Plasma corticotrophin-releasing factor (CRF) in normal pregnancy

Exercise and pregnancy in recreational and elite athletes: 2016 evidence summary from the IOC expert group meeting, Lausanne. Part 2-the effect of exercise on the fetus, labour and birth

This is Part 2 of 5 in the series of evidence statements from the IOC expert committee on exercise and pregnancy in recreational and elite athletes. Part 1 focused on the effects of training during pregnancy and on the management of common pregnancy-related symptoms experienced by athletes. In Part 2, we focus on maternal and fetal perinatal outcomes.

Reduced expression of corticotropin-releasing hormone receptor type-1 alpha in human preeclamptic and growth-restricted placentas

Placentally derived CRH seems to play a major role in the mechanisms controlling human pregnancy and parturition, via activation of specific receptors widespread in reproductive tissues. In the human placenta, CRH seems to modulate vasodilation, prostaglandin production, and ACTH secretion. It has also been suggested that CRH might act as a placental clock, determining the length of gestation. In addition, maternal plasma CRH concentrations are further elevated in pregnancies associated with abnormal placental function, such as preeclampsia and intrauterine growth retardation (IUGR). In this study, we sought to investigate the expression of CRH-R1 alpha levels in placentas from women who have undergone normal deliveries (control group) and patients who have been diagnosed as having preeclampsia or IUGR. Results showed that placental CRH-R1 alpha mRNA levels (as shown by quantitative RT-PCR) and protein levels (shown by Western blotting analysis) were significantly (P < 0.05) reduced in all of the complicated pregnancies. In contrast, levels of the angiotensin II receptor were elevated in preeclampsia and reduced in IUGR subjects, as shown by RT-PCR and Western blotting analysis. These findings might suggest that changes in receptor expression may contribute toward dysregulation of the dynamic balance controlling vascular resistance.

Placental corticotrophin-releasing hormone, local effects and fetomaternal endocrinology

The human placenta produces corticotrophin-releasing hormone (CRH) in exponentially increasing amounts during pregnancy with peak levels during labour. CRH in human pregnancy appears to be involved in many aspects of pregnancy including placental bloodflow, placental prostaglandin production, myornetrial function, fetal pituitary and adrenal function and the maternal stress axis. Since fetal cortisol levels are associated with pulmonary development and maturity, placental CRH may have an indirect role in fetal development.Although the precise role of placental CRH in the regulation of gestational length and timing of parturition is unclear it appears to be involved in a placental clock. While glucocorticoids inhibit hypothalamic CRH production they stimulate CRH gene expression in the placenta.This difference may allow the fetal and maternal stress axes to influence this placental clock.Maternal CRH levels are elevated in many pathological conditions of pregnancy where fetal well-being is compromised, and in these situations it may act to maintain a stable intrauterine environment. Therefore, CRH appears to link placental function, maternal well-being, fetal well-being and fetal development to the duration of gestation and the timing of parturition.

Glucocorticoid regulation of human and ovine parturition: the relationship between fetal hypothalamic-pituitary-adrenal axis activation and intrauterine prostaglandin production

Birth in many animal species and in humans is associated with activation of hypothalamic-pituitary-adrenal function in the fetus and the increased influence of glucocorticoids on trophoblast cells of the placenta and fetal membranes. We suggest that in ovine pregnancy glucocorticoids directly increase fetal placental prostaglandin production, and indirectly increase prostaglandin production by maternal uterine tissues through the stimulation of placental estradiol synthesis. The events of ovine parturition are compared with those of human parturition. In the latter, we suggest similar direct effects of glucocorticoids on prostaglandin synthesis and metabolism in fetal membranes and similar indirect effects mediated by glucocorticoid-stimulated increases in intrauterine corticotropin-releasing hormone expression.

The role of corticotropin-releasing hormone receptors in placenta and fetal membranes during human pregnancy

Corticotropin-releasing hormone (CRH) is a 41 amino acid polypeptide that exerts a wide spectrum of hypothalamic and extrahypothalamic functions. Moreover, the placenta and other intrauterine tissues produce and secrete immunoreactive CRH. It has been demonstrated that placental CRH is secreted into the maternal circulation in large amounts during the third trimester of human pregnancy and may play an important role in the onset of labor. CRH exerts a number of functions within the intratuterine environment like induction of prostaglandin production and maintenance of the placental blood flow. Here we present an overview of current knowledge about the CRH receptor subtypes and their signaling properties within the feto-placental unit.

Endocrine and paracrine regulation of birth at term and preterm

We have examined factors concerned with the maintenance of uterine quiescence during pregnancy and the onset of uterine activity at term in an animal model, the sheep, and in primate species. We suggest that in both species the fetus exerts a critical role in the processes leading to birth, and that activation of the fetal hypothalamic-pituitary-adrenal axis is a central mechanism by which the fetal influence on gestation length is exerted. Increased cortisol output from the fetal adrenal gland is a common characteristic across animal species. In primates, there is, in addition, increased output of estrogen precursor from the adrenal in late gestation. The end result, however, in primates and in sheep is similar: an increase in estrogen production from the placenta and intrauterine tissues. We have revised the pathway by which endocrine events associated with parturition in the sheep come about and suggest that fetal cortisol directly affects placental PGHS expression. In human pregnancy we suggest that cortisol increases PGHS expression, activity, and PG output in human fetal membranes in a similar manner. Simultaneously, cortisol contributes to decreases in PG metabolism and to a feed-forward loop involving elevation of CRH production from intrauterine tissues. In human pregnancy, there is no systemic withdrawal of progesterone in late gestation. We have argued that high circulating progesterone concentrations are required to effect regionalization of uterine activity, with predominantly relaxation in the lower uterine segment, allowing contractions in the fundal region to precipitate delivery. This new information, arising from basic and clinical studies, should further the development of new methods of diagnosing the patient at risk of preterm labor, and the use of scientifically based strategies specifically for the management of this condition, which will improve the health of the newborn.

The production of interleukin-1beta from human fetal membranes is not obligatory for increased prostaglandin output

Bacterial endotoxin increased the expression of mRNA (maximal after 4 hr) for interleukin-1beta (IL-1beta) and the release of mature protein from intact human fetal membranes. In contrast, the change in expression of mRNA for type 2 cyclo-oxygenase (COX-2) was biphasic, with peaks after 0.5-1 hr and after 8 hr of culture. An antibody to IL-1beta was without effect after 4 hr of culture, inhibited endotoxin-stimulated prostaglandin E2 (PGE2) production after 8 hr of culture, and caused a parallel decrease in the expression of mRNA for COX-2. We conclude that endotoxin induced the expression of COX-2 through IL-1beta-independent and IL-1beta-dependent mechanisms, and these differences are time dependent. Corticotrophin-releasing hormone (CRH) or platelet-activating factor (PAF) also increased the expression of mRNA for IL-1beta and the release of IL-1beta from some, but not all, fetal membranes. The antibody to IL-1beta did not affect CRH-stimulated or PAF-stimulated PGE2 production or COX-2 expression. We conclude that CRH and PAF can induce the expression of IL-1beta, but this is not obligatory for increased PGE2 release, and the effect of these stimuli on COX-2 expression is a direct, IL-1beta-independent effect.

Prenatal psychosocial factors and the neuroendocrine axis in human pregnancy

OBJECTIVE

Physiological processes including neuroendocrine function have been proposed as mediators of the relationship between prenatal psychological state and pregnancy outcome; however, there are virtually no human studies that have systematically assessed such mechanisms. Neuroendocrine processes are significantly altered during pregnancy, and are characterized by the evolution of a transient neuroendocrine system, the placenta, and modifications in endocrine control mechanisms. Because these alterations have implications for neuroendocrine responsivity to exogenous conditions, the aim of the present study was to examine the cross-sectional association between prenatal psychosocial factors and stress-related neuroendocrine parameters during human pregnancy.

METHOD

Fifty-four adult women with a singleton, intrauterine pregnancy were recruited before 28 weeks of gestation. Maternal antecubital venous blood samples were withdrawn at 28 weeks of gestation for bioassays of adrenocorticotropin hormone (ACTH), beta-endorphin (beta E), and cortisol. Measures of prenatal stress, social support, and personality were collected using a two-part, self-report questionnaire administered at 28 and 30 weeks of gestation. Biomedical data were obtained from the medical record. Factors known to influence neuropeptide and hormone levels during pregnancy were controlled, including gestational age, circadian variation, and obstetric risk.

RESULTS

In the present sample, prenatal psychosocial stress, social support, and personality variables were associated with neuroendocrine parameters in two primary ways. First, certain psychosocial factors were significantly associated with plasma levels of ACTH, beta E, and cortisol, and second, psychosocial factors were associated with a measure of disregulation of the normal relationship between two pro-opiomelanocortin (POMC) derivatives, ACTH and beta E. Furthermore, a combination of the maternal psychosocial and sociodemographic factors during pregnancy accounted for 36% of the variance in ACTH, 22% of the variance in the ACTH-beta E disregulation index, 13% of the variance in cortisol, and 3% of the variance in beta E.

CONCLUSIONS

The present findings are consistent with the premise that maternal-placental-fetal neuroendocrine parameters are significantly associated, both in magnitude and specificity, with features of maternal psychosocial functioning in pregnancy despite the systemic alterations associated with the endocrinology of pregnancy. These findings provide a basis for further investigations of the role of the neuroendocrine system as a putative mediating pathway between prenatal psychosocial factors and birth outcome, and possibly also as a mechanism linking features of the maternal psychosocial environment to fetal/infant brain development.

Corticotropin-releasing factor and its binding protein: maternal serum levels in term and preterm deliveries

OBJECTIVE

The primary objective of this investigation was to evaluate whether maternal serum corticotropin-releasing factor levels during pregnancy were predictive of spontaneous preterm delivery.

STUDY DESIGN

Maternal serum levels of corticotropin-releasing factor and its binding protein were measured from 20 weeks of gestation in a cross-sectional study of 396 asymptomatic women at high risk for preterm delivery.

RESULTS

Gestational age-specific corticotropin-releasing factor levels were not consistently or substantially increased for preterm compared with term deliveries, whether preterm delivery was due to preterm labor or preterm premature rupture of membranes. The binding protein for corticotropin-releasing factor did not vary according to gestational age until term, when it dropped substantially.

CONCLUSION

Serum corticotropin-releasing factor levels do not appear to be an important predictor of preterm birth in asymptomatic patients who subsequently have either preterm labor or preterm premature rupture of membranes. Nevertheless, the drop in the corticotropin-releasing factor binding protein level at term suggests that the bioavailability of corticotropin-releasing factor increases as parturition approaches.

Corticotropin-releasing factor increases [Ca2+]i via receptor-mediated Ca2+ channels in human epidermoid A-431 cells

Corticotropin-releasing factor (CRF) has been shown to attenuate vascular leakage in injured skin, mucous membrane, muscle, and brain. Calcium is thought to play an important role in many of the physiological responses to CRF, but there has been little characterization of how calcium is involved in process by which CRF protects damaged tissues. The goal of this study was to characterize changes in cytosolic free calcium concentrations ([Ca2+]i) in human epidermoid A-431 cells exposed to human/rat-CRF and to investigate the mechanisms by which these changes occur. The resting [Ca2+]i in normal cells at 37 degrees C was 66 +/- 4 nM (n = 32). When cells were treated with CRF, [Ca2+]i increased immediately. The increase depended on CRF concentration, with a median effective concentration of 11 pM. This increase in [Ca2+]i depended on external Ca2+ but not Na+, Mg2+, or K+. La3+ (10 microM) and Co2+ (10 microM) inhibited the CRF-induced [Ca2+]i increase, whereas verapamil and nifedipine tested at concentrations up to 1 mM did not. alpha-Helical CRF-(9-41), a synthetic CRF receptor antagonist, and pertussis toxin blocked the increase in [Ca2+]i induced by CRF, which suggests that the entry of extracellular Ca2+ is mediated by receptor-operated Ca2+ channels coupled with pertussis toxin-sensitive G proteins. Although 420 pM CRF stimulated an immediate increase in [Ca2+]i, inositol trisphosphate and cellular cAMP levels did not change within 1 min either in the presence or absence of external Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Silent ischemia: a hypothetical mechanism

Ischemia of visceral organs, especially the heart, is often a painful and potentially life-threatening condition. However, in at least 75% of all cases myocardial ischemia may be "silent" (i.e., without pain or sensation). Yet, the mechanisms responsible for silent ischemia are not well understood. As such, many different theories have been advanced to explain silent ischemia; however, none have been able to adequately explain all of the experimental and clinical findings. This paper proposes a hypothetical mechanism that may help to understand mechanisms of silent ischemia.

Elevated maternal plasma corticotropin-releasing hormone levels in pregnancies complicated by preterm labor

OBJECTIVES

We investigated whether maternal plasma levels of the placental hormone corticotropin-releasing hormone are elevated in pregnancies complicated by preterm labor.

STUDY DESIGN

Mean maternal corticotropin-releasing hormone levels were studied in women who met specific criteria for preterm labor and in women with normal pregnancies. Levels were also compared in the latent and active phases during term labor.

RESULTS

In pregnancies complicated by preterm labor, maternal corticotropin-releasing hormone levels were higher than in normal pregnancies; this elevation occurred before labor was diagnosed clinically (p less than 0.05). When preterm labor was associated with infection, the mean levels were not elevated. Mean plasma levels were similar in latent and active phases during labor at term.

CONCLUSION

Maternal plasma corticotropin-releasing hormone levels are elevated in association with preterm labor. This elevation does not appear to be due to labor itself and may reflect an early activation of the placenta before the onset of preterm labor.

Maternal plasma corticotrophin-releasing hormone--elevated in preterm labour but unaffected by indomethacin or nylidrin

The role of corticotrophin-releasing hormone (CRH) in preterm labour was studied in 23 women in preterm labour at between 26 and 33 weeks gestation who were randomly allocated to receive treatment with indomethacin (n = 11) or with nylidrin a beta-sympathomimetic agent (n = 12). Maternal plasma CRH in the preterm group (median 70, range 9-597 pmol/l) before therapy was higher (P less than 0.05) than that in 23 control pregnancies, without uterine contractions, matched for gestational age (median 51, range 4-127 pmol/l). CHR levels determined after 3 and 24 h of treatment showed a 10% decrease in the indomethacin group and 10-20% decrease in the nylidrin group, but these changes were not statistically significant. After cessation of uterine contractions during tocolysis, 12 women proceeded to give birth preterm (less than 37 weeks) and their pretreatment CRH levels (median 195, range 9-597 pmol/l) were higher (P less than 0.05) than those in women whose pregnancy proceeded to term (median 52, range 16-207 pmol/l). In another group of women, full-term labour was not accompanied by any changes in maternal CRH levels. Umbilical plasma CRH levels were 1.1-9.8% of the paired maternal levels and did not rise with advancing gestational age. Nor had the type of delivery (elective caesarean section before labour, or preterm or term vaginal delivery) any effect on fetal CRH levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-releasing factor: an inhibitor of vascular leakage in rat skeletal muscle and brain cortex after injury

Corticotropin-releasing factor (CRF) and other peptides of the corticoliberin superfamily inhibit development of edema in skin and mucosa after noxious stimuli. Here, the breadth of CRFs protective activity on small blood vessels was examined after injury to skeletal muscle or to brain cortex. Male rats (243 +/- 15 g) were anesthetized with sodium pentobarbital 60 mg/kg i.p. and Monastral blue 60 mg/kg i.v. was injected 3 min before mechanical injury to muscle produced by a 4 cm midline surgical incision in the rectus abdominis or before freeze injury to the cortex produced by applying a cold probe (-50 degrees C) to the skull for 4 min. Vascular leakage, measured as area of dye staining multiplied by its light intensity, was quantified with an image-analysis system. CRF, having the human/rat sequence, 30 micrograms/kg s.c., injected once (30 min) or twice (30 min and 10 min) before injury to muscle or to brain, inhibited the lesion size by 58% and 55%, respectively (tissues taken at 0.5 and 1 h). Microscopy showed that CRF inhibited Monastral blue labeling of small blood vessels. The ED50 (95% C.L.) of CRF for reducing vascular leakage in muscle after celiotomy was 24 (9 to 64) micrograms/kg s.c. h/rCRF injected 30 micrograms/kg s.c. 2 h before celiotomy inhibited vascular leakage after celiotomy in adrenalectomized rats and this effect was not obtained with dexamethasone phosphate, 1 mg/kg s.c. alpha-Helical CRF (9-41), a CRF receptor antagonist, attenuated the actions of CRF on celiotomy. Laser-Doppler flowmeter measurements of skeletal muscle showed that the anti-inflammatory effects of CRF occurred when there were no significant concurrent changes in blood flow. From these results, we surmise that CRF has a versatile protective effect on small blood vessels when it inhibits leakage within different vascular beds.

Corticotrophin-releasing hormone production by the placenta and fetal membranes

Maturation of the fetal hypothalamic-pituitary-axis may be an important factor in the stimulation of the onset of parturition. Recent studies have found that corticotrophin-releasing hormone (CRH), the hypothalamic component of this axis is also present in the placenta and the fetal membranes. We review the evidence demonstrating that glucocorticoids stimulate the production of CRH by these tissues towards term, and this is manifest by increases in CRH concentrations in maternal and fetal plasma and in placental extracts, and by increased abundance of CRH mRNA in the placenta. We discuss how CRH secretion by the placenta and fetal membranes is controlled. We hypothesize that CRH may be an important signal in initiating of the onset and maintenance of term labour and may also be a factor in the etiology of premature labour, through stimulation of the fetal HPA axis, and through paracrine/autocrine interactions within the placenta, fetal membranes and decidua.

Neuroendocrinology of the hypothalamo-pituitary-adrenal axis in pregnancy and the puerperium

Plasma cortisol, adrenocorticotrophic hormone (ACTH), beta-endorphin and corticotrophin releasing hormone or factor (CRF) all rise progressively as pregnancy advances, and fall postnatally. The placenta produces large amounts of CRF in the third trimester and this is released into the maternal circulation. Present evidence suggests that it stimulates the maternal pituitary to produce ACTH while desensitizing the maternal pituitary to further stimulation with CRF. Maternal control of ACTH production is retained, allowing a persistent response to stress and a diurnal rhythm, perhaps through the secretion of vasopressin. The placenta also produces pro-opiomelanocortin peptides; however, the nature of the fragments produced from the precursor differs from that formed in the anterior pituitary of the mother and the role of these fragments in the control of maternal adrenal function is unclear. These changes in the hypothalamo-pituitary-adrenal axis during pregnancy are associated with loss of the normal suppression of cortisol by dexamethasone and elevated basal levels of cortisol with preservation of a diurnal rhythm, features also found in some patients with endogenous depression. Several studies have suggested a relationship between alterations in maternal concentrations of cortisol and beta-endorphin and the development of postnatal mood disturbances.

Binding of corticotropin-releasing hormone (CRH) in maternal and fetal plasma and in amniotic fluid

Placenta secretes corticotropin-releasing hormone (CRH) into the maternal and fetal circulation, but a CRH binding protein in plasma may decrease its biological activity. Using a charcoal adsorption method we found that 92% of added 125I-Tyr-CRH was bound to a binding protein in the nonpregnant plasma, 72% in the plasma at term pregnancy, 90% in umbilical cord plasma, 82% in the amniotic fluid in the second and 25% in the third trimester. CRH added to plasma inhibited the binding of 125I-Tyr-CRH over the concentration range of 0.1-8.8 nmol/l in plasma and of 0.1-2.2 nmol/l in amniotic fluid. There was a significant negative correlation (R = -0.80) between the binding capacity of the CRH-binding protein and CRH concentration in maternal plasma. Plasma or amniotic fluid was incubated with 125I-Tyr-CRH and subjected to gel filtration on Sephadex G-50. The bound radioactivity was eluted at the region of Mr 25-40 kDa and the unbound radioactivity at the location of synthetic CRH. Bound and unbound CRH concentrations were determined using charcoal adsorption method and gel filtration on Sephadex G-50 in ten maternal plasma samples at the third trimester of pregnancy. Following mean percentages were found to be bound: charcoal method 61.9 +/- 6.80% (SE) and gel filtration 62.8 +/- 6.33%. We conclude that the bulk of CRH is bound to a binding protein in maternal and fetoplacental circulation, whereas at term pregnancy the role of the binding is small in amniotic fluid.

The rate of rise of corticotrophin releasing factor and endogenous digoxin-like immunoreactivity in normal and abnormal pregnancy

Maternal plasma concentrations of corticotrophin releasing factor (CRF) and endogenous digoxin-like immunoreactivity (EDLI) were estimated in 80 normal and 88 abnormal pregnancies which were sampled sequentially from 24 weeks gestation to delivery. A slope was fitted for each woman's antenatal EDLI and CRF values, both of which rose significantly during gestation, and the mean of the slopes for the normal and abnormal groups for each value compared. There was no evidence of significant mean differences between groups for EDLI but there was evidence of a significant mean difference for CRF (P less than 0.05). After adjustment for other variables which may affect pregnancy outcome, the slopes for CRF were found not to be significantly related to outcome.

Response of plasma immunoreactive beta-endorphin and corticotropin to isometric exercise in uncomplicated pregnancy and in pregnancy-induced hypertension

The response of plasma immunoreactive beta-endorphin (ir-beta E) and corticotropin to isometric exercise was studied in 10 women with pregnancy-induced hypertension (PIH) and in nine healthy women subjected to a handgrip test in the third trimester of gestation. The mean basal concentration of corticotropin was higher in the PIH than in the control group, 3.8 +/- 0.3 (SE) pmol/l and 2.2 +/- 0.2 pmol/l, respectively (p = 0.002). No significant difference was found in the basal ir-beta E level, 6.9 +/- 0.9 pmol/l and 6.1 +/- 1.0 pmol/l, respectively. In response to the handgrip test, the corticotropin and ir-beta E concentrations rose significantly in all subjects (p = 0.001 and p = 0.02, respectively) without any significant differences between the groups. These findings indicate that an isometric exercise is sufficient to increase the secretion of ir-beta E and corticotropin during pregnancy. Increased basal concentration of corticotropin in women with PIH may be explained by significantly increased circulating corticotropin-releasing hormone, 1451 +/- 323 pmol/l, as compared to 528 +/- 190 pmol/l in the control group.

Decreased inflammatory responsiveness of hypophysectomized rats to heat is reversed by a corticotropin-releasing factor (CRF) antagonist

Hypophysectomy, but not adrenalectomy, decreased (relative to sham-operated controls) the swelling and Evans blue dye extravasation responses of the anesthetized rat's pawskin to thermal injury. alpha-Helical CRF (9-41), a synthetic competitive antagonist of corticotropin-releasing factor (CRF) on isolated pituitary cells, did not affect in sham-operated rats the swelling response after immersion of the paw in 58 degrees C water for 30 s. Swelling was measured over a 1 h period using the fluid displacement method for quantifying paw volume. But, when alpha-helical CRF (9-41) was injected 92 micrograms/kg i.v. 10 min before or immediately after heat exposure, it both attenuated and reversed the insensitive state produced by hypophysectomy: that is, the swelling response reappeared. Under the same test conditions, naloxone hydrochloride, an opioid antagonist, was ineffective. The results suggest that hypophysectomy may induce a condition whereby endogenous CRF or CRF-like peptides may act as an anti-inflammatory agent.

Elevated maternal plasma corticotropin releasing hormone levels in twin gestation

The placenta secretes large amounts of the hypothelamic hormone, corticotropin releasing hormone (CRH) into the maternal and fetal circulation during pregnancy. We and other investigators have shown that during normal pregnancy, maternal plasma CRH levels begin to rise in the second trimester with a dramatic increase in CRH levels during the 5-6 weeks preceding the onset of labor. This rise in maternal plasma CRH is parallel to the rise of placental CRH mRNA which has been reported to occur with gestational maturation. Mechanisms underlying the control of CRH secretion by the placenta have not yet been determined. In twin gestation, increased fetal-placental mass has been shown to be associated with elevated maternal levels of several placental hormones as compared to singleton gestation. We measured maternal plasma CRH in both twin and singleton gestation to investigate whether the larger size of the fetal-placental unit in twin gestation is associated with elevated maternal CRH levels. Seventy-six serial venous blood samples were collected from 20 women with twin gestation and 40 samples were obtained from 27 women with uncomplicated singleton gestation. Gestational age was determined by history of a known last menstrual period and first trimester clinical examination and confirmed by ultrasound examination. CRH was extracted from 1-2 ml plasma with SEP-Pak C18 cartridges and eluted with triethylamine-formic-acid propranolol. CRH was measured by radioimmunoassay (RIA) with human CRH standard and antiserum to human CRH raised in our laboratory. Mean CRH levels were calculated for four week intervals. In both singleton and twin gestation, the maternal plasma CRH levels increased with advancing gestational age. After 29 weeks of gestation, maternal plasma CRH levels in twin gestation were significantly higher than those in singleton gestation (p less than 0.01). At 37 to 40 weeks of gestation, mean maternal CRH was 1167 +/- 237 pg/ml in singleton gestation as compared to 6927 +/- 1725 pg/ml in twin gestation (p less than 0.05). In addition, the rapid rise in plasma CRH levels which occurs near term in singleton gestation, occurred earlier in twin gestation. This early rise in maternal CRH levels persisted when the data from twin pregnancies complicated by preterm labor were removed from the analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Placental corticotrophin releasing factor may modulate human parturition

The interactions of corticotrophin releasing factor (CRF) and oxytocin on myometrial contractility were studied in isolated gestational myometrium in vitro. Acting alone oxytocin showed a significant dose related inotropic effect (P less than 0.001), whereas CRF did not. Dose-response curves of oxytocin in the presence of a fixed dose of CRF showed a threefold increase in the response to oxytocin without CRF present (P = 0.0019). When this combined priming and potentiating effect was investigated separately, priming of the myometrial strips with CRF prior to stimulation with oxytocin significantly enhanced the inotropic effect of oxytocin (P = 0.01) and when given together a significant potentiating effect was seen (P = 0.008). It is suggested that placental CRF may act as an important modulator of the inotropic effect of oxytocin on myometrium. The interaction between the two peptides may be similar to that which occurs between CRF and vasopressin in the anterior pituitary gland.

Plasma corticotrophin-releasing factor (CRF) in abnormal pregnancy

Maternal plasma levels of cortiocotrophin-releasing factor (CRF) have been measured in abnormal pregnancy states to assess their potential as biochemical markers for at-risk pregnancies. CRF levels were not significantly altered in patients with hydatidiform mole, polyhydramnios or diabetes. CRF levels were elevated in pregnancies complicated by accidental antepartum haemorrhage at 28 weeks (P less than 0.03) but not for the rest of the third trimester. In twin pregnancies CRF levels were significantly raised throughout the third trimester (28-32 weeks, P less than 0.01; 34-36 weeks, P less than 0.001). In patients with pregnancy-induced hypertension (28 weeks, P less than 0.001; 32-36 weeks, P less than 0.001; and 38-40 weeks, P less than 0.01), preterm labour and premature rupture of the membranes (28 weeks, P less than 0.004; 30-32 weeks, P less than 0.002; and 34-36 weeks, P less than 0.001), CRF levels were significantly raised and in some patients levels were elevated 11 weeks before the onset of signs or symptoms. These observations raise the possibility that maternal CRF measurement may be of use as a predictive indicator of certain at-risk pregnancies.