Some new aspects of the endocrinological response to pregnancy

Leptin in human pregnancy: the relationship with gestational hormones

OBJECTIVES

The aims of the study were (1) to examine the relationship between leptin and placental hormones by measuring serial changes in serum levels of leptin during and after pregnancy and (2) to study the effects of several gestational hormones on leptin release from fully differentiated 3T3-L1 adipocyte cell cultures.

STUDY DESIGN

Serum levels of leptin were measured throughout pregnancy and at 3 months post partum in 29 healthy women and were also measured in 18 healthy women at delivery by cesarean section and on postpartum day 3. In addition, 3T3-L1 mouse adipocytes were incubated for 24 hours in media containing various reproductive hormones and leptin production was measured.

RESULTS

Serum leptin levels increased significantly (8.4 +/- 0.9 vs 13.5 +/- 1.5 ng/mL; P <.001) between the first 2 trimesters of pregnancy but not between the second and third trimesters. These changes in leptin did not correlate significantly with changes in body mass index. Leptin levels dropped significantly during the immediate postpartum period, from 34.1 +/- 4.9 at cesarean delivery to 7.3 +/- 1.4 ng/mL on postpartum day 3 (P <.001). Fasting insulin level did not correlate significantly with leptin level during pregnancy but did so during the postpartum period (r = 0.60; P <.05). Leptin secretion from 3T3-L1 adipocytes was increased significantly when cells were cultured with human chorionic gonadotropin (150%, P <.01) and also when they were cultured with estrogen (120%, P <.03).

CONCLUSION

The data suggest that leptin production by adipose tissue is stimulated by several hormones of pregnancy, which may contribute to the increased leptin levels observed during gestation.

Endometrial estrogen and progesterone receptors within 2-14 days of missed menses in the human

Serial changes in the endometrial levels of estrogen and progesterone receptors (ER and PR) were measured in 50 women from days 2 to 14 of missed menses and correlated with the plasma concentrations of hCG, progesterone and 17 beta-estradiol. Both ER and PR of nuclei were higher than cytosolic proteins, with a shift in the ratio of nER/nPR to nPR from 4th day after missed menses. On Scatchard analysis of the cytosolic and nuclear binding proteins, two classes of proteins, corresponding to Type I and II, were found. While the increasing levels of hCG maintained luteal secretion of progesterone and 17 beta-estradiol at normal mid-luteal phase levels, a gradual increase in 17 beta estradiol from 9th day of missed menses was noted. This delicate balance between circulating levels of progesterone and 17 beta-estradiol and their nuclear receptors at early stages of pregnancy may be of significance.

Responses of placental steroids, prostacyclin and thromboxane A2 to thermal stress during pregnancy

The effect of heat stress on plasma prostacyclin and thromboxane A2 and serum estradiol, estriol and progesterone responses was studied in pregnant and non-pregnant women. Group I consisted of 15 healthy non-pregnant women, group II of 23 women 13-14 weeks pregnant, and group III of 23 women 36-37 weeks pregnant. Blood samples were taken before the heat stress, at the end of the stress (70 degrees C for 20 min) and 20 min and/or 45 min after the end of stress. The rectal temperature increased 0.3-0.4 degrees C. The concentration of progesterone did not change during the experiment but that of estradiol increased by 11% (P less than 0.005) in group II and by 10% (P less than 0.01) in group III after the end of the stress. Estriol increased only in group III (by 12%, P less than 0.005) after the end of the stress and the increase was higher as compared to group II (P less than 0.005). The metabolite of prostacyclin increased only in group III by 15% (P less than 0.05) during the heat stress. The metabolite of thromboxane A2 decreased in group II by 20% (P less than 0.005) at the end of the stress while there was no change in group III. The fetal heart rate reactivity remained unchanged and only few uterine contractions were recorded. The small changes found in the levels of prostanoids and placental steroids in response to heat stress do not seem to have any deleterious effects on fetal well-being. The slightly increased concentration of placental steroids may rather reflect changes in metabolism than an increase in uteroplacental blood flow.

Effect of thermal stress on serum prolactin, cortisol and plasma arginine vasopressin concentration in the pregnant and non-pregnant state

The thermal responses of serum prolactin, cortisol and plasma arginine vasopressin were studied on pregnant and non-pregnant women. Group I consisted of 15 healthy non-pregnant women, group II of 23 women 13-14 weeks pregnant and group III of 23 women 36-37 weeks pregnant. Blood samples were taken before the stress (21-23 degrees C), at the end of a 20 min stay in a heat chamber (70 degrees C, 15% relative humidity) and 20 min and 45 min after the stress (21-23 degrees C). The rectal temperature increased 0.3-0.4 degrees C. Serum concentration of prolactin increased from the pre-stress level by 82% in group I (NS), by 25% in group II (P less than 0.05) by the end of the stress but declined steadily in group III by 12% till the end of the recovery period (P less than 0.001). The cortisol concentration increased only in group II during the recovery period (54-72%, P less than 0.05). In this group the subjects who felt discomfort after the stress had higher cortisol levels already before the stress. Arginine vasopressin levels increased significantly only in group I by 17% (P less than 0.05) and there were no differences in the proportional changes between the groups. The response of prolactin to thermal stress seems to be abolished at late pregnancy while the responses of cortisol and arginine vasopressin are not influenced by pregnancy.

Some endocrinological events associated with early pregnancy failure

Serial measurements of serum progesterone, oestradiol, human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) have been determined in 33 women experiencing early pregnancy failure and compared with the values of the same hormones in 72 healthy women having uncomplicated pregnancies. Steroid production by the corpus luteum seemed similar in both groups up to 6 weeks gestation but thereafter placental steroidogenesis was not evident in those women in whom spontaneous pregnancy losses occurred. Placental production of the two protein hormones, hCG and hPL, did take place, and whereas the circulating levels were not as high as in normal pregnancies, levels did usually increase before clinical evidence of miscarriage occurred. hCG was not a sensitive discriminator of subsequent failure. In these women there were no significant hormone differences between those with evidence of a fetus and those without.

Volume homeostasis and osmoregulation in human pregnancy

This chapter reviews alterations in volume and sodium homeostasis and osmoregulation during human pregnancy. Pregnant women undergo extracellular and plasma volume increases of 50-70%, and these changes accompany marked cumulative sodium retention shared by both mother and fetus. Pregnancy alters several factors with opposing effects on renal salt handling; however, mechanisms by which gestational sodium accumulation and volume expansion are achieved remain obscure. Furthermore, despite substantial increases in absolute blood volume, considerable uncertainty exists as to how this volume is sensed, particularly in late pregnancy when a rapid increase in volume is associated with decreases in peripheral resistance and blood pressure. Attempts to assess 'effective' intravascular volume suggest that pregnant women sense their volume as normal. Osmoregulation is also changed. Body tonicity and the osmotic thresholds for AVP release and thirst decrease by about 10 mosm/kg. The mechanisms responsible for the osmoregulatory changes are obscure. Haemodynamic stimuli such as decrements in blood pressure and of 'effective circulating volume' do not seem to account for them. Of the many increments in hormone levels known to accompany gestation, only hCG has so far been implicated in these changes. Pregnant women experience three- to fourfold increments in AVP disposal rates between early and mid pregnancy; this may be caused by the striking rise in circulating cystine-aminopeptidase (vasopressinase) which also occurs during this period. The increments in MCR may be one reason why the hormonal response to a given osmotic stimulus appears to decrease in late pregnancy. All these alterations permit speculation on the manner in which the decrease in Posm occurs and is maintained within narrow limits. Lowering the osmotic threshold to drink stimulates a rise in water intake and dilution of body fluids. Since AVP release is not suppressed at the usual level of hypotonicity, AVP continues to circulate at levels sufficient to permit water retention. Posm continues to decline until it decreases below the new osmotic thirst threshold, when a new steady state is established. At this point water turnover, too, resembles that in the non-pregnant state. The change in MCR and the marked increment in plasma vasopressinase may explain certain observations regarding disordered water metabolism during late pregnancy. These are the transient DI syndromes due either to subclinical hypothalamic disease or to a disorder peculiar to pregnancy which is AVP-resistant but dDAVP-responsive; the latter analogue resists degradation by vasopressinase.

Isolation and characterization of the human chorionic gonadotropin beta subunit (CG beta) gene cluster: regulation of transcriptionally active CG beta gene by cyclic AMP

The alpha and beta subunit genes encoding chorionic gonadotropin (CG) are regulated transcriptionally in placental cells by cyclic AMP (cAMP). The regulatory response sequences of the alpha gene have been studied extensively. Similar studies of the CG beta subunit (CG beta) gene have not been possible because transcriptionally active sequences have not been identified in the clones isolated to date. The CG beta subunit genes form a complex cluster of seven structurally similar genes that include six CG beta-like genes and a single luteinizing hormone beta subunit (LH beta) gene. We isolated overlapping clones containing the entire CG beta/LH beta gene cluster (68 kilobases) from a human genomic cosmid library. The organization of the gene cluster was similar to that found in previous analyses, as determined by Southern blots of genomic DNA, but differed from some of the gene assignments, as determined by fragments cloned in lambda phage. The 5'-flanking sequence of the most active CG beta gene (CG beta 5) was linked to the chloramphenicol acetyltransferase (CAT) coding sequence for analyses of transient expression in different cell types. CG beta CAT was expressed preferentially in JEG-3 choriocarcinoma cells, and expression was markedly stimulated by treatment with 8-bromo-cAMP. Deletion mutagenesis of the CG beta 5'-flanking sequence revealed that multiple regions were required for maximal expression. The kinetics for cAMP stimulation of alpha CAT and CG beta CAT expression were different, suggesting that different pathways may be involved in cAMP-stimulated expression of the alpha and CG beta genes.

Rising human chorionic somatomammotropin predicts ectopic pregnancy rupture following methotrexate chemotherapy

In the medical management of ectopic pregnancy, human chorionic somatomammotropin (hCS) proved to be a more sensitive indicator of continued trophoblastic activity than either beta-human chorionic gonadotropin (beta-hCG) or progesterone (P). In the authors' series of 21 women treated with methotrexate for ectopic pregnancies, only two ruptured. In both cases, hCS levels continued to rise during and after methotrexate treatment. Concomitantly, beta-hCG and P decreased in both of these patients. The authors thus interpret increasing hCS as a reflection of continued syncytiotrophoblast growth, signalling impending rupture. Furthermore, patients with levels of hCS less than 10 ng/ml may require neither medical nor surgical therapy.

A longitudinal study of circulating progesterone, oestradiol, hCG and hPL during pregnancy in type 1 diabetic mothers

Serum progesterone, oestradiol, human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) were determined serially throughout 27 pregnancies in insulin-dependent diabetic patients from Newcastle (UK), 15 such patients from Stockholm (Sweden) and in 69 normal women having uncomplicated pregnancies. Mean progesterone, oestradiol and hCG concentrations were somewhat higher in the diabetic women during the third trimester but hPL values were not different from normal. The increased hormone concentrations did not relate to the increased birthweights or placental weights in the diabetic women. It is suggested that the usual physiological endocrine changes during normal pregnancy are relatively undisturbed by insulin-dependent diabetes or the degree of diabetes control achieved.

Isolation and characterization of the human chorionic gonadotropin beta subunit (CG beta) gene cluster: regulation of transcriptionally active CG beta gene by cyclic AMP

The alpha and beta subunit genes encoding chorionic gonadotropin (CG) are regulated transcriptionally in placental cells by cyclic AMP (cAMP). The regulatory response sequences of the alpha gene have been studied extensively. Similar studies of the CG beta subunit (CG beta) gene have not been possible because transcriptionally active sequences have not been identified in the clones isolated to date. The CG beta subunit genes form a complex cluster of seven structurally similar genes that include six CG beta-like genes and a single luteinizing hormone beta subunit (LH beta) gene. We isolated overlapping clones containing the entire CG beta/LH beta gene cluster (68 kilobases) from a human genomic cosmid library. The organization of the gene cluster was similar to that found in previous analyses, as determined by Southern blots of genomic DNA, but differed from some of the gene assignments, as determined by fragments cloned in lambda phage. The 5'-flanking sequence of the most active CG beta gene (CG beta 5) was linked to the chloramphenicol acetyltransferase (CAT) coding sequence for analyses of transient expression in different cell types. CG beta CAT was expressed preferentially in JEG-3 choriocarcinoma cells, and expression was markedly stimulated by treatment with 8-bromo-cAMP. Deletion mutagenesis of the CG beta 5'-flanking sequence revealed that multiple regions were required for maximal expression. The kinetics for cAMP stimulation of alpha CAT and CG beta CAT expression were different, suggesting that different pathways may be involved in cAMP-stimulated expression of the alpha and CG beta genes.

Effect of fetal growth on maternal protein metabolism in postabsorptive rat

Rates of protein synthesis were measured in whole fetuses and maternal tissues at 17 and 20 days of gestation in postabsorptive rats using continuous infusion of L-[1-14C]leucine. Fetal protein degradation rates were derived from the fractional rates of synthesis and growth. Whole-body (plasma) leucine kinetics in the mother showed a significant reduction of the fraction of plasma leucine oxidized in the mothers bearing older fetuses, a slight increase in the plasma flux, with total leucine oxidation and incorporation into protein remaining similar at the two gestational ages. Estimates of fractional protein synthesis in maternal tissues revealed an increase in placental and hepatic rates at 20 days of gestation, whereas the fractional synthetic rate in muscle remained unchanged. A model for estimation of the redistribution of leucine between plasma and tissues is described in detail. This model revealed a more efficient utilization of leucine in fetal protein synthesis in comparison with other maternal tissues, a greater dependency of the fetus on plasma supply of leucine, and a significant increase (2-fold) in the release of leucine from maternal muscle as the fetal requirements increased proportionately with its size. The latter conclusion, supported by nitrogen analysis and the ratio of bound-to-free leucine in maternal tissues, confirms the importance of maternal stores in maintaining the homeostasis of essential amino acids during late pregnancy.

A prospective study to compare serum human placental lactogen and menstrual dates for determining gestational age

In a group of 575 healthy pregnant women with certain menstrual dates the estimation of the length of gestation from maternal serum human placental lactogen concentrations has been compared with gestational age calculated from the last menstrual period and ultrasonic measurements of the fetal biparietal diameter. In 412 of these patients labor started spontaneously, and the estimated dates of delivery determined by these three methods were also compared. In the range of 9 to 17 weeks of pregnancy, gestational age can be determined by human placental lactogen measurement to within 7 days (+/- 1 SD) which compares favorably with other methods. Regarding the prediction of the expected date of delivery, 88% were delivered within 2 weeks of the date predicted by last menstrual period, 82% within 2 weeks of the sonar date, and 80% by the date determined by human placental lactogen assessment. Prediction of delivery in a further group of 139 women with uncertain dates gave 73% within 2 weeks by sonar date and 69% within 2 weeks by human placental lactogen determination. We suggest human placental lactogen measurements should become part of routine antenatal care complementing rather than replacing the role of ultrasonic scanning. For those doctors and patients who wish to avoid more exposure to ultrasonic scanning than absolutely necessary, human placental lactogen estimates offer an alternative method for assessing the length of gestation.

Steroid hormones in emetic and non-emetic pregnancy

Nausea and/or vomiting in early pregnancy is common enough to be generally accepted as normal or 'physiological'. The specific etiology of these complaints is still obscure. One possibility is that endocrine factors may play some part. In this study, 102 healthy pregnant women, of whom 62 complained of nausea, were followed throughout pregnancy and the circulating levels of cortisol, testosterone, dehydroepiandrosterone sulphate (DHEA-S), progesterone, oestradiol and total and free oestriol were measured. In early pregnancy, serum levels of cortisol and progesterone were significantly lower in emetic subjects. In the last trimester, significantly higher DHEA-S concentrations and lower testosterone values were found in women who had suffered from nausea and vomiting in early pregnancy compared to asymptomatic subjects. Overt differences were found between emetic and non-emetic pregnancy and it is concluded that endocrine factors are of etiological importance in emesis gravidarum.

Endocrinologic events in early pregnancy failure

Fourteen women experiencing early pregnancy failure have been studied during the time of conception and at frequent intervals until spontaneous abortion occurred. Serial measurements of serum estradiol, progesterone, 17 alpha-hydroxyprogesterone, prolactin, human placental lactogen (hPL), and human chorionic gonadotropin (hCG) were determined; regular sonar scanning allowed the time of fetal death to be determined to within 7 days in six patients and a diagnosis of blighted ovum to be made in the remainder. In all patients serum progesterone and estradiol concentrations were within the normal range up to 7 weeks but appeared to decrease from about 8 weeks' gestation whether or not a living fetus was present. The placenta continued to produce hCG and hPL but, despite the continuing presence of hCG, the levels of 17 alpha-hydroxyprogesterone declined to concentrations below those associated with normal pregnancy. These data suggest that the placenta may require a particular stimulus to take over production of progesterone and estradiol.

Accurate assessment of early gestational age in normal and diabetic women by serum human placental lactogen concentration

Serum human placental lactogen (hPL) and human chorionic gonadotropin (hCG) were assayed and fetal crown-rump length (CRL) was determined by sonar in three groups of pregnant women--35 with uncomplicated pregnancies, 13 with insulin-dependent diabetes mellitus, and 21 who represented a general pregnancy population. Each patient had a regular cycle and recorded last menstrual period, ovulated spontaneously, and was delivered of a single live baby. Serum hPL concentrations within the range 0.01-0.80 microU/ml in patients in the first group gave estimates of gestation with an SD of 6.3 days which was the same as the SD derived from CRL measurements. When the hPL regression equation was applied to the diabetic mothers the difference between the gestational age estimated from hPL and that estimated from LMP had a mean value of - 0.9 days with an SD of 6.2 days; this difference was not significantly different from zero. The third group of patients had a mean difference between hPL and LMP derived gestational age of 0.7 days (+/- 6.7 SD). Serum hPL offers a method of estimating gestation sufficiently precise to be used as a practical alternative to sonar measurements of CRL.