Maternal serum corticotropin-releasing hormone at midgestation in Hispanic and white women.

OBJECTIVE: Maternal circulating corticotropin-releasing hormone analysis at midgestation has been proposed as a parameter for the prediction of preterm birth. However, one recent study has reported that corticotropin-releasing hormone concentrations at midgestation differ in the black and white populations. These findings led us to investigate whether other populations have differing concentrations of maternal circulating corticotropin-releasing hormone that may require reference to specific population-based medians for optimal midgestational screening. METHODS: In this study we have defined the mean and median concentrations of maternal circulating corticotropin-releasing hormone in Hispanic and white populations at each gestational week from 14 to 18 weeks of pregnancy, using a sensitive and specific radioimmunoassay. RESULTS: Corticotropin-releasing hormone concentrations were found to be significantly lower in the Hispanic population as compared with whites at 16, 17, and 18 weeks' gestation. The distribution of corticotropin-releasing hormone, expressed as multiples of the median (MoM) using the appropriate ethnicity-related median, was estimated for each gestational week and for each population. No differences were observed in the distribution of the ethnicity-adjusted MoM for Hispanics and whites. CONCLUSION: These data demonstrate that ethnicity is a significant factor affecting corticotropin-releasing hormone concentrations at midgestation in the Hispanic and white populations. The use of ethnicity-specific medians to estimate the ethnicity-specific MoM for the corticotropin-releasing hormone concentrations may enhance the predictive value of midgestational maternal corticotropin-releasing hormone as a screening parameter for the prediction of preterm birth.

Effects of cocaine on basal and pulsatile prolactin levels in rhesus monkeys.

OBJECTIVES: Cocaine abuse is often associated with reproductive cycle dysfunction including altered menstrual cyclicity and decreased ovulation rates. Cocaine might also alter prolactin (PRL) secretion, presumably through the effects of this drug on hypothalamic dopamine, the primary factor regulating pituitary PRL secretion. We assessed basal and pulsatile PRL levels to determine whether hyperprolactinemia is associated with cocaine-induced disruption of menstrual cyclicity in rhesus monkeys. METHODS: Normally cycling, drug-naïve monkeys were studied. Cocaine-treated animals were pair-fed with controls to minimize cocaine-related differences in caloric intake. Twenty-eight monkeys were randomized to receive daily intravenous (iv) infusion of saline or cocaine (1, 2, or 4 mg/kg) on cycle days 2-14. Daily blood samples were obtained through indwelling catheters for measurement of ovarian steroids, gonadotropins, and PRL. Laparoscopy was performed 2 days after the midcycle estradiol surge to document ovulation. Sixteen other monkeys were randomized to receive daily iv infusion of saline or cocaine (4 mg/kg). Blood samples were obtained every 15 minutes for 8 hours in the early (cycle day 1-5), mid- (cycle day 6-10), and late (cycle day 11-15) follicular phase. Plasma was assayed for PRL, and pulses were identified by cluster analysis. RESULTS: All seven control monkeys had laparoscopically confirmed ovulation compared to two of seven monkeys receiving 1 mg/kg, three of seven monkeys receiving 2 mg/kg, and one of seven receiving 4 mg/kg of cocaine hydrochloride. Cycle length was normal in six of seven controls, and in one of seven, two of seven, and two of seven monkeys receiving the 1, 2, and 4 mg/kg of cocaine, respectively. Estradiol levels were significantly higher in controls versus cocaine-treated monkeys, but there was no difference in basal gonadotropin levels during treatment. Mean PRL levels during treatment were significantly lower (P <.05) in controls (4.6 +/- 0.2 ng/mL) as compared to monkeys receiving 1 (6.5 +/- 0.6 ng/mL), 2 (6.1 +/- 0.4 ng/mL), and 4 mg/kg (7.2 +/- 0.6 ng/mL) of cocaine. There was no significant difference in PRL pulse amplitude or frequency between controls and cocaine-treated monkeys during each cycle phase. CONCLUSIONS: Circulating PRL levels were slightly higher in monkeys receiving cocaine during the follicular phase. Although this increase was statistically significant, PRL levels remained well within the euprolactinemic range in cocaine-treated monkeys.

Cocaine impairs ovarian response to exogenous gonadotropins in nonhuman primates.

OBJECTIVE: Determine whether cocaine directly impairs ovarian steroid production and ovulation. METHODS: Normally cycling adult female rhesus monkeys received daily intravenous normal saline (control; n = 8) or cocaine (4 mg/kg; n = 8) through the follicular phase. Monkeys were injected daily with human menopausal gonadotropin (hMG; Pergonal) at a dose of 6 IU/kg intramuscularly beginning on cycle day 2. Daily blood samples were obtained, and serum estradiol (E(2)) and progesterone (P(4)) were measured by radioimmunoassay. When serum levels of E(2) declined, plateaued, or exceeded 600 pg/mL, laparoscopy was performed to count the number of follicles. If no new corpus luteum was present, monkeys were injected intramuscularly with 1000 IU of hCG. Laparoscopy was repeated 2 days later to document the number of ovulatory stigma. RESULTS: During ovarian stimulation, cocaine-treated monkeys required an average additional 1.5 days of hMG injections (P =.01), and this resulted in a greater total dose of hMG compared with control monkeys (351 +/- 16 IU versus 297 +/- 15 IU [mean +/- standard error of the mean], P =.03). For spontaneous and hCG-triggered ovulation, the number of ovulatory stigma was significantly lower (P <.003) in the cocaine-treated versus control monkeys (16 versus 31). Peak E(2) levels were significantly (P =.05) lower in cocaine-treated monkeys compared with controls. Luteal phase P(4) levels were lower in the cocaine-treated monkeys, but the difference was not statistically significant when compared with controls. CONCLUSION: Cocaine impaired ovarian responsiveness to exogenous gonadotropins and decreased ovulatory stigma in nonhuman primates. These findings suggest that cocaine has direct ovarian effects.

Salmon GnRH and its analogues bind the human placental receptor.

OBJECTIVE: The presence of GnRH receptors in the human placenta has been recognized for a number of years. However, mammalian GnRH, which is expressed in placental tissues, has limited affinity for the chorionic receptor. On the basis of immunological and bioactivity data, we have previously proposed that the chorionic GnRH may differ from mammalian GnRH. METHODS: We have studied the affinity of another isoform of GnRH (ie, salmon GnRH and stable analogues of this GnRH isoform), and compared their receptor affinity to that of mammalian GnRH and its analogues. RESULTS: Using our receptor assay method with the labeled mammalian GnRH analogue Buserelin, salmon GnRH had a twofold greater affinity for the placental GnRH receptor than did mammalian GnRH and for the stable salmon GnRH analogue the affinity was increased tenfold. Using a homologous receptor assay method with a stable salmon GnRH analogue as label, the affinity for this salmon GnRH analogue had a K(d) of 101 nmol/L. CONCLUSION: The presence of these higher affinity receptors for non-mammalian GnRH in the human placenta has led us to propose that the chorionic tissues may express more than one isoform of GnRH and that non-mammalian GnRH, such as salmon GnRH, may be potent regulators of placental functions.

Action of chicken II GnRH on the human placenta.

The stability, receptor binding, bioactivity, and production of chicken II GnRH and its analogs in the human placenta were studied. Both chicken II and mammalian GnRH are rapidly degraded by placental enzymes, yet the chicken II isoform is six times more stable. Analogs of chicken II GnRH were synthesized, and their stability in the presence of placental enzymes was tested. The D-Arg(6)-chicken II GnRH-aza-Gly(10)-NH(2) analog was found to be resistant to enzymatic degradation. The placental receptor binding activity of the chicken II GnRH analogs and chicken II GnRH was compared with that of mammalian GnRH and its analogs. Because D-Arg(6)-chicken II GnRH-aza-Gly(10)-NH(2) had the highest affinity for the placental receptor and was stable in placental extracts, the bioactivity of this analog on the regulation of placental human CG (hCG) release was compared with that for mammalian and chicken II GnRH using a human term placental explant culture system. This chicken II GnRH analog effected a stimulation of hCG at the lowest concentration studied (250 nM). With extended exposure and/or higher concentrations of this chicken II GnRH analog, the release of hCG from human placental explants was inhibited. Using a placental explant perifusion system and a highly specific RIA for chicken II GnRH, the pulsatile release of chicken II GnRH from the early human placenta was demonstrated. These studies are the first to demonstrate bioactivity of a second form of GnRH in a human tissue and to identify the pulsatile release of chicken II GnRH from a human tissue. These data led us to propose that chicken II GnRH and its synthetic analogs may be potent ligands for hormone regulation during pregnancy.

Effect of ethanol on thromboxane and prostacyclin production in the human placenta.

Fetal alcohol syndrome (FAS) is frequently associated with intrauterine growth retardation (IUGR). One cause of ethanol-induced IUGR is thought to be related to increased pressor activity in the human placenta, resulting in decreased oxygenation and nutrient transport to the fetus. Thus, we have investigated the effect of ethanol on paracrine substances, such as thromboxane and prostacyclin, that act as vasoregulators within the intrauterine tissues. In these studies we have utilized the perfused single human cotyledon system to study the effect of ethanol on placental prostanoid production. We assessed the effect of longer (240 min) and more acute (60 min) exposure to ethanol on release of thromboxane B(2) (TxB(2)) and 6-keto-prostaglandin F(1 alpha) (6-keto-PGF(1 alpha)) at the maternal and fetal sides of the placenta. Thromboxane was increased by both longer and shorter ethanol exposure, especially on the fetal side of the placenta. Prostacyclin was essentially unchanged with exposure to ethanol. The thromboxane:prostacyclin ratio also tended to increase with both 60- and 240-min ethanol exposure, but a statistically significant increase was seen only at a few time points. In the 60-min ethanol exposure, an increase in thromboxane was observed both during and following exposure to ethanol. The increase in the thromboxane milieu observed with ethanol exposure may lead, at least in part, to the IUGR which is frequently associated with FAS. Prevention of this effect of ethanol on thromboxane production might be a beneficial intervention for FAS.

Low-dose follicular-phase cocaine administration disrupts menstrual and ovarian cyclicity in rhesus monkeys.

OBJECTIVE: To evaluate the effects of daily low-dose follicular-phase cocaine administration on menstrual cyclicity, ovulation rates, corpus luteum function, and hormone levels in rhesus monkeys. METHOD: Normally cycling, drug-naive, adult rhesus monkeys were randomized to receive either 1 mg/kg of cocaine (n = 7), 2 mg/kg of cocaine (n = 7), or normal saline (n = 7) daily on cycle days 2 to 14. Daily blood samples were obtained through indwelling catheters for measurement of serum gonadotropins and ovarian steroids. Daily vaginal swabs were obtained to determine onset of menses. Laparoscopy was performed 2 days after the midcycle estrogen peak to document ovulation. Daily caloric intakes as well as pretreatment and posttreatment weights were recorded. RESULTS: Two of seven monkeys receiving 1 mg/kg per day and two of seven monkeys receiving 2 mg/kg per day of cocaine had timely ovulation and normal menstrual cycle lengths. One monkey receiving the 2-mg/kg dose ovulated on cycle day 24 and had a short luteal phase (7 days) with a mean progesterone level of 2.4 ng/mL. All seven saline-treated control monkeys ovulated normally; the mean cycle length was 29 days and all had adequate luteal phases. The difference in ovulation rates between cocaine-treated and control monkeys was statistically significant (P = .003). There were no differences in basal levels of LH or FSH between treatment groups. There were no significant differences in weight change or caloric intake among groups. One third of the subsequent menstrual cycles in cocaine-treated monkeys were of abnormal duration. CONCLUSION: Daily low-dose follicular-phase cocaine administration disrupts menstrual cyclicity and folliculogenesis. This effect is independent of weight loss, caloric intake, and basal gonadotropin levels. Cocaine exposure may have a persistent effect on menstrual and ovarian cyclicity in some monkeys.

Cocaine impairs follicular phase pulsatile gonadotropin secretion in rhesus monkeys.

OBJECTIVE: To assess cocaine's effect on follicular phase pulsatile gonadotropin secretion in normally cycling rhesus monkeys. METHODS: Sixteen monkeys were paired by body weight and randomized to receive intravenous saline (n = 8) or cocaine (4 mg/kg, n = 8) daily on cycle days 2 to 14. Monkeys were chronically cannulated to allow frequent blood collections without anesthesia. Blood samples were obtained every 15 minutes for 8 hours in early (EFP; cycle days 1 to 5), mid-(MFP; cycle days 6 to 10), and late (LFP; cycle days 11 to 15) follicular phase. Plasma concentrations of LH, FSH, and estradiol-17 beta (E2) were determined by radioimmunoassay. Pulses were identified by cluster analysis. Statistical differences were determined by analysis of variance (ANOVA) and Sidak's multiple comparison test. RESULTS: Seven out of eight monkeys in the control group demonstrated timely ovulation. Only one monkey in the cocaine-treated group ovulated. Similar gonadotropin pulse intervals (70 to 90 minutes) were observed throughout the follicular phase in both the controls and cocaine-treated monkeys. LH and FSH pulse amplitudes increased significantly from the EFP/MFP to the LFP in controls. In cocaine-treated monkeys, gonadotropin pulse amplitudes remained at EFP/MFP levels throughout the study period. The mean gonadotropin pulse amplitude and the mean E2 levels in the LFP were significantly greater in controls as compared with cocaine-treated monkeys (P < .001). CONCLUSION: These findings demonstrate that cocaine suppresses the normal increase in LH and FSH pulse amplitude seen in the LFP. Further studies are in progress to determine the mechanism of cocaine's disruption of the hypothalamic-pituitary-ovarian axis.

Placental IGF-I in severe intrauterine growth retardation.

IGF-I, which is produced by intrauterine tissues including the placenta, has been implicated as a possible factor in intrauterine growth retardation (IUGR). We hypothesized that placental IGF-I production may be aberrant in pregnancies affected by IUGR. A placental perifusion system was utilized to study the release of IGF-I in placentas from normotensive severe IUGR (birthweight < 5%, (n = 9)) and normal control pregnancies (n = 5). For each placenta, tissues were perifused and samples were collected from hour 5 to hour 10. IGF-I was measured by radioimmunoassay after acid extraction. The cumulative release of total IGF-I from the control placentas from hour 5 to hour 10 of perifusion was 15,417 +/- 1,337 pg/g (mean +/- SEM), and decreased approximately 45% from hour 5 through hour 10 of perifusion. The pattern of IGF-I release, as well as the absolute mass of IGF-I, from six of the nine IUGR placentas was similar to the controls. However, three of the nine IUGR placentas demonstrated a significantly different IGF-I release pattern, i.e., IGF-I release did not decrease throughout the perifusion period. These three placentas also had abnormal absolute production rates of IGF-I, i.e., significantly elevated in one and significantly decreased in two. IGF-I production and release were normal in some IUGR placentas, although in certain cases of IUGR, the placental production and release pattern were aberrant. We conclude that abnormal regulation and production of IGF-I by the placenta may be a factor affecting certain pregnancies complicated by IUGR.

Effects of follicular-phase cocaine administration on menstrual and ovarian cyclicity in rhesus monkeys.

OBJECTIVE: The purpose of this study was to evaluate the effects of daily follicular-phase cocaine administration on menstrual cyclicity, gonadotropin and ovarian steroid levels, ovulation rates, and corpus luteum function in cycling rhesus monkeys. STUDY DESIGN: Thirteen normally cycling, drug-naive adult rhesus monkeys were randomized to receive daily intravenous injections of either 4 mg/kg cocaine or an equal volume of saline solution. Treated animals were yoked to pair-fed controls to minimize differences in caloric intake. Daily blood samples were obtained through indwelling catheters for measurement of serum gonadotropin and ovarian steroid levels. Daily vaginal swabs were obtained to determine the onset of menses. Laparoscopy was performed 2 days after the midcycle estrogen peak to check for ovulation. Daily caloric intakes and pretreatment and posttreatment weights were recorded. RESULTS: All six of the control monkeys had laparoscopically confirmed ovulation compared with one of seven in the cocaine-treated group (p < 0.004). Cycle length was normal in five of six controls versus one of seven cocaine-treated monkeys. Estradiol levels were significantly higher in the controls versus the cocaine-treated monkeys (p = 0.01) during the first 14 days of the treatment cycle. There were no differences in basal plasma gonadotropin levels between groups. Luteal-phase lengths and luteal-phase plasma progesterone levels were similar in the controls and the single ovulatory cocaine-treated monkey. There were no significant differences in weight change or caloric intake between the two groups. CONCLUSIONS: Daily follicular-phase cocaine administration disrupts menstrual cyclicity and folliculogenesis independent of weight loss, caloric intake, and basal gonadotropin levels.

The effect of dexamethasone on CRH and prostanoid production from human term placenta.

The human placenta at term produces large quantities of corticotropin releasing hormone (CRH) and prostanoids. These hormones play an important role in the maintenance of pregnancy, and the initiation and progress of labor; yet little is known of factors affecting their regulation and the interrelationship of CRH and prostanoid production. In these studies we have investigated the effect of dexamethasone on the production of CRH and prostanoids from fresh human term placental tissues. The basal release of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), thromboxane B2 (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) from human term placental explants increased from the fifth hour in culture, while the release of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) was not significantly changed during this period. The addition of dexamethasone (10(-8) M) to the perifusing medium resulted in a rapid and dramatic inhibition of PGE2, PGF2 alpha, PGFM, TxB2 and 6-keto-PGF1 alpha release. On the other hand, CRH release was not significantly changed throughout the seven hours of incubation with dexamethasone. These data demonstrate that glucocorticoids at physiologic concentrations can inhibit human term placental prostanoid production, and thus glucocorticoid production may play an important role in the physiological regulation of placental prostanoid production in the human placenta. However, dexamethasone did not alter CRH release, demonstrating that the inhibition of placental prostanoids by dexamethasone is not a CRH mediated event.

Effect of excessive GnRH-binding substance on circulating maternal hCG in human pregnancy.

Gonadotropin-releasing hormone (GnRH) can stimulate the release of placental human chorionic gonadotropin (hCG). Thus, at the onset of these studies it was the objective to define the relationship of hCG to GnRH in the maternal circulation throughout pregnancy, focusing on early pregnancy. Blood samples were collected at 8, 10, 12, 14, 16, 28 and 36 weeks of gestation during labor and the GnRH and hCG levels were determined by radioimmunoassay. Of 39 pregnancies, a GnRH-binding substance was found in the maternal circulation of three. This GnRH-binding substance resulted in erroneous GnRH levels, due to the very high non-specific binding. In the pregnant women without this GnRH-binding substance, GnRH attained highest concentrations at 12-14 weeks. The typical peak of hCG at 8-10 weeks of gestation was observed in this group, while the group of patients having the GnRH-binding substance had significantly lower hCG levels. Each of the patients with circulating GnRH-binding substance had prior pregnancy(s) and two of the three had a prior pregnancy loss. The nature of this GnRH-binding substance was investigated using gel chromatography. After incubation of [125I]GnRH with patient plasma for 3 days this substance was shown to be of high molecular weight which was ethanol precipitable. This binding substance may therefore be an antibody, since it appears to be a high molecular weight protein requiring a number of days to bind the [125I] GnRH. This GnRH-binding substance may be of physiological importance, since the circulating hCG level was significantly less in the group of patients with this substance than in those without.

Effect of IGF-I on placental thromboxane and prostacyclin release in severe intrauterine growth retardation.

Our recent findings that IGF-I inhibits placental thromboxane (TxB2) release (1, 2) and that prostanoid release from placentas or certain pregnancies complicated by intrauterine growth retardation (IUGR) is decreased [Sorem KA, Siler-Khodr TM, Placenta, 16:503-515, 1995] led us to investigate the effect of IGF-I on prostanoid release from placentas of IUGR pregnancies. The placental response of 6-keto-prostaglandin F1a (6-keto-PGF1a) and thromboxane (TxB2) to IGF-I in severe IUGR (n = 5) was compared with the response in normal pregnancies (n = 6). Placentas were perifused with medium containing IGF-I at doses of 0, 5.2, 10.4, 20.8, and 83.3 ng/ml. In three of the five IUGR placentas (responsive group), incubation with IGF-I resulted in an inhibition of TxB2, attaining significantly greater inhibition at a lower dose of IGF-I than the normal placental response. However, in two of the five IUGR placentas (non-responsive group), the TxB2 was insensitive to the normal inhibitory action of IGF-I. The baseline production of prostanoids from the IUGR placentas was not predictive of their response to IGF-I. Moreover, 6-keto-PGF1a was not inhibited in any of the placentas, IUGRs, or normals. However, the ratio for TxB2 over 6-keto-PGF1a basal production rate from the zero treatment time to the fifth hour was significantly less in the nonresponsive IUGR placentas than for the responsive IUGR placentas or for the normal placentas. Certain IUGR placentas demonstrated a significant suppression of TxB2 with IGF-I, whereas other IUGR placentas were insensitive to exogenous IGF-I. A decreased and unchanging ratio of TxB2/6-keto-PGF1a production rate was characteristic of the nonresponders.

Circulating maternal corticotropin-releasing hormone and gonadotropin-releasing hormone in normal and abnormal pregnancies.

OBJECTIVE: Corticotropin-releasing hormone and gonadotropin-releasing hormone are produced by the human placenta and have been measured in the maternal circulation during pregnancy. Our objective was to determine concentrations of these substances in maternal plasma throughout normal pregnancies and in early pregnancy loss. STUDY DESIGN: Fifty-one pregnant women were followed up prospectively and plasma samples were drawn at 8, 10, 12, 14, 16, 28, and 36 weeks' gestation and during labor. Specific and sensitive radioimmunoassays were used to determine corticotropin-releasing hormone and gonadotropin-releasing hormone concentrations in these samples. RESULTS: Blood samples were drawn at all time points and outcome data were available from 33 women who completed their pregnancies at term without complications. In this normal group circulating corticotropin-releasing hormone concentrations increased from low or undetectable concentrations at 8 weeks (< or = 23.2 +/- 1.3 pg/ml, mean +/- SEM) to measurable values at 16 weeks (34.3 +/- 2.2 pg/ml). Thereafter there was a significant increase to 1294 +/- 113 pg/ml in labor. Gonadotropin-releasing hormone demonstrated a trimodal distribution, increasing significantly from 8 to 14 weeks, decreasing at 16 weeks, and increasing again by term. The ratio of corticotropin-releasing hormone to gonadotropin-releasing hormone in the normal group demonstrated a 30-fold increase from 8 weeks to term. In eight cases of early pregnancy loss corticotropin-releasing hormone and gonadotropin-releasing hormone concentrations were not significantly different from those of the normal group in early pregnancy. In two cases of premature delivery gonadotropin-releasing hormone concentrations and ratios were within the normal range; corticotropin-releasing hormone levels were normal in both cases of premature delivery. CONCLUSION: In this study we determined maternal concentrations of corticotropin-releasing hormone and gonadotropin-releasing hormone in normal pregnancies and in labor at term. Neither maternal concentrations of corticotropin-releasing hormone nor gonadotropin-releasing hormone were useful in identifying pregnant women at risk for early pregnancy loss.

Dose-related action of estradiol on placental prostanoid prediction.

Prostanoids play an important role throughout all of pregnancy and during the initiation and progress of labor. The human placenta at term produces large quantities of prostanoids, yet little is known of the factors that regulate their biosynthesis. Herein, we report the effect of estradiol or estradiol and progesterone on the basal release of placental prostanoids from fresh human term placental explants using a perifusion system. The basal release of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), thromboxane (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) increased about 50% from the fifth to the ninth hour in culture, while the release of 13, 14-dihydro-15-keto-PGF (PGFM) remained constant and hCG release decreased. The dose-related effect of estradiol (20-2,000 ng/ml) in the perifusing medium starting at the fifth hour of perifusion (i.e., the zero treatment time) effected no change in the release of TxB2, PGF2 alpha, PGFM or hCG. A biphasic action on the release of 6-keto-PGF1 alpha was observed, i.e. it was significantly decreased when incubated with 20 ng/ml of estradiol, but effected an increase after exposure to 200 ng/ml. The concomitant addition of progesterone (2,000 ng/ml) with estradiol (200 ng/ml) significantly inhibited the stimulatory action of estradiol at this dose. The release of PGF2 was inhibited in a dose-related fashion with increasing dose of estradiol. The addition of progesterone with estradiol (2,000 and 200 ng/ml, respectively) reversed the inhibition of PGE2 by estradiol alone. These data demonstrate that physiologic levels of estradiol affect 6-keto-PGF1 alpha and PGE2 release from the human term placenta, but do not significantly alter production of TxB2, PGFM or hCG under these conditions.

Placental prostanoid release in severe intrauterine growth retardation.

Our objective was to evaluate prostanoid release from the placentae of pregnancies complicated by severe intrauterine growth retardation (IUGR) and without hypertension, compared with placentae from normal, uncomplicated term pregnancies. A perifusion system was utilized to study the release of prostanoids 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), thromboxane B2(TxB2), prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) from human placentae from pregnancies complicated by normotensive severe IUGR (n = 9, five at term and four preterm) and normal control pregnancies (n = 6). For each placenta, triplicate chambers of tissue were perifused at a rate of 6 ml/h, and samples were collected from hours 5-10. Prostanoids were measured using specific and sensitive radioimmunoassays. In the IUGR group, the basal placental production of the vasoconstrictor thromboxane was not increased, nor was the ratio of cumulative TxB2 to 6-keto-PGF1 alpha elevated compared with normal term controls. In three term IUGR placentae, the ratio was significantly decreased compared with controls. The basal placental production of the vasoconstrictor PGF2 alpha was likewise not increased compared with controls, nor was the ratio of PGF2 alpha to PGE2 elevated. Two of the placentae in the term IUGR group demonstrated significant elevations of PGE2 and 6-keto-PGF1 alpha. Overall, the IUGR placentae released normal or low normal levels of the prostanoids studied. The pattern of placental prostanoid release over time was similar to that of the normal term placentae. The term and preterm placentae of pregnancies complicated by severe IUGR did not exhibit an excess production of vasoconstrictor prostanoids. Therefore, strategies designed to reduce thromboxane production in severe IUGR without hypertension may be unjustified.

Dose-related effect of IGF-I on placental prostanoid release.

Prostanoids play an important role throughout all of pregnancy and during the initiation and progress of labor. The human placenta at term produces large quantities of prostanoids, yet little is known of the factors regulating their biosynthesis. In a previous study we observed that insulin-like growth factor I (IGF-I) specifically inhibits thromboxane B2 (TxB2) and prostaglandin F2 alpha (PGF2 alpha) from human term placental explants. In these studies we have defined the dose-related action of IGF-I on the release of placental prostanoids. With use of a perifusion system, the basal release of prostaglandin E2 (PGE2), PGF2 alpha, TxB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) from human term placental explants increased from the fifth hour in culture, while the release of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) remained constant. The addition of IGF-I (5.2-83.3 ng/mL) to the perifusing medium effected an inhibition of TxB2 and PGF2 alpha. The release of TxB2 was inhibited in a dose-related fashion from the initiation of IGF-I treatment and throughout the five hours of treatment, whereas the inhibition of PGF2 alpha was significant only at a dose of 83.3 ng/mL of IGF-I. Yet, the release of 6-keto-PGF1 alpha, PGE2, or PGFM was not altered by any dose of IGF-I studied. Because both TxB2 and PGF2 alpha are vasoconstrictors, we have proposed that IGF-I may enhance vasodilation in the placenta. Therefore, IGF-I may allow for increased blood flow, thus affecting the maintenance of pregnancy and the supply of nutrients available for the growth of the fetus.

Effect of IGF-1 on placental prostanoid production.

Prostanoids play an important role throughout all of pregnancy and during the initiation and progress of labor. The human placenta, at term, produces large quantities of prostanoids, yet little is known of the steps regulating their biosynthesis. In these studies, the effect of IGF-I on the release of placental prostanoids was investigated. The basal release of prostaglandin E (PGE), prostaglandin F (PGF), thromboxane (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) increased from the fifth hour in culture, while the release of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) remained constant and hCG release decreased. The addition of IGF-I (10(-8) M) to the perfusing medium effected an inhibition of TxB2 and PGF within two and one-half hours of exposure. However, the release of PGE, PGFM, 6-keto-PGF1 alpha or hCG was not altered by IGF-I. Because both TxB2 and PGF are vaso-constrictors, we have proposed that IGF-I may enhance vasodilation in the placenta. Therefore, IGF-I may allow increased blood flow, thus affecting the maintenance of pregnancy and supply of nutrients for the growth of the fetus.

Effect of exogenous arachidonic acid and enzyme inhibitors on placental prostanoid production.

Prostanoids play an important role throughout pregnancy and during the initiation and progress of labor. The human placenta, at term, produces large quantities of prostanoids, yet little is known of the rate-limiting steps regulating their biosynthesis. In these studies, the effect of exogenous arachidonic acid and of enzyme inhibitors on the release of placental prostanoids was investigated. Basal prostaglandin E (PGE), prostaglandin F (PGF), thromboxane (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) increased from the fifth hour in culture, yet the increased PGF release did not result in further 13,14-dihydro-15-keto-PGF2 alpha (PGFM) production. Addition of varying doses of arachidonic acid (0.2-10 micrograms/ml) had no significant effect on PGFM, TxB2 or 6-keto-PGF1 alpha, although the endogenous arachidonate was similar to or much less than the doses studied. Only at the 10 micrograms/ml dose was a delayed increase of PGE and PGF observed. Incubation with indomethacin resulted in an immediate inhibition of PGE, PGF, TxB2 and 6-keto-PGF1 alpha, with a delayed inhibition of PGFM. The phospholipase A2 inhibitor, quinacrine (10 microM), had no significant effect on PGE, PGFM, TxB2 or 6-keto-PGF1 alpha. PGF was inhibited within the first hour of quinacrine exposure, but no significant inhibition was observed thereafter. Ca2+ chelator, EDTA, effected an inhibition of only 6-keto-PGF1 alpha. Nordihydroguaiaretic acid, a leukotriene inhibitor, reduced PGE release as well as 6-keto-PGF1 alpha. These data demonstrate the high biosynthetic competence of the human term placenta to produce prostanoids. This capacity does not appear to be rate-limited by arachidonic acid availability. However, the metabolism of PGF to PGFM appears to be saturated. In addition, the production of placenta prostacyclin may be affected by Ca2+ levels, as chelating agent inhibited the release of 6-keto-PGF1 alpha.

Chorionic peptidase inactivates GnRH as a post-proline peptidase.

Recently, we have described a chorionic peptidase (C-ase-1) which inactivates gonadotropin releasing hormone (GnRH), oxytocin, angiotensin II and thyrotropin releasing hormone. Since all these hormones contain a proline residue, we proposed that C-ase-1 may act as a post-proline peptidase. Using HPLC and amino acid analyses, we have defined the products which resulted from enzymatic inactivation of GnRH by C-ase-1. The N-terminal nonapeptide of GnRH was isolated by HPLC and confirmed by amino acid composition analyses. Thus, it was demonstrated that C-ase-1 acts as a post-proline peptidase when inactivating GnRH, yielding the nonapeptide, i.e., des-Gly10-NH2-GnRH, and Gly-NH2. The levels of intrauterine GnRH, angiotensin II, oxytocin and thyrotropin releasing hormone may be affected and integrated by this enzyme. Thus, C-ase-1 may play an important role in the regulation of the paracrine and endocrine function during pregnancy.