PubMed Health⌕ Search

Biomedical subjects

S Nandi

Publications and source records attributed to S Nandi.

At least 217 records · Page 12Linked to original sources
PubMed1978

Role of hormones in mammary neoplasia.

A testable hypothesis for the role of hormones in mammary carcinogenesis with implications for other endocrine-related carcinogenesis is presented. The hypothesis is based on these observations: (a) hormones are involved, directly or indirectly, in regulating cell division in normal mammary cells: (b) emergence of overt mammary tumors requires hormonal stimulation of cells receiving carcinogenic stimulus; (c) normal mammary cells are of finite divisional capabilities, whereas neoplastic cells appear to have infinite divisional life; and (d) normal cells, when present in large quantities relative to the neoplastic cells, inhibit the growth of the latter cells. According to the hypothesis hormones play at least two roles in mammary carcinogenesis induced by diverse agents, such as viruses, chemicals, and radiation. First, hormones are necessary for DNA synthesis and mitosis of initial transformed cells for their conversion into fixed transformed cells with heritable characteristics. Second, hormones, by increasing the rate of cell division, shorten the reproductive life span of normal cells, eventually causing a reduction in the normal to transformed cell ratio in the population--a condition that allows the emergence of tumor cells by overriding the inhibitory influence of normal cells.

Animals↗
PubMed1978

Primary culture of rat mammary epithelial cells. II. Cytotoxic effect and metabolism of 7,12-dimethylbenz[a]anthracene and N-nitroso-N-methylurea.

To determine the cytotoxicity of 7,12-dimethylbenz[a]anthracene (DMBA) and N-nitroso-N-methylurea (NMU) on primary cultures of rat mammary cells, cultures were exposed to various concentrations of these carcinogens. Cytotoxicity was evident after exposure for 24 hours to as little as 0.1 microgram DMBA/ml. Cytotoxicity was evident after exposure for 2 hours with NMU at concentrations between 80 and 160 microgram/ml. Primary cultures of rat mammary cells were also examined for their ability to metabolize [3H]DMBA into water-soluble products. During a 48-hour period, mammary cells could convert 2.2% [3H]DMBA to water-soluble metabolites. The cells retained (for at least 4 days) small quantities of [3H]DMBA that were insoluble in organic solvents.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1977

A sensitive radioimmunoassay for a component of mouse casein.

Mouse casein (m.w. 22,000 daltons) has been purified by employing Sephadex G-100 and DEAE-cellulose column chromatographies. A sensitive radioimmunoassay method has been developed by using [125I]-labelled casein and antiserum elicited in rabbits after injection of glutaraldehyde-treated casein. The assay method is capable of detecting as little as 0.1 ng of casein. The use of the present radioimmunoassay method in detecting casein production in cultured mouse mammary explants has also been demonstrated.

Animals↗
PubMed1977

Hormonal control of milk protein synthesis in cultured mouse mammary explants.

SDS-urea polyacrylamide gel electrophoresis of mouse milk proteins revealed the presence of three major phosphoproteins (caseins) of m.w. 44,000, 26,000 and 22,000 daltons. By using an antiserum against crude casein fraction, an immunoprecipitation method was developed for the quantitative measurement of the rate of milk protein synthesis in the mouse mammary tissue. Cultivation of mammary explants with insulin, cortisol and prolactin resulted in the induction of milk protein synthesis as evidenced by the incorporation of [3H]amino acid and [32P]orthophosphate into immune precipitable materials. The present immunoprecipitation method coupled with a simplified explant culture technique provides a suitable procedure for the study of mouse mammary gland differentiation.

Animals↗
PubMed1977

Hormonal effects on intracellular and secreted casein in cultures of mouse mammary epithelial cells on floating collagen membranes.

Cultured on floating collagen membranes in the presence of lactogenic hormones, dissociated normal mammary epithelial cells from prelactating mice acquire the ultrastructural and biochemical characteristics of differentiated mammary secretory cells in vivo. The cells on floating collagen membranes in medium containing insulin alone have sparse secretory organelles, and a small amount of casein can be detected in these cells with a sensitive radioimmunoassay. These cells resemble counterpart cells in early-pregnant mice. When the cells are exposed to insulin, cortisol, and prolactin, the secretory apparatus is elaborated and significant increases in intracellular and extracellular casein are observed. In this environment, the intracellular casein content is generally four to eight times greater than in freshly dissociated cells or cells cultured in insulin alone. The amount of casein secreted into the medium by floating-collagen-membrane cultures in the three hormones is from 25 to 200 times greater than that secreted by cultures in insulin alone. Cells cultured on plastic substrates in either hormone combination fail to show any increase in intracellular or extracellular casein. On floating collagen membranes, the cells differentiate in response to hormones as they do in vivo and in organ culture. This cell-culture system provides an opportunity to study direct effects of environmental factors on mammary differentiation at the cellular level.

Animals↗
PubMed1977

Cyclic AMP regulation of mammary tumor virus production.

Addition of dibutyryl cyclic AMP (cAMP) and agents (isoproterenol and epinephrine) that stimulate the activities of adenylate cyclase enhance the stimulation of mammary tumor virus (MTV) production two- to threefold by glucocorticoid in short-term primary cultures of mammary tumors. This cAMP potentiation seems to depend on the stimulated level of MTV production by glucocorticoid alone, which increases MTV production 5- to 10-fold over basal level but varies greatly in absolute terms. When the stimulated level by glucocorticoid alone is suboptimal, cAMP seems to restore the sensitivity of the cells to the stimulatory effect of glucocorticoid to its maximum.

Adenylyl Cyclases↗
PubMed1977

Regulation of mammary tumor virus production by prolactin in BALB/cfC3H mouse normal mammary epithelial cells in vitro.

Hormonal regulation of mammary tumor virus (MTV) production, has been analyzed with normal mammary epithelial cells from chronically infected BALB/cfC3H mice. The effect of prolactin in terms of increased MTV production was not reproducibly observed in cells cultured in tissue culture dishes, whereas the cells grown on floating collagen gels consistently responded to prolactin in a dose-dependent manner. Of the three media tested. Dulbecco's modified Eagle's medium was found to be the best in terms of responsiveness to prolactin and in maximal MTV production. Specificity studies with other pituitary and placental hormones in place of prolactin have shown that both growth hormones and human placental lactogen can replace prolactin, whereas follicle-stimulating hormone, luteinizing hormone, and thyrotrophin were ineffective. Contrary to the mammary tumor systems, where it has been shown that insulin and glucocorticoid can maximally stimulate MTV production, these hormones alone elicited only a small response in the absence of prolactin in normal mammary epithelial cells. Although prolactin alone had very little effect by itself, its presence was necessary (permissive effect) in order for the glucocorticoids to be able to maximally stimulate MTV production in normal cells.

Animals↗
PubMed1976

Biochemical studies on mitochondria isolated from Normal and Neoplastic Tissues of the Mouse Mammary Gland.

Mitochondria isolated from spontaneous and transplanted mammary adenocarcinomas of two strains of mice were compared, by various biochemical criteria, to mitochondria from mammary glands of midpregnant or hormonally stimulated, cancer-free mice. The specific activities of several mitochondrial enzymes including cytochrome oxidase, alpha-glycerophosphate oxidase, and succinate dehydrogenase were twofold to threefold lower, whereas the activity of monoamine oxidase was two fold higher in tumor mitochondria. Malate dehydrogenase, adenylate kinase, and NADH oxidase showed similar levels of activity in tumor and midpregnant mammary gland mitochondria. In addition, mitochondrial polypeptide composition was analyzed by electrophoresis on sodium dodecyl sulfate-urea polyacrylamide gels. Midpregnant mammary gland and mammary tumor mitochondria were similar in polypeptide composition; however, several differences were observed. A high-molecular-weight polypeptide, present in mid-pregnant mammary gland mitochondria was absent from tumor mitochondria. Also, tumor mitochondria contained an additional high-molecular-weight polypeptide not found in the midpregnant mammary gland. There were numerous differences in the relative proportions of many polypeptides common to both tumor and midpregnant mammary gland mitochondria.

Adenocarcinoma↗
PubMed1975

Intracellular synthesis of mouse mammary tumor virus polypeptides: indication of a precursor glycoprotein.

Mouse mammary tumor virus polypeptides were detected in the cytoplasm of mouse mammary tumor cell cultures using immunological precipitation techniques. The anti-mouse mammary tumor virus serum precipitated the major virion glycoproteins gp49 and gp37.5/33.5 and a viral-related nonvirion glycoprotein of 76,000 daltons. Subcellular fractionation studies revelaed that the cell-associated virion glycoproteins were present in the membrane fraction. Pulsechase experiments indicated that a viral-related nonvirion glycoprotein of 76,000 daltons may be a precursor to one or more of the virion glycoproteins.

Adenocarcinoma↗
PubMed1975

Identification of a precursor protein to the major glycoproteins of mouse mammary tumor virus.

Mouse mammary tumor virus-producing cultures of mouse mammary tumor cells synthesize a viral-related polypeptide of molecular weight of 73,000 (gp 73) which is rapidly labeled during a short pulse but disappears during the chase concomitantly with the appearance of label in the virion glycoproteins gp 49 and gp 37.5/33.5. The addition of the protein synthesis-inhibitor cycloheximide to the chase medium has little effect on this conversion. Treatment of the proposed precursor with alpha-chymotrypsin leads to the formation of a polypeptide of molecular weight 49,000, similar to the major virion glycoprotein. A comparison of tryptic digest maps of the glycoproteins involved supports the hypothesis that both the viral glycoproteins gp 49 and gp 37.5/33.5 are derived from gp 73.

Animals↗