Maternal melatonin selectively inhibits cortisol production in the primate fetal adrenal gland

We tested the hypothesis that in primates, maternal melatonin restrains fetal and newborn adrenal cortisol production. A functional G-protein-coupled MT1 membrane-bound melatonin receptor was detected in 90% gestation capuchin monkey fetal adrenals by (a) 2-[(125)I] iodomelatonin binding (K(d), 75.7 +/- 6.9 pm; B(max), 2.6 +/- 0.4 fmol (mg protein)(-1)), (b) cDNA identification, and (c) melatonin inhibition of adrenocorticotrophic hormone (ACTH)- and corticotrophin-releasing hormone (CRH)-stimulated cortisol but not of dehydroepiandrosterone sulphate (DHAS) production in vitro. Melatonin also inhibited ACTH-induced 3beta-hydroxysteroid dehydrogenase mRNA expression. To assess the physiological relevance of these findings, we next studied the effect of chronic maternal melatonin suppression (induced by exposure to constant light during the last third of gestation) on maternal plasma oestradiol during gestation and on plasma cortisol concentration in the 4- to 6-day-old newborn. Constant light suppressed maternal melatonin without affecting maternal plasma oestradiol concentration, consistent with no effect on fetal DHAS, the precursor of maternal oestradiol. However, newborns from mothers under constant light condition had twice as much plasma cortisol as newborns from mothers maintained under a normal light-dark schedule. Newborns from mothers exposed to chronic constant light and daily melatonin replacement had normal plasma cortisol concentration. Our results support a role of maternal melatonin in fetal and neonatal primate cortisol regulation.

Bile acids increase response and expression of human myometrial oxytocin receptor

OBJECTIVE

We tested the hypothesis that during intrahepatic cholestasis of pregnancy bile acids activate the myometrial oxytocin receptor pathway.

STUDY DESIGN

Myometrial sensitivity to oxytocin and oxytocin-receptor messenger RNA and protein level was investigated. The ability of cholic acid to mediate such changes was evaluated.

RESULTS

Cholestasis patients required lesser oxytocin to elicit four uterine contractions in 10 minutes (1.3+/-0.6 vs 3.6+/-0.8 U, P<.05, n=7) and had lower in vitro ED(50) (1.6 x 10(-10) mol/L vs 1.0 x 10(-8) mol/L, P<.05, n=7) than controls. The 24-hour incubation of control myometrial strips (n=7) with cholic acid (20 micromol/L) increased oxytocin sensitivity. Incubation of cultured myometrial cells (n=5) with cholic acid increased oxytocin-receptor expression (messenger RNA and protein).

CONCLUSION

We demonstrate that during intrahepatic cholestasis of pregnancy, an activation of the oxytocin receptor pathway occurs. This event seems to be the result of a cholic acid-mediated increase in oxytocin-receptor expression.

mt1 Melatonin receptor in the primate adrenal gland: inhibition of adrenocorticotropin-stimulated cortisol production by melatonin

The pineal hormone melatonin participates in circadian, seasonal, and reproductive physiology. The presence of melatonin binding sites in human brain and peripheral tissues is well documented. However, in the mammalian adrenal gland, low-affinity melatonin binding sites have been detected only in the rat by some but not all authors. Conflicting evidence for a regulatory role of melatonin on adrenal cortisol production, prompted us to investigate this possibility in a New World primate, the capuchin monkey. Expression of melatonin receptors in the adrenal cortex was demonstrated through pharmacological characterization and autoradiographic localization of 2-[125I]iodomelatonin binding sites (dissociation constant = 96.9 +/- 15 pM; maximal binding capacity = 3.8 +/- 0.4 fmol/mg protein). The mt1 identity of these receptors was established by cDNA sequencing. Melatonin treatment of dispersed cells and explants from adrenal gland did not affect basal cortisol production. However, cortisol production stimulated by 100 nM ACTH was significantly inhibited by low melatonin concentrations (0.1-100 nM); this inhibitory effect was reversed by the mt1/MT2 melatonin antagonist luzindole. Melatonin also inhibited dibutyril-cAMP-stimulated cortisol production, suggesting that melatonin acts through a cAMP-independent signaling pathway. The present data demonstrate that the primate adrenal gland cortex expresses functional mt1 melatonin receptors and shows that melatonin inhibits ACTH-stimulated cortisol production.

Perinatal neuroendocrine regulation. Development of the circadian time-keeping system

During gestation, the perinatal neuroendocrine axis keeps clock time. In primates, the suprachiasmatic nucleus (biological clock in mammals), shows oscillatory function by midgestation. There is evidence in rodents that the mother, during pregnancy, entrains the fetal suprachiasmatic nucleus (SCN) and newborn circadian rhythms. We are investigating the role of maternal melatonin as an entraining signal for the newborn circadian time-keeping system in the Cebus apella (New World non-human primate). Twenty-four hour rhythms of temperature and cortisol are present in the 4 days old C. apella newborn. Preliminary data suggests that inhibition of maternal melatonin by exposing pregnant females to constant light alters these rhythms. We have found binding sites for melatonin and expression of mRNA for Mel 1A receptor in hypothalamus, kidney and testis. These preliminary results suggest that maternal melatonin may play a role in relating the perinatal circadian time-keeping system to environmental signals.

The development of circadian rhythms in the fetus and neonate

The circadian time-keeping system is the neural system that allows predictive adaptation of individuals to the reproducible 24-hour day/night alternations of our planet. A biological clock, the suprachiasmatic nucleus, receives environmental information and imposes a circadian pattern to physiological functions. Since the suprachiasmatic nucleus develops early in gestation and circadian rhythms are present in the fetus and newborn, the circadian system seems to be functional in fetal life and can receive circadian inputs through the mother. The neonate moves to an environment in which the main time giving signal is the light:dark cycle. Teleologically, a term newborn should be fit to face this challenge. But this may be quite different for a preterm infant that trades the circadian environment to which it was previously exposed for the timeless environment of the Neonatal Intensive Care Nursery. Scientists and physicians should seek new experimental and clinical approaches to answer the challenging questions of perinatal chronomedicine.

Fetectomy alters maternal pituitary-adrenal function in pregnant rhesus macaques

The interplay between the fetus and mother may play a key role in the regulation of primate pregnancy and parturition. This study was designed to test the hypothesis that fetectomy alters maternal pituitary-adrenal function. Between 117 and 122 days of gestation (term = 167 days), six rhesus macaques underwent surgery for catheter implantation. At surgery the fetuses were removed while the membranes and placenta were left in situ. Six additional intact catheterized pregnant animals served as controls. Animals were maintained under a 12L:12D cycle with lights-on from 0700 to 1900 h. Beginning at least 1 wk after surgery, maternal arterial blood samples were collected at 3-h intervals for 24 h for hormone and catecholamine analysis. This sampling protocol was repeated at weekly intervals until cesarean delivery at 151-157 days of gestation. Following fetectomy, plasma ACTH, dehydroepiandrosterone sulfate (DHEAS), and cortisol levels were significantly lower (36%, 35%, and 44%, respectively) compared with control animals (P;lt 0.05). Despite a significant reduction in overall levels, the rhythm in maternal plasma cortisol was maintained following fetectomy. Plasma dopamine and norepinephrine were also depressed (P;lt 0.05), whereas epinephrine remained unaffected. Our data clearly demonstrate the role of the fetus in the regulation of the maternal pituitary-adrenal axis during gestation. This interaction plays a significant role in the regulation of maternal endocrine function that may influence the initiation of labor.

Twenty-four-hour pattern of cortisol in the human fetus at term

OBJECTIVES

Indirect evidence suggests that adrenal steroid production in the human fetus may have a circadian rhythm. To assess whether there is a 24-hour rhythm of fetal cortisol in the human fetus, we investigated the relationship between fetal and maternal cortisol and cortisone concentrations in maternal, umbilical arterial, and umbilical venous blood samples over a 24-hour period.

STUDY DESIGN

Elective cesarean sections were scheduled every 2 hours around the clock in 57 term (38-41 weeks' gestation) nonlaboring pregnant women. Plasma cortisol and cortisone concentrations were measured by high-pressure liquid chromatography.

RESULTS

The mean 24-hour cortisol concentration was higher in umbilical arterial than in umbilical venous blood samples, 63.6 +/- 4.6 ng/mL (SEM) versus 48.7 +/- 3.2 ng/mL, respectively (P <.05). Fetal plasma cortisol showed a rhythm in the umbilical artery (acme from noon to 4 PM ) (1-way analysis of variance and least significant difference test; P <.05) but not in the umbilical vein. Umbilical arteriovenous differences showed no net transfer of cortisol to the fetus at any time of the day and net fetal production of cortisol from 8 AM to 6 PM. There was limited transfer of cortisone to the fetus and only in the 2 AM -to-noon time interval.

CONCLUSION

These data suggest the presence of a 24-hour rhythm of fetal adrenal cortisol secretion that may be controlled by a fetal circadian pacemaker.

An oxytocin receptor antagonist (atosiban) in the treatment of preterm labor: a randomized, double-blind, placebo-controlled trial with tocolytic rescue

OBJECTIVES

This study was designed to evaluate the efficacy and safety of the oxytocin receptor antagonist atosiban in the treatment of preterm labor.

STUDY DESIGN

A multicenter, double-blind, placebo-controlled trial with tocolytic rescue was designed. Five hundred thirty-one patients were randomized to receive, and 501 received, either intravenous atosiban (n = 246) or placebo (n = 255), followed by subcutaneous maintenance with the assigned agent. Standard tocolytics as rescue tocolysis were permitted after 1 hour of either placebo or atosiban if preterm labor continued. The primary end point was the time from the start of study drug to delivery or therapeutic failure. Secondary end points were the proportion of patients who remained undelivered and did not receive an alternate tocolytic at 24 hours, 48 hours, and 7 days.

RESULTS

No significant difference was found in the time from start of treatment to delivery or therapeutic failure between atosiban and placebo (median, 25.6 days vs 21.0 days, respectively; P =.6). The percentages of patients remaining undelivered and not requiring an alternate tocolytic at 24 hours, 48 hours, and 7 days were significantly higher in the atosiban group than in the control group (all P < or =.008). A significant treatment-by-gestational age interaction existed for the 48-hour and 7-day end points. Atosiban was consistently superior to placebo at a gestational age of > or =28 weeks. Fourteen atosiban-treated patients and 5 placebo-treated patients were randomized at <24 weeks; the incidence of fetal-infant deaths was higher for the atosiban group at <24 weeks. Maternal-fetal adverse events were similar except for injection-site reactions, which occurred more often with atosiban.

CONCLUSIONS

In this trial the treatment of patients in preterm labor with atosiban resulted in prolongation of pregnancy for up to 7 days for those at a gestational age > or =28 weeks, and this occurred with a low rate of maternal-fetal adverse effects. In addition, at a gestational age > or =28 weeks, the infant morbidity and mortality of atosiban-initiated standard care were similar to those with placebo-initiated standard care. Given that all patients in this study were eligible for tocolysis and that, in practice, nearly all patients who are eligible for a tocolytic receive one, the benefit of using atosiban is the placebo-like maternal-fetal side effect profile. These observations support the use of this oxytocin receptor antagonist in the treatment of patients in preterm labor with intact membranes. Efficacy and infant outcome data at <28 weeks are inconclusive.

Maintenance treatment of preterm labor with the oxytocin antagonist atosiban. The Atosiban PTL-098 Study Group

OBJECTIVES

Patients admitted with an acute episode of preterm labor who respond to early intravenously administered tocolysis remain at risk of having subsequent episodes of preterm labor and preterm delivery. Several pharmacologic agents have been used in an attempt to reduce subsequent episodes of preterm labor, and all are associated with significant side effects. Atosiban, an oxytocin receptor antagonist, is effective in the treatment of an acute episode of preterm labor. This study was designed to compare the efficacy and safety of atosiban with those of placebo maintenance therapy in women with preterm labor who achieved uterine quiescence with intravenous atosiban.

STUDY DESIGN

A multicenter, double-blind, placebo-controlled trial was designed for patients in preterm labor who responded to early intravenous treatment with atosiban. Five hundred thirteen patients were randomly assigned to receive maintenance therapy, 252 to receive atosiban, and 251 to receive matching placebo. Maintenance therapy was administered as a continuous subcutaneous infusion, via pump, of 30 microg/min to the end of 36 weeks' gestation. The primary end point was the number of days from the start of maintenance therapy until the first recurrence of labor. A secondary end point was the percentage of patients receiving subsequent intravenous atosiban therapy.

RESULTS

The time (median) from the start of maintenance treatment to the first recurrence of labor was 32.6 days with atosiban and 27.6 days with placebo (P =.02). At least one subsequent intravenous atosiban treatment was needed by 61 atosiban patients (23%) and 77 placebo patients (31%). Except for injection site reactions, adverse event profiles of atosiban and placebo were comparable. There were 4 neonatal deaths reported in the atosiban group and 5 in the placebo group after the start of maintenance therapy. Infant outcomes (including birth weight) were comparable between maintenance and treatment groups.

CONCLUSIONS

Maintenance therapy with the oxytocin receptor antagonist atosiban can prolong uterine quiescence after successful treatment of an acute episode of preterm labor with atosiban. Treatment was well tolerated.

Preterm labor: placental pathology and clinical correlation

OBJECTIVE

To determine the relevance of ischemia in the incidence of preterm labor. A second objective was to document perinatal outcomes for patients with preterm labor classified according to its clinical, functional, and pathologic characteristics (infectious, ischemic, mixed, or idiopathic).

METHODS

Perinatal outcomes were evaluated for 145 consecutive patients with preterm labor, subdivided into etiologic categories according to clinical, functional (Doppler), and morphologic (placental pathology) characteristics. A group of 44 normal pregnancies delivered at term served as controls.

RESULTS

Of the preterm labor group, 28.3% were classified as ischemic, compared with 4.5% of the control group (odds ratio and 95% confidence interval = 8.28 [1.8, 51.8]; P < .05). Compared with the control group, the preterm labor patients who delivered preterm had higher rates of ischemia (31.4% compared with 4.5%; P < .05) and infection (16.1% compared with 2.3%; P < .05). Among the preterm labor group, patients classified in the infectious or ischemic subgroups had a higher rate of preterm delivery (95.0% and 90.2% compared with 73.2%; P < .05), admission to the neonatal intensive care unit (75.0% and 61.0% compared with 40.0%; P < .05), and newborn weight under 1500 g (35.0% and 19.5% compared with 3.7%; P < .05) than the idiopathic subgroup.

CONCLUSION

Preterm labor resulting from infection or ischemia is associated with a higher perinatal complication rate than idiopathic preterm labor.

Diurnal changes in light intensity inside the pregnant uterus in sheep

Penetration of light into the pregnant sheep uterus was studied in 9 ewes, gestational ages 40 to 142 days (term 147 days). Light sensors were placed inside the pregnant horn and over the flank skin overlying the position of the uterine horn. To perform the experiments, the ewes were placed in a study cage outdoors and light sensors were connected to a luxometer. Simultaneous measurements were obtained from the intrauterine and the external sensors in the shade at noon. The amount of light detected inside the uterus increased with gestational age from two lux at 40 days to 51.1 +/- 16.5 (n = 5) lux at 142 days (0.2 and 5.4% of the amount of light detected at the maternal flank). Measurements through the 24 h were done in four pregnant ewes at 142 days gestation under natural photoperiod (13.5 light:10.5 dark). In these experiments, the intensity of intrauterine light changed through the 24 h, reflecting the changes in the intensity of the sunlight. Maximal intrauterine light values were observed at noon, corresponding to 4.7% of incident light. Small but detectable values were observed at 0900 and 1800 h. Our data show that, at mid gestation, light reaches the pregnant uterus and that, at late gestation, changes in intrauterine lighting throughout the 24 h are present reflecting the changes in external daylight. Therefore the sheep fetus is exposed to light-dark transitions at dawn and dusk, and to a peak of light at midday.

Dose ranging study of the oxytocin antagonist atosiban in the treatment of preterm labor. Atosiban Study Group

OBJECTIVE

To evaluate the minimal effective dose regimen of the oxytocin antagonist atosiban in the treatment of acute preterm labor and the effect of a bolus on uterine activity within the first 2 hours compared with no bolus and the same infusion rate.

METHODS

A randomized, double-blind (except the ritodrine group), parallel group, multicenter study compared four different intravenous atosiban regimens (6.5 mg bolus plus 300 micrograms/minute, placebo bolus plus 300 micrograms/minute, 2mg bolus plus 100 micrograms/minute, and 0.6 mg plus 30 micrograms/minute) and intravenous ritodrine with respect to the cessation of uterine contractions for 1 hour or more during infusion, four or fewer contractions per hour in the last hour of therapy, and discontinuation because of adverse experiences. Three hundred two patients were enrolled.

RESULTS

The lowest dose of atosiban (0.6 mg plus 30 micrograms/minute) was significantly less effective than ritodrine with respect to cessation of contractions and four or fewer contractions per hour in the last hour of therapy. Other atosiban regimens were comparable to ritodrine, except for the drug discontinuation rate for adverse experiences. Bolus therapy with high-dose atosiban resulted in a significantly greater proportion of patients who stopped contracting within the first 2 hours of treatment (17 of 63) compared with those not receiving a bolus (six of 58, P = .017). Because of adverse experiences, the study drug was discontinued in one of 244 atosiban patients and 15 of 58 ritodrine patients.

CONCLUSION

Atosiban's effect on uterine activity in preterm labor was enhanced by bolus infusion and was similar to the effect of ritodrine, but with fewer side effects.

Effect of constant light on fetal and maternal prolactin rhythms in sheep

A 24-h rhythm of plasma PRL is present in fetal sheep. This rhythm is synchronized to an environmental clue (zeitgeber). We determined whether the light-dark cycle (L:D) is a zeitgeber for the fetal PRL rhythm and, if so, whether the mother might convey this zeitgeber to the fetus. We kept nine ewes (twin pregnancies) in constant light (L:L) and five ewes (singleton) in 14:10 L:D from 110 days gestation. Fetuses and mothers were catheterized at 119 days gestation. Blood samples were taken hourly for 24 h after 16 days under L:L or L:D. A mean 24-h rhythm of PRL was found (by RIA) in fetuses under L:D, but not in those under L:L. However, fetuses under L:L showed individual 24-h PRL rhythms (cosinor analysis) whose acrophases were distributed around the clock. Nonsynchronized rhythms persisted after 23 and 30 days of L:L. Acrophases of PRL rhythms within a set of twins were closer than those between sets, suggesting that twins were responding to a common signal. These findings indicate that the L:D cycle is a zeitgeber for the PRL rhythm in fetal sheep and suggest that the mother might convey the zeitgeber.

Effect of chronic hypoxia on myometrial responsiveness in the pregnant rat

Mechanisms involving the timing of normal parturition are not well understood in most animal species. To gain a greater understanding of the mechanisms, we employed hypoxia to perturb the normal system of parturition. The present study was designed to investigate the effects of chronic hypoxia on myometrial contractility in the near-term pregnant rat. Rats were exposed to room air (control) or to continuous hypoxia (10.5% O2) either from experimental days 19 through 21 (2-day exposure) or from experimental days 15 through 21 (6-day exposure). On day 21, blood was collected for hormone assays, and the uterine horns were collected from each dam. One horn was snap-frozen in liquid nitrogen for oxytocin (OT) receptor analysis, and the other was used for in vitro assessment of myometrial contractile responses to cumulative doses of OT or arginine vasopressin (AVP). Hypoxic exposure resulted in approximately 60% reduction of the maximal myometrial contractile response to OT and a significant reduction in OT binding sites from 256.9 +/- 34.9 to 84.9 +/- 21.3 fmol/mg protein (P<0.01). In contrast, the contractile response to AVP was unaffected after exposure to chronic hypoxia (P> 0.05). Additionally, we observed no difference in the plasma concentrations of estrogen, progesterone, and corticosterone. We conclude that chronic hypoxia decreased the effectiveness of OT-specific contractile mechanisms, at least partially through a decrease in OT binding sites.

Transvascular albumin transport and protein replenishment after haemorrhage in the chronically catheterized pregnant rabbit

Pregnancy is characterized by increases in both blood and interstitial volumes, but the mechanisms are unknown. To test the hypotheses that blood volume (BV) recovery after haemorrhage in pregnant (P) is faster than in nonpregnant (NP) rabbits, and that this can be explained by a higher capillary filtration, a 20% BV haemorrhage was produced in a group of 7 P and 7 NP rabbits. We determined the BV recovery (measured by 99Tc), the total plasma protein mass and the haematocrit at 10, 20, 30, 60 and 1440 min after haemorrhage. Arterial and venous pressures and heart rate were measured during a 30-min control period, during the 10 min of haemorrhage, and for the following 70 min. In a separate group of P and NP rabbits, 125I-labelled albumin was infused and blood samples were obtained at 10, 20, and 30 min. Capillary filtration was expressed as the percentage of radioactive albumin that left the intravascular space after 30 min. No differences were found in the rate of BV recovery, arterial and venous pressures, or heart rate response between P and NP animals (P > 0.1). By 24 h total plasma protein mass (TPPM) was significantly increased above baseline in the P rabbits by an average+SEM of 13 + 3.7%, but not in NP rabbits (5 + 4.5%). At 30 min, the amount of labelled albumin in the intravascular space decreased by 15.4 + 3.4% for Pv. 8.2 + 1.2% for NP rabbits (P < 0.05). There was a high correlation between TPPM recovery and BV recovery in the P (r = 0.96) and NP rabbits (r = 0.95). In conclusion, we did not find differences in the rate at which the BV recovered during pregnancy, despite the increased capillary permeability. During pregnancy, the combination of the latter with an increase in the TPPM elevation above pre-haemorrhage levels suggests a faster rate of protein mobilization.

Endothelin-1 potentiates the in vitro contractile response of pregnant human myometrium to oxytocin

OBJECTIVE

This study was designed to test the hypothesis that endothelin-1 pretreatment of human myometrium at subcontractile doses in vitro will enhance the contractile response to oxytocin.

STUDY DESIGN

In vitro contractile oxytocin dose-response curves were generated by use of myometrial strips collected from nonpregnant women (n = 7), pregnant patients at elective cesarean section (n = 7), and patients in active labor (n = 7) in the presence or absence of 10(-9) mol/L endothelin-1. Contractile responses were analyzed by on-line computer, and data were normalized to the maximum response to potassium.

RESULTS

Pretreatment with endothelin-1 significantly increased the maximal contractile response of pregnant myometrium (p < 0.01 compared with control). In marked contrast myometrium from nonpregnant patients was unaffected by endothelin-1 pretreatment. Values for the two-point discrimination and Hill coefficient were not different among the treatment groups.

CONCLUSION

Endothelin-1 potentiates the oxytocin response of myometrium from pregnant but not nonpregnant women. We speculate that a high circulating level of a uterotonin-like oxytocin may not be necessary to initiate labor. The synergistic interaction between different uterotonins may be sufficient.

Placental passage of the oxytocin antagonist atosiban

OBJECTIVE

We wanted to determine the degree of placental transfer of atosiban (Antocin), an oxytocin antagonist, in pregnant women at term. We also assessed the effects of the infusion on umbilical cord blood gases at birth and the maternal hematocrit drop after cesarean section.

STUDY DESIGN

Eight women undergoing elective cesarean section at term were studied. Each received an infusion of 300 micrograms/min of atosiban over 208 to 443 minutes; the infusion was continued up to the time of cord clamping. Uterine vein and umbilical blood samples were obtained simultaneously. They were assayed by specific radioimmunoassay. Cord blood gases were obtained and compared with those from a control group of women undergoing elective cesarean section.

RESULTS

The mean (+/- SD) maternal uterine vein concentration was 331.9 +/- 42.9 ng/ml, compared with 42 +/- 13 ng/ml in the umbilical vein (p < 0.05). The mean maternal/fetal was 12 +/- 0.03, which was not affected by the length of infusion. There was no significant difference in the hematocrit drop between the cesarean delivery groups: 5.9 +/- 0.4 for the control group versus 5.8 +/- 1.1 for the atosiban group (p > 0.1). The mean cord pH was 7.27 for the atosiban group versus 7.27 for the control group (n = 141) (p > 0.1). One year follow-up of the infants (n = 7) was normal.

CONCLUSIONS

Our results show minimal placental transfer of atosiban. Drug levels did not increase with longer infusions, and no effect was seen on umbilical cord gases. Administration of atosiban even at high doses up to the time of delivery did not increase maternal blood loss at cesarean section.

Is uterine blood flow controlled locally or systemically in the pregnant rabbit?

OBJECTIVE

We tested the hypothesis that uterine blood flow is regulated by systemic circulating factors. The alternative hypothesis is that uterine blood flow is regulated by local factors.

STUDY DESIGN

Adult female New Zealand White rabbits were subjected to a unilateral tubal ligation and thereafter allowed to become pregnant (n = 9). A group of nonpregnant one-tube-ligated animals served as controls (n = 8). On day 21 of gestation uterine blood flow in the pregnant and nonpregnant uterine horns were measured with 15 microns microspheres. The concentration of prostaglandin E2 metabolites were measured in blood from the uterine veins and from the arterial circulation.

RESULTS

Absolute uterine blood flow in the pregnant uterine horn was 12.9 +/- 4.7 versus 5.2 +/- 1.4 ml in the nonpregnant horn (p < 0.05). However, when expressed by blood flow per gram of tissue they were not different (p > 0.1). The uterine blood flow for the nonpregnant uterine horn in the pregnant animals was the same as that of the horns from nonpregnant animals. The level of prostaglandin E metabolites was greater in the uterine vein draining the pregnant horn compared to the nonpregnant horn (p < 0.05).

CONCLUSION

These data support the conclusion that the increase in uterine blood flow observed during pregnancy is controlled largely by local factors induced by pregnancy.

Fetectomy alters maternal endocrine and uterine activity rhythms in rhesus macaques during late gestation

OBJECTIVE

The current study was designed to test the hypothesis that fetectomy will eliminate or substantially alter rhythms in maternal estradiol concentrations and subsequently reduce or eliminate uterine activity rhythms.

STUDY DESIGN

Six rhesus macaques underwent surgery for catheter implantation between days 117 and 122 of gestation (term = 167 days). At surgery the fetuses were removed and the membranes and placenta remained intact. Thirteen additional catheterized pregnant animals served as controls. Maternal arterial blood samples were collected for hormone analysis at 3-hour intervals for 24 hours, starting at 9 AM. This sampling protocol was performed four times at weekly intervals until 151 to 157 days' gestation.

RESULTS

A significant rhythm (p < 0.01) in estradiol was determined in the control animals with peak concentrations observed in the morning hours whereas the progesterone peak was observed at night. In the fetectomy group mean plasma estradiol concentrations decreased significantly from 312 +/- 34 to 110 +/- 8 pg/ml throughout the study (p < 0.01). Despite a trend toward elevated morning levels, the estradiol rhythm was ablated. The uterine contractile rhythm observed in the control animals with peak activity between 10 PM and midnight (p < 0.01) was also ablated after fetectomy. Basal concentrations of progesterone were significantly lower than control values.

CONCLUSIONS

(1) Fetectomy resulted in the elimination of the maternal estradiol rhythm. (2) The uterine activity rhythm was lost after fetectomy. These data suggest that the fetus, by supplying precursors of estrogen, may play an indirect role in the regulation of maternal estradiol rhythms, which in turn appear to play a key role in regulating uterine activity rhythms.

Physiology of uterine activity in pregnancy

During the past few years enormous progress has been made in the understanding of the molecular mechanisms involved in parturition; however, the answer to the fundamental question of how labor is initiated remains elusive. This is a very important question because alterations in the timing of birth (preterm and post-term deliveries) are associated with much of perinatal morbidity and mortality. Currently available treatments for preterm labor are not clearly effective. Prevention of preterm delivery by home uterine monitoring has been proposed; however, the value of this technique has not been conclusively shown. A variety of substances have been implicated in the genesis of labor, including oxytocin, prostaglandins, cytokines, and endothelin. The role of infection in preterm labor has also been extensively studied, but it seems clear that a relatively small percentage of preterm labor is caused by infection. Attention has also focused on the role of estrogen and progesterone, and the possible uses of progesterone antagonists in the induction of labor. A better understanding of the relationship of intrauterine hypoxia and preterm delivery may also help us in establishing treatment and prevention strategies.