THE LACTOGENIC EFFECTS OF PROLACTIN AND GROWTH HORMONE ON MAMMARY GLAND EXPLANTS FROM VIRGIN AND PREGNANT SPRAGUE-DAWLEY RATS

Abstract

SUMMARY Explants of mammary glands from mature virgin and pregnant Sprague—Dawley rats were maintained in organ culture for up to 96 h. The effects of insulin, corticosterone, ovine prolactin and bovine growth hormone on the synthesis of DNA, RNA and casein in the explants were studied. DNA synthesis in explants from virgin rats was maintained by insulin but was not increased by the addition of the other hormones tested. DNA synthesis in explants from pregnant rats was increased by insulin, and the addition of corticosterone and either prolactin or growth hormone to the culture medium increased this synthesis. The rate of RNA synthesis in explants from virgin rats was similar in medium 199 with or without additional hormones. RNA synthesis in explants from pregnant rats was increased by the addition of insulin or insulin plus corticosterone to the medium. In explants from both virgin and pregnant rats the maximal rate of hormone-stimulated DNA or RNA synthesis occurred during the first 24 h of culture. Casein synthesis, as measured by the uptake of 32P-labelled orthophosphate by explants from virgin and pregnant rats, was increased by insulin plus corticosterone plus either prolactin or growth hormone. The rate of casein synthesis was maximal between 48 and 72 h and was reduced by actinomycin D. In the pregnant rats no significant differences were demonstrated between the effects of the hormones on DNA, RNA or casein synthesis in explants from the 5th, 10th, 16th or 19th day of pregnancy.