ORIGIN OF ESTROGEN IN WOMEN PREGNANT WITH AN ANENCEPHALIC FETUS

Dehydroepiandrosterone Research: Past, Current, and Future

The discovery of "oestrus-producing" hormones was a major research breakthrough in biochemistry and pharmacology during the early part of the 20th century. The elucidation of the molecular weight and chemical structure of major oxidative metabolites of dehydroepiandrosterone (DHEA) led to the award of the Nobel Prize in 1939 to Adolf Frederick Johann Butenandt and Leopold Ruzicka. Considered a bulk androgen in the circulation, DHEA and its sulfated metabolite DHEA-S can be taken up by most tissues where the sterols are metabolized to active androgenic and estrogenic compounds needed for growth and development. Butenandt's interactions with the German pharmaceutical company Schering led to production of gram quantities of these steroids and other chemically modified compounds of this class. Sharing chemical expertise allowed Butenandt's laboratory at the Kaiser Wilhelm Institute to isolate and synthesize many steroid compounds in the elucidation of the pathway leading from cholesterol to testosterone and estrogen derivatives. As a major pharmaceutical company worldwide, Schering AG sought these new biological sterols as pharmacological agents for endocrine-related diseases, and the European medical community tested these compounds in women for conditions such as postmenopausal depression, and in men for increasing muscle mass. Since it was noted that circulating DHEA-S levels decline as a function of age, experimental pathology experiments in animals were performed to determine how DHEA may protect against cancer, diabetes, aging, obesity, immune function, bone density, depression, adrenal insufficiency, inflammatory bowel disease, diminished sexual function/libido, AIDS/HIV, chronic obstructive pulmonary disease, coronary artery disease, chronic fatigue syndrome, and metabolic syndrome. While the mechanisms by which DHEA ameliorates these conditions in animal models have been elusive to define, even less is known about its role in human disease, other than as a precursor to other sterols, e.g., testosterone and estradiol. Our groups have shown that DHEA and many of its oxidative metabolites serve as a low-affinity ligands for hepatic nuclear receptors, such as the pregnane X receptor, the constitutive androstane receptor, and estrogen receptors α/β (ERα/ERβ) as well as G protein-coupled ER (GPER1). This chapter highlights the founding research on DHEA from a historical perspective, provides an overview of DHEA biosynthesis and metabolism, briefly summarizes the early work on the beneficial effects attributed to DHEA in animals, and summarizes the human trials addressing the action of DHEA as a therapeutic agent. In general, most human studies involve weak correlations of circulating levels of DHEA and disease outcomes. Some support for DHEA as a therapeutic compound has been demonstrated for postmenopausal women, in vitro fertilization, and several autoimmune disorders, and adverse health effects, such as, acne, embryo virilization during pregnancy, and possible endocrine-dependent cancers.

Evolution of steroids during pregnancy: Maternal, placental and fetal synthesis

Progesterone, estrogens, androgens and glucocorticoids are involved in pregnancy from implantation to parturition. Their biosynthesis and their metabolism result from complex pathways involving the fetus, the placenta and the mother. The absence of expression of some steroïdogenic enzymes as CYP17 in placenta and in adrenal fetal zone and the better determination of the onset and variation of others especially HSD3B2 during the pregnancy explain the production of the steroid hormones. Moreover the consequences of some disorders of steroidogenesis (especially aromatase, POR, CYP11A1 and 21-hydroxylase deficiencies) in fetus and mother during the pregnancy have permit to elucidate these complex pathways. This better knowledge of steroid hormones production associated with their dosages in maternal plasma/urine or amniotic fluid using new specific assays as LC-MS MS could facilitate the follow-up of normal and pathological pregnancies. Moreover, these advances should be a basis to evaluate the impact of multiple pathologies of the pregnancy and pharmacologic and xenobiotic consequences on their metabolism.

Fetal and maternal adrenals in human pregnancy

Human pregnancy is marked by alterations in several endocrine systems--perhaps most notably, the striking increase in steroid hormone production by the adrenals of the fetus and mother. Morphologically and physiologically, the human fetal adrenal glands are remarkable organs. In proportion to the adult organs, the adrenal cortex is the largest organ of the fetus. At term, they produce more steroid and weigh the same as adrenal glands of the adult. Much of the steroid that is released by the fetal and maternal adrenals during pregnancy is the sulfated form of dehydroepiandrosterone (DHEA-S), which is used by the placenta to produce estrogens. Herein, we discuss the physiologic and pathophysiologic hormonal changes of the fetal and maternal adrenals during the course of pregnancy.

Adrenocortical zonation and ACTH

The clear morphological distinction between the cells of the different adrenocortical zones has attracted speculation and experiment to interpret their functions and the ways in which they are regulated. Considerable data have been produced in recent years that has benefited a fuller understanding of the processes of steroidogenesis and of cell proliferation at the molecular level. This now enables the reexamination of earlier concepts. It is evident that there is considerable species variation, and this article, dealing mainly with the rat, reaches conclusions that do not necessarily apply to other mammals. In the rat adrenal, however, the evidence suggests that the greatest differences between the functions of the zones are between the glomerulosa and the fasciculata. Here the sometimes all-or-nothing demarcation in their complement of components associated with steroidogenesis or with cell proliferation suggests a stark division of labor. In this model the fasciculata is the main engine of steroid hormone output and the glomerulosa is the site of cell proliferation, recruitment, and differentiation. Regulating these functions are angiotensin II and other paracrine components that modulate and maintain the glomerulosa, and ACTH, that maintains the fasciculata, and recruits new fasciculata cells by transformation of proliferating glomerulosa cells. Grafted onto this mostly vegetative function of the glomerulosa is CYP11B2, limited to just a fraction of the outer glomerulosa in rats on a normal laboratory diet and generating aldosterone (and 18-hydroxycorticosterone) from precursors whose origin is not, from the evidence summarized here, very clear, but may include the fasciculata, directly or indirectly. The biosynthesis of aldosterone in the rat certainly requires reinterpretation.

Second trimester levels of maternal serum inhibin A in pregnancies affected by fetal neural tube defects

Inhibin A is effective as a second trimester maternal serum marker for Down syndrome screening. In the present study, inhibin A levels were measured in second trimester maternal serum samples from 28 pregnancies affected with open neural tube defects; 12 associated with open spina bifida and 16 associated with anencephaly. Each measurement was expressed as a multiple of the median (MoM) for control singleton pregnancies (n=1464) of the same completed week of gestation. Inhibin A levels were not significantly altered in cases of open neural tube defects; the median value was 0.96 MoM in cases of open spina bifida and 1.19 MoM in cases of anencephaly. Therefore, second trimester maternal serum inhibin A levels will not have an impact on prenatal detection of open neural tube defects.

Elevated maternal serum alpha-fetoprotein with low unconjugated estriol and the risk for lethal perinatal outcome

OBJECTIVE

To determine whether a combination of elevated maternal serum alpha-fetoprotein (MSAFP) and low unconjugated estriol (E3) concentration identifies pregnancies at particularly high risk for fetal abnormality or poor outcome.

METHODS

Pregnancy outcomes were reviewed for women with elevated MSAFP (> or =2.0 MoM) from our database of 50,315 women who had received triple marker testing from 1993-1998. Outcomes for those with low E3 (< or =0.7 MoM) were compared with those with normal E3 (>0.7 MoM). The incidences of fetal death, neural tube defects, chromosome abnormalities, congenital abnormalities, preterm birth, small-for-gestational age (SGA), twins, and inaccurate dates were compared in the two groups using Fisher's exact test with P < 0.05 considered significant.

RESULTS

Of the 50,315 women screened, 1,435 (2.85%) had an elevated MSAFP. Pregnancy outcomes were obtained in 94% of those with elevated MSAFP and 70% of all patients screened. Neural tube defects were present in 57 fetuses/infants (21 anencephalic, 29 spina bifida, 7 encephalocele) of which 46 (81%) had an elevated MSAFP. Of the 1,435 women with an elevated MSAFP, 199 (14%) had a low E3. Compared to those women with elevated MSAFP but normal E3, women with elevated MSAFP and low E3 were at significantly increased risk for fetal death (20.6% vs. 2.8%, relative risk (RR) 8.9), anencephaly (9.0% vs. 0.1%, RR 122.8) and chromosome abnormality (2.5% vs. 0.6%, RR 4.0).

CONCLUSIONS

Pregnancies complicated by elevated second trimester MSAFP and low E3 are at a particularly high risk (32%) for lethal perinatal outcomes. Twins, while a common cause of elevated MSAFP, are rarely found when an elevated MSAFP is associated with low E3.

Combination of elevated maternal serum alpha-fetoprotein (MSAFP) and low estriol is highly predictive of anencephaly

Increased levels of second trimester maternal serum alpha-fetoprotein (MSAFP) have long been established as a marker for neural tube defects (NTDs). In addition, decreased levels of maternal estriol in the third trimester have been reported in pregnancies with anencephalic fetuses. The purpose of this study was to evaluate whether early second trimester unconjugated serum estriol (uE3) is an independent predictor of NTDs. The study included 57,031 patients who underwent maternal serum screening with MSAFP at 14-22 weeks gestation. Of these, 23,415 also had uE3 measurements. There were 63 cases of NTD, an overall incidence of 1.1 per 1,000. Elevated MSAFP (> or =2.5 MOM) was detected in 1,346 patients, 48 of which had NTDs. Decreased uE3 (< or =0.5) was detected in 1,437 patients, 17 of which had NTDs. The incidence of NTDs was significantly higher in patients with low uE3, compared to patients with normal/high uE3 (1.15% vs. 0.09%, P < 001). Finally, 51 patients had both increased MSAFP and decreased uE3; 16 of these had NTDs, 14 of which were anencephalics. In conclusion, both elevated MSAFP and low maternal serum estriol are predictive of NTD but have a low sensitivity. The combination of abnormally elevated MSAFP and low estriol is highly predictive of NTD in particular anencephaly.

New developments in congenital lipoid adrenal hyperplasia and steroidogenic acute regulatory protein

To date, studies of patients with lipoid CAH have shown the indispensable role of StAR in the production of steroids by adrenal gland and gonads. Lipoid CAH is the first and so far only inborn disorder of steroid hormone synthesis and metabolism that is not caused by a defective steroidogenic enzyme but rather by a defect in cholesterol transport.

Second-trimester levels of maternal serum unconjugated oestriol and human chorionic gonadotropin in pregnancies affected by fetal anencephaly and open spina bifida

Unconjugated oestriol (uE3) and human chorionic gonadotropin (hCG) levels were determined in second-trimester maternal serum (MS) samples from 21 pregnancies associated with fetal anencephaly and 15 pregnancies associated with fetal open spina bifida. Each measurement was expressed as a multiple of the median (MoM) for unaffected pregnancies for each completed week of gestation. In pregnancies associated with anencephaly, the median value for MSuE3 was very low (0.17 MoM, range less than 0.12-0.33 MoM), suggesting a functional defect in the fetal adrenal prior to 20 weeks' gestation; the median value for MShCG was also low (0.73 MoM), although not to the same extent as for MSuE3. A biological explanation for the hCG result is not apparent. In pregnancies associated with open spina bifida, the MSuE3 and MShCG values were unremarkable, consistent with a lack of involvement of these open fetal defects in the synthesis and secretion of uE3 and hCG.

The binding and metabolism of low-density lipoprotein by skin fibroblasts of fetuses and newborns with anencephaly

We have previously demonstrated that the fetus with anencephaly is hypercholesterolemic. The plasma levels of total cholesterol and low-density lipoprotein cholesterol are threefold greater than those of normal fetuses. We have provided evidence that elevated low-density lipoprotein cholesterol levels were caused by reduced uptake and metabolism of low-density lipoprotein by atrophic adrenal glands deficient in low-density lipoprotein receptors. The purpose of the present investigation was to determine if other tissues, namely, skin fibroblasts, of the fetus with anencephaly were also deficient in low-density lipoprotein receptors. We compared the binding and metabolism of low-density lipoprotein by skin fibroblasts of fetuses with anencephaly and normal subjects. Cultures of skin fibroblasts were grown to confluency. Thereafter, the medium was changed to lipoprotein-deficient serum for 24 hours. The rate of uptake and degradation of iodine 125-iodo-LDL was determined as a function of time and concentration of low-density lipoprotein. The maximal specific binding of low-density lipoprotein was also determined. The rate of uptake, degradation, and the maximal binding of low-density lipoprotein was similar in skin fibroblasts of infants with anencephaly and normal subjects. We conclude that the elevated level of low-density lipoprotein cholesterol in cord blood of fetuses with anencephaly is not caused by deficiency of low-density lipoprotein receptors and metabolism in skin fibroblasts but instead by deficiency of low-density lipoprotein receptors and metabolism by atrophic adrenal glands.

Umbilical cord plasma concentrations of deoxycorticosterone sulfate in anencephalic fetuses

In the present investigation, we determined the levels of deoxycorticosterone sulfate in mixed umbilical cord plasma of anencephalic abortuses and newborn infants. The anencephalic fetus is an interesting model with respect to the production of deoxycorticosterone and deoxycorticosterone sulfate on several accounts. There is profound adrenal atrophy in most such fesuses, and, in consequence, there also is relatively profound hypoestrogenism. This is an important consideration in the formation of deoxycorticosterone and deoxycorticosterone sulfate since it is known that estrogen acts to stimulate extra-adrenal steroid 21-hydroxylase and 21-hydroxysteroid sulfotransferase activities. The plasma levels of deoxycorticosterone sulfate in 22 anencephalic abortuses and newborn infants delivered between 21.5 and 45.5 weeks of gestation ranged from 1.8 to 30.3 ng/ml. The concentrations of deoxycorticosterone sulfate in umbilical cord plasma of anencephalic fetuses and newborn infants were not related to gestational age or method of delivery and, at term, were less than 13% of those in umbilical cord plasma of normal newborn infants. These data can be interpreted to indicate (1) that deoxycorticosterone sulfate normally is secreted directly by the fetal adrenal or (2) that placental estrogen normally derived largely from fetal adrenal dehydroisoandrosterone sulfate is essential for the maintenance of plasma deoxycorticosterone sulfate levels in the fetus by stimulating extra-adrenal deoxycorticosterone sulfate production from plasma progesterone, or both.

The effect of hypertension in pregnant women on fetal adrenal function and fetal plasma lipoprotein-cholesterol metabolism

In the present investigation, we evaluated the effect(s) of long-term hypertension and pregnancy-induced hypertension in women on the activity of the adrenals of their fetuses. We measured dehydroisoandrosterone sulfate, cortisol, and lipoprotein-cholesterol in umbilical cord plasma of newborn infants delivered (30 to 41 weeks' gestation) of 120 women whose pregnancies were uncomplicated and of 98 women with pregnancy-induced or long-term hypertension. Umbilical cord plasma levels of cortisol were similar in both groups of newborn infants at each gestational period. Fetal plasma levels of dehydroisoandrosterone sulfate also were similar in both groups at 30 to 33 weeks of gestation but were significantly reduced in newborn infants of hypertension women who were delivered between 34 and 41 weeks of gestation compared with those of newborn infants of normal women who were delivered at a similar gestational age. At term, umbilical cord plasma levels of total cholesterol and low-density lipoprotein-cholesterol were significantly higher in the newborn infants of hypertensive women compared with those levels in newborn infants of normotensive women; fetal plasma levels of high-density lipoprotein-cholesterol and very low-density lipoprotein-cholesterol were similar in both groups of newborn infants. The lowest plasma levels of dehydroisoandrosterone sulfate and the highest plasma levels of total cholesterol and low-density lipoprotein-cholesterol were found in newborn infants of women with the most severe pregnancy-induced hypertension. Based on these findings, we conclude that maternal hypertension effects a decrease in the rate of steroidogenesis of the fetal zone of the fetal adrenal cortex but does not act in a similar manner to effect steroidogenesis of the neocortical zone and leads to hypercholesterolemia in the fetus as a consequence of reduced adrenal utilization of low-density lipoprotein-cholesterol. In addition, the effects of pregnancy-induced hypertension appear to be manifest in the fetus late in pregnancy at a time when the fetal adrenal normally undergoes an accelerated rate of growth and steroid biosynthesis.

Extra-adrenal deoxycorticosterone production in hypoestrogenic pregnancies: Serum concentrations of progesterone and deoxycorticosterone in anencephalic fetuses and in women pregnant with an anencephalic fetus

In a continuing effort to define the origin of and the regulation of the production of deoxycorticosterone, we measured deoxycorticosterone and progesterone in the umbilical cord plasma of 16 anencephalic fetuses and newborn infants (21 to 45 weeks' gestation) and deoxycorticosterone, progesterone, 17 beta-estradiol, and estriol in the plasma of 18 women pregnant (16 to 45 weeks) with an anencephalic fetus. Whereas umbilical cord plasma levels of progesterone in the anencephalic fetuses were similar to those of normal abortuses and newborn infants, those of deoxycorticosterone (1.3 +/- 0.21 ng/ml, mean +/- SE) were significantly lower (P less than 0.001) than those in normal abortuses and newborn infants delivered between 31 and 42 weeks' gestation (3.94 +/- 0.26 ng/ml). We found that plasma levels of deoxycorticosterone were significantly correlated (P less than 0.001) to those of progesterone in women pregnant with an anencephalic fetus, as well as in women pregnant with a normal fetus. Plasma levels of deoxycorticosterone (range = 0.14 to 0.92 ng/ml) in women pregnant with an anencephalic fetus were significantly lower than those in women pregnant with a normal fetus; plasma levels of progesterone were similar in both groups. The plasma levels of 17 beta-estradiol and of estriol were extremely low in women pregnant with an anencephalic fetus compared with those in women with a normal fetus and did not vary as a function of gestational age. In one subject who was pregnant with an anencephalic fetus, we found that estrogen treatment (100 mg of diethylstilbestrol/day) for 6 days caused a progressive increase in the serum levels of deoxycorticosterone and in the ratio of the concentration of concentration of deoxycorticosterone to that of progesterone in serum. Both the serum levels of deoxycorticosterone and the ratio of the concentration of deoxycorticosterone and in the ratio of the concentration of deoxycorticosterone to that of progesterone declined after cessation of estrogen treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of extraadrenal steroid 21-hydroxylase activity. Increased conversion of plasma progesterone to deoxycorticosterone during estrogen treatment of women pregnant with a dead fetus

We measured deoxycorticosterone (DOC) and progesterone (P) in plasma of 47 women pregnant with a dead fetus and sequentially throughout gestation in 35 women pregnant with a live fetus. When P levels in plasma were low, the plasma levels of DOC in women pregnant with a dead fetus varied but usually were similar to those in women pregnant with a live fetus. However, when P levels were high, the levels of DOC in some women pregnant with a dead fetus were considerably lower than those in women pregnant with a live fetus. To test whether this finding was due to loss of transfer of DOC from fetus to mother or else loss of extraadrenal steroid 21-hydroxylase activity in the mother after death of the fetus, we conducted several studies. The levels of P and DOC in plasma of one woman remained constant from 30 min after fetal death until delivery occurred 13 h later. Estrogen treatment of four women pregnant with a dead fetus brought about an increase in plasma levels of DOC in three of the women. In one woman the ratio of plasma DOC to P was 0.015, a value similar to that found before fetal death, but was 0.003 after fetal death but before estrogen treatment. In two women pregnant with a dead fetus the transfer constants of conversion of plasma P to DOC were 0.011 and 0.005 before, and 0.024 and 0.013, respectively, during estrogen treatment. In one woman pregnant with a deformed fetus with adrenal agenesis, the metabolic clearance rates of DOC before and during estrogen treatment were similar, whereas the plasma production rates of DOC were 2.75 before and 4.31 mg/24 h during estrogen treatment. We suggest that (a) the DOC in plasma of near-term pregnant women arises in part by extraadrenal 21-hydroxylation of plasma P and (b) estrogen stimulates steroid 21-hydroxylase activity in extraadrenal tissues.

Placental clearance rate of maternal plasma androstenedione through placental estradiol formation: an indirect method of assessing uteroplacental blood flow

The metabolism of androstenedione (A) by the placenta in late pregnancy and the early puerperium was studied. The metabolic clearance rate of A (MCR-A) was increased in pregnant women, 2,825 +/- 207 L/24 hr (mean +/- SEM), compared to 2,020 +/- 140 L/24 hr in nonpregnant women of similar body weight. The immediate puerperal MCR-A was 2,538 +/- 50 L/24 hr. Therefore, approximately 10% of maternal plasma A was cleared by the placenta. In the latter half of pregnancy, the extent of conversion of maternal plasma A through estradiol formation, (rho)AE2, was increased, whereas in the immediate puerperium it was normal, 0.018. Moreover, 90% of aromatase activity was attributed to the placenta in late pregnancy. From these data, we computed that the placental clearance rate of A through estradiol (PCAE2) from whole blood was 497 +/- 41 ml/min in women with a single fetus and 691 +/- 102 ml/min in women with twin fetuses. Thus, it appears that the PCAE2 is a sensitive index of maternal-placental perfusion.

Relationship of maternal placental blood flow to the placental clearance of maternal plasma dehydroisoandrosterone sulfate through placental estradiol formation

We have suggested that the placental clearance of maternal plasma dehydroisoandrosterone sulfate (DS) through estradiol (E2) formation (PC-DSE2) is reflective of uteroplacental blood flow (F). Clewell and Meschia13 suggested that PC-DSE2 is related to F as follows: Cobs = F(1-e-C/F), where Cobs = PC-DSE2 and C = total placental clearance of maternal plasma DS. This equation contains two unknown quantities, F and C. To solve the equation, Clewell and Meschia assumed that C was constant. Using 19.7 ml/min for C, they allowed PC-DSE2 to vary widely and computed F. Upon finding that F was unrealistically low for some values of PC-DSE2, they concluded that reductions in PC-DSE2 do not reflect alterations in uteroplacental blood flow. In the analysis of the relationship of F to PC-DSE2, it is important to know the value of C. Since the direct measurement of C is not possible at this time, we have evaluated C by measuring the difference between the metabolic clearance rate of DS (MCR-DS) prior to and immediately following delivery. Any change in MCR-DS before and after delivery should be a reflection of the amount of maternal plasma DS cleared by the placenta through all metabolic routes including PC-DSE2, providing nonplacental clearances of maternal plasma DS before and immediately after delivery are the same. We measured MCR-DS and PC-DSE2 in 15 pregnant women within 5 days before delivery and repeated the MCR-DS measurement in these women beginning 90 minutes after delivery. Among these 15 women, C ranged from a low of 4.7 ml/min in a woman with severe pre-eclampsia to a high of 28.5 ml/min in a woman with twins. In addition to the finding that C varied widely, it was also ascertained that PC-DSE2 was positively correlated with C (r = 0.908; p less than 0.001). The finding that low or high values for PC-DSE2, observed in complicated pregnancies, were associated with similar changes in C is suggestive that a change in PC-DSE2 is reflective of a change in uteroplacental blood flow.

An analysis of the utility of plasma immunoreactive estrogen measurements in determining delivery time of gravidas with a fetus considered at high risk

Although maternal estrogen excretion and plasma estrogen levels are widely used to assess fetal health, the utility of these tests in lowering perinatal mortality rates has not been established. In order to ascertain if, with the help of plasma immunoreactive estrogen measurements, a reduction in perinatal deaths could be achieved, a population of women with a fetus at high risk were randomly divided into two groups and studied prospectively: in 315 gravidas, the estrogen results were reported (Group A); in 307, they were not reported (Group B). Nine perinatal deaths occurred in Group A, 10 in Group B. Ten Group B women whose infant ultimately did well would have been delivered 28 days or more prematurely if management had been based solely on the basis of abnormal immunoreactive estrogen levels. Measurement of estrogen levels is of little value in management of women with a fetus at risk; it may even lead to erroneous premature delivery.

The pattern and rates of metabolism of maternal plasma dehydroisoandrosterone sulfate in human pregnancy

The present study was done to map the metabolic pathways and rates of maternal plasma clearance of dehydroisoandrosterone sulfate (MCRDS) in pregnancy. In the present study, maternal plasma dehydroisoandrosterone sulfate (DS) metabolism was largely accounted for by two major pathways not present or not prominent in the nonpregnant woman. The first major pathway was clearance of maternal plasma DS by placental aromatization of DS to form estradiol (E2). This pathway accounted for approximately 35 per cent of the total clearance. The second major pathway of metabolism of maternal plasma DS was by 16 alpha-hydroxylation within the maternal compartment. This pathway accounted for approximately 32 per cent of maternal plasma DS clearance. Two other minor pathways of DS metabolism, that is, loss to the fetus and excretion as unaltered DS into urine, accounted for less than 1 per cent of total metabolism in each instance. The final pathway of DS metabolism was excretion as neutral steroids such as urinary 17-ketosteroids and other undefined losses. By combining the rate of DS clearance (MCRDS) from maternal plasma via all pathways with that fraction of DS removed uniquely by placental conversion of DS to estradiol (DS leads to E2), the placental clearance of DS leads to E2 (PCDSE2) may be measured. The measurement of PCDSE2 may be expected to reflect uteroplacental perfusion and as such may provide an investigative tool capable of assessing the dynamics of uteroplacental function in a variety of clinical conditions.

The ontogenesis of human fetal hormones. III. Prolactin

The synthesis and release of human prolactin (hPRL) in the human fetus was assessed by radioimmunoassay analysis of the content and concentration of hPRL in 82 pituitary glands and the concentration of serum hPRL in 47 fetuses of gestational age 68 days to term. Fetal hPRL exhibited parallelism with the reference standard (Lewis 203-1). hPRL was detected by 68 days of gestation (10 wk), the earliest fetal pituitary gland studied; 8 out of 33 pituitaries had a prolactin (PRL) content above 2.0 ng between 10-15 wk gestation. The mean ocntent of PRL in the pituitary gland increased sharply from 14.8 plus or minus 4.6 ng at 15-19 wk to 405 plus or minus 142 ng at 20-24 wk and 542 plus or minus ng at 25-29 wk gestation. By term, the mean content was 2,039 plus or minus 459 (range 493-3,689) and the mean concentration 15.9 plus or minus 2.4 ng/mg (range 7-20). There was a significant positive correlation (P less than 0.001) between the hPRL and human growth hormone (hGH) content of fetal pituitary glands; at term the hPRL/hGH ratio was 1/290. The concentration of serum hPRL between 12 and 24 wk ranged from 2.9 to 67 ng/ml, mean 19.5 plus or minus 2.5 ng/ml )n = 21); by 26 wk fetal serum hPRL increased sharply and attained levels of 300-500 ng/ml in late gestation. At delivery, the mean plasma concentration of hPRL was 167 plus or minus 14.2 ng/ml in 36 umbilical venous specimens and 111.8 plus or minus 12.3 ng/ml in the matched maternal venous specimens. No correlation between serum hPRL and the pituitary content or concentration of hPRL was demonstrable in 12 matched fetal specimens. In five anencephalic infants, umbilical venous hPRL levels were between 65 and 283 ng/ml. In two anencephalic infants, thyrotropin releasing factor (TRF) (200 mug IV) evoked a rise in serum hPRL in one patient from 43 to 156 ng/ml at 30 min, and in the other from 65 to 404 ng/ml at 120 min. In both patients, plasma thyroid-stimulating hormone (TSH) rose from undetectable base-line levels to peak levels of 97 and 380 muU/ml, respectively. The pattern of change in serum hPRL in the human fetus contrasts sharply with that of serum hGH, luteinizing hormone, or follicle-stimulating hormone. These observations in the fetus and in anencephalic infants suggest that the striking elevation of serum PRL in the fetus is neither mediated by a putative PRL releasing factor or by TRF, nor is a consequence of suppression or absence of PRL release inhibiting factor alone, as a functional hypothalamus is not required to attain the high PRL concentration at term. Several lines of evidence support the view that high plasma estrogen levels characteristic of gestation act directly on the fetal anterior hypophysis to stimulate PRL secretion or to sensitize the secretory mechanism of the lactotrope, increasing its responsiveness to other stimuli.

The effects of estradiol and estriol on plasma levels of cortisol and thyroid hormone-binding globulins and on aldosterone and cortisol secretion rates in man

The effects of estriol and estradiol on the plasma levels of cortisol- and thyroxine-binding globulin activity, and on the secretion rates of aldosterone and cortisol were studied in man. The metabolite estriol had no consistent or significant influence on plasma levels of the hormone-binding globulin activities; the hormone estradiol increased these binding capacities significantly, as expected. Cortisol secretion rate rose slightly after estriol but was unchanged after estradiol. Both compounds induced substantial increases in the aldosterone secretion rate of most treated subjects. The mechanism of this apparently paradoxical effect of estrogens is not clear; it is suggested that the "salt-retaining" action of estrogens is mediated in part by the rapid enhancement of aldosterone output which follows their administration in man. Balance experiments in four subjects suggest that both estradiol and estriol may induce a transient early natriuresis in man; but other mechanisms for estrogen stimulation of aldosterone secretion may be operative as well.