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The distribution of cell division in the tissues of the mouse uterus changes in a characteristic manner during the first few days of pregnancy due to changes in the secretion of ovarian hormones. Pregnant mice were ovariectomized at various times and attempts made to reproduce the pattern of cell division with exogenous hormones. The schedule of hormone injections producing a pattern of uterine mitoses which most closely approached that of pregnancy suggested that secretion of both oestrogen and progesterone started about 48 hours after mating and continued, possibly increasing, until after implantation had started. This conflicts with the oestrogen surge hypothesis. Further experiments were carried out to determine the optimum hormone treatment schedules for sensitivity to induction of the oil decidual cell reaction. Multiple small doses of oestradiol allowed the production of greater deciduomas than a single dose, thus again suggesting that the oestrogen surge hypothesis may not be correct.

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In a recent study of renal function in supposedly pregnant rabbits, much time and effort was wasted because about half the mated females failed to become pregnant. On retrospective analysis, the daily sodium excretion was different in the animals which became pregnant as compared with those which failed to become pregnant and which were presumably pseudopregnant. The main difference was apparent on day 4 after mating. We are now using sodium excretion as a simple diagnostic test of pregnancy in rabbits.

Fifteen animals were kept in metabolism cages for 20 days before mating and for the duration of the supposed pregnancy. Only eight of the 15 actually became pregnant. All the urine excreted by each animal each day was collected, its volume measured and its sodium concentration estimated by flame photometry. For each animal the mean daily excretion during the 20-day control period was defined as 100%. Figure 1 shows

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Most studies on the relationship between the pineal gland and reproductive function have been concerned with the effects of pinealectomy or pineal extracts on reproduction (for review see Kitay & Altschule, 1954), but the effects of the state of the reproductive system on the pineal gland have been little investigated. The effects of castration have been studied by Borell & Örström (1947) and Quay & Levine (1957), and the effects of sex hormone administration by Brewer & Quay (1958). However, no studies seem to have been made of the pineal body during pregnancy in the rat.

Fifty female rats, aged 3 months, were mated with males of similar age and thirty-eight became pregnant. The 1st day of pregnancy was defined as the 1st day on which sperms were found in vaginal smears, or vaginal plugs were seen. Twenty-five female rats of the same age and similar body weight served as

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Miller, Owen & Emmens (1968) described the changes in uridine incorporation into uterine and vaginal RNA during early pregnancy and pseudopregnancy in the mouse and discussed their significance. A large increase in uridine incorporation occurred in the uteri in both conditions between 10.30 hr. on day 2 and 10.30 hr. on day 3, with a further increase from day 4 onwards only in the uteri of pregnant mice. The former increase is in both cases believed to reflect increasing ovarian oestrogen secretion, a conclusion supported by the studies of Finn & Martin (1967), Martin & Finn (1968) and Galassi (1968). In view of the widely held belief in a discrete surge of ovarian oestrogen on day 4 of pregnancy in the rat (Tic, Marcus & Shelesnyak, 1967) it was considered desirable to study the corresponding changes in this species.

Randomly bred female rats of the Wistar strain, weighing 200–280 g.,

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LL Anderson, DL Hard, LS Carpenter, EK Awotwi, MA Diekman, AH Trenkle, and J Cho

Progesterone secretion is crucial for maintaining pregnancy to parturition in mammalian species, and in cattle the corpus luteum is the primary source of this hormone. This study determined the roles of prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) in the luteotropic process in beef heifers hypophyseal stalk-transected (HST, n=7) or sham operated (sham operated controls, SOC, n=9) during midgestation. The main finding was that endogenous PRL and GH maintained progesterone secretion in HST heifers in a similar manner to that in SOC throughout pregnancy. Serum PRL averaged 37 vs 187 and GH 2 vs 4 ng/ml in HST heifers compared with SOC, whereas LH abruptly decreased to undetectable levels after HST compared with a modest 0.4 ng/ml in SOC heifers. The second finding was that parturition and lactation occurred in HST heifers with calf delivery induced to occur at the same time as SOC. Milk production in HST animals was severely limited, and postpartum estrus obliterated compared with SOC. The suckling stimulus sustained milk ejection in HST heifers in spite of diminished PRL, GH, thyroid stimulating hormone, thyroxine and tri-iodothyronine secretion. The results suggest that PRL, GH and possibly placental lactogen are luteotropic during pregnancy in cattle.

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The urinary excretion of 17-hydroxycorticosteroids (17-OH CS) and of one of their subgroups—the 21-deoxyketols (17-hydroxy-20-oxopregnanes)—has been measured in the course (5th to 10th lunar month) of human pregnancy. In twenty-six cases with a normal course of pregnancy the average excretion of 17-OH CS rose slowly to values 40% above the normal average. An additional sharp increase occurred following parturition, but 1 day later the urinary levels returned to normal. The average excretion of 21-deoxyketols rose more steeply to values 800% above the normal average and returned to normal 2 days after delivery.

Following intrauterine death (five cases) the excretion of 17-OH CS and of 21-deoxyketols returned to normal values. No such drastic change was found in three cases of stillbirth and in four cases of toxaemia.

The significance of these findings is discussed. It is suggested that in pregnancy (i) the urinary excretion of the main metabolites of cortisol is essentially unchanged, while the excretion of 21-deoxycorticosteroids of unknown origin is greatly increased; (ii) 21-deoxyketols are unlikely to derive from cortisol; (iii) the high plasma levels of cortisol indicate that the compound is metabolized at a reduced rate rather than that the activity of the adrenal cortex is enhanced.

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G Kovalevskaya, S Birken, T Kakuma, and JF O'Connor

Human chorionic gonadotropin (hCG) exhibits molecular heterogeneity in both its protein and carbohydrate moieties. This communication describes changes in hCG isoforms detected directly in clinical samples. These isoforms, quantified in blood or urine specimens, show a progression of change throughout normal pregnancy. Early pregnancy produces a type of hCG that resembles, in terms of immunoreactivity, a major form of hCG excreted in choriocarcinoma. The isoforms predominate for the first 5-6 weeks of gestation and then diminish, being replaced with the hCG isoforms which predominate throughout the remainder of pregnancy. The alteration in hCG isoform content occurs in both blood and urine. The progression of isoforms is best delineated by calculating the change in the ratio of the two forms, as many hCG assays either do not detect or fail to discriminate among these isoforms. An analogous pattern of hCG isoforms was observed in patients with in vitro fertilization pregnancies. hCG isolated from the pituitary displayed binding characteristics similar to those of the hCG derived from normal pregnancy urine. The early pregnancy hCG isoforms appear to have a differential expression in normal pregnancy as opposed to pregnancies which will not carry to term, suggesting that a determination of the relative balance of hCG isoforms may have diagnostic application in predicting pregnancy outcome.

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1. Observations on foetal growth in human pregnancy are recorded on 22,454 single, 325 twin, 249 triplet and 27 quadruplet maternities.

2. Mean birth weights of singletons, twins, triplets and quadruplets are respectively 7·43, 5·27, 4·00 and 3·07 lb.

3. For single, twin, triplet and quadruplet pregnancies, mean durations of gestation (in days) are 280·5, 261·6, 246·8 and 236·8.

4. Mean birth weight is greater for small than for large litters even when comparison is restricted to births delivered after the same period of gestation (see Table 4).

5. It is suggested that these observations, which are in accord with reports on experimental animals, raise two questions: (a) why is foetal growth retarded in multiple pregnancy during the last weeks of gestation? and (b) why is onset of labour earlier in multiple than in single pregnancy?

6. In consideration of 5 (a) it is shown that:

(i) Mean foetal weight appears to be independent of litter size until about the 27th week of gestation.

(ii) The rate of growth of multiple foetuses is slower than that of single foetuses from a stage of gestation which varies with size of litter as follows: quadruplets from about 26 weeks; triplets from 27 weeks; and twins from 30 weeks. In the case of singletons, foetal growth is linear between 30 and 36 weeks; after 36 weeks the rate of growth is reduced.

(iii) At the times from which the respective rates of foetal growth are retarded, mean litter weights of twins, triplets and quadruplets are approximately the same. These mean litter weights (in lb.) are: quadruplets at 26 weeks, 7·6; triplets at 27 weeks, 6·9; twins at 30 weeks, 6·9. The mean weight of single births at 36 weeks is 6·5 lb.

(iv) From the time that foetal growth is retarded, litter weight increment is approximately the same for every size of litter.

Support is provided for the view that (a) retardation of foetal growth in large litters is attributable, at least in part, to crowding in the uterus (see Table 6); and (b) the restriction on foetal growth in the crowded uterus may be imposed by the placenta (see Table 7).

7. In consideration of 5 (b) it is shown that mean litter weights of singletons, twins, triplets and quadruplets at birth are respectively 7·43, 10·53, 12·00 and 12·28 lb. It is suggested that these observations are not inconsistent with the view that the early onset of labour in multiple pregnancy is due to distension of the uterus, if we suppose that the amount of distension which the uterus will tolerate during the last weeks of gestation decreases as pregnancy advances.

8. Mean litter weights of multiple births increase with birth order.

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T Walther and H Stepan

C-type natriuretic peptide (CNP) belongs to the natriuretic peptide family that consists of three structurally related peptides with a 17-amino acid ring linked by a disulfide bond. In contrast to atrial and brain natriuretic peptides that are mainly cardiovascular hormones, CNP acts predominantly in an autocrine/paracrine fashion, is commonly considered to be an endothelial hormone with antimitogenic properties, and is characterized as a regulator of endochondral ossification. Its biological effects are mediated by an intracellular cGMP accumulation via specific membrane-bound guanylyl cyclase B (GC-B) activation. There is growing evidence that this peptide is also involved in various reproductive processes as well as in embryonic and fetal development. In rodents, CNP and its receptor are highly expressed in the uterus and ovaries with specific regulation during the estrous cycle. During pregnancy, CNP mRNA is detectable in mice embryos and shows an organ-specific expression in maternal reproductive tIssues with the highest concentration in the placenta. This could indicate a defined biological function of the CNP/GC-B/cGMP axis in gestation e.g. antagonizing vasoconstrictive peptides like angiotensin II. In humans, besides a postulated fetal de novo synthesis of CNP, both the peptide and its receptor are expressed in the placenta and myometrium with opposite regulation of CNP in pregnancies complicated by pre-eclampsia or intrauterine growth retardation. Since the maternal plasma levels do not reflect these alterations, one can conclude that this part of the natriuretic peptide system acts locally suggesting that CNP-stimulated cGMP release exhibits organ-specific effects. Importantly, CNP has also become a peptide with a distinct role in male reproductive processes, since endocrine function of the testis and the regulation of penile erection are regulated by the CNP/GC-B axis. This review gives a comprehensive overview of the multiple functions of CNP in reproduction and pregnancy as well as in embryonic and fetal development.

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Maria E C Amaral, Daniel A Cunha, Gabriel F Anhê, Mirian Ueno, Everardo M Carneiro, Lício A Velloso, Silvana Bordin, and Antonio C Boschero

Introduction The growth and differentiation of the endocrine pancreas during the perinatal period and pregnancy are controlled by many factors, including a variety of hormonal, chemical and neural signals to the islets. Of these