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SUMMARY
Either one or two 60-h morulae were transferred to one uterine horn of Polish, Dutch or Strain A rabbits in which the mean number of ovulations was 4·3, 6·4 and 10·8. The pregnancy rate, as determined by palpation on day 10, varied from 45–65% (mean 53%) in recipients of one egg to 69–71% with two eggs. Only 20% of the does carrying one foetus maintained pregnancy to term compared with 87% of those with two implants. If pregnancy failed this usually occurred between days 15 and 20. In a further experiment, in which additional eggs were transferred to the contralateral horn, it was shown that all single conceptuses were inherently capable of surviving to term.
It is concluded that irrespective of breed and ovulation rate, two conceptuses are normally required to prevent regression of corpora lutea on about day 17. Treatment with follicle-stimulating hormone in mid-pregnancy or removal of the barren uterine horn on day 13 failed to maintain pregnancies involving only one conceptus.
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SUMMARY
The concentration of ovine placental lactogen (oPL) was measured by radioimmunoassay in plasma samples from chronically catheterized ewes and their fetuses from day 110 of gestation to term (about day 145).
Concentrations of oPL in the plasma of the mother and fetus were raised after surgery, and remained raised for 3–5 days after the operation. Concentrations of oPL were greatest in the fetus at days 120–124 of gestation, and then declined until delivery. Mean concentrations of oPL in the fetus in late pregnancy for single, twin and triplet pregnancies were 101±6 (s.e.m.), 100±11 and 117±59 ng/ml respectively and were not significantly different.
Mean concentrations of oPL in the mother in late pregnancy for single, twin and triplet pregnancies were 718±227, 1387±160 and 1510±459 ng/ml respectively; the difference between these means was significant (P <0·05). Peak concentrations were noted at days 130–139 of gestation after which concentrations fell and were significantly lower on the day of delivery (P <0·01). Concentrations of oPL in the mother showed no circadian rhythm. The mean concentrations of oPL in maternal plasma during late pregnancy was significantly correlated to the combined fetal weight at birth (r = 0·624, P <0·01).
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Adrenal cells were prepared from non-pregnant (anoestrous) sheep, from ewes at days 50, 100 and 130 of pregnancy and at term, and from animals at 1–5 days post partum. The ability of the cells to respond to adrenocorticotrophin (ACTH1–24), α-melanocyte-stimulating hormone (α-MSH), or combinations of these peptides has been examined in vitro. There was a progressive rise in the basal output of cortisol during pregnancy and in the absence of adrenocorticotrophin the cortisol output from adrenal cells of late pregnant and post-partum sheep was significantly greater than that from the non-pregnant animals. Adrenocorticotrophin increased cortisol output by adrenal cells at all times tested. In anoestrous sheep the amount of ACTH required to produce half the maximum output of steroid (ED50) was 8 pg/ml. The ED50 increased in early pregnancy to 112 pg/ml and then fell to < 5 pg/ml between day 100 and term. At term both the stimulation ratio and the absolute increment in cortisol output elicited by a maximal concentration of ACTH were greater than at any other time tested in pregnant or non-pregnant sheep. Cortisol output during pregnancy was not increased by α-MSH, although at term the stimulatory effect of ACTH1–24 was partially antagonized by α-MSH.
These results suggest that there may be an increase in the responsiveness of the maternal adrenal during pregnancy, although the factor(s) responsible remains unknown.
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ABSTRACT
To study the potential role of GH-releasing hormone (GHRH) in maintaining circulating levels of GH during pregnancy, 302 maternal plasma samples were collected from non-fasted subjects at various stages of pregnancy and assayed for GHRH using a 'two-site' immunoradiometric assay. The GH and placental lactogen levels were also determined. In addition, maternal plasma samples taken during labour, amniotic fluid and cord blood were also assayed for these hormones.
Maternal plasma GHRH levels were similar to non-pregnant levels throughout gestation despite fluctuations in GH values which were always higher than non-pregnant levels. There was no significant difference between GHRH levels in maternal plasma and cord blood although high GH levels were observed in the latter. These findings suggest that peripheral GHRH levels do not play an important role in maintaining circulating GH levels during pregnancy.
Journal of Endocrinology (1990) 125, 161–167
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Search for other papers by JUNE EAST in
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SUMMARY
In many rodents, including the rat and the mouse, implantation of the fertilized ovum fails to take place at the normal time if the female is lactating. The delay in implantation tends to be longer the larger the litter suckling, and pregnancy may be prolonged for several days. Observations carried out on normal mice showed that when pregnancy was of normal length in spite of a large suckling litter many of the young were stillborn and there was a reduction in litter size. The stillbirth rate of litters carried during a concurrent lactation was within normal limits only when the delay in implantation was at least 4 days.
Litter size at birth from delayed pregnancies was normal.
Lactation was unaffected by the presence of a second litter in utero.
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In spite of the importance of prolactin and adrenal corticosteroids in the normal control of the mammary gland (Cowie & Tindal, 1971) there has been no report of their simultaneous measurement in rat plasma during pregnancy and lactation. There is no agreement on the pattern of change in corticosteroid concentration at the time of lactogenesis and parturition (Gala & Westphal, 1965; Kuhn, 1969).
Primiparous CFE strain rats, allotted randomly to groups on day 0 of pregnancy, were decapitated without prior disturbance within 1 min after removal from their cage, between 08.30 and 09.30 h. Plasma was stored at −20 °C, total body weight after bleeding and adrenal weight were recorded. The day on which a vaginal plug was found and the day of parturition were designated day 0 of pregnancy and lactation respectively. Litter size was adjusted to six on day 0 of lactation.
Plasma prolactin concentration was assayed in
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SUMMARY
The concentration of progesterone and oestradiol-17β in peripheral plasma was determined by radioimmunoassay on each day of pregnancy in the mouse. The progesterone concentration, low on days 1 and 2, correlated with the histological development of the corpora lutea. Progesterone levels during the first half of pregnancy rose to a peak on day 6 with a significant decrease (P < 0·02) on day 7. Peripheral progesterone concentration during the second half of pregnancy rose on days 12–13 with a peak on days 14–17, and declined after day 17, 3 days before the onset of parturition.
Oestradiol-17β concentrations were high on day 1, declined precipitously to low levels on days 2 and 3 recovering slightly on day 4. The levels then fell and remained low from day 5 to days 15–16, when there was a significant increase in oestradiol-17β concentration which continued until day 20.
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In the previous report [Hain, 1940], with a view to examining hormone changes associated with the birth mechanism, the author investigated the output of pregnanediol and of the two combined oestrogens in women approaching parturition and also in one woman throughout the whole of a normal pregnancy. The larger series comprised both normal and toxaemic patients, none of whom received therapy; in no instance was the amount of free oestrogen excreted estimated.
The present series investigates the problem of pregnancy and parturition from a different angle, in that it seeks to ascertain the hormone output associated with abortion. The series consists of women with histories of previous miscarriage or showing signs of threatened abortion in the pregnancy investigated, and falls into two parts: the first consisting of five women in whom both the oestrogen and the pregnanediol outputs were ascertained at very frequent intervals, and the second of over 100
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SUMMARY
Uterine alkaline phosphatase and β-glucuronidase activity were assayed during the first 8 days of pregnancy in rats after unilateral tubal ligation and section. The results were as follows. Alkaline phosphatase increased in the pregnant horn from days 5 to 8 while the activity of the nonpregnant horn remained unaltered. This enhanced phosphatase activity was localized exclusively at the implantation sites. β-Glucuronidase steadily decreased during the first 8 days of pregnancy in both the gravid and non-gravid horns. The occurrence of a 'peak' in β-glucuronidase activity during the oestrogen surge on day 4 of pregnancy reported previously by Prahlad (1962) was not observed.
The results are discussed in relation to an interaction between the implanting blastocyst and the hormonally conditioned uterus.
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