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Biomedical subjects

F F Bolander

Publications and source records attributed to F F Bolander.

At least 37 records · Page 2Linked to original sources
PubMed1989

Prolactin regulation of mouse mammary tumor virus (MMTV) expression in normal mouse mammary epithelium.

The hormonal regulation of mouse mammary tumor virus (MMTV) RNA in normal mouse mammary epithelium was studied in an explant system. In tissue from parous mice, physiological concentrations of prolactin stimulated MMTV expression, while only pharmacological concentrations of cortisol were effective. Regulation in explants from virgin mice was similar to that in parous animals except that the former were less sensitive to prolactin; this relative unresponsiveness may explain why uninduced tissue from virgin mice does not express MMTV RNA, while that from parous mice does exhibit some basal production. These results suggest that prolactin plays a major role in MMTV expression in normal mammary epithelium and that glucocorticoids may only have a permissive effect or may act through an indirect mechanism requiring high concentrations. These data also suggest that the greater susceptibility of parous mice to MMTV-induced tumorigenesis may reflect the greater prolactin sensitivity in the glands from these animals.

Animals↗
PubMed1986

The interrelationships among poly(ADP-ribosyl)ation, DNA synthesis and mammary gland differentiation.

Because mammary epithelium from virgin mice must undergo DNA synthesis prior to differentiation and because poly(ADP-ribosyl)ation has been linked to the cell cycle, it was hypothesized that this requirement for DNA synthesis might be related to the poly(ADP-ribosyl)ation of nuclear proteins. However, 3-methoxybenzamide, an inhibitor of poly(ADP-ribosyl)ation, stimulates alpha-lactalbumin accumulation even when added after DNA replication is completed. Furthermore, in parous mice this compound is still effective when DNA synthesis is blocked by cytosine arabinoside-beta-D-arabinofuranoside. Therefore, poly(ADP-ribosyl)ation appears to be associated, not with DNA synthesis, but with some other event in mammary gland differentiation.

Animals↗
PubMed1986

Involvement of protein kinase C in mouse mammary gland development.

The relationship between kinase C activity and mammary gland differentiation was investigated by following kinase activity throughout the mouse reproductive cycle and by pharmacologically perturbing the kinase, while monitoring biochemical differentiation. Protein kinase C activity declined during pregnancy and remained low throughout lactation, suggesting an inverse relationship with milk protein expression. This negative association was further supported by the use of quercetin (50-100 mumol/l) and gossypol (50 mumol/l), which are both protein kinase C inhibitors. These compounds doubled alpha-lactalbumin levels in mammary explants cultured with hormones. However, a phorbol ester, known to activate protein kinase C, had no effect on alpha-lactalbumin production, although it did stimulate this milk protein 2.5-fold in the presence of the calcium ionophore, A23187. In the absence of raised calcium levels, protein kinase C activity therefore appeared to be inversely correlated with biochemical differentiation; but, in the presence of increased calcium concentrations, both calcium and the kinase acted synergistically to augment hormone-induced alpha-lactalbumin expression.

Animals↗
PubMed1986

Hormonal regulation of protein kinase C in the mouse mammary gland.

The hormonal regulation of protein kinase C (PKC) induction over 3 to 14 days was investigated in the mouse mammary gland in vitro and in vivo. In intact mice, estradiol (1 microgram/mouse injected daily for 2 weeks) stimulated PKC activity 70%, while progesterone (1 mg/mouse injected daily) inhibited it by 30%. Prolactin, whose levels were elevated for 2 weeks by two pituitary isografts, had no effect. When mammary gland explants were cultured in insulin and cortisol, the further addition of estradiol (1 ng/ml), progesterone (1 microgram/ml), or prolactin (1 microgram/ml) did not alter PKC activity after 3 days. These data suggest the following conclusions: although previous studies have implicated prolactin in the transient, calcium-phospholipid activation of PKC, it does not appear to elevate total levels of this kinase over prolonged periods. In contrast, the sex steroids do appear to affect long-term levels of this kinase; furthermore, this latter effect may be indirect.

Animals↗
PubMed1985

The relationship between adenosine diphosphate-ribosylation and mammary gland differentiation.

Poly(adenosine diphosphate [ADP]-ribosyl)ation, although associated with differentiation in many systems, exhibited a reciprocal relationship with mammary gland differentiation, and both the synthetic and degradatory pathways complemented each other in this regard. Poly(ADP-ribosyl)synthetase activity declined during pregnancy and lactation, while poly(ADP-ribose) degradatory activity rose late in pregnancy and peaked during lactation. In explant cultures, similar changes occurred and appeared to be under separate hormonal control; prolactin suppressed the synthetase activity, whereas insulin stimulated the poly(ADP-ribosyl)glycohydrolase activity. This latter effect may be mediated by a decline in cAMP levels for the following reasons: the glycohydrolase is known to be inhibited by cAMp, insulin decreased cAMP concentrations in mammary explants by 70%, and cholera toxin blocked the effects of insulin on poly(ADP-ribose) degradation. This reciprocal relationship between poly(ADP-ribosyl)ation and mammary gland differentiation is further supported by pharmacological studies: in the presence of insulin, cortisol, and prolactin, an inhibitor of the synthetase stimulated alpha-lactalbumin three-fold over hormone stimulation alone. However, this inhibitor was unable to induce differentiation in the absence of prolactin. Therefore, although there is a close association between a decline in enzyme activity and mammary differentiation, the data are insufficient to support a causal relationship.

Animals↗
PubMed1985

Possible roles of calcium and calmodulin in mammary gland differentiation in vitro.

In response to insulin, cortisol and prolactin, mammary gland explants from virgin mice will undergo differentiation, as measured by lactose synthetase activity and casein synthesis. W-13 (N-(4-aminobutyl)-5-chloro-2-naphthalenesulphonamide), a calmodulin inhibitor, reduced prolactin-induced differentiation by 80% while inhibiting insulin- and cortisol-induced RNA synthesis only 40%. However, tissue levels of calmodulin did not change during a 3-day culture, with or without prolactin, suggesting that the regulatory component of the calcium-calmodulin system was the intracellular calcium concentration. In support of this hypothesis, verapamil, a calcium channel blocker, also preferentially inhibited prolactin-induced differentiation and prolactin did stimulate calcium accumulation (from a control value of 3.8 +/- 1.3 (S.E.M.) pg calcium/mg wet tissue per 15 min to 61.4 +/- 7.0). On the other hand, A23187, a calcium ionophore which mimicked prolactin actions on calcium accumulation, was not able to induce differentiation in the absence of prolactin; in fact, high concentrations of either A23187 or extracellular calcium actually inhibited lactose synthetase activity, although casein synthesis was relatively unaffected. Therefore, it appears that the calcium-calmodulin system is involved in prolactin-induced differentiation of mammary gland explants but that it cannot be the only mediator of prolactin actions; i.e. it is necessary but not sufficient. There also appears to be another, separate action of calcium on casein synthesis which involves increasing the mammary epithelial sensitivity toward prolactin with respect to casein synthesis but not lactose synthetase activity.

Animals↗
PubMed1984

Enhanced hormonal responsiveness in mammary glands from parous mice: molecular mechanisms.

Mammary glands from parous mice required lower concentrations of hormones in vitro than those from virgins to effect differentiation, as measured by lactose synthetase activity. This phenomenon could not be explained by changes in receptor levels, since both mammary gland insulin and prolactin binding, although elevated at midpregnancy, returned to baseline in tissue from parous mice. Ethidium bromide, an intercalating dye, was a potent inhibitor of lactose synthetase induction in explants from virgins but much less potent in tissue from pregnant mice; explants from parous animals displayed intermediate sensitivity, suggesting that DNA structure was permanently altered. However, casein synthesis in glands from parous mice required hormone concentrations as high as in virgins and are just as susceptible to ethidium bromide as in virgins. Similarly, the vulnerability of the casein gene to DNAase I digestion is low in mammary epithelial cells from virgins, high in cells from pregnant mice, and low again in cells from parous animals. These data suggest that during the first pregnancy of mice, there are changes in the chromatin configuration that may facilitate the transcription of milk-related mRNA. Furthermore, after mammary gland involution these changes in the casein gene undergo reversion, while those involved with lactose synthetase activity persist; this may explain the disparate hormonal responsiveness seen in these animals with respect to casein and lactose synthesis.

Animals↗
PubMed1984

Enhanced endocrine sensitivity in mouse mammary glands: hormonal requirements for induction and maintenance.

This laboratory has previously shown that mammary epithelium from pregnant and parous mice are 5-7 times more sensitive in vitro to insulin, cortisol, and PRL than tissue from virgins, with respect to lactose synthetase activity. In the present studies, virgin mice were treated for 2 weeks with either progesterone or a pituitary allograft to increase PRL levels, and the mammary explants exhibited the same heightened sensitivity to all three hormones that was noted in pregnant animals. Treatment with estradiol or T4 was without effect. However, this effect was transient, since the tissue lost its elevated hormonal responsiveness 4 weeks after progesterone withdrawal, suggesting that the permanent effect seen in nonpregnant nonlactating parous mice involves a more complex series of events than simply elevated progesterone or PRL levels. Even tissue from parous mice reverted to a reduced insulin and PRL sensitivity, if the tissue was initially cultured in the absence of any hormones. Although the increased sensitivity to cortisol did appear to be permanent under the culture conditions used, the maintenance of a heightened insulin responsiveness required the continuous presence of insulin, cortisol, and PRL, while that for PRL needed at least two of these three hormones. In summary, progesterone and/or PRL may be partly responsible for the increased hormonal sensitivity first manifest during pregnancy, but a normal endocrine milieu is required to maintain this responsiveness in vitro.

Animals↗
PubMed1983

Loss of differentiative potential of the mammary gland in ovariectomized mice: altered estrogen responsiveness in parous mice.

Previously, estrogen had been shown to be essential for the maintenance of differentiative potential in the mammary gland of virgin mice; the purpose of this study was to evaluate the role of these steroids in nonpregnant, nonlactating parous mice. To this end, parous mice were either ovariectomized or adrenalectomized and ovariectomized for 4-6 weeks before hormonally induced differentiation was attempted in culture. Although mammary glands from virgin mice lose their differentiative potential in vitro following ovariectomy, tissue from castrated parous mice exhibit only a partial loss of activity. Since combined adrenalectomy and ovariectomy in parous animals virtually abolished differentiation and since exogenous estradiol preserved it, it would appear that mammary gland differentiation in parous mice, as in virgins, requires estrogens, but that tissue from the former is more sensitive. This difference between virgins and parous mice is not related to differences in either the capacity or affinity of the cytosol estrogen receptor, as these parameters are identical in all experimental groups.

Adrenalectomy↗
PubMed1983

Deoxyribonucleic acid synthesis-dependent casein gene expression: species differences.

Mammary gland explants from mature virgin mice, rats, and rabbits exhibit an increased rate of both DNA and casein syntheses when cultured in the presence of specific combinations of insulin, hydrocortisone, and PRL. If cytosine arabinoside, a potent inhibitor of DNA synthesis, is added to the culture medium, casein synthesis is inhibited in explants from mice but not in those from rats or rabbits. This inhibition is at the level of accumulation of casein mRNA; an 89% reduction of stimulated levels was observed. The nature of this block was investigated further by examining the general response of mature virgin mouse mammary explants to hydrocortisone and PRL, hormones considered essential for casein gene expression in this species. Cytosine arabinoside did not prevent an increment in either hydrocortisone-induced NADH-cytochrome c-reductase or PRL-induced total RNA synthesis. Previous work has shown that certain insulin-induced responses are also unaffected. Taken collectively, these results suggest that the lesion induced by cytosine arabinoside inhibition of DNA synthesis is distal to the receptor for one or more of these hormones. The necessity for coupling DNA synthesis with overt differentiation in the mature virgin mouse, but not in the rat or rabbit, is one of numerous examples of species variation in regard to the interaction of hormones with the mammary gland.

Animals↗
PubMed1983

Persistent alterations in hormonal sensitivities of mammary glands from parous mice.

Mammary gland explants from virgin mice required supraphysiological concentrations of insulin, cortisol, and PRL for the induction of casein synthesis and lactose synthetase activity; dose-response curves for any one hormone were identical for each parameter of differentiation. Tissue from midpregnant mice was 5-7 times more sensitive to hormonal induction, responding to near-physiological concentrations of insulin, cortisol, and PRL; again, both casein synthesis and lactose synthetase activity required the same amounts of any individual hormone. Induction of lactose synthetase activity in glands from nonlactating nonpregnant parous mice required as little hormone as tissue from pregnant animals; however, induction of casein synthesis required a higher concentration of hormones, as was observed with glands from virgins, leading to a discrepancy between the optimal hormonal concentrations required for these two markers of differentiation in parous mice. Similar data were found in the time courses. Induction in explants from midpregnant animals was 1-2 days faster than that in virgins; in parous mice, induction of lactose synthetase activity was as rapid as in midpregnant mice, but induction of casein synthesis was slower and shifted toward that for the tissue from virgins. These data suggest that those mechanisms responsible for the rapid induction and increased hormonal sensitivity of the mammary gland during pregnancy are still operative after involution of the gland with respect to at least one parameter of differentiation.

Animals↗
PubMed1981

Insulin is essential for accumulation of casein mRNA in mouse mammary epithelial cells.

In the presence of cortisol and prolactin, insulin at concentrations as low as 1 ng/ml significantly stimulates casein synthesis in mammary explants from midpregnant mice; maximal synthesis occurs at 10 ng/ml. However, in the absence of insulin, no detectable immunoprecipitable casein is produced. Insulin also supports enhanced accumulation of casein mRNA in the presence of cortisol and prolactin; neither epidermal growth factor nor somatomedin C has this effect. These inductive actions of insulin are not secondary to a general maintenance effect on the mammary epithelial cell; insulin, epidermal growth factor, and somatomedin C can support the accumulation of RNA in rough endoplasmic reticulum equally well. In addition, these effects do not reflect a specific insulin requirement for prolactin sensitivity; epidermal growth factor can support prolactin-induced total RNA synthesis as well as insulin can. The results demonstrate that, although insulin, epidermal growth factor, and somatomedin C can all function as cell maintenance agents, only insulin, together with cortisol and prolactin, can induce casein mRNA accumulation.

Animals↗
PubMed1981

The asynchronous hormonal induction of lactose synthetase components, alpha-lactalbumin and galactosyltransferase, in relation to lactose secretion by mouse mammary explants.

Hormonal induction of the lactose synthetase components, alpha-lactalbumin and galactosyltransferase, in relation to the induced levels of lactose synthetase activity and lactose secretion by mammary gland explants from mature virgin mice was examined. During 6 days of culture in the presence of insulin, cortisol, prolactin and triiodothyronine mammary explants accumulated progressively increasing amounts of alpha-lactalbumin. By contrast, galactosyltransferase and lactose synthetase activities were maximal on day 3, and then declined; the time course of lactose secretion was similar to that of galactosyltransferase and lactose synthetase activities. Cortisol concentration studies revealed the following dependencies on the steroid: alpha-lactalbumin content was maximal between 0.01 and 0.1 microgram and, at 10 microgram/ml fell below the baseline level observed without cortisol. On the other hand, galactosyltransferase, lactose synthetase and lactose secretion were only slightly increased at 0.01 microgram/ml, were maximal between 0.1 and 1.0 microgram/ml, and at 10 microgram/ml were still considerably above the baseline levels observed without cortisol. These results indicate that lactose formation and secretion by mammary explants from virgin mice correspond more closely to the hormone-induced activity of galactosyltransferase than to that of alpha-lactalbumin, and that asynchrony can arise between the induction of alpha-lactalbumin and the induction of lactose.

Animals↗
PubMed1981

Loss of differentiative potential of the mammary gland in ovariectomized mice: identification of a biochemical lesion.

The differentiative functions, lactose synthetase activity and casein synthesis, can be induced in mammary gland explants from intact mice when insulin, cortisol, and PRL are present in the medium. By contrast, the tissue from mice castrated for 1--2 months does not differentiate in vitro. Explants from these ovariectomized animals retain their sensitivity toward insulin, as evidenced by the ability of this hormone to stimulate DNA synthesis, alpha-aminoisobutyric acid accumulation, and glucose-6-phosphate/gluconate-6-phosphate dehydrogenase activities. This tissue also remains sensitive to cortisol, as evidenced by the ability of this steroid to stimulate NADH-cytochrome c reductase activity. However, the tissue from ovariectomized mice has lost biological responsiveness to PRL. Such insensitivity may be due to a deficiency of PRL receptors, which are reduced in the glands from castrated mice to 20--25% of control values. However, a second defect between the receptor and the genome is also likely, since PRL unresponsiveness is still present in the tissue of ovariectomized animals whose mammary PRL-binding has been partially maintained by elevating serum PRL levels with a pituitary transplant. Therefore, this system may be useful for the study of cellular processes related to PRL action beyond the receptor level.

Aminoisobutyric Acids↗
PubMed1980

Stimulation of lactose synthetase activity and casein synthesis in mouse mammary explants by estradiol.

17 beta-Estradiol (E2; 1 ng/ml) can significantly (P less than 0.05) augment lactose synthetase activity (85%) and casein synthesis (65%) in mammary gland explants (from midpregnant C3H/HeN mice) cultured in medium 199 containing insulin, cortisol, PRL, and T3. Both T3 (0.65 ng/ml) and a physiological concentration of PRL (50 ng/ml) are required for stimulation by E2; at higher PRL levels, the effects of E2 are obscured. Sex steroid specificity was supported by the observations that the E2 effects are blocked by the antiestrogen nafoxidine (5 micrograms/ml), and that 17 alpha-estradiol (5 ng/ml) was inactive; however, at 5 ng/ml, estrone and diethylstilbestrol were equipotent to E2. Testosterone (5 micrograms/ml) and progesterone (1 microgram/ml) were inhibitory, although progesterone did not suppress casein synthesis. Since E2 did not alter the amount of epithelial DNA, its effects represent an increase in biological activities per cell. E2, therefore, in conjunction with the classical lactogenic hormones and T3 can act directly on mammary tissue by promoting differentiation.

Animals↗
PubMed1980

Loss of differentiative potential of the mammary gland in ovariectomized mice: prevention and reversibility of the defect.

The differentiative functions, lactose synthetase activity and casein synthesis, are not expressed in vitro in mammary gland explants from female virgin mice castrated for 1-2 months. 17 beta-Estradiol (E2) treatment (3 micrograms, twice weekly) initiated immediately after ovariectomy completely preserves this ability for as long as 2 months; however, elevating serum PRL levels by either perphenazine treatment or pituitary transplantation under the renal capsule is ineffective. Therefore, the loss of differentiative potential in the mammary gland appears to be a result of E3 deprivation and not depressed serum PRL concentrations. E2 therapy for 5 weeks also partially restores this potential in animals whose mammary glands have previously lost it. Complete reversal of this defect occurs when the tissue from mice castrated for 4 weeks is transplanted into the cleared fat pads of intact virgins. These data suggest that E2 has an important role in differentiation of the mouse gland in addition to its known role in mammary epithelial growth.

Animals↗