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Biomedical subjects

M Peaker

Publications and source records attributed to M Peaker.

At least 37 records · Page 2Linked to original sources
PubMed1991

Regulation of mouse mammary cell differentiation by extracellular milk proteins.

Differentiation of mammary epithelial cells prepared from pregnant mice was stimulated by culture on floating collagen gels in the presence of lactogenic hormones. Differentiation was measured by the induction of casein synthesis and fatty acid synthase activity, both of which increased by up to 15-fold during 12 days of culture. Addition of a 10-30 kDa fraction of goat whey proteins to culture medium from day 3 inhibited casein synthesis by greater than 20% compared with control cultures on days 4-12, and prevented further induction of fatty acid synthetase activity. Inhibition of secretory cell differentiation by this fraction, which is known to inhibit milk synthesis acutely in explant culture and lactating goats, suggests that similar autocrine mechanisms may mediate the sequential local effects on milk yield and cell differentiation elicited by manipulation of milking frequency or efficiency.

Animals↗
PubMed1991

Endometrial relaxin: effects of mastectomy in the cyclic and pregnant guinea pig.

Mastectomy in the guinea pig increases the incidence of still births and neonatal deaths compared with intact animals. The guinea pig has the endometrial gland cells (EGC) as the major source of relaxin, and this hormone has possible roles in uterine quiescence, cervical dilatation, and lengthening of the interpubic ligament in pregnancy. An effect of mastectomy on uterine relaxin has been sought by immunocytochemical localization during the estrous cycle, mid and late pregnancy and on endometrial relaxin gene expression in the late pregnant mastectomized animal by Northern analysis. Endometrium from midpregnant (day 35) and late pregnant (day 63) and from lactating (days 5, 21, and 28) guinea pigs immunostained with antiserum to porcine relaxin by the avidinbiotin technique. By increasing the sensitivity of the latter, relaxin immunostaining was also detected for the first time in EGC from cyclic animals (days 9 and 14). A pattern and intensity of relaxin immunostaining could be readily assigned to each of the stages examined: estrous cycle, midpregnancy, late pregnancy, lactation, and post weaning. The dark uniform staining of the EGC in late pregnancy was followed by sporadic staining of the EGC in lactation, returning to the cyclic picture after weaning. Endometrium from mastectomized cyclic and late pregnant guinea pigs showed a reduction in the amount of immunostaining compared with the relevant control animals. The reduction was most pronounced in the mastectomized late pregnant guinea pig. This result was reflected in an apparently lower level of relaxin mRNA in the endometrium of these animals compared to intact controls. These data indicate a novel linkage between the mammary gland, either directly or indirectly, to the nonpregnant or pregnant uterus. The loss of this signal appears to be associated with subsequent problems at parturition which may be linked to the reduction in endometrial gland relaxin production. The nature of this signal from the mammary gland, normally considered to be an exocrine rather than an endocrine gland, is unknown.

Animals↗
PubMed1990

Some effects of mastectomy on reproductive success in the guinea-pig.

Virgin guinea-pigs were mastectomized in two stages between 11 and 18 weeks of age and then mated, starting 19 weeks after final surgery. In the subsequent first pregnancy, the incidence of still-births and neonatal deaths was significantly higher in the mastectomized animals (6 out of 12 mothers (50%) and 14 out of 49 young (29%) compared with intact guinea-pigs (1 out of 15 mothers (7%) and 1 out of 58 young (2%)). There was no significant effect of mastectomy on litter size and weight or on gestation period. The still-born were not significantly different in weight from those born alive. A significant relation was found between maternal weight changes in the period 20 to 5 days before parturition and the occurrence of still-births and neonatal deaths; still-births were associated with a period of reduced weight gain. No effect of mastectomy on the length of the oestrous cycle was apparent but a significant increase in the incidence of non-pregnancy was found. The results provide further evidence that mastectomy influences reproductive success in the guinea-pig and suggest that parturition is a key process affected.

Animals↗
PubMed1990

Oestrogen production by the goat mammary gland: transient aromatase activity during late pregnancy.

Mammary tissue from goats had significantly higher aromatase activity at 148-149 days of pregnancy than earlier in pregnancy or during lactation. Aromatase activity was determined by production of 3H2O from [1 beta-3H]androstenedione that was inhibited by 4-hydroxyandrostenedione. The time of maximum aromatization was during peak mammary output of oestradiol-17 beta described previously in vivo in the same species. Aromatase activity in the mouse mammary gland was low and no peak was observed in late pregnancy. It is concluded that the oestrogens produced by the mammary gland in the late-pregnant goat are formed by aromatization of androgens.

Animals↗
PubMed1989

Metabolic adaptations in goat mammary tissue during long-term incomplete milking.

Lactating goats were milked incompletely in one gland and normally in the other gland twice daily for 24 weeks. Yields of the incompletely milked glands were adjusted so that a calculated 100 ml milk remained in the gland at the end of milking. On average this residual volume was greater by 7.6% of the total milk volume than that left after normal milking and was 25.9% greater than the capacity of the alveoli. After 24 weeks, the weekly milk yield of the incompletely milked gland was 23.8% lower than that of the other gland (P less than 0.001) when expressed in relation to cell number. The metabolic capacity of secretory cells in the two glands was measured in serial tissue biopsies. Two weeks of incomplete milking had no effect on enzyme activities or metabolic fluxes in the incompletely milked gland, but after 24 weeks the activities of several key enzymes were significantly lower in this gland. This was associated with a reduced rate of synthesis of total protein and casein in explants freshly prepared from the tissue. The rate of lactose synthesis also tended to be lower in explants from the incompletely milked gland. Secretory cell number in the two glands was similar at the end of incomplete milking. The data indicate that incomplete milking over a long period caused partial secretory cellular involution via a local chemical feedback mechanism in the gland.

Adaptation, Physiological↗
PubMed1989

Relaxin detected by immunocytochemistry and northern analysis in the mammary gland of the guinea pig.

Relaxin is a product of the endometrial gland cells in the guinea pig. Mammary tissue was collected from intact cyclic animals, on days 35 and 63 of pregnancy, days 5 and 21 of lactation, and day 28 postpartum. Tissue was collected from six cyclic hysterectomized animals. Sections of mammary gland were immunostained with the avidin-biotin immunoperoxidase method, and antisera to porcine relaxin which were raised to different preparations in different laboratories. Light uniform staining was evident in the cytoplasm of all of the cuboidal epithelial cells forming the mammary duct system in cyclic animals; mammary gland from hysterectomized animals showed similar staining. At midpregnancy light staining was seen in some epithelial cells, and by late pregnancy there was only faint staining. On day 5 of lactation there was intense and uniform staining throughout the epithelial cells of the alveoli. By day 21 of lactation the cells still immunostained for relaxin, but on day 28 postpartum there was a return to the cyclic staining pattern. Endometrium from animals at 55-60 days of pregnancy and mammary gland from day 6 of lactation were used for poly(A)+ RNA isolation and Northern analysis. Three 48-mer oligonucleotide probes were used. Poly(A)+ RNA from endometrium of late pregnant guinea pigs and from the mammary gland in lactation hybridized with the same two probes and failed to hybridize with a third under moderate stringency conditions. The results suggest that the major source of relaxin in the guinea pig is sequential, the pregnant uterus and the lactating mammary gland. The local and/or systemic significance is not known.

Animals↗
PubMed1988

Distribution of milk in the goat mammary gland and its relation to the rate and control of milk secretion.

Changes with time in the distribution of milk between different storage regions of the mammary gland were studied in goats. Milk was allowed to drain from the gland through a catheter (catheter milk); the gland was then milked by hand, before (hand milk) and after the administration of oxytocin (alveolar or residual milk). The hand-milk fraction was of negligible volume. There was an essentially linear increase in the catheter-plus hand-milk fraction from 0 to 16 h. The alveolar fraction increased up to 6 h, but thereafter remained constant to 16 h. There was considerable but consistent variation between animals in the alveolar fraction as a proportion of total milk volume. The proportion of residual milk was inversely related to milk secretory rate per unit weight of mammary tissue. The hourly administration of oxytocin without milking had no apparent effect on the distribution of milk in the gland 1 h later.

Animals↗
PubMed1988

Feed-back inhibition of milk secretion: the effect of a fraction of goat milk on milk yield and composition.

A milk fraction containing whey proteins of 10-30 kDa was injected into one mammary gland of lactating goats via the teat canal. This fraction produced a temporary dose-dependent reduction in milk yield in the treated gland; the milk yield of the other gland, which received an equal volume of carrier solution, was not affected. Injection of a second fraction, containing whey proteins of greater than 30 kDa, affected milk secretion only at high doses, and this effect was not wholly specific to the treated gland. The 10-30 kDa fraction and the greater than 30 kDa fraction produced similar transient changes in the concentrations of several ions and lactose in milk of the treated gland, but not in that of the untreated gland. These data indicate that a milk constituent present in the 10-30 kDa whey inhibits milk secretion in a temporary and reversible manner. The results are discussed in relation to regulation of milk secretion through local feedback inhibition.

Animals↗
PubMed1988

Effect of ionic composition of milk on transepithelial potential in the goat mammary gland.

1. A method is described for altering the ionic composition of the alveolar (residual) milk in the goat mammary gland. Transepithelial (blood-milk) potential difference (PD) was recorded before and after composition was changed. 2. When [Na+] and [K+] were varied while [Na+ + K+] and [Cl-] were maintained constant, there were no significant changes in PD. 3. When [Na+] was varied, with [K+] and [Cl-] constant, there was a linear relation between PD and log [Na+], with a change of 18 mV per tenfold change in concentration. 4. When [K+] was varied, with [Na+] and [Cl-] constant, there was a linear relation between PD and log [K+], with a change of 24 mV per tenfold change. 5. In view of the lack of discrimination between Na+ and K+ in the first experiment, the sum of [Na+] and [K+] was considered. In the experiments in which [Na+] or [K+] were varied, there was a change of 37 and 38 mV, respectively, per tenfold change in [Na+ + K+]. The quantitative effects on PD of changing [Na+] or [K+] when expressed as changes in [Na+ + K+] were not significantly different. 6. When [Cl-] was varied, with [Na+] and [K+] constant, there was a linear relation between PD and log [Cl-], with a change of 22 mV per tenfold change. 7. The results are discussed in relation to the types of ion channel that might be present in the apical membrane of the secretory cell and in relation to hypotheses on the mechanisms of ion transport in the mammary gland.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Identification of mRNA for relaxin in the endometrium of the pregnant guinea-pig.

The endometrium of late pregnant guinea-pigs was found to contain mRNA for relaxin. Poly(A)+RNA hybridized to 32P-labelled porcine relaxin-specific oligonucleotide probes. These probes corresponded to the C-peptide region of the prohormone. There was no hybridization to a 32P-labelled probe to the B-chain of porcine relaxin even under conditions of low stringency. The size of the relaxin mRNA was approximately 1.0 kb and similar to that found for relaxin mRNA from the pregnant sow ovary. This is the first study on relaxin mRNA from a uterine source.

Animals↗
PubMed1987

The effect of goat milk fractions on synthesis of milk constituents by rabbit mammary explants and on milk yield in vivo. Evidence for autocrine control of milk secretion.

Lactose and casein synthesis by rabbit mammary explants in organ culture was inhibited when fractions of goat milk were included in the culture medium. Inhibition was dose-dependent, and readily reversed when milk fractions were removed. The pattern of effects obtained with various fractions of milk indicated that inhibition was caused by a protein of 10,000-30,000 Da, which was present in the milk serum or whey fraction. The inhibitor fraction decreased milk accumulation when injected into lactating rabbit mammary glands via the teat ducts, whereas other milk proteins had no effect. Results are discussed in terms of autocrine regulation of milk synthesis through negative feedback by milk constituents.

Animals↗
PubMed1987

Effects of removing milk from the mammary ducts and alveoli, or of diluting stored milk, on the rate of milk secretion in the goat.

Goats were milked frequently (at 10.00, 11.30, 13.00 and 14.30 h) between normal morning and afternoon milking, using a catheter to drain the milk stored in the cistern and large ducts of the mammary gland; no increase in the rate of milk secretion occurred. When the same study was repeated but oxytocin was injected to elicit milk ejection and empty the alveoli, the rate of milk secretion increased significantly. The stimulatory effect of frequent catheter-milking plus exogenous oxytocin was evident at peak lactation as well as during declining lactation. When milk stored in the mammary gland was diluted with an isosmotic sucrose solution, the rate of milk secretion increased significantly. Again this effect was apparent at all stages of lactation. These results are discussed in relation to the local inhibitor hypothesis on the modulation of milk secretion.

Animals↗
PubMed1985

Milk accumulation and secretion in the rabbit.

Over the 24 h period after suckling, total mammary-gland weight increased linearly indicating no reduction in the rate of milk secretion during the relatively long interval between sucklings in the rabbit. Thus, storage capacity is matched to the long storage period. Beyond 24 h in the absence of suckling at 24 h, the rate of milk accumulation declined rapidly. This decline was not prevented by the administration of ovine prolactin or by permitting suckling of sealed teats at 24 h. During the decline in secretory rate after 24 h, milk [Na] and [Cl] increased while [K] and [lactose] decreased, as in other species. It is concluded that the decrease in secretory rate after cessation of suckling is not caused by lack of hormonal stimulation; it is suggested that mammary distension caused by accumulation of milk is responsible.

Animals↗
PubMed1985

The effects of long-term thrice-daily milking on milk secretion in the goat: evidence for mammary growth.

Goats were milked twice daily for 2-4 weeks after parturition. For the remaining 9 months of lactation, the right mammary gland was milked thrice daily while the left gland was milked twice daily. In the first and second weeks of thrice-daily milking the milk yield of the right gland increased relative to the left gland. Subsequently there was only a slight increase in the difference in milk yields between the glands, which reached a maximum after 10 weeks. Total yield of the right gland for the period of thrice-daily milking was significantly higher, by 30%, than that of the left gland. The peak yield of the right gland was significantly greater, by 29%, than that of the left gland. There was no significant difference between the rates of decline of yield (persistency) from peak lactation. There were no significant differences in the composition of the milk from the two glands with respect to Na+, K+, Cl-, lactose, protein, citrate, fat or calcium. At 40 weeks of lactation the weight of the right gland was significantly higher than that of the left gland and the weight of the parenchyma of the right gland was also significantly higher, by a similar percentage. At this stage of lactation, milk yield of the right gland was 43% higher than the left gland, while the weight of tissue was 34% higher. Thus over three-quarters of the difference in yield was accounted for by the greater gland size, and the remainder by greater milk secretion per unit weight of tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗