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SUMMARY

Ovarian follicles develop to the stage where they are competent to ovulate in response to exogenous gonadotrophin at the same rate during early pregnancy as in a normal 4-day cycle in the rat. The length of time during which this competency is retained appears to be shorter than after the blockade of ovulation by pentobarbitone administered at pro-oestrus in rats that are not pregnant. Evidence from oviduct:plasma (O:P) and uterus:plasma (U:P) ¹³¹I ratio measurements indicating high progesterone and low oestrogen levels at this stage of pregnancy may be relevant to this finding. Some evidence for a 3-day cycle of follicle development after day 6 of pregnancy was obtained but the high O:P ratios suggest that little oestrogen secretion is associated with this.

Oestradiol benzoate (6·25–100 μg.) administered after day 3 of pregnancy will induce ovulation when competent follicles are present. The thyroid:plasma (T:P) concentration ratio for 131I does not rise in association with ovulation induced by exogenous gonadotrophin. After oestrogen administration, the T:P ratio may increase regardless of whether ovulation is induced or not. The results are discussed in relation to the studies of other workers on the induction of ovulation during pregnancy and to earlier work on the relationship between ovulation and changes in thyroid gland activity.

ABSTRACT

The distribution of isomorphic forms of prolactin in the serum of pregnant women was studied by gel filtration chromatography. Using this technique we were able to resolve three peaks, detected by radioimmunoassay: they were termed 'big-big', 'big' and 'little' prolactin in order of decreasing size, with approximate molecular weights > 100 000, 50 000 and 21 000 respectively. They displayed a comparable immunoreactivity to the antiserum employed in the radioimmunoassay, as determined in competition experiments. The relative amount of each hormone form in serum changed during the third trimester of pregnancy. At week 33 of pregnancy, 'little' prolactin accounted for 63·2 ± 7·7% of the total circulating hormone present in the serum of five normal pregnant women. During the progression of pregnancy, there was a gradual increase in the low molecular weight prolactin, so that, at the time of delivery, the larger forms of the hormone were present only in small amounts.

J. Endocr. (1985) 106, 81–85

Mechanical stimulation of the uterus by means of bougies can promote uterine contractility at any time after mid-pregnancy. This principle is commonly used for mid-term abortion as well as for inducing full-term delivery in Japan (Manabe, 1969). Foetuses are normally delivered alive and the placentae are free from any notable histological damage during treatment. In an attempt to assess the possible endocrine control of the onset of labour by this method, the author reported that levels of urinary metabolites of oestrogen and progesterone did not change significantly before and during abortion (Manabe, 1968). The present study was designed to see whether placental progesterone synthesis was maintained at normal levels during bougie-induced abortion in mid-pregnancy. Progesterone levels in peripheral blood were serially estimated during the course of treatment.

Five normal women ranging from the 16th to 27th week of pregnancy were used in this study. One or two sterilized rubber bougies

ABSTRACT

Maternal plasma concentrations of immunoreactive endothelin (ir-ET) during pregnancy, labour and after birth were measured by radioimmunoassay. Concentrations of ir-ET in the umbilical artery, umbilical vein, amniotic fluid and neonatal urine were also examined.

The mean (± s.e.m.) plasma ir-ET concentration in early pregnancy (4–7 weeks) was 13·7±0·5 pmol/l, which was significantly higher than that in non-pregnant women (5·9±0·3 pmol/l). During pregnancy, plasma ir-ET concentrations gradually decreased to a minimum of 11·5±0·4 pmol/l in weeks 20–23, and then increased again towards term (12·5±0·4 pmol/l after 36 weeks of pregnancy). In women undergoing vaginal delivery, the mean plasma ir-ET concentration (17·1±0·7 pmol/l) increased significantly, compared with that in late pregnancy. After delivery, the plasma ir-ET concentration decreased abruptly to 4·0±0·2 pmol/l on the first day.

Plasma ir-ET concentrations in umbilical vessels were significantly higher than those in maternal plasma. In addition, concentrations in the umbilical artery were significantly higher than those in the umbilical vein in cases of vaginal delivery.

Concentrations of ir-ET in amniotic fluid were much higher than those in maternal or fetal plasma. ir-ET concentrations in neonatal urine on day 1 after birth were below the detection limit (< 0·1 pmol/l) by radioimmunoassay in 70% of the cases examined but on day 5 after birth ir-ET was present at measurable concentrations in all cases.

It is suggested that endothelin may act as a circulating hormone during pregnancy and labour in both maternal and fetal circulations.

Journal of Endocrinology (1991) 129, 301–307

ABSTRACT

Ovaries from pregnant and postpartum Sprague–Dawley rats were examined for content of immunoreactive β-endorphin by radioimmunoassay, and for its localization by the peroxidase-antiperoxidase technique. In addition, the molecular forms of β-endorphin immunoreactivity were separated by gel chromatography and reverse-phase high performance liquid chromatography (RP-HPLC). Ovaries from rats early in pregnancy showed intense granular cytoplasmic staining of luteal cells, with an even distribution of granular material throughout the cytoplasm. By middle to late pregnancy the staining pattern was changed, with immunoreactive material showing a less granular and unevenly distributed staining pattern and with some areas of the cytoplasm totally devoid of immunoreactive material. The concentrations of immunoreactive β-endorphin measured during pregnancy were significantly lower than levels in mature non-pregnant rat ovary. The ovarian concentration of immunoreactive β-endorphin fell progressively during pregnancy and early lactation, returning to normal cyclic rat levels at 20 days post partum. The ovarian concentration of β-endorphin-like material was lowest at 6 days post partum (0·53 ± 0·08 ng/g wet weight; mean ± s.e.m.), representing approximately 10% of the concentration found in pooled ovaries from randomly cyclic adult rats. Gel chromatography revealed only a single peak of immunoreactive β-endorphin, co-eluting with 3·5 kD molecular weight ovine β-endorphin(1–31). This contrasts with gel profiles of adult cyclic rat ovary, where large molecular weight species pro-opiomelanocortin (31 kD) and β-lipotrophin (11·5 kD) are also present. On RP-HPLC the predominant species of low molecular weight immunoreactive material co-eluted with β-endorphin(1–31).

These data show that pregnancy in the rat is associated with marked changes in the levels, cellular localization and chromatographic profiles of ovarian β-endorphin. The aetiology and physiological significance of these changes remains to be established.

J. Endocr. (1986) 108, 343–350

SUMMARY

The association between duration of gestation and (a) parental height, and (b) mother's parity is examined in 1028 single and 375 twin maternities. With increasing height of mother, duration of gestation increases in multiple pregnancy; the two variables are unrelated in single pregnancy. With increasing parity, duration of gestation increases in multiple pregnancy and decreases slightly in single pregnancy. It is suggested that these observations provide support for the view that the early onset of labour in multiple pregnancy may be due to the size of the foetuses.

Department of Physiology, Faculty of Medicine, University of Manitoba, 770 Bannatyne Avenue, Winnipeg, Canada, R3E 0W3

(Received 7 April 1977)

Binding of prolactin to the rat mammary gland is low during pregnancy and only increases at parturition (Holcomb, Costlow, Bushchow & McGuire, 1976). Holcomb et al. (1976) have suggested that failure to demonstrate binding of prolactin may be related to occupancy of the prolactin receptor by placental lactogen. However, the rabbit apparently does not produce a placental lactogen (Kelly, Tsushima, Shiu & Friesen, 1976; McNeilly & Friesen, 1977), and it was therefore of considerable interest to determine whether the results of binding of prolactin to the rabbit mammary gland during pregnancy showed significant differences from those obtained in the rat.

Mammary glands were taken from pregnant New Zealand White rabbits killed by an i.v. overdose of sodium pentobarbitone on each of days 10, 15, 20, 25, 28, 29, 30 and

SUMMARY

Adrenal and plasma corticosterone levels were determined in rat foetuses and in intact or adrenalectomized mothers during late pregnancy. Foetal adrenal and plasma corticosterone concentrations reached a peak on day 19 of pregnancy, while maternal plasma corticosterone increased on day 18 and remained high until parturition. From day 18, mothers adrenalectomized on day 14 had corticosterone levels similar to those of intact pregnant rats. At every stage of gestation (except day 21) plasma corticosterone levels were higher in the foetuses than in the mothers. The corticosterone concentration in the maternal plasma correlated with the number of live foetuses during the last 3 days of gestation.

These results suggest that corticosterone can cross the placenta from foetus to mother as early as day 18 and that the foetus contributes to the maternal corticosterone pool after day 18.

Institute of Obstetrics and Gynaecology, Queen Charlotte's Hospital, Goldhawk Road, London, W6 OXG

(Received 4 September 1974)

It is well established that the rise in total plasma cortisol which follows the administration of corticotrophin (ACTH) or tetracosactrin is greater in late pregnancy than in non-pregnant women (Jailer, Christy, Longson, Wallace & Gordon, 1959; Campbell, Bain, Dewhurst & Fotherby, 1970; Johnstone & Campbell, 1974). However, it is not clear whether this can be completely explained by the increased corticosteroidbinding globulin levels in pregnancy (Doe, Fernandez & Seal, 1964; De Moor, Steeno, Brosens & Hendrikx, 1966) or whether there is a true rise in tissue exposure to unbound cortisol. In non-pregnant subjects, 1·0 mg depot tetracosactrin (Ciba) appears to give a maximal adrenal stimulus, at least over the first 4 h (Besser, Butler & Plumpton, 1967; Nelson, Neill, Montgomery, Mackay, Sheridan & Weaver, 1968), and we have described the total 11-hydroxycorticosteroid patterns