Prolactin synthesis in bovine pituitary: no evidence for regulation by estrogen in vivo

Protein synthesis in bovine pituitaries was measured by incubation of tissue slices with radioactive amino acids, followed by gel electrophoresis. PRL and GH syntheses were estimated by determining the amount of radioactivity comigrating with standards of these hormones. Pituitary tissue removed from adult animals demonstrated a high percentage of PRL synthesis regardless of the sex of the donor animal. PRL constituted 13--17% of the newly synthesized protein in pituitary slices from both male and female animals. In addition, the reproductive state of the female did not influence the percentage of PRL synthesis. Reduction of in vivo estrogen levels by adrenalectomy and ovariectomy did not result in any change in the percentage of PRL synthesis. The percentage of PRL synthesis observed in pituitaries from fetuses or bull calves was much lower than that observed in the adult animals (5--6% of the newly synthesized protein). Estrogen administration to bull calves did not result in any changes in the percentage of PRL synthesis. These studies suggest that estrogen may not play a physiological role in the regulation of PRL synthesis in the bovine. The percentage of GH synthesis was 5--6% in steers and cows, and above 10% in bulls, bull calves, and fetuses.