A Biochemical Comparison of the Lactogenic Effect of Prolactin and Growth Hormone on Mouse Mammary Gland in Organ Culture

Abstract

A biochemical comparison of the lactogenic effect of ovine prolactin and of bovine growth hormone on pregnant mouse mammary gland in organ culture was made. No qualitative differences were observed; both hormones (in the presence of insulin and corticosterone) stimulated the synthesis of casein and RNA in mouse mammary gland explants. The inhibition of RNA synthesis with actinomycin D was associated with a decrease in casein synthesis. However, quantitatively, prolactin was more efficient than growth hormone in stimulating casein synthesis.The synthesis of casein in mouse mammary gland explants incubated in the presence of various combinations of hormones gave results which suggested that prolactin and growth hormone are operating on the same sites of action.Analysis of, and purification by, polyacrylamide gel electrophoresis of the bovine growth hormone showed that the lactogenic effects were not due to the presence of prolactin as an impurity, but were an intrinsic property of the growth hormone.

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

“…The effects of insulin, corticosterone, prolactin and growth hormone on the synthesis of DNA, RNA and casein by expiants of mammary glands from SpragueDawley rats in mid-pregnancy were similar to those reported for Schneider mice at the same stage (Wang et al 19726). DNA synthesis was insulin-dependent and was not stimulated by either prolactin or growth hormone.…”

“…The 0-4 h rate of DNA synthesis was similar in expiants from virgin or pregnant rats but the stimulation by insulin or IB at 20-24 h in culture could be demonstrated only in expiants from pregnant rats. RNA synthesis in mammary gland expiants from Schneider mice in mid-pregnancy was increased between 44 and 48 h of culture in IBP or IBG when compared with expiants cultured in IB (Wang et al 19726). However, this stimulation was not seen in expiants from Sprague-Dawley rats.…”

“…The prolactin and growth hormone were kindly supplied by the National Institutes of Health, Bethesda, U.S.A. The growth hormone batches contained less than 1 % bovine prolactin (Wang et al 19726). Carrier rat casein was prepared from pooled Sprague-Dawley rat milk by centrifugation (Hallowes & Lewis, 1971 Animals.…”

“…Determination of the rate of synthesis of DNA, RNA and casein. The methods were identical to those used in our previous study (Wang et al 19726). The rates were determined over a 4-h period using [methyl-3H]thymidine, [5-3H]uridine, and [32P]orthophosphate at concentrations of 2, 1 and 10/tCi/ml respectively.…”

“…The growth of mammary tumours induced in rats by 9,10-dimethyl-l,2-benzanthracene is main¬ tained in vivo by prolactin but not by growth hormone (Nagasawa & Yanai, 1970) and is inhibited by the anti-prolactin compounds ergocornine and ergocryptine (Cassell, Meites & Welsch, 1971). The effects of prolactin and growth hormone on the synthesis in vitro of DNA, RNA, casein and milk-specific fatty acids have been studied in the normal mouse mammary gland (Wang, Hallowes, Bealing, Strong & Dils, 1972a;Wang, Hallowes, Smith, Amor & Lewis, 19726). A similar study was made to determine the hormone-specific responses of expiants of normal mammary glands from Sprague-Dawley rats.…”