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Contents The oxytocin receptor (OTR) plays a central role in the functioning of the reproductive tract in the female ruminant. During the oestrous cycle endometrial OTR is suppressed through most of the cycle, probably in a progesterone-dependent manner, to be massively up-regulated during the few days before and after oestrus. At this time, luteal OT triggers a positive feedback loop, the endometrial OTR mediating the release of luteolytic PGF2α which feeds back to the corpus luteum to cause the secretion of more OT and to induce luteolysis. This feedback is only interrupted if a newly formed blastocyst is present. Ruminant blastocysts secrete the cytokine interferon-τ, which interacts directly with the endometrial epithelial cells, preventing the up-regulation of OTR in late luteal phase. During early pregnancy the levels of OTR in endometrium remain very low whereas myometrial OTR are less affected. OTR in endometrium are up-regulated around day 50 and then progressively increase to reach a maximum at the onset of labour; those in the myometrium are upregulated somewhat later in gestation, around day 100. The OTR in the cervix are differently regulated: their concentrations are very low through most of the cycle and gestation and do not increase until pro-oestrus and at parturition when they abruptly rise to high values. Ligand binding to the mucosal and endometrial OTR causes specific release of prostaglandins, which in turn activate paracrine pathways in the surrounding tissues to induce softening of the connective tissue of the uterine wall during pregnancy, and of the cervix at term. Additionally, local uterine contractions induced by OT and potentiated by prostaglandins may serve a physiological function during pregnancy by improving uterine blood flow. Due to the appearance of gap junctions in myometrium at term the OT-induced contractions become synchronized and well propagated and because of concomitant cervical softening the contractions become expulsive. Although OTR-dependent physiology correlates well with the levels of circulating gonadal steroids, there is no evidence for any direct effect of steroids either on the OTR gene or OTR protein. Instead, progesterone appears to exert an indirect inhibitory effect on the OTR gene, probably mediated via other cell types. This is in contrast to the inhibition by interferon-τ which appears to activate a pathway which directly suppresses the OTR gene expression. The important role of OTR in female uterine physiology, and its value as an indicator molecule, make it imperative to understand the complex molecular mechanisms underlying its regulation. These are likely to be of fundamental importance for many aspects of uterine function both in ruminants and in other species, including the human.

Summary. The concentrations of 13,14-dihydro-15-keto-prostaglandin F2α (PGFM) and oxytocin were measured by radioimmunoassay in the peripheral plasma of 21 women with low Bishop scores in whom cervical ripening and labour were induced with a cervical cap containing 1.5 mg of prostaglandin (PG) E2, left in place for 6 h. Blood samples were taken before and at 3, 6, 9 and 24 h after the cap was applied. Four women (control group) had a cap without PGE2. Labour began in 13 women receiving PGE2, 12 of whom were delivered within 24 h. In these women plasma PGFM rose progressively to levels seen during spontaneous labour, paralleling the changes in cervical dilatation. The increase became significant at 6 h, when cervical dilatation was 4.5 cm (SEM 0.5). Plasma oxytocin also increased significantly while the cap was in place and then decreased. Plasma PGFM and oxytocin did not change in the control subjects, and in the eight women needing further induction of labour the initial rises were transient and not statistically significant.

Summary. Determinations of the various phosphorus fractious in the guinea pig placenta in a series of experiments on the placental transfer of phosphate have shown that the orthophosphate concentration is very high in the placental tissue as compared with the maternal and foetal plasma. The concentration increases slowly from the 29th to the 59th day of gestation and may decrease thereafter. Thirty minutes after intravenous injection of radioactive phosphate into the mother the orthophosphate in the placenta has reached a specific activity of one third of that of the inorganic phosphate in the maternal plasma. It has the highest specific activity of the placental phosphorus fractions. Adenosine diphosphate and triphosphate are found in approximately the same concentrations as in the uterine muscle during pregnancy in the rat, the rabbit and the human. The labile phosphorus of these compounds is in equilibrium with the orthophosphate with regard to radioactive phosphorus. Glucose-1-phosphate is present in a low concentration, but it acquires a high relative specific activity. More glucose-6-phosphate is present, but with a low relative specific activity. The inorganic phosphate in the foetal plasma obtains in thirty minutes a specific activity of about half that of the placental orthophosphate.

Summary. In a study of the placental transfer of phosphorus in the guniea pig the transfer of inorganic phosphate from foetus to mother has been investigated in the last part of gestation with the aid of radioactive phosphorus. The quantity transferred in this direction across the placenta is approximately 25 % of the amount which is transmitted from mother to foetus at the same stage of gestation. The amount transferred from mother to foetus is about equal to the amount retained in foetal growth plus the amount returned to the mother. The return of phosphate from foetus to mother is facilitated by the concentration gradient from the foetal to the maternal plasma.

Summary The effect of ethanol on the response of the human uterus to oxytocin and vasopressin was studied in 11 women during the menstrual cycle. In 4 cases, the response was enhanced and in 5 it was unchanged. In 2 subjects the response after ethanol was reduced, but no more than was seen with successive doses of oxytocin and vasopressin without ethanol. It is concluded that ethanol, in doses giving blood concentrations up to 0·18 per cent, does not inhibit the response of the nonpregnant uterus to the neurohypophysial hormones.