The Lactogenic Effects of Prolactin and Growth Hormone on Mammary Gland Explants From Virgin and Pregnant Sprague-Dawley Rats

Abstract

Explants of mammary glands from mature virgin and pregnant Sprague\p=m-\ 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 of32P-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.

Effect of Various Concentrations of Prolactin and Growth Hormone on the Magnitude of Stimulation of RNA Synthesis, Casein Synthesis and Ornithine Decarboxylase Activity in Mouse Mammary Gland Explants

“…They observed no response at 10~9 M prolactin (about 20 ng/ml), but a maximal response at the next highest concentration tested, 10-8 M (about 200 ng/ml). These results are in contrast to those of Turkington [ 17] using cultured mouse tissues and Hallowes et al [ 18] using cultured rat tissues; these authors observed maximal rates of [32P] incorporation into casein with prolactin concentrations as high as 0.5-5 pg/ml. Since the experiments of Stockdale et al [16], Turkingion [17] and Hallowes et al [18] were all carried out with (a) prolactin present in the culture medium for 48 h and (b) prolactin present from the time of preparation of the explants, it seems possible that hormone degradation during culture may explain why these authors had to use such high concentrations of prolactin to obtain maximal effects on casein synthesis.…”

Mitogenic activity of pituitary hormones on cell cultures of normal and carcinogen-induced tumor epithelium from rat mammary glands

“…Rabbit antimouse casein (5) and rat and mouse caseins were gifts from Dr. M. Feldman (Children's Hospital Medical Center, Oakland, Calif.) and Dr. S. Young (I. C. R. F., London, England), respectively. The antiserum was absorbed with mouse serum and stored with 0.01% methiolate in phosphate-buffered saline, while the caseins were prepared from milk by precipitation with renin (11,39). Cell culture media, medium 199, Dulbecco's modified Eagle's medium (DEM), and Waymouth's medium (24) were supplied by the I. C. R. F., fetal calf serum was purchased from Gibco-Biocult (Glasgow, Scotland).…”

“…PRIMARY CULTURES: After a total of 67 h of incubation, 1 ~tCi/ml of [aH]thymidine at 1 ~tM was added to the cultures. 2 h later, the cultures were washed and the uptake of [SH]thymidine incorporated into DNA (aH-cpm/#g of DNA) was determined as before (11,17). Results given are the mean of three separate dishes -+ the standard error.…”

Effect of human, bovine and ovine prolactin on DNA synthesis by organ cultures of benign human breast tumours

“…In mice, Mayne & Barry (1970) and Oka & Topper (1972) found no stimulatory effect of prolactin on DNA synthesis by organ cultures of mammary gland, whereas Mukherjee et al (1973) have provided evidence to the contrary. In rats, Dilley (1971) and Hallowes et al (1973) have reported that prolactin is mitogenic in vitro to the mammary epithelium, whereas Koyama et al (1972) did not see any stimulatory effect of prolactin on mammary-gland growth in vitro.…”