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PubMed1981

Plasma concentrations of oestrone, progesterone and corticosteroids during late pregnancy and after parturition in the harbour seal, Phoca vitulina.

Blood samples were taken at weekly intervals during the last 2 months of pregnancy from a mature (7-year-old) harbour seal which had conceived and was kept in captivity. The concentrations of oestrone, oestrone sulphate, progesterone and glucocorticoids were determined by radioassays. The plasma levels of unconjugated oestrone were slightly greater than those of oestrone sulphate. Total oestrone declined steadily over the last month from a peak of 2.3 ng/ml at 30 days before parturition. Plasma progesterone concentrations rose to 61 ng/ml at 2 weeks before parturition and fell to about half that value by 2 days before birth of a normal male pup. Plasma glucocorticosteroids reached a peak of 164 ng/ml, also at 2 weeks, but showed only a slight decline thereafter. A higher value (392 ng/ml) was recorded 5 days after parturition.

Animals↗

PubMed1982

Myoelectrical changes in the uterus of the sheep around parturition.

Myoelectrical activity in the uterus of late-pregnant sheep was recorded by the chronic implantation of bipolar electrodes in the myometrium. Three distinct patterns of electrical activity were recognizable: irregular trains of action potentials (greater than 120 sec), long spike bursts (7--120 sec), or short spike bursts (less than 7 sec) each exhibiting high (greater than 100 muV) or low (50--100 muV) amplitude. The duration of spike activity was expressed as the myoelectrical index (MI), i.e. the fraction of the hour during which a given category of activity is exhibited. The increase in the overall MI which represents daily average values regardless of the class of amplitude from 72 h pre partum up to parturition was significantly (P less than 0.05) more pronounced in the uterine horn than in the body of the uterus. During the last 6--7 days of gestation high-amplitude irregular trains and long spike bursts were significantly (P less than 0.05) more frequent than these activity patterns with low amplitude. Regardless of the amplitude, the incidence of irregular trains began to decline rapidly 48 h pre partum with an abrupt cessation following parturition. The frequency of long spike bursts increased 72 h pre partum to reach a maximum which coincided with parturition.

Action Potentials↗

PubMed1984

Effects of progesterone on parturition in the tammar, Macropus eugenii.

Tammar wallabies were treated with progesterone injections or implants during late pregnancy to determine whether progesterone withdrawal was essential for parturition. Neither physiological (implanted group) nor pharmacological (injected group) levels of circulating progesterone prevented parturition occurring at about the expected time in about two-thirds of animals that were pregnant. The neonates of both groups were normal in size and weight, but about a third of treated pregnant animals retained their fetuses or aborted. The retained fetuses were retarded in development. Therefore, progesterone treatment had no influence on the duration of gestation, or parturition, in the tammar wallaby, but high progesterone concentrations may interfere with the normal course of development and birth in a proportion of treated animals.

Animals↗

PubMed1984

Oestradiol in follicular fluid and in utero-ovarian venous and peripheral plasma during parturition and postpartum oestrus in the tammar, Macropus eugenii.

Oestradiol-17 beta was measured in plasma and follicular fluid by a radioimmunoassay validated for the tammar. Plasma was sampled from the peripheral circulation and both utero-ovarian veins to assess the contribution of oestradiol from the corpus luteum in one ovary and from the Graafian follicle in the other during late pregnancy, parturition, post-partum oestrus and ovulation. Concentrations of oestradiol in the peripheral plasma and in the vein draining the CL remained less than 5 pg/ml on all days except the day of parturition, when they were 12.7 pg/ml and 14.3 pg/ml respectively. Mean oestradiol concentration in the vein draining the Graafian follicle was significantly higher than the mean peripheral concentration on Days 24-27. The highest average concentration (36.5 pg/ml) occurred on Day 27 coincident with parturition and before oestrus. These latter concentrations were significantly correlated with the concentration and total oestradiol in the fluid of the preovulatory Graafian follicle (r = 0.73 and r = 0.82 respectively), thus providing strong evidence that the Graafian follicle is the main source of oestradiol in the peripheral circulation at this time.

Animals↗

PubMed1986

Evidence for a noradrenergic transmission in the control of parturition in the rat.

6-Hydroxydopamine, when injected at 14:00 h on Days 21 and 22 of pregnancy in the rat (2 X 50 mg/kg), markedly decreased plasma and uterine noradrenaline concentrations (-60% and -82% respectively; P less than 0.001). As a consequence of this treatment, there was severe disturbance in the distribution pattern of parturitions: 61% of rats had suppressed parturition and 31% of rats displayed a lengthened or interrupted labour. A bolus dose of prazosin (3 mg/kg) administered at 12:00 h on Day 22 completely blocked the normal process of parturition throughout the next 6 h, a result which is compatible with the half-life of the drug (2.9 +/- 0.8 h). Administration of phentolamine (3 mg/kg) at term induced a significant decrease of uterine activity (frequency X duration of bursts of spike potentials) as revealed by electromyographic recordings in vivo. These results suggest that noradrenaline released from sympathetic nerve terminals interacts with alpha-adrenoceptors located post-synaptically to improve the overall excitability of the myometrium at the onset of labour.

Animals↗

PubMed1988

Fetal role in the control of parturition in the tammar, Macropus eugenii.

When female tammars carrying dormant blastocysts were injected with progesterone at the time of removal of their pouch young the development of the fetus was advanced and parturition occurred 5 days earlier than in the control tammars. In these tammars the prolactin pulse was also advanced by 5 days but the usually concomitant fall in progesterone was not. In non-pregnant tammars similar injections of progesterone did not advance the subsequent fall in progesterone, oestrus, or the LH pulse. In non-pregnant tammars injected with ovine prolactin on Day 26, to mimic the prolactin pulse, plasma progesterone was reduced to basal levels within 12 h, significantly earlier than in controls. Conversely, in 5 pregnant and 1 non-pregnant tammar injected with ovine prolactin on Day 23, to mimic the condition induced by advancing the time of parturition with progesterone, the decline in plasma progesterone was not advanced and the endogenous prolactin pulse, parturition, post-partum ovulation and the LH pulse all occurred after intervals similar to those of controls. The results support the view that the fetus is associated with the pre-partum prolactin pulse in maternal plasma and that a prolactin pulse at this stage is luteolytic in non-pregnant tammars.

Animals↗

PubMed1990

Beta-endorphin and met-enkephalin in plasma of cattle during pregnancy, parturition and the neonatal period.

Plasma concentrations of beta-endorphin and met-enkephalin were measured, with appropriate radioimmunoassays, in cows during gestation and at parturition and in newborn calves. During pregnancy beta-endorphin immunoreactivity (IR) concentration increased, but values during the last month of gestation were not different from those at parturition. Highest met-enkephalin IR levels were obtained in cows during calving. A term Caesarean section caused an increase in plasma beta-endorphin and met-enkephalin IR concentrations, but no such increase occurred in cases of a preterm Caesarean section. In calves beta-endorphin IR values were lower before umbilical cord rupture than immediately after birth. Values decreased continuously thereafter. This was also the case for met-enkephalin IR concentrations in calves born at term. In preterm calves met-enkephalin IR values were low immediately after delivery and increased during the first hour of life. A significant correlation existed between the degree of acidosis and plasma levels of both opioid peptides in the calves. We conclude that a direct stimulation of peripheral beta-endorphin release by the pain or stress associated with calving does not seem to exist in cattle, whereas met-enkephalin seems to be more directly related to parturition. In calves the change to the extrauterine environment causes an immediate, increased release of both opioids.

Animals↗

PubMed1991

Pituitary and ovarian responses to luteinizing-hormone-releasing hormone during pregnancy and after parturition in brown hares (Lepus europaeus).

Female hares were given an i.v. injection of 5 micrograms luteinizing-hormone-releasing hormone (LHRH) between Days 7 and 19 (n = 21), 20 and 33 (n = 17) and 34 and 41 (n = 17) of pregnancy, and in the 3 days after parturition (n = 16). Whatever the stage of pregnancy, the LHRH injection induced a release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and an acute secretion of progesterone; these hormonal responses increased significantly during pregnancy, to reach values similar to those observed in nonpregnant, nonpseudopregnant females during the breeding season in the 3 days after parturition. However, the release of LH remained monophasic in pregnant and post-partum females, in contrast to the unmated females during the reproductive season, in which there was a biphasic profile. The proportion of ovulating females after LHRH treatment was approximately 60% at the beginning and end of pregnancy; and, after parturition, fell to 23% between Days 20 and 33. After Day 33, the pituitary response to LHRH was significantly higher in ovulating than in nonovulating females. At the beginning of pregnancy, 67% of females aborted after LHRH injection; after Day 20, the incidence of abortion decreased significantly and was 0% from Day 34. The amplitude and duration of progesterone secretion by the new corpora lutea resulting from ovulation after LHRH injection were similar to those of corpora lutea induced in nonpregnant females during the breeding season.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Oxygen consumption and evaporation during parturition in a vespertilionid bat (Pipistrellus pipistrellus).

Oxygen consumption and evaporation were measured in a single pregnant pipistrelle bat during labour and parturition of twins, using an open-flow respirometry system. During 233 min of measurements, three distinct phases were noted, which we suggest represent prelabour, labour and grooming or suckling the young. On the basis of this hypothesis, during labour and parturition, oxygen consumption was a maximum of 8.9% of daily energy expenditure, evaporation was 2.7% of daily water turnover, and total water loss was 5.5% of daily water turnover in free-living bats in early lactation. We estimated that, for the mother and young combined, oxygen consumption associated with grooming and suckling would be equivalent to 37.5% of daily energy expenditure of the mother, if carried out continuously. Similarly, evaporation due to grooming and suckling would be equivalent to 16.4% of daily water turnover. In terms of daily energy expenditure and daily water turnover, labour and parturition are therefore cheap, but grooming and suckling (even ignoring costs in terms of losses in the milk) are expensive.

Animals↗

PubMed1994

Evidence for the essential role of prostaglandins for parturition in a marsupial, Macropus eugenii.

Female tammar wallabies were treated prepartum with the prostaglandin synthase inhibitor indomethacin, with or without the dopamine agonist bromocriptine, to suppress the peripartum pulses of plasma prostaglandin and prolactin. The animals were observed continuously to detect birth, and a series of blood samples taken to define the hormonal profiles before and immediately after parturition. Birth was observed in ten of twelve control animals but not in the six animals treated with indomethacin alone or the six animals treated with indomethacin and bromocriptine. Indomethacin disrupted the normal profile of PGF2 alpha metabolite 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) concentrations, and in the females treated with bromocriptine plus indomethacin the pulse of prolactin normally seen at parturition was completely abolished. Plasma progesterone concentrations fell slowly in treated animals, whereas in control animals they fell steeply immediately after parturition. Postpartum oestrus was delayed or absent in treated and most control animals, suggesting that the frequent blood sampling and disturbances in the peripartum period interfered with these endocrine processes. We conclude that prostaglandin is essential for normal birth. Prolactin, in the apparent absence of a prostaglandin peak, does not induce birth or rapid luteolysis. Prostaglandin release may synchronize the rapid fall in progesterone concentrations associated with birth, but in the absence of this signal, the corpus luteum undergoes a less rapid, autonomous decline.

Animals↗

PubMed2001

Corticotrophin-releasing hormone and human parturition.

Corticotrophin-releasing hormone (CRH), the hypothalamic peptide that controls function of the pituitary-adrenal axis in response to stress, is expressed in abundance in the human placenta and is present in high concentrations in maternal and fetal plasma during late pregnancy. A number of lines of evidence now imply a role for this hormone in the control of parturition and fetal maturation in humans. It has been proposed that CRH, through interactions with oestrogen, adrenal steroids, prostaglandins and oxytocin, establishes positive-feedback loops that initiate parturition and labour. Excessive production of placental CRH has also been linked to preterm labour. However, there are a number of significant gaps in our knowledge of the function of this peptide in pregnancy. This review examines current evidence regarding the putative role of CRH in human parturition.

Animals↗

PubMed2003

Effects of in vivo administration of epidermal growth factor (EGF) on uterine contractility, prostaglandin production and timing of parturition in rats.

Prostaglandins synthesized by cyclooxygenases elicit uterine contractions during labour. Nitric oxide synthases (NOS) produce nitric oxide (NO), which maintains uterine quiescence during pregnancy. Epidermal growth factor (EGF) interacts with prostaglandins and NO in many biological systems. The aim of this work was to study the effect of the in vivo administration of EGF on uterine contractility, prostaglandin production and timing of parturition in rats. EGF was injected into the uterine lumen of pregnant rats on day 20, 21 or 22 of gestation. Intra-uterine administration of 500 ng EGF on day 21 of gestation delayed parturition for 18 h compared with control rats. Administration of EGF was able to: (i) reduce cyclooxygenase expression in the uterus (determined by western blot analysis) and production of prostaglandins by the uterus (evaluated by conversion of [(14)C]arachidonate to labelled prostaglandins); (ii) decrease prostaglandin concentrations in amniotic fluid (radioimmunoassay); (iii) increase NO production (evaluated by conversion of [(14)C]arginine into [(14)C]citrulline); (iv) increase serum progesterone concentrations to more than control concentrations (P<0.05; radioimmunoassay); and (v) reduce the amplitude of the uterine contractions. The overall effect was a delay in the onset of delivery. This in vivo effect raises the question of whether exogenous EGF plays a role in the initiation of parturition.

Amniotic Fluid↗

PubMed1976

Bilateral adrenalectomy of lambs in utero: effects on maternal hormone levels at induced parturition.

Progesterone, 17 alpha, 20 alpha-dihydroxypregn-4-en-3-one, androstenedione, total unconjugated oestrogen and oestrone sulphate have been measured by radioimmunoassays in maternal utero-ovarian venous, maternal peripheral venous and/or foetal posterior vena caval plasma from six sheep bearing bilaterally adrenalectomized lambs, in which premature parturition was induced by administration of glucocorticoid. Three of the ewes were overiectomized, and in one of these three animals the foetal testes were also excised, at the time of foetal adrenalectomy. Adrenalectomy was judged to be complete on the basis of plasma cortisol levels in the neonatal lambs, and by examination of the site of ablation at necropsy. In all cases foetal administration of glucocorticoid led to the onset of labour, and lambing, and in all animals the hormonal changes preceding parturition were indistinguishable (either qualitatively or quantitatively) from the changes observed in animals carrying intact lambs. Since therapy with glucocorticoid alone successfully compensates for ablation of the foetal adrenal cortex, it is suggested that glucocorticoid is the only adrenal product required to cause parturition, and that foetal adrenal secretion of androgens may be unnecessary.

17-alpha-Hydroxypregnenolone↗

PubMed1978

Initiation of parturition in the goat: evidence for control by foetal glucocorticoid through activation of placental C21-steroid 17alpha-hydroxylase.

Infusion of dexamethasone into chronically catheterized foetal kids induced delivery in 41--65 h. Changes in the concentrations of placental and ovarian steroids in the maternal circulation at dexamethasone-induced delivery mimicked those preceding spontaneous kidding at term; in both instances the peripheral concentration of progesterone fell and the concentration of oestradiol-17beta rose. The concentration of cortisol in the foetus was low at dexamethasone-induced delivery. Metabolism of pregnenolone, progesterone, 17alpha-hydroxyprogesterone and androst-4-ene-3,17-dione by extracts of foetal placenta was investigated in late pregnancy, after premature parturition induced with dexamethasone or prostaglandins and after spontaneous parturition at term. In placenta obtained before the onset of labour (or from animals induced to kid by administration of prostaglandins), the main product of progesterone metabolism was a 5beta-pregnane-3,20-diol. In contrast, placentae from animals in which the foetal level of glucocorticoid had been raised (after spontaneous parturition or by administration of dexamethasone to the foetus) were able to 17alpha-hydroxylate and progesterone was metabolized to 5beta-pregnane-3alpha/3beta,17alpha,20alpha-triols and 17alpha,20alpha-dihydroxypregn-4-en-3-one. The appearance of placental 17alpha-hydroxylase was correlated with raised maternal concentrations of 17alpha,20alpha-dihydroxypregn-4-en-3-one and androstenedione. The induction or activation of placental 17alpha-hydroxylase may represent the mechanism by which foetal glucocorticoid controls the onset of labour in the goat.

Animals↗

PubMed1979

Concentrations of 6-oxo-prostaglandin F 1 alpha in the maternal and foetal plasma of sheep during spontaneous and induced parturition.

The concentrations of 6-oxo-prostaglandin F 1 alpha (6-oxo-PGF 1 alpha) have been determined in maternal and foetal plasma from nine chronically catheterized sheep during late pregnancy and parturition. Labour occurred either spontaneously (three sheep) or was induced by continous intrafoetal infusion of Synacthen (ACTH 1-24; 0.24 mg/24 h; three sheep) or dexamethasone (1 mg/24 h; three sheep). During spontaneous and Synacthen-induced parturition, concentrations of 6-oxo-PGF 1 alpha in maternal and foetal plasma remained at basal levels until 24 h before delivery. At varying times during the 24 h before delivery, levels of 6-oxo-PGF 1 alpha in maternal and foetal plasma were generally increased. When parturition was induced with dexamethasone, however, no increase was observed in the foetal plasma although the concentration of 6-oxo-PGF 1 alpha in maternal plasma was raised close to delivery.

Animals↗

PubMed1981

Plasma levels of androstenedione, epitestosterone, testosterone and oestrogens in cows at parturition.

The concentration of total unconjugated oestrogens in the peripheral plasma of cows increased from 2.00 +/- 0.20 (S.E.M.) ng/ml 7 days before to 3.87 +/- 0.50 ng/ml 1 day before parturition and declined to values below 0.30 ng/ml on day 2 post partum. The concentrations of androstenedione, epitestosterone and testosterone remained approximately constant at 0.90 +/- 0.10, 0.92 +/- 0.08 and 0.40 +/- 0.20 ng/ml respectively during the last week of pregnancy. After parturition the concentration of the three androgens declined rapidly. Similar to data obtained in goats we did not find a marked increase in androgen levels in the peripheral blood of cows before parturition.

Androstenedione↗

PubMed1983

Hormonal changes at oestrus, parturition and post-partum oestrus in the tammar wallaby (Macropus eugenii).

Concentrations of progesterone, prolactin, LH and 13,14 dihydro-15-keto-prostaglandin F2 alpha (PGFM) were measured in plasma of eight tammar wallabies at 8-hourly intervals during the end of pregnancy and post-partum oestrus initiated by removing the pouch young, and during the end of the oestrous cycle, similarly initiated. In the non-pregnant cycle oestrus occurred 29.7 +/- 0.7 (mean +/- S.E.M.) days after initiation of the cycle, was preceded by a slow decline in progesterone concentration from 1.6 nmol/l to less than 0.64 nmol/l and was followed by a preovulatory peak of LH 5.3 +/- 3.9 h later. In the pregnant cycle birth occurred 26.1 +/- 0.2 days after removing the pouch young and was followed 8.0 +/- 2.1 h later by oestrus and 16.0 +/- 2.5 h by an LH peak. The latter events thus occurred 3.2 days earlier in the pregnant than in the non-pregnant cycle. Parturition coincided with a very rapid decline in progesterone and a transient high peak of prolactin. In two females sampled less than 25 min after parturition there was a transient peak of PGFM but in all others the concentrations of PGFM remained basal throughout. It is suggested that the fetus and/or placenta is involved in both the premature decline in progesterone and the initiation of parturition and that onset of oestrus and ovulation, being a consequence of a decline in progesterone, are therefore also determined by the fetus.

Animals↗

PubMed1983

Concentrations of prolactin in the plasma of fetal sheep and in amniotic fluid in late gestation and during dexamethasone-induced parturition.

The concentration of prolactin in samples of fetal plasma and amniotic fluid collected from sheep with indwelling catheters has been measured by radioimmunoassay. There was considerable variation between animals in the concentration of prolactin in fetal plasma which ranged from less than 2 micrograms/l to greater than 50 micrograms/l. In five out of eight fetuses which were sampled at intervals throughout the last 30 days of pregnancy, there was an increase in the concentration of prolactin in the plasma before parturition. The concentration of prolactin in amniotic fluid was consistently low (approximately 1 microgram/l). Induction of premature parturition by intrafetal infusion of dexamethasone was accompanied by an increase in the concentration of prolactin in only one of three fetuses infused. These results indicated that prolactin is present in fetal plasma but that an increase in prolactin in fetal plasma before the onset of parturition does not always occur. The low concentration of prolactin in amniotic fluid contrasts with the high concentrations of this hormone found in the amniotic fluid of the primate.

Amniotic Fluid↗