H]leucine. Cortisol inhibited the rate of 3H]leucine incorporation into protein during the initial 4h of incubation, but it had no effect at subsequent times. 3H]Leucine uptake was unaffected by cortisol, but amino14C]isobutyric acid uptake was inhibited after a 4h exposure period to this hormone. Prolactin stimulated the rate of 3H]leucine incorporation into protein when tissues were exposed to this hormone for 4h or more; up to 4h, however, no effect of prolactin was detected. At all times tested, prolactin had no effect on the uptake of either amino14C]isobutyric acid or 3H]leucine. Incubation with actinomycin D abolished the prolactin stimulation of protein biosynthesis, but this antibiotic did not affect the insulin response. A distinct difference in the mechanism of action of these hormones on protein biosynthesis in the mammary gland is thus apparent. |
