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Biomedical subjects

G Shyamala

Publications and source records attributed to G Shyamala.

At least 73 records · Page 4Linked to original sources
PubMed1980

Progesterone receptors in normal mammary gland: receptor modulations in relation to differentiation.

The biological basis for the observed modulation in cytoplasmic progesterone receptors (PgR) of normal mammary gland occurring during mammary development was investigated. Specifically, the relative roles of hormones vs. differentiation on (a) the decrease in PgR concentration during pregnancy and lactation and (b) the loss of mammary responsiveness to estrogen during lactation were examined. PgR were measured using the synthetic progestin, R5020, as the ligand. The hormones estrogen and progesterone were tested in vivo for their effect of PgR concentration. Mammary gland differentiation was assessed morphologically and by measuring enzymatically active alpha-lactalbumin. These studies show that there is a stepwise decrease in PgR that occurs in two stages. The first decrease is completed by day 12 of pregnancy and the second decrease occurs only after parturition. There appears to be a hormonal basis for the first decrease and it appears to be caused by the negative effect of progesterone on estrogen-mediated increase in PgR. In direct contrast, the absence of PgR during lactation and the mammary tissue insensitivity to estrogenic stimulation of PgR were not related to the hormonal milieu of lactation but were directly related to the secretory state of the mammary gland and lactation per se.

Animals↗
PubMed1979

Distinction between progestin- and glucocorticoid-binding sites in mammary glands. Apparent lack of cytoplasmic progesterone receptors in lactating mammary glands.

The cytosol fraction of the lactating mammary glands of mice does not appear to contain detectable amounts of progesterone receptors. Mixing experiments indicate that the absence of receptors is not due to interference by other factors in the cytosol. However, in the cytosol of mammary glands, there is specific binding or progestins to certain low-affinity sites which have characteristics of specific glucocorticoid-binding sites.

20-alpha-Dihydroprogesterone↗
PubMed1979

Progesterone receptors in normal mammary glands of mice: characterization and relationship to development.

Although progesterone receptors have been characterized in a number of target tissues for progesterone, including some mammary tumors, relatively little is known about these receptors in normal mammary tissues. In the present study using R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione), a synthetic progestin, we have identified and characterized the cytoplasmic progesterone receptors in normal mammary glands of mice. The receptor had a high binding affinity (Kd = 2.8 X 10(-9)M) for R5020 and was specific for progestins. The levels of receptor varied at different stages of mammary gland development; the levels were inversely proportional to the secretory activity of the gland. This negative corelation between receptors and secretion was further observed in studies in which lactational involution was induced experimentally. We propose that the functional significance of the modulation of progesterone receptors in normal mammary glands may be related to the known different effects of progesterone in this tissue.

Animals↗
PubMed1976

Relationship between receptor and mammary tumour virus production after stimulation by glucocorticoid.

A short exposure of primary cultures of mouse mammary tumour cells to glucocorticoids results in at least a three-fold stimulation of mammary tumour virus (MTV) production. Specific interaction of glucocorticoids with the cytoplasmic and nuclear receptors can also be demonstrated. The biological potency of various steroids to stimulate MTV is related directly to the retention of the steroid-receptor complex in the nuclei. Progesterone has a high affinity for the cytoplasmic receptor, is not retained by the nuclei and does not stimulate or block the basal level of MTV production. It is, however, quite effective in abolishing the glucocorticoid-mediated stimulation of MTV and thus behaves as an antagonist of glucocorticoid.

Animals↗
PubMed1975

Glucocorticoid receptors in mouse mammary tumors: Specific binding to nuclear components.

The specific interaction of glucocorticoids with nuclei of mouse mammary tumor was studied in vitro by incubation of the tissue with [3H]dexamethasone at 25 degrees. It was demonstrated that the mammary tumors contain a limited number of specific nuclear binding sites which were saturated with low hormone concentrations (10-8 M)9 The concentrations of specific binding sites in the nuclei were related to the concentration of cytoplasmic binding sites of unincubated tissues and varied between individual tumors. The binding component in the nuclei appeared to be a protein and was easily solubilized with 0.4 M KCl containing buffers. The ability of various corticoids to block the nuclear localization of the steroid correlated well with their glucocorticoid potency. Estradiol and progesterone at concentrations of 10-6 M were also effective in competing for the glucocorticoid receptor binding sites. However, while the glucocorticoids such as hydrocortisone and corticosterone translocated to nuclear sites also specific for dexamethasone, estradiol and progesterone competed for the cytoplasmic binding sites and did not translocate to the nucleus. The possible significance of the interaction of various steroids with the glucocorticoid receptors in mammary tumors is discussed.

Animals↗