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Biomedical subjects

I A Forsyth

Publications and source records attributed to I A Forsyth.

At least 55 records · Page 3Linked to original sources
PubMed1981

Mammary-tumour incidence in Sprague-Dawley rats treated with 7,12-dimethylbenz(a)anthracene: effect of pregnancy and lack of effect of unilateral lactation.

Mammary teat removal (thelectomy) was performed unilaterally in female Sprague-Dawley rats at 35 days of age. They were given 7,12-dimethylbenz(a)anthracene (DMBA) when aged either 55 days or 79 days. One third were unmated; one third were mated one week and one third mated more than 3 weeks after DMBA administration. Animals were killed when tumour-positive or after one year, when mammary lesions had developed in 99% of rats. The mean latent period for adenocarcinomas was 18.9 +/- 2.0 weeks. Benign mammary tumours, mainly secretory adenomas, developed significantly later (39.2 +/- 1.7 weeks). The rapid unilateral involution of the thelectomized glands at parturition had no effect on the localization of either adenocarcinomas or benign mammary tumours. Pregnancy and delayed DMBA administration markedly reduced the incidence of adenocarcinomas; lactation had no significant effect. In a separate experiment, precocious puberty induced with pregnant-mare-serum gonadotrophin in 30-day-old female Sprague-Dawley rats enabled their first pregnancy and lactation to be completed by 80 days of age. Parity before carcinogen administration significantly delayed the development of adenocarcinomas.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1980

Influence of local vascularity on hormone receptors in mammary gland.

Procedures, such as teat removal (thelectomy) or teat duct ligation, which prevent removal of milk, lead to rapid involution of the lactating mammary gland; performed unilaterally they have been used previously to study the biochemistry of involution, enabling a comparison of normal and involuting glands in the same animal against the same systematic hormonal environment. Both the protein hormone prolactin and the steroid hormone oestrogen are of importance in the development and function of the mammary gland. In the present experiments, female Sprague-Dawley rats were unilaterally thelectomised and the binding to the mammary gland of prolactin and oestrogen was examined through pregnancy, lactation and weaning. There was an effect of thelectomy during lactation only, when levels of both receptors increased in the intact lactating gland but failed to rise in the thelectomised, involuting gland. Capillary closure is known to occur in the mammary glands of rats after 36-48 h of milk accumulation. The rate of delivery of hormones to the tissue will be drastically reduced and it is concluded that this, rather than systemic hormone levels, is of importance in controlling receptor levels.

Animals↗
PubMed1980

Placental lactogen in the goat in relation to stage of gestation, number of fetuses, metabolites, progesterone and time of day.

Placental lactogen has been measured in goats throughout pregnancy by radioreceptor assay of prolactin-like activity. Lactogenic activity, which is not prolactin, increased from less than 5 nmol/l in week 8 to 27 nmol/l by week 16. There was no further change until term. Plateau concentrations (week 16 to term) were highest in animals carrying triplets, 49.5 nmol/l. There were marked functuations in placental lactogen over a 24 h period. These short-term fluctuations were not related to changes in glucose, non-esterified fatty acids or, in two animals, progesterone. However, there was a negative correlation between mean concentrations of placental lactogen and glucose in plasma of 20 goats sampled over a 24 h period between weeks 15 and 20 of gestation. There was no difference in placental lactogen concentration from week 16 to term between goats in their first and second pregnancies although the normal period of increase in placental lactogen was delayed by some 3 weeks in goats in their second pregnancy. In hemimastectomized goats, hypophysectomy on day 60 did not affect placental lactogen but daily treatment with bromocriptine (5 mg/day) from day 60 to day 120 blocked the normal rise in concentration.

Animals↗
PubMed1979

Ontogeny and control of prolactin receptors in the mammary gland and liver of virgin, pregnant and lactating rats.

Prolactin receptors were identified and partially characterized in the mammary gland of the rat. The binding of 125I-labelled ovine prolactin to a subcellular particulate fraction of rat mammary gland decreased between days 30 and 100 of age. Over the same period, binding to the liver increased and there was a significant negative correlation between prolactin binding in the two tissues. Binding to the mammary gland was low during pregnancy, increased in early lactation and declined after the litters were weaned. Binding to the liver was lower during lactation than during pregnancy or the period after weaning suggesting that tissue-specific factors may operate in the control of this receptor. In virgin rats, prolactin binding by the mammary gland was increased by oestrogen. This effect was blocked by hypophysectomy and partially restored by replacement therapy with prolactin. Hypothyroidism and treatment with progesterone also reduced the response to oestrogen. The maintenance of prolactin binding by the mammary gland of lactating rats depends on the presence of the ovaries and pituitary, thyroid and adrenal glands. Examination of the ratio epithelium: stroma suggests that prolactin acts by increasing the number of epithelial cells in the mammary gland and that thyroid, adrenal and ovarian hormones modulate the number of receptors per cell.

Animals↗
PubMed1979

Effect of number of young born (litter size) on milk yield of goats: role for placental lactogen.

Relationships of number of fetuses, placental mass, and lactogenic activity of plasma to development of mammary gland during pregnancy and of litter size to milk yield were examined in British Saanen goats. In late pregnancy lactogenic activity, measured in plasma by radioreceptor assay, increased with number of fetuses. Total weight of placentomes increased with total fetal weight and, hence, fetal number. The weight of the lobulo-alveolar component of the udders was correlated positively with placental mass and fetal number. In hand -milked goats which bore triplets or twins, mean milk yield was 47% and 27%, respectively, higher than in mothers of single kids after correction for lactation number. Milk yield was correlated with the weekly mean of placental lactogen titers between wk 11 and term. This supports the view that placental lactogen has a significant role in the control of normal mammary development and function in goats.

Animals↗
PubMed1979

Changes in mammary development and composition of secretion during late pregnancy in the mare.

Small samples of mammary secretion were taken for analysis from Thoroughbred mares during the last 3 weeks of pregnancy up to the time of foaling. The concentrations of sodium and chloride decreased while those of lactose, potassium, citrate, phosphate, calcium, magnesium and protein increased. The time-course of these changes showed marked variation between animals. The concentration of whey proteins began to increase about 10 days before parturition. The appearance of the secretion and the size of the mammary glands increased in the last few days of pregnancy. It is suggested that the concentration of calcium in mammary secretion could provide the basis of a test for impending parturition in this species.

Animals↗
PubMed1978

Inhibition by low concentrations of ouabain of prolactin-induced lactogenesis in rabbit mammary-gland explants.

1. Explants of mammary tissue from pseudopregnant rabbits were cultured at 37 degrees C in air for 24-48h in Medium 199 buffered with 20mm-Hepes [4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid]. The medium contained insulin and corticosterone, or insulin, corticosterone and sheep prolactin in the presence or absence of ouabain, an inhibitor of Na(+)/K(+)-dependent adenosine triphosphatase. The responses of explants were assessed histologically, by measuring the tissue concentration of K(+), and by rates of synthesis of RNA, protein and fatty acids. The effect of ouabain on Na(+) and K(+) concentrations in slices of lactating rabbit mammary-gland tissue incubated for 1h at 37 degrees C in Krebs bicarbonate buffer was also studied. 2. Prolactin increased the concentration of K(+) in mammary explants, an effect prevented by ouabain. In slices of lactating tissue, there was a linear relationship between the log dose of ouabain (from 0.1 to 10mum) and increased Na(+) and decreased K(+) concentrations in the tissue. 3. Ouabain at concentrations up to 1mum did not affect the rate of synthesis of RNA, protein or fatty acids by explants cultured with insulin and corticosterone. By contrast, the stimulatory effect of prolactin on protein synthesis was diminished and the induction of medium-chain fatty acid synthesis by prolactin was almost abolished. RNA synthesis was unaffected. Histological examination showed no tissue damage by 1mum-ouabain. 4. Explants cultured in the presence of 2mum-ouabain for 24h retained their ability to respond to prolactin when the ouabain was removed from the culture medium. Between 24 and 48h they showed responses to prolactin of a magnitude similar to those of explants never exposed to ouabain. 5. These results show that a fully functional Na(+)/K(+)-dependent adenosine triphosphatase system is necessary for prolactin to promote secretory activity in rabbit mammary gland.

Animals↗
PubMed1978

A pigeon crop sac radioreceptor assay for prolactin.

Ovine prolactin, labelled with 125I by either lactoperoxidase or a mild chloramine T method, bound to receptors from the pigeon crop sac mucosa cells of prolactin-injected pigeons. Binding was demonstrated in a crude homogenate of mucosal cells removed from the crop by scraping and in a subcellular fraction in which 5'-nucleotidase activity was enhanced two- to threefold. The binding was specific, dependent on time, temperature and the concentration of receptors and had a dissociation constant of 7 X 10(-10) mol/l. The binding capacity of the crop tissue was 71 fmol/mg membrane protein. Nine purified preparations of prolactin from four species were assayed by local pigeon crop sac bioassay and by radioreceptor assay. The two methods were highly correlated (r = 0.934). The regression equation was radioreceptor assay = 1.22 bioassay--0.18 indicating a 1 : 1 correspondence between the two methods for prolactin purified from sheep, rat, horse and pig anterior pituitary glands.

Animals↗
PubMed1976

Placental lactogen in the cow.

Placental lactogen secretion has been demonstrated in cows on days 36, 178, 182 and 270 of pregnancy by co-culture of cotyledonary tissue with mouse mammary gland explants. Bovine placental lactogen probably originated from the foetal cotyledon and showed no detectable cross-reaction in immunoassays for bovine prolactin or growth hormone. Peripheral plasma samples collected from seven primiparous heifers at 2-week intervals throughout pregnancy showed a seasonal rhythm in prolactin concentration, measured by radioimmunoassay, with high levels in the summer. Monthly samples were bioassayed for total lactogenic activity by a rabbit mammary gland organ culture method. Postive responses were obtained only when prolactin levels were high (greater than 70 ng/ml), indicating that levels of placental lactogen in the circulation are much lower in the cow than in sheep, goats or women.

Animals↗
PubMed1976

Placental lactogen (chorionic mammotrophin) in the field vole, Microtus agrestis, and the bank vole, Clethrionomys glareolus.

Placental lactogen has been detected in the field vole, Microtus agrestis, and the bank vole, Clethrionomys glareolus, using a co-culture technique. In field voles this activity could be detected from about day 8 of pregnancy to shortly before term, and stimulated both mouse and vole mammary gland to secrete in vitro. Partial immunological cross-reaction was detected in a radioimmunoassay system between rat prolactin and either extracts of vole pituitaries or media on which vole pituitaries had been cultured; vole placental lactogen showed no cross-reaction with rat prolactin. One site of origin for this hormone is probably the trophoblastic giant cells.

Animals↗