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SUMMARY
Biochemical and immunological studies were performed on milk secreted spontaneously by 1-yr-old virgin female Sprague—Dawley rats. They had received 30 mg 9,10-dimethyl-1,2-benzanthracene when 50 days old and most had mammary gland tumours. No milk secretion was found specifically in any of these tumours. The fat content of the secretion was twice that of post-partum milk and slight differences were demonstrated in the saturated fatty acid composition. The protein concentration was doubled but both casein and milk plasma proteins were identical to those of post-partum milk. The lactose concentration was one quarter that of post-partum milk but similar milk specific carbohydrates were present. Lactate dehydrogenase isoenzymes were quantitatively similar in each. It was shown that the secretion by virgin rats closely resembled post-partum milk.
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SUMMARY
Explants from 32 mammary tumours induced in Sprague—Dawley rats by 9,10-dimethyl-1,2-benzanthracene (DMBA) were maintained in organ culture for up to 48 h. Insulin, corticosterone, prolactin, growth hormone and oestradiol were added to the culture medium in various combinations and their effects on the DNA synthesis of the explants was studied.
DNA synthesis was stimulated by insulin in explants from 30 out of the 32 tumours examined and this group of 30 responsive tumours could be further subdivided. Explants from 16 tumours showed a greater rate of DNA synthesis in medium containing insulin plus corticosterone plus prolactin than in medium containing insulin alone and this higher rate was decreased by oestradiol; this group is referred to as 'prolactin-responsive'. Explants from the remaining 14 tumours did not show a greater rate of DNA synthesis in medium that contained insulin plus corticosterone plus prolactin than in medium containing insulin alone and neither rate was decreased by oestradiol; this group is referred to as 'insulin-responsive'. Explants from two tumours were not stimulated by insulin and these tumours are referred to as 'non-responsive'. After oophorectomy or administration of ergocryptine to tumour-bearing rats, the prolactin-responsive tumours regressed whereas the non-responsive tumours continued to grow. Explants taken from prolactin-responsive tumours 2 weeks after either oophorectomy or administration of ergocryptine were still prolactin-responsive but those taken from insulin-responsive tumours 2 weeks after the same treatment were now also prolactin-responsive. The non-responsive tumours remained non-responsive.
The effects of hormones on the DNA synthesis in vitro of explants from growing DMBA-induced tumours were thus different from those on explants of mammary glands from virgin or pregnant Sprague—Dawley rats. It was concluded that it was possible to predict by organ culture techniques the response in vivo of growing mammary tumours to oophorectomy and ergocryptine administration.
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SUMMARY
Explants of mammary glands and of subcutaneous body fat from sexually mature virgin and from 19-day pregnant Sprague-Dawley rats and of mammary gland from 5-day lactating Sprague-Dawley rats, were maintained in organ culture for up to 96 h. The effects of insulin (I), corticosterone (B), prolactin (P) and growth hormone (G) on the rate of fatty acid synthesis were measured by the incorporation of [14C]acetate. The effect of these hormones on the synthesis of various carbon-chain length fatty acids was measured by radio gas-liquid chromatography.
Explants from both tissues had a reduced rate of fatty acid synthesis after 24 h in medium 199, but this rate was increased by the addition of insulin. In explants of subcutaneous fat from virgin rats, the rate was further increased by culture in IBP or IBG, but this increase was not blocked by actinomycin D. In explants from subcutaneous fat of 10-day pregnant rats the rate was not increased by the addition of B, P or G to the insulin-containing medium. In mammary gland explants from virgin rats, IBP stimulated a greater rate of fatty acid synthesis than did insulin alone. In mammary gland explants from 10-day pregnant rats, the rate of fatty acid synthesis was increased by both IBP and IBG. In mammary gland explants from rats on the 5th day of lactation, both IBP and IBG increased the rate of fatty acid synthesis compared with insulin or IB. Actinomycin D blocked the increased fatty acid synthesis produced by prolactin or growth hormone but not that produced by insulin alone.
Mammary gland explants from rats on the 5th day of lactation were cultured for the first 4 h after excision in medium 199 that contained sodium [14C]acetate. Sixty-eight per cent of the 14C was incorporated into C8-C12 fatty acids. In explants from subcutaneous fat none of the hormones tested increased 14C incorporation in these fatty acids. In mammary gland explants from virgin or 10-day pregnant rats, insulin, corticosterone and prolactin increased the incorporation in these fatty acids. Growth hormone was less efficient than prolactin in stimulating C8-C12 fatty acid synthesis.
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SUMMARY
The effect of various hormones on the incorporation of [14C]acetate into the fatty acids of pregnant mouse mammary gland explants in organ culture was studied.
Of the hormones insulin (I), ovine prolactin (P), bovine growth hormone (GH) and cortisol (F) tested singly, only insulin stimulated fatty acid synthesis. There was synergism between cortisol or prolactin with insulin. The greatest stimulation in fatty acid synthesis occurred when explants were incubated in a medium containing either I + F + P or I + F + GH.
Analysis by radio-gas-liquid chromatography of the fatty acids synthesized by explants after 14C labelling, showed that the pattern of fatty acids formed in the presence of I + F was distinctly different from that produced in the presence of I + F + P or I + F + GH. In the presence of I + F, the pattern of fatty acids resembled that found in mouse adipose tissue, whilst with I + F + P or I + F + GH the pattern resembled that of mouse milk fat.
Synthesis of RNA was essential for the stimulation of fatty acid synthesis in explants incubated in medium containing I + F + P or I + F + GH. Results obtained when DNA synthesis was blocked with mitomycin C suggest that mitosis is important for the induction of milk-fatty acid synthesis.
Puromycin had no effect for up to 8 h on explants which had been previously cultured in medium containing I + F, I + F + P or I + F + GH. This suggests a slow turnover rate of the enzymes involved in the synthesis of milk fatty acids.
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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.
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SUMMARY
Increases in uterine capillary permeability after the injection of oestradiol into spayed mice, appeared to be caused by the development of vascular fenestrations and not by the separation of adjoined endothelial cells. Progesterone did not prevent the uterine weight, oedema and vascular responses to the first of two injections of oestradiol but inhibited those to the second. It was concluded that the failure of repeated oestrogen-treatment to produce uterine oedema in progesterone-treated mice resulted from the refractory state which develops after the first injection and which extends to the endometrial vasculature.
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SUMMARY
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.
