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SUMMARY
Stimulation of the nipple lines and genital and pelvic regions by self-licking, found previously to increase during pregnancy in the rat, was studied for its effect on mammary gland development. Licking was prevented by fitting wide rubber collars around the necks of rats for the entire period of pregnancy or for either the first half (days 1–12) or the second half (days 12–22) of pregnancy. The percentage of secretory tissue, and ratings of lobulo-alveolar (L-A) development and secretory (S) activity were used to measure the development of the gland on either the 22nd or the 12th day of pregnancy. Notched collars, which permitted licking, were used as a control for any stress effects that resulted from the collars, and injections of formalin were used as a control for any stress produced by the collar. Mammary development was reduced to only 50% of normal, and L-A development and S-activity ratings showed a corresponding retarded development in animals wearing a collar throughout pregnancy. Notched collars did not affect gland development and formalin injections accelerated it. There was no difference in the effects of wearing a collar during the first or second half of pregnancy: both groups were equal in gland development on the 22nd day and their glands were more developed than those of females wearing a collar throughout pregnancy. In animals that wore collars from the beginning of pregnancy, gland development was already retarded (28%) by mid-pregnancy. Rats whose glands were reduced in development during the first half of pregnancy showed less nipple-line licking during the second half of pregnancy. These findings indicate that stimulation provided by self-licking contributes significantly to mammary gland development during pregnancy and, therefore, the activity of the gland before parturition, like lactation post partum, is regulated in part by external stimulation.
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Pregnancy is associated with adaptive changes including increased number and size of beta cells and enhanced gap-junctional coupling among beta cells, increased glucose-induced insulin response and decreased glucose stimulation threshold. The role exerted by pregnancy steroids and lactogenic hormones in the development of islets upregulation during pregnancy has been widely investigated. In the present study we studied the possibility that pregnancy steroids induce functional modifications of beta cells involving the expression and function of glucokinase. Our results indicate that estradiol and progesterone do not influence significantly glucokinase mRNA expression, while they induce a dose-dependent and time-dependent increase of glucokinase activity in RIN 1046-38 cells. The increased enzymatic activity results in an increased glucose-induced insulin release. Therefore it is possible to hypothesize that pregnancy steroids influence glucokinase expression in beta cells at a post-transcriptional level and that this effect contributes to the development of hyperinsulinemia during pregnancy.
Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, USA
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Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, USA
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Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, USA
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Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, USA
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Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, USA
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Introduction To accommodate the increased demand for insulin during pregnancy, pancreatic islets of Langerhans undergo structural and functional changes leading to increased insulin release under normal glucose homeostasis ( Parsons
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During normal human pregnancy alterations in liver function similar to those seen in cholestasis occur (Tindall & Beazley, 1965; Haemmerli & Wyss, 1967). Adlercreutz & Tenhunen (1970) concluded that oestrogens were primarily responsible for this effect. In a previous report from this laboratory (Tikkanen, 1972) progressive changes, including decreasing proportions of OE3-3Gl† and increasing proportions of OE3-3S,16Gl†, in the urinary excretion of oestriol conjugates during pregnancy were noted, which were regarded as reflections of changes in the excretory function of the liver. Since a clear consistent change in urinary oestriol conjugate pattern was not observed in all the pregnancies studied, it appears that some women are more susceptible than others to this action of oestrogens on liver function. In multiple pregnancies Beazley & Tindall (1966) noted changes in the excretory function of the liver that were similar to but greater than those previously observed in singleton pregnancies. Accordingly, it might
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Reports on the fertility rate and the outcome of pregnancy in alloxan diabetic rats are conflicting. In part this is due to the differing conditions of the experiments, some authors having induced diabetes before pregnancy [Davis, Fugo & Lawrence, 1947], others after conception [Miller, 1947]. In general, observations have been limited to animals which had only recently been made diabetic, and, as such, are open to the objection that alloxan diabetes in its early stages may fluctuate markedly in severity. It therefore seemed of importance to study female rats with long-standing diabetes, particularly in respect to fertility rate and outcome of pregnancy. Human diabetic pregnancy results in delivery of large babies and a high late foetal and neonatal mortality. The outcome of pregnancy in the alloxan diabetic animal has therefore been studied particularly from these two aspects. The problem of high foetal loss has already been the subject of discussion
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. 2001 ). Enhanced vasodilator production is an important physiological endpoint to study in UAEC, because augmented vasodilator production is essential for normal pregnancy outcomes. Preeclampsia and intrauterine growth retardation are both associated
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1. The fertility and outcome of pregnancy have been studied in alloxan diabetic rats treated with insulin. The diabetes was only partly controlled, but the general condition of the diabetic mothers was good.
2. Fertility rate was increased compared with that in animals in which the diabetes was not treated with insulin. Stillbirth rate and neonatal death rate (5% combined loss) and the percentage of weaned animals (89%) were normal, as contrasted with a 37% combined stillbirth and neonatal mortality rate and 50% death-rate before weaning in the offspring of untreated diabetic mothers.
3. It is concluded that alloxan diabetes does not adversely affect the foetal mortality, neonatal death-rate or the feeding of young animals unless it impairs the general health of the mother.
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Using the intravaginal tetrazolium method of Martin (1964), the oestrogenic activity in plasma samples (5–10ml.) taken monthly from three sows during pregnancy has been estimated.
(1) 'Free' oestrogens were extracted from the plasma with ethyl acetate. This extract was passed through a florisil column to remove corticosteroids and oestriol (Saba, 1964a). The eluate, which would contain oestradiol, oestrone and progesterone, was evaporated to dryness. The dry residue was taken up in a mixture of benzene—petroleum ether (50:50, v/v) and the phenolic oestrogens were extracted with n-NaOH. This alkaline extract was acidified and extracted with ether (Saba, 1964b).
(2) 'Bound' oestrogen. After removal of the residual ethyl acetate, the plasma was hydrolysed in 1·5n-HCI (Preedy & Aitken, 1957) and extracted with ether as described above. The residue was partitioned between benzene—petroleum ether and NaOH as under (1).
The mean recovery of oestrone added to plasma
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SUMMARY
The plasma 17:21-dihydroxy-20-keto-corticosteroid levels in the cow in late pregnancy (33–0 days before calving) are only slightly higher than in the cow soon after calving (0–99 days). A larger rise was sometimes seen in the last few days before calving.
Except in one case where calving was difficult, no evidence of increased levels associated with the time of labour was found.
Higher levels in the first day or two after calving were seen in some cases, but subsequently levels were uniformly low—the difference from earlier levels being statistically significant (P=0·01).
In general, these results are in contrast with the human picture. Possible reasons for these findings are discussed.
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Little is known of the changes occurring in the liver during pregnancy and lactation. The ratios of liver weight and liver protein to body weight are increased in pregnant rats [Bokelmann & Scheringer, 1932], and more of the maternal protein is apportioned to the liver in pregnant rats than in non-pregnant controls [Poo, Lew & Addis, 1939; Poo, Lew, Lee & Addis, 1940]. The total nucleic acid content is considerably raised, both deoxyribonucleic and ribonucleic acids taking part [Davidson & Waymouth, 1944]. There is an increase of the ascorbic acid content of the livers of mice and rats during pregnancy [Kennaway & Kennaway, 1944; Kennaway & Tipler, 1947]. The arginase content of the liver of rats is normal during pregnancy but increased during lactation [Folley & Greenbaum, 1947].
Since during pregnancy and lactation the maternal organism has to provide the material for a very rapid protein synthesis, considerable changes in
