Localization of prostaglandin H synthase, prostaglandin dehydrogenase, corticotropin releasing hormone and glucocorticoid receptor in rhesus monkey fetal membranes with labor and in the presence of infection.

Prostaglandins (PGs) play a central role in primate parturition by their actions on uterine contractility and on cervical ripening. Rhesus monkey placentation is hemochorial and the endocrine events surrounding parturition are qualitatively similar to human pregnancy. Although there is an increase in PG production before the onset of labor, little is known about the cellular localization of the PGH synthase (PGHS) or the 15-hydroxy PG dehydrogenase (PGDH) in the fetal membranes of nonhuman primates and whether it changes at term in spontaneous labor or during preterm labor associated with infection. Placental corticotropin releasing hormone (CRH) and the glucocorticoid receptor (GR) have also been implicated as mediators in parturition by virtue of their roles in PG production. We utilized immunohistochemical methods to localize the inducible isoform PGHS-2, PGDH, GR and CRH in rhesus monkey amnion, chorion and attached decidua. Tissues were obtained at cesarean section during late pregnancy, in spontaneous labor at term and in premature labor induced by Group B streptococcal intraamniotic infection. Specific staining for immunoreactive (ir)-PGHS-2 was observed in amnion epithelial and mesenchymal cells and to a lesser extent in chorion and decidua. In contrast, ir-PGDH was localized primarily to the extravillous trophoblast layer of chorion. GR was localized to both the cytoplasm and nucleus of amnion epithelial cells, subepithelial fibroblasts, chorion trophoblasts and in decidua. Immunostaining for CRH was found in amnion and in scattered decidual cells but was most intense in the chorion trophoblast layer. There was no demonstrable change in this overall pattern of immunostaining in association with the onset of labor at term except for a decrease in staining for ir-PGDH in chorion. Experimental Group B streptococcal chorioamnionitis resulted in preterm labor and extensive necrosis of extravillous trophoblast cells with subsequent loss of chorionic ir-PGDH and relative sparing of ir-PGHS-2 in amnion epithelium which favors the net production of PGs. The expression pattern of these effectors in the rhesus monkey fetal membranes points to a functional role of PGs and glucocorticoids in the process of term and preterm parturition which is similar to that in human pregnancy.

Comparison of plasma oxytocin and catecholamine concentrations with uterine activity in pregnant rhesus monkeys.

Pregnant rhesus monkeys exhibit diurnal changes in uterine activity (UA), with episodes of increased UA during the early hours of darkness. The estrogenic environment during late pregnancy serves a permissive role in the maintenance of nocturnal UA episodes and may involve myometrial interactions with oxytocin (OT) and/or alpha-adrenergic stimuli. In the present study we have used chronically catheterized pregnant rhesus monkeys to measure diurnal changes in maternal plasma OT, epinephrine, norepinephrine, and dopamine. We also determined the effects of infusing an OT antagonist (ORF 22164) and the alpha-adrenergic antagonist phentolamine on nocturnal UA episodes. Animals were exposed to a 16-h light, 8-h dark photo-period, with the hours of darkness between 2300-0700 h. Maternal plasma samples were collected at 3-h intervals for 36 h and analyzed by RIA for OT and by high performance liquid chromatography for catecholamines. Plasma OT was correlated with UA in animals that displayed nocturnal UA episodes (r = 0.76; P less than 0.01). Maximal OT concentrations occurred at 2400 h in these animals; plasma OT was higher during the hours of darkness compared to levels during the light phase (10.4 +/- 1.9 and 3.0 +/- 0.3 pmol/L, respectively; n = 4). Some animals did not display nocturnal episodes of increased UA and showed no increase in OT concentrations during the hours of darkness. Maternal plasma catecholamine concentrations were not correlated with nocturnal UA and were maximal during the light phase. Nocturnal UA was abolished within 30 min of infusion of the OT antagonist, but phentolamine infusions had no effect on nocturnal UA. We conclude that 1) changes in maternal plasma catecholamine concentrations are not involved in the generation of nocturnal UA; 2) the presence of episodes of increased UA at night results from increased maternal plasma OT concentrations; and 3) the absence of nocturnal UA in some animals can be explained by a reduced level of OT secretion.

The effect of relaxin infusion on prolactin and growth hormone secretion in monkeys.

To test the hypothesis that relaxin may affect pituitary hormone secretion, synthetic human relaxin was infused into cycling and pregnant rhesus monkeys. Doses ranging from 0.154-1540 ng/kg.min were calculated to achieve circulating relaxin concentrations of 1 pM to 10 nM. Low (0.154 and 1.54 ng/kg.min), intermediate (15.4 and 154 ng/kg.min), and high (1540 ng/kg.min) doses of relaxin were infused for 15 min each hour into ovulating monkeys at the midluteal phase of the menstrual cycle in two separate experiments. Serum GH and PRL were measured by RIA, and serum relaxin was determined by enzyme-linked immunosorbent assay. Relaxin was undetectable in peripheral plasma during the control saline infusion and during infusion of the lowest dose of relaxin. Serum relaxin levels reached 0.011, 0.119, 0.965, and 13.0 nM with 1.54, 15.4, 154, and 1540 ng/kg.min, respectively. Serum GH was significantly elevated over basal levels upon infusion of relaxin from 1.54-1540 ng/kg.min; however, a plateau was observed with the intermediate doses, and a decrease in the magnitude of the response was observed at the highest dose. Serum PRL increased over basal levels with 15.4 and 154 ng/kg.min, but there was no difference in the magnitude of the increase between these doses. PRL levels during infusion of the highest dose of relaxin were similar to control levels. These data suggest that relaxin can stimulate secretion of GH and PRL in cycling monkeys within a defined dose range, but that a decrease in pituitary responsiveness occurs at higher doses. One high dose of relaxin (2600 ng/kg.min) was infused for 1 h into the maternal and then the fetal circulations of chronically catheterized and tethered pregnant monkeys between 120-140 days gestation. Upon infusion of relaxin into the maternal circulation, there was a significant elevation of PRL in the mother but not the fetus. Upon infusion of relaxin into the fetus, there was no consistent change in PRL secretion in either the mother or the fetus. In conclusion, relaxin may have a heretofore undescribed role in pituitary physiology during the menstrual cycle and in pregnancy.

Uterine estrogen receptors are increased by RU486 in late pregnant rhesus macaques but not after spontaneous labor.

Progesterone withdrawal as a mechanism for parturition in primates is controversial. The progesterone antagonist RU486, given in late pregnancy to rhesus monkeys at a dose of 47 mmol/kg.day (20 mg/kg.day), causes an increase in uterine activity, but not the expected increase in amniotic fluid prostaglandins or cervical dilatation. We, therefore, studied the effect of RU486 on estrogen receptor (ER) localization and concentration in reproductive tract tissues in rhesus monkeys during late gestation and after spontaneous labor at term. Distribution of ER in pregnant uterine tissues was studied by immunocytochemical techniques and quantified by a biochemical assay, both of which employed a monoclonal antibody specific for ER. ER was not present in amnion and chorion by immunocytochemical investigation; however, a significant increase in receptor staining was seen in decidua and myometrium after RU486 treatment compared to that in both pregnant control tissues and parturient tissues. Sucrose gradient assay of nuclear (n) and cytosolic (c) ER revealed a low level of ER (expressed as fmol of estradiol bound/mg of DNA) in pregnant and parturient decidua (pregnant: nER = 7.3 +/- 2.4, cER = 17.1 +/- 6.4; parturient, nER = 7.7 +/- 3.1, cER = 16.4 +/- 8.8) and myometrium (pregnant: nER = 21.7 +/- 4.1, cER = 20.8 +/- 5.3; parturient: nER = 30.0 +/- 2.8, cER = 10.7 +/- 6.7). In contrast, tissues collected from RU486-treated animals contained high levels of ER in decidua (nER = 52.3 +/- 16.8, cER = 240.5 +/- 145.3) and myometrium (nER = 77.0 +/- 19.2; cER = 66.5 +/- 31.6). We conclude that 1) the increase in ER in decidua and myometrium after RU486 treatment is the result of a decrease in the inhibitory action of progesterone on ER and documents the progesterone receptor antagonism by RU486 during induced myometrial contractility in late pregnant rhesus monkeys; 2) the absence of ER from amnion and chorion indicates that the normally observed increase in prostaglandin production by rhesus fetal membranes during labor is not mediated by ER; and 3) the absence of a change in the concentration of ER in decidua and myometrium from pregnant control monkeys and those in spontaneous labor indicates that an increase in ER (and, by inference, a withdrawal of receptor-mediated progesterone inhibition) is not part of the normal events in preparation for parturition in primates.

Interleukin-1 beta intra-amniotic infusion induces tumor necrosis factor-alpha, prostaglandin production, and preterm contractions in pregnant rhesus monkeys.

OBJECTIVE: To describe the temporal and quantitative consequences of intra-amniotic interleukin-1 beta infusion in a nonhuman primate model. METHODS: On days 128-138 of gestation (term 167 days), four chronically instrumented rhesus monkeys (Macaca mulatta) underwent serial intra-amniotic infusions of 2, 5, and 10-20 micrograms recombinant human interleukin-1 beta. Each infusion was for 2 hours, and subsequent infusions were at least 48 hours later. Amniotic fluid was sampled serially both before and after infusion for interleukin-1 beta, tumor necrosis factor-alpha (TFN-alpha), and prostaglandin (PG) E2 and F2 alpha by specific assays, and uterine activity in each monkey was recorded continuously. RESULTS: Intra-amniotic concentrations of interleukin-1 beta rose dramatically after infusion. This rise was rapidly followed by the appearance of TNF-alpha in the amniotic cavities of all animals, with maximal levels reached 5 hours after the initiation of the infusion. Both interleukin-1 beta and TNF-alpha were rapidly cleared from the amniotic fluid and returned to baseline levels by 24-48 hours. Increases in PGE2 and F2 alpha paralleled those of the two cytokines but remained elevated for the duration of the experiments. The stimulation of uterine contractility from a pre-infusion level of 200 mmHg. seconds/hour to 6000 mmHg. seconds/hour occurred an average of 6-10 hours after interleukin-1 beta infusion. These stimulations were transient, usually abating by 22 hours after infusion, and did not result in frank labor. CONCLUSION: In the rhesus monkey, intra-amniotic infusion of interleukin-1 beta rapidly induces production of intra-amniotic TNF-alpha as well as PGE2 and F2 alpha, followed by uterine contractility. Uterine activity diminishes as cytokine levels return to pre-infusion levels, even in the presence of elevated intraamniotic PG levels. Tumor necrosis factor-alpha may act synergistically with interleukin-1 beta in the pathophysiology of cytokine-related preterm labor.

Progesterone receptor localization and isoforms in myometrium, decidua, and fetal membranes from rhesus macaques: evidence for functional progesterone withdrawal at parturition.

OBJECTIVE: It is not known whether withdrawal of progesterone (P) action is a prerequisite for parturition in women or in nonhuman primates because concentrations of circulating progesterone or progesterone receptors (PR) in myometrium and decidua do not decrease before delivery. To examine this potentially important regulatory mechanism, we determined PR isoforms, PR localization, and mRNA in myometrium, decidua, and fetal membranes from rhesus monkeys during pregnancy and in spontaneous labor at term. METHODS: Gestational tissues were obtained midpregnancy (day 80-100), late pregnancy (day 130-145), and during spontaneous labor at term (day 161-167). Samples of rhesus monkey myometrium, decidua, chorion-decidua, and amnion were collected and analyzed for total nuclear and cytosolic PR by competitive binding assay. Progesterone receptor isoforms were identified and quantified by Western blot analysis, and PR mRNA was determined by a specific ribonuclease protection assay. Nuclear PR was localized by immunohistochemistry with monoclonal anti-PR (JZB39) after microwave stabilization. RESULTS: Myometrium and decidua showed no change in total PR during pregnancy and labor. Nuclear PR was not detected in fetal membranes by binding assay but was localized in amnion epithelial and mesenchymal cells and in chorion laeve cytotrophoblasts by immunohistochemistry. Staining for PR was substantially less by serial antibody dilution in fetal membranes than in decidua. Message for PR was confirmed in all tissues analyzed. A significant (P <.05) shift in the ratio of PR isoforms (from PR-B dominance at midpregnancy to PR-A dominance in labor) was observed in myometrium but not in decidua. Both PR-A and PR-B isoforms and PR nuclear staining were nearly undetectable in amnion obtained during labor. CONCLUSION: A shift to PR-A dominance in myometrium at term together with a loss of PR in fetal membranes provides evidence for a functional progesterone withdrawal mechanism, which may facilitate the initiation of parturition in primates.

Predictive utility of pre-partum temperature changes in the mare.

Rectal temperature was recorded from 22 mares at 0700, 1500 and 2300 h daily for seven days pre-partum and one day post partum. A circadian variation in rectal temperature was present with the lowest temperature recorded at 0700 h. Because of this, the mares were divided into three groups based on time of parturition; those foaling between 0700 and 1500 h (n = 2); between 1500 and 2300 h (n = 13); and between 2300 and 0700 h (n = 7). On the day prior to delivery (Day -1) the circadian pattern was absent because the nocturnal increase did not occur. A significant decrease in temperature was recorded prior to parturition in the group foaling between 1500 and 2300 h. A distinct decrease in temperature occurred in the majority of mares in the other two groups but this was not statistically significant. After parturition, rectal temperature increased to supranormal levels before returning to normal.

[Pregnancy and labor in the mare: uterine activity and endocrinology]. / Trächtigkeit und Geburt bei der Stute: uterine Aktivität und Endokrinologie.

Electromyographic (EMG) recordings were made during the last two weeks of pregnancy from two mares. Four bipolar EMG electrodes were implanted in the uteri of the mares; near the tubo-uterine junction and bifurcation of the pregnant horn, in the body of the uterus and near the cervix. Plasma samples were collected every 4 hours during the same period and more intensely during parturition. Estradiol 17 beta, progesterone, PGF2 alpha metabolite and oxytocin were measured by radioimmunoassay. During the last week preceding delivery, EMG activity was elevated and was greatest at night. EMG activity was further increased during the last 24 hours before delivery of the foal and reached its highest intensity for 7 to 13 hours immediately prepartum. This period of intense activity is described as stage I of parturition. EMG activity decreased to very low levels 2 to 4 hours before delivery but abruptly increased again at rupture of the choriollantois and continued through delivery when activity decreased again until delivery of the placenta. The ratio of estradiol 17 beta to progesterone (E 17 beta/P) increased through the last week prepartum due to an increase in the level of estradiol 17 beta concentrations and during the last 24 hours the change in the E 17 beta/P ratio was due to a significant decrease in progesterone. Oxytocin and PGF2 alpha metabolite increased abruptly just before rupture of the fetal membranes and there is some evidence that oxytocin increased prior to PGF2 alpha metabolite. We hypothesize that the increasing E 17 beta/P ratio allows the evolution of labor to occur during the daylight hours preceding parturition.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in plasma concentrations of oestradiol-17 beta and their relationship to those of progesterone, 13,14-dihydro-15-keto-prostaglandin F-2 alpha and oxytocin across pregnancy and at parturition in pony mares.

Concentrations of plasma progesterone were similar to values reported in the literature except that a significant decrease in progesterone during the last day, but before parturition, was detected by systematic, high-intensity blood sampling. Mean concentrations of oestradiol-17 beta increased sharply and significantly, plateaued for 132.8 +/- 1.5 days (mean +/- s.e.m., N = 9), then declined sharply in each mare. There was obvious variation between the mares in when these increases and decreases in oestradiol-17 beta occurred, with the events being related closely to ambient photoperiod conditions rather than to the stage of pregnancy. Concentration of 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM) remained at low levels (less than 400 pg/ml) until Day 200 then increased to peak pregnancy levels (greater than 2000 pg/ml) by Day 300 and remained at this value until parturition. The concentrations of oxytocin remained basal (less than 15 microU/ml) throughout pregnancy and increased only at the beginning of the expulsive stage of labour. There was an increase, although not statistically significant, in the relative concentrations of oestradiol-17 beta to progesterone beginning 3 days before parturition, with the highest value of the ratio occurring at fetal delivery. Far more striking were acute changes in PGFM and oxytocin during parturition. Maximal concentrations of PGFM (approximately 30 ng/ml) and oxytocin (greater than 200 microU/ml) were measured between rupture of the chorioallantois and the completion of delivery. Closely timed samples from one animal showed that oxytocin increased (more than 10 standard deviations of the mean levels during late pregnancy for this animal) before any change in PGFM. In another dystocic mare, both oxytocin and PGFM peaked in the initial stages of delivery but only oxytocin remained elevated until the dystocia was remedied. The results suggest that an abrupt increase in oxytocin secretion precipitates the expulsive phase of parturition in mares.

Amniotic fluid lipoxygenase metabolites during spontaneous labor and after RU486 treatment during late pregnancy in rhesus macaques.

To determine changes in amniotic fluid (AF) lipoxygenase metabolites prior to spontaneous labor and after RU486 administration, we implanted AF and vascular catheters and myometrial electromyographic (EMG) electrodes in 8 rhesus macaques at 120-130 days of pregnancy (term = 167 days). Four animals had AF samples taken serially until they delivered their infants normally at term. The other four animals received RU486 (20 mg/kg/day) for 3 days. AF samples were collected every 2-3 days and at 12 hour intervals for 72 hours before and after treatment with RU486. Uterine activity was monitored continuously. LTB4, 5-HETE and 15-HETE were measured by radioimmunoassay. In untreated animals, LTB4 and 5-HETE concentrations in AF increased significantly (P less than 0.05) 4 days before delivery with no change in 15-HETE. After RU486, mean levels of LTB4 and 5-HETE were increased although the difference was not statistically significant. No change in 15-HETE levels was observed. In conclusion, LTB4 and 5-HETE increase in AF before the onset of spontaneous labor. Progesterone receptor blockade by RU486 does not reproduce the changes in AF lipoxygenase metabolites observed during normal parturition.

Inhibition and augmentation of progesterone production during pregnancy: effects on parturition in rhesus monkeys.

OBJECTIVES: Uterine quiescence during mammalian pregnancy is attributed to progesterone. However. systemic progesterone levels remain elevated in primates before parturition. Epostane, a selective 3beta-hydroxysteroid dehydrogenase inhibitor, and progesterone (with or without epostane) were administered to late pregnant rhesus monkeys to clarify the role of progesterone in primate parturition. STUDY DESIGN: On days 122 to 132 of gestation (term 167 days), 11 rhesus monkeys (Macaca mulatta) with timed pregnancies were divided into three treatment groups: (1) epostane alone (10 mg/kg subcutaneously), (2) epostane with progesterone subcutaneously in Silastic silicone rubber capsules, and (3) progesterone implants only with no surgical instrumentation. Maternal and fetal blood and amniotic fluid were sampled for progesterone, estrone, estradiol, cortisol, testosterone, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and amniotic fluid was sampled for prostaglandins E2 and F2alpha. Uterine activity was monitored continuously by electromyography and intraamniotic pressure. Cervical status was assessed by a modified Bishop's score. Production of prostaglandins E2 and F2alpha by amnion was determined by tissue superfusion. The group of three noninstrumented monkeys, which received only progesterone Silastic silicone rubber implants subcutaneously at 146 to 148 days, were observed until spontaneous vaginal delivery. RESULTS: Epostane reduced maternal and fetal progesterone levels by 75% and 50%, respectively, followed by increased uterine activity and cervical ripening within 24 hours and vaginal delivery within 48 hours. Amniotic fluid progesterone decreased to undetectable levels. Progesterone implants prevented the epostane-induced decrease in maternal and fetal progesterone levels and the associated myometrial and cervical changes until the implants were removed. Alterations in other steroid hormones were consistent with inhibition of 3beta-hydroxysteroid dehydrogenase. Amniotic prostaglandin E2 production was increased sixfold by epostane (p < 0.05) but did not reach the high levels normally seen at spontaneous parturition. Animals that received progesterone implants alone had markedly elevated circulating progesterone concentrations yet were delivered spontaneously at term (range 163 to 167 days). CONCLUSIONS: Progesterone withdrawal induces preterm labor and delivery (which can be blocked by progesterone substitution) but exogenous progesterone, even in substantial quantities, does not prevent parturition at term.

Electromyographic properties of the myometrium of the pony mare during pregnancy.

Recordings of uterine electrical activity were made from 5 pregnant pony mares from Day 141 to 320 of pregnancy. Three types of activity were identified. Short, medium and long bursts were quantified as the percentage of time each occurred during the hour analysed and further categorized according to frequency, amplitude and duration. The uterus was most active during the early stages recorded and became increasingly quiescent after Day 240. Short-burst activity was greatest when the uterus was most quiescent. Long bursts showed the greatest percentage of activity until Day 220 and then decreased. Medium-burst activity was present throughout the period studied and high amplitude synchronous medium bursts peaked at Day 221-240.

Electromyographic properties of the myometrium correlated with the endocrinology of the pre-partum and post-partum periods and parturition in pony mares.

A complete set of electromyographic recordings, plasma samples and behavioural observations were collected from 2 mares beginning 7 days pre partum, through parturition and into the early post-partum period. During the week pre partum, EMG activity was elevated, occurring 26-73% of the time. Activity was least during the day and greatest at night with no significant difference for the hours of the day or between days pre partum. During the 24 h before delivery, EMG activity was increased for 7-13 h (55-80%) during the daylight hours. EMG activity decreased 2-4 h immediately preceding delivery of the foal, with an abrupt increase at rupture of the chorioallantois. At delivery, EMG activity consisted of events containing a series of 10-13 discrete bursts of increasing amplitude occurring in rapid succession. After fetal delivery there was a reduction in activity until placental delivery followed by very long (2-22 min) trains of potentials.

The ratio of progesterone receptor isoforms changes in the monkey corpus luteum during the luteal phase of the menstrual cycle.

Recent evidence suggests that progesterone is required for ovulation, luteinization, and the maintenance of luteal structure and function in primates. Progesterone action is mediated by intracellular progesterone receptors (PRs), and PRs are detectable by immunocytochemistry in the monkey corpus luteum. However, changes in total luteal PR and PR isoform expression have not been quantitated in the corpus luteum during its life span in the menstrual cycle. This study was initiated to identify and quantify PR isoforms in the macaque corpus luteum throughout the luteal phase of the natural cycle by means of Western blotting. Several antibodies generated against the human PR recognized two bands of consistent molecular weights in monkey tissues, and these bands comigrated with PR-A and PR-B from human T47D cells. Taken together, these data suggest that the two proteins identified were macaque PR-A and PR-B. The estimated molecular weights of monkey PR-A and PR-B were approximately 90,000 and 120,000, respectively. PRs were detected in a variety of macaque tissues, including the endometrium, whole ovary, and decidua, but not in spleen, which is PR-negative by other techniques. Whereas PR-A was the predominant isoform observed in endometrium and decidua, PR-B predominated in the ovary without a dominant follicle or corpus luteum as well as in the corpus luteum. In luteal tissue, PR-A levels decreased (p < 0.05) over the course of the luteal phase, while PR-B levels were unchanged. Hence the ratio of PR-B to PR-A (PR-B:PR-A) increased (p < 0.05) from early to very late luteal phase. Since PR-B:PR-A can alter gene expression in response to progestins and antiprogestins in vitro, the temporal changes in PR-B:PR-A in the monkey corpus luteum may contribute to functional differences in luteal responses to progesterone and other steroids in vivo.

Induction of interleukin-1 receptor antagonist in rhesus monkeys after intraamniotic infection with group B streptococci or interleukin-1 infusion.

OBJECTIVE: Interleukin-1 receptor antagonist is a natural inhibitor of interleukin-1, a cytokine implicated in the initiation of preterm labor after intraamniotic infection. The effects of intraamniotic infection and interleukin-1 infusion on the appearance of interleukin-1 receptor antagonist in amniotic fluid and fetal and maternal plasma were assessed with a monkey model. STUDY DESIGN: On day 130 of pregnancy four chronically catheterized rhesus macaques received intraamniotic inoculations of group B streptococci, three monkeys received intraamniotic infusions of recombinant human interleukin-1 beta, and three monkeys received buffered saline solution infusions. At timed intervals samples of amniotic fluid, fetal plasma, and maternal plasma were assayed for interleukin-1 beta and interleukin-1 receptor antagonist by immunoassays. Uterine activity was continuously monitored by intraamniotic pressure catheters and by electromyographic activity. RESULTS: Interleukin-1 receptor antagonist, but not interleukin-1 beta, was present in the amniotic fluids of all monkeys before intervention. Infection induced the appearance of interleukin-1 beta and an increase in interleukin-1 receptor antagonist in the amniotic fluid. Interleukin-1 beta infusion resulted in a similar increase in the intraamniotic concentration of interleukin-1 receptor antagonist. Both infection and interleukin-1 beta infusion were followed by the transient appearance of interleukin-1 receptor antagonist in the plasma of all fetuses. The subsequent decrease in plasma levels was paralleled by increased amniotic fluid levels of interleukin-1 receptor antagonist. Interleukin-1 beta and interleukin-1 receptor antagonist were not detected in maternal plasma. Both infection and interleukin-1 infusion induced preterm labor in all treated animals. CONCLUSIONS: Interleukin-1 receptor antagonist is a normal component of monkey amniotic fluid. Intraamniotic infection or the appearance of interleukin-1 beta in the amniotic fluid results in increased production of interleukin-1 receptor antagonist. Under physiologic conditions interleukin-1 receptor antagonist in amniotic fluid may inhibit interleukin-1-induced preterm labor.

Prostaglandin production during spontaneous labor and after treatment with RU486 in pregnant rhesus macaques.

The production of prostaglandins from amnion, chorion, decidua, and myometrium was studied in a superfusion system to determine the level of prostaglandin production during late pregnancy, during spontaneous labor, and after in vivo treatment with RU486. Tissues were divided into three groups: those from pregnant control animals, those from animals receiving RU486 (20 mg/kg/day for 3 days) in vivo, and those from animals in spontaneous term labor. Tissues were collected at cesarean section and placed in the superfusion system. After a 30-min equilibration period, fractions of media were collected after passing through the tissue chambers and were assayed for prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2). The results showed a significant increase in PGF2 alpha from decidua of animals treated with RU486 compared to pregnant controls (pregnant: 3.01 +/- 0.45 ng/g/min; RU486: 4.45 +/- 0.28 ng/g/min; p < 0.05). There was a dramatic increase in PGE2 production by amnion from animals in spontaneous labor but not after RU486 treatment (pregnant: 0.21 +/- 0.06 ng/g/min; RU486: 0.56 +/- 0.09 ng/g/min; spontaneous labor: 5.83 +/- 0.43 ng/g/min; p < 0.01). We conclude that while progesterone is important for maintaining uterine quiescence during pregnancy, progesterone receptor blockade by RU486 does not lead to an increase in PGE2 production by amnion as is shown during normal spontaneous labor.

Breed differences in circulating equine relaxin.

Equine relaxin has been previously determined in a small number of pregnant Thoroughbred mares. To better define the normal pregnancy pattern of relaxin, the current study reports on a much larger number of mares. It also was designed to determine if all equids have the same gestational pattern of relaxin secretion. Plasma samples were collected weekly in 24 Standardbred mares, every 7-10 days in 10 pony mares, and daily in late pregnancy from 16 burros. Standardbreds had higher concentrations of relaxin than that reported for Thoroughbreds during most of gestation and did not exhibit the midpregnancy nadir in relaxin concentrations observed in Thoroughbreds. Relaxin concentrations in Standardbreds showed a small but steady decline from Day 150 until delivery. Pony mares had lower relaxin concentrations throughout pregnancy than other mares and had continuously increasing concentrations during gestation. Burros had relaxin concentrations intermediate to ponies and other mares in late gestation. Burros induced to foal with oxytocin showed a sharp increase in relaxin concentrations. No effect of the sex of the offspring was observed in relaxin profiles in Standardbred mares. Each of three Standardbreds with abnormal termination of pregnancy exhibited abnormally low relaxin concentrations at some point in the gestation prior to termination of the pregnancy. Thus, relaxin may be an indicator of placental functioning and used to assess at-risk pregnancies in mares.

Plasma oxytocin and nocturnal uterine activity: maternal but not fetal concentrations increase progressively during late pregnancy and delivery in rhesus monkeys.

OBJECTIVE: The purpose of the study was to determine whether rising maternal or fetal plasma oxytocin concentrations could be responsible for the increasing levels of nocturnal uterine activity on the nights preceding delivery. STUDY DESIGN: Chronically catheterized pregnant rhesus monkeys were exposed to a 16-hour light, 8-hour dark photoperiod (dark 11 PM to 7 AM). Uterine activity and maternal arterial plasma oxytocin concentrations were measured concurrently at weekly intervals in late gestation, on the night preceding term delivery (158 to 167 days, n = 4), and during delivery (149 to 170 days, n = 6). Fetal carotid arterial plasma oxytocin levels were measured during episodes of nocturnal uterine activity in six animals. The effect of oxytocin infusions into the fetus (30 to 480 ng/kg/hr) on uterine activity and on maternal and fetal plasma oxytocin levels was also determined (n = 3). RESULTS: Maximal nocturnal oxytocin concentrations in the maternal plasma rose progressively during late gestation from 9.9 +/- 3.5 pg/ml at 130 to 139 days to 28.7 +/- 9.8 pg/ml on the night preceding term delivery (p < 0.005); a significant increase in nocturnal uterine activity accompanied this rise (p < 0.001). Maternal oxytocin concentrations were elevated during labor and increased further at delivery (62.5 +/- 5.5 pg/ml, p < 0.05). There was no increase in fetal plasma oxytocin during nocturnal uterine activity (3.1 +/- 0.2 pg/ml) or during labor. Fetal oxytocin infusions raised fetal plasma oxytocin concentrations sixtyfold but had no effect on maternal plasma oxytocin concentrations or on uterine activity. CONCLUSIONS: Elevated maternal plasma oxytocin concentrations are responsible, at least in part, for the increasing magnitude of nocturnal uterine activity episodes as term approaches and for the elevated uterine activity before delivery at night. Fetal plasma oxytocin does not contribute to nocturnal uterine activity or to maternal plasma oxytocin concentrations.

Fetal and maternal endocrine responses to experimental intrauterine infection in rhesus monkeys.

OBJECTIVE: Our purpose was to describe the temporal and quantitative relationships among intrauterine infection, fetal-placental steroid biosynthesis, and preterm labor in a nonhuman primate model. STUDY DESIGN: On approximately day 130 of gestation (term 167 days) chronically instrumented rhesus monkeys (Macaca mulatta) were infected with 10(6) colony-forming units of group B streptococci either by intraamniotic (n = 4) or choriodecidual (n = 2) inoculation. As controls, four additionally chronically instrumented noninfected monkeys were followed up to spontaneous parturition. Amniotic fluid and maternal and fetal arterial blood were serially sampled in all monkeys (both before and after infection) for progesterone, estrone, estradiol, dehydroepiandrosterone, dehydroepiandrosterone sulfate, androstenedione, and cortisol by specific radioimmunoassays, and uterine activity was continuously recorded. RESULTS: Spontaneous parturition was preceded by gradual and significant increases in the plasma concentrations of fetal dehydroepiandrosterone, dehydroepiandrosterone sulfate, and androstenedione and fetal and maternal levels of estrone, estradiol, and progesterone but not by changes in cortisol. In contrast, infection-associated parturition (either intraamniotic or choriodecidual) was characterized by abrupt increases in fetal dehydroepiandrosterone, dehydroepiandrosterone sulfate, androstenedione, progesterone, and cortisol but not by increases in maternal or fetal estrone or estradiol. Infection-associated steroid changes occurred concurrently with or after increases in uterine activity. CONCLUSION: Infection-associated preterm parturition is associated with dramatic increases in fetal adrenal steroid biosynthesis but not by corresponding increases in placental estrogen biosynthesis. This suggests that fetal stress in accompanied by placental dysfunction and that infection-associated parturition is not dependent on the increased estrogen biosynthesis observed in spontaneous parturition.