Induction of casein synthesis by prolactin and inhibition by progesterone in the pseudopregnant rabbit treated by colchicine without any simultaneous variations of casein mRNA concentration

Causes of Low Milk Supply: The Roles of Estrogens, Progesterone, and Related External Factors

Low milk supply (LMS) poses a significant challenge to exclusive and continued breastfeeding, affecting ∼10% to 15% of mothers. Milk production is intricately regulated by both endocrine and autocrine control mechanisms, with estrogens and progesterone playing pivotal roles in this process. In addition to endogenously produced hormones, external substances capable of interfering with normal hormonal actions, including phytoestrogens, mycoestrogens, synthetic estrogens, and hormonal contraceptives, can influence milk production. The effects of these extrinsic hormones on milk production may vary based on maternal body mass index. This comprehensive review examines the multifaceted causes of LMS, focusing on the involvement of estrogens, progesterone, and related external factors in milk production. Furthermore, it investigates the interplay between hormonal factors and obesity, aiming to elucidate the endocrine mechanisms underlying obesity-associated LMS. Insights from this review provide valuable perspectives for developing interventions to improve milk production and address the challenges associated with LMS.

Growth hormone promotion of tubulin polymerization stabilizes the microtubule network and protects against colchicine-induced apoptosis

We have investigated the effect of GH on microtubular physiology in Chinese hamster ovary (CHO) cells stably transfected with the complementary DNA for the rat GH receptor (CHO-GHR(1-638)). We show here that after 30 min of human GH (hGH) treatment of CHO-GHR(1-638) cells, there was a significant increase in the level of polymerization of all four tubulin isoforms (alpha-, beta-, gamma-, and tyrosinated alpha-tubulin) compared with the serum-deprived state. However, this transient increase in the levels of polymerized tubulin after hGH treatment was particularly pronounced for beta- and tyr alpha-tubulin. For alpha- and gamma-tubulin, the hGH-induced increase in polymerization state lasted to approximately 3 h and then declined by 7 h, whereas for beta- and tyr alpha-tubulin there was a decrease in the polymerization state at 1-2 h after hGH treatment compared with the level at 30 min (but still greater than the serum-deprived state) followed by a second but lesser wave of increased polymerization lasting to 7 h. The changes in the polymerization state of the tubulins were not accompanied by comparative changes in the level of total cellular tubulin. The proline rich box 1 region of the GH receptor was required for hGH to stimulate tubulin polymerization indicative that this event is JAK dependent. Increased tubulin polymerization still occurred in response to hGH in a receptor truncation lacking the carboxyl terminal half of the intracellular domain of the GH receptor indicative that hGH induced changes in intracellular calcium concentration is not required for tubulin polymerization. Prior treatment of CHO-GHR(1-638) cells with hGH retarded colchicine induced microtubule depolymerization and also prevented colchicine induced apoptotic cell death. The integrity of the microtubule network was not required for GH-induced STAT5 mediated transcription as treatment of cells with colchicine, vincristine, or vinblastine did not alter the fold stimulation of the STAT5 mediated transcriptional response to GH. Thus one consequence of cellular treatment with GH is alteration in microtubule physiology.

Progress in understanding breast cancer: epidemiological and biological interactions

Little progress has been made recently in our understanding of the epidemiology of breast cancer. While results from epidemiologic studies regarding reproductive factors remain fairly reproducible from one study to another, other associations such as that between breast cancer risk and dietary fat intake, although biologically plausible, are not consistently found in direct study of humans, while yet other associations, which appear less plausible biologically, become stronger (such as the increased risk associated with modest levels of alcohol consumption). In this paper we attempt to review the epidemiology and biology of breast cancer jointly and describe possible mechanisms of breast cancer induction, the cellular composition of the breast, the epidemiology of breast cancer, and salient biological features, and attempt to reconcile the biology and epidemiology. It becomes obvious that future progress depends on better biological thinking by epidemiologists, and vice-versa. Areas of further research are suggested and discussed, concluding that the ability to measure diet with greater precision could have an important role to play in clarifying our understanding of breast cancer.

Variation among species in the endocrine control of mammary growth and function: the roles of prolactin, growth hormone, and placental lactogen

Prolactin, growth hormone, and placental lactogen form a family of structurally related hormones, which may have evolved from a common ancestral peptide. Prolactin and growth hormone are present in all mammals, but the biological activity associated with placental lactogen has been detected in only some groups. Attempts to detect placental lactogen using bioassay and radioreceptor assay are reported and have been unsuccessful in an insectivore (the shrew), a bat, an edentate (the armadillo), a lagomorph (the rabbit), several carnivores (dog, cat, ferret), perissodactyls (horse, zebra, rhino), and, within the artiodactyls, pigs. Placental lactogenic activity has been detected in primates (chimpanzee, orangutan), rodents (voles, Pinon mouse, guinea-pig, mara), and in numerous artiodactyls (llama, giraffe, several species of deer, antelope, gnu, gazelle, musk ox, cape buffalo, Barbary sheep, several sheep of the genus Ovis, goat, and cow). These results confirm and extend the work of others and are discussed in relation to the evolution of these hormones. In synergism with steroid and thyroid hormones, protein hormones of the prolactin and growth hormone family play a crucial role in stimulating the development of the mammary gland, the differentiation and function of mammary cells to secrete milk, and in the systemic adjustments in maternal metabolism in pregnancy and lactation. Studies in vitro have shown that mammary tissues from several species synthesize milk components in response to insulin plus adrenal corticoid plus prolactin. However, there are also species differences in minimal hormonal requirements for lactogenesis. In vivo, for example, rabbits will initiate or sustain lactation in response to prolactin alone, whereas sheep and goats require prolactin plus growth hormone plus adrenal corticoid plus thyroid hormone. Measurement of hormone concentrations in the plasma of pregnant animals shows considerable differences among species in the pattern of secretion of lactogenic hormones to bring about mammary development. A surge of prolactin secretion occurs at parturition but may not be essential in the initiation of lactation. The timing of progesterone withdrawal correlates well with lactogenesis in eutherian mammals, but species differ in the mechanisms at parturition which bring this about. Marsupials show a quite different pattern of suckling-induced lactation. In maintaining lactation the greatest contrast is between ruminants, in which growth hormone is of particular importance, and other mammals, in which reduction of prolactin secretion with bromocriptine rapidly suppresses milk synthesis and secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Degradation of newly-synthesised casein in mammary explants from pregnant and lactating goats

Casein degradation was measured by a pulse-chase method in explants from freshly-prepared from goat mammary tissue. An initial increase in L-[5-3H]proline radioactivity incorporated in casein during the chase period was followed in some conditions by a decrease resulting from intracellular degradation of the major casein polypeptides. Differences in the proportion of casein degraded in explants cultured with or without prolactin suggested that the process was under hormonal control. Greater degradation of casein by explants obtained in late pregnancy and early lactation suggested that the process may affect net casein production in vivo.

Hormonal action controlling mammary activity

Mammary gland differentiation includes multiplication of cells, activation of genes specific to milk synthesis, and activation of "house-keeping" genes. These events are controlled by multiple hormones, the roles of which are not known in detail. Prolactin induction of milk synthesis is accompanied by accumulation of casein messenger ribonucleic acid resulting from acceleration of casein gene transcription as well as stabilization of messenger ribonucleic acid. Prolactin also favors translation of casein messenger ribonucleic acid. Glucocorticoids amplify and progesterone inhibits prolactin action on transcription of casein genes.

Colchicine inhibition of insulin induction of stearoyl-CoA desaturase and fatty acid synthetase in cultured avian liver explants

Chicken embryo liver explants cultured in chemically defined medium in the absence of serum provide a unique system to probe into the mechanism of insulin induction of lipogenic enzymes. Colchicine at concentrations of 0.2 and 1 microM in the culture medium caused inhibition of insulin induction of stearoyl-CoA desaturase and fatty acid synthetase by 50 and 90%, respectively. As measured by immunochemical techniques, the inhibition of the induction of these two enzyme systems resulted from the decreased content of the delta 9-terminal desaturase component of the stearoyl-CoA desaturase and the fatty acid synthetase. Colchicine, however, had no effect on the general protein synthesis, nor did it affect the malic enzyme, which is induced by triiodothyronine but not by insulin. Also, colchicine had no influence on the binding of 125I-insulin to isolated plasma membrane. Pretreatment of liver explants with insulin for 0.5-1 h and subsequent incubation in insulin-free media for 48 h resulted in induction of the desaturase and fatty acid synthetase. However, inclusion of colchicine in the media for 3 h subsequent to the treatment with insulin completely abolished the inductive effect of insulin, suggesting that colchicine affects events occurring subsequent to insulin binding to the cell surface membranes. Since lumicolchicine, an inactive isomer of colchicine, had no effect on insulin action, it is suggested that the inhibition of insulin induction of the desaturase and synthetase is related to the depolymerizing action of colchicine. Therefore, in eliciting long-term responses to insulin, microtubular integrity of the cell may be required for the transfer of a putative from cell surface insulin receptor to intracellular sites.

Comparative measurement of the lactogenic activity of ovine placental lactogen in rabbit and ewe mammary gland

Ovine placental lactogen is known to bind to prolactin receptors and to initiate milk synthesis in the rabbit mammary gland. However, this hormone exhibited a very low capacity of competing with 125I-labeled human growth hormone for the binding to membranes extracted from ewe mammary gland. Ovine placental lactogen was very efficient in provoking the accumulation of beta-casein mRNA in rabbit mammary explants but was much less active on ewe mammary explants. These data indicate that the placental hormone is not a potent lactogen in the homologous species and that its role in the control of mammary gland development and activity may have been previously overestimated.

Induction of differentiation in a rat mammary epithelial stem cell line by dimethyl sulphoxide and mammotrophic hormones

Rama 25 is a clonal epithelial cell line derived from a dimethylbenzanthracene-induced rat mammary adenocarcinoma. In the presence of the mammotrophic hormones, insulin, hydrocortisone, estrogen and prolactin, Rama 25 produces small amounts of casein and forms domes at a low rate. The rates of both these processes can be greatly increased by the addition of dimethyl sulphoxide or hexamethylenebisacetamide which are also known to induce the differentiation of Friend erythroleukemia cells. Other compounds which stimulate the differentiation of Rama 25 cells include linoleic acid and 6-thioguanine. The intracellular pathways triggering changes in the two markers of differentiation are partially separable using different combinations of hormones, prolactin and hydrocortisone being the most important for the production of casein and the formation of domes respectively. The kinetics of differentiation, as judged by the appearance of these two markers, are characterised by two phases, a fixed period of 8 h (lag phase), the length of which is independent of the dimethyl sulphoxide concentration and a second phase where their rates are dependent on the concentration of dimethyl sulphoxide. Rama 25 cells do not become committed to differentiate during this lag phase but increasing numbers of cells do so after this period. We suggest that the differentiation processes occur in two stages. The first stage, involving the inducer, commits Rama 25 cells to a new differentiated state. The second stage, involving the hormones, modulates the expression of different markers of this state. Both casein production and dome formation can be blocked by inhibitors of DNA synthesis and show reciprocal changes with the rates of cellular DNA synthesis. Thus, in its hormonal and DNA synthetic requirements for differentiation, Rama 25 cells appear to resemble some of the mammary epithelial cells of mature virgin rats.

In vivo lactogenic effects of anti prolactin receptor antibodies in pseudopregnant rabbits

Antibodies generated against partially purified prolactin receptors from rabbit mammary gland membranes were tested for their effects on prolactin binding to receptors and for their in vivo biological potencies. These antibodies are able to inhibit prolactin binding to crude rabbit mammary gland membranes. When administered intravenously or intramuscularly to pseudopregnant rabbits, they induce respectively an accumulation of beta-casein or an enhancement of beta-casein synthesis and mRNA concentration in the mammary gland. Moreover the stimulatory effect of these anti-prolactin receptor antibodies on casein synthesis is totally abolished by a simultaneous treatment with progesterone, which is a potent in vivo inhibitor of prolactin action. These results better establish the prolactin-like activities of these antibodies previously observed in vitro and give strong support to the hypothesis that prolactin molecule is not required beyond the initial binding to its receptor to induce hormonal effects.

Characterization and cloning of the mRNAs specific for the lactating mouse mammary gland

We have characterized and cloned the lactation-specific mRNAs of mouse mammary glands. The group of eight milk-protein-specific mRNAs were identified (a) by size and antigenic properties of their translation products in vitro and (b) by characterization of their respective cDNA clones. Two alpha-caseins (43 kDa and 39 kDa) are encoded by mRNAs of 1600 nucleotides and two beta-caseins (26 kDa) are encoded by mRNAs of 1450 nucleotides in length. Three smaller caseins, gamma-casein (23.7 kDa), delta-casein (21 kDa) and epsilon-casein (14.5 kDa) are synthesized by mRNAs of 880, 1150 and 860 nucleotides. Beside these casein mRNAs a mammary specific 620 nucleotide mRNA codes for a novel acidic whey protein (13.7 kDa). cDNA clones corresponding to the mRNAs for the lactation-specific proteins have been isolated from a mammary-specific cDNA library. Cloned alpha-casein cDNA hybridizes to both alpha-casein specific mRNAs and cloned beta-casein cDNAs hybridize with both beta-casein specific mRNAs. By RNA blot analysis we show that the cloned cDNAs for mouse alpha-casein, beta-casein, gamma-casein and epsilon-casein and the acidic whey protein cross-hybridize with mRNAs of the rat, demonstrating partial sequence homology between the corresponding mRNAs of those species.

[Role of membrane colchicine binding proteins in the transmission of prolactin message to casein genes in the rabbit mammary gland]

Previous work demonstrated that tubulin binding drugs specifically inhibit the capacity of prolactin to initiate casein and DNA synthesis in the mammary cell. It was concluded that microtubules or other tubulin containing cellular structures were involved in the transmission of the prolactin message to genes. In the present work, it is shown that griseofulvin, an antimitotic drug which alters microtubule structure and function, does not prevent prolactin actions. Autoradiographic studies showed that [3H]colchicine binds preferentially to plasma and Golgi membranes in the mammary cell. Short term cultures of mammary explants with [3H]colchicine demonstrated that the labelled drug binds to membranous cellular structures which were isolated from explants at the end of the culture. Fractions containing plasma and Golgi membranes contained the highest amount of radioactivity. Solubilisation of the membranes by Triton X-100 dissociated the [3H]colchicine from the prolactin receptors as judged by a chromatography of the soluble fraction on a Sepharose 6 B column. On the column, the labelled colchicine remains associated with a molecular entity which may be free tubulin. In all cases, the binding of [3H]colchicine was greatly attenuated by an excess of unlabelled colchicine but was only slightly affected by the competition with lumicolchicine. These results suggest that mammary membranes contain tubulin and that binding of drugs to this molecule inhibits the generation of the prolactin second messengers eliciting the hormonal actions in the mammary cell. This also suggests that microtubules are probably not involved in the mechanism of prolactin action.

Prolactin-like activity of anti-prolactin receptor antibodies on casein and DNA synthesis in the mammary gland

Prolactin receptors were partially purified from rabbit mammary gland membranes by using an affinity chromatography technique. Antibodies against this prolactin receptor preparation were obtained in guinea pig and sheep. Both antisera were able to inhibit the binding of 125I-labeled ovine prolactin to rabbit mammary gland membranes. When added to culture media of rabbit mammary explants, the anti-prolactin receptor antiserum inhibited the capacity of prolactin to initiate casein synthesis and casein mRNA accumulation as a function of the antiserum concentration. However, in the absence of prolactin, both antisera (guinea pig and sheep) at moderate concentrations were capable of mimicking prolactin action on casein gene expression and on DNA synthesis. At higher concentrations, the anti-prolactin receptor antibodies inhibited their own actions. Several characteristics of the prolactin effect were also observed with the anti-prolactin receptor antibody: the stimulatory effect of the antibody was amplified by glucocorticoids; colchicine, which was capable of blocking prolactin action, also prevented the induction by the antibody. Lysosomotropic agents, which do not interfere with prolactin action, did not alter the response observed with the antibody. These results indicate that an anti-prolactin receptor antibody can mimic two major actions of prolactin obtained in mammary explant culture and suggests that the prolactin molecule is not required beyond the initial binding to its receptor.