Insulin as an effector of human ovarian and adrenal steroid metabolism

Evidence is accumulating that insulin is a potent effector of human steroid hormone metabolism. In this article, we have reviewed primarily in vivo studies showing that physiologic elevations in serum insulin levels can increase circulating ovarian androgens, decrease serum levels of adrenal androgens, and decrease serum SHBG levels. In addition, insulin resistance at the level of the adrenals appears to be associated with loss of responsiveness to the suppressive effect on adrenal androgens. We have proposed an integrated hypothesis as to how these complex actions of insulin might all come into play in the genesis of a common endocrinopathy--PCO. At least one clinically relevant aspect of these findings is that therapies aimed at reducing the magnitude of hyperinsulinemic insulin resistance in women with PCO may ameliorate the hyperandrogenism. One example of this possibility is the well recognized observation that substantial weight loss is associated with a reduction in serum androgen levels and clinical manifestations of hyperandrogenism in this disorder.

Regulated expression of sterol carrier protein 2 in the ovary: a key role for cyclic AMP

Sterol carrier protein 2 (SCP2) is believed to play an important role in the intracellular movement of cholesterol in steroidogenic cells. We examined the distribution of SCP2 gene expression in the rat ovary and the role of gonadotropins and cyclic AMP in the regulation of SCP2 mRNA levels. In situ hybridization revealed that the most steroidogenically active ovarian compartments (e.g., corpora lutea and theca cells) contain significant amounts of SCP2 mRNA whereas granulosa cells have modest levels. Gonadotropins, which promote follicular growth and luteinization, increased the ovarian content of SCP2 mRNA as assessed by Northern blotting along with increases in cytochrome P450scc mRNA. Using steroidogenic transformed rat granulosa cells (Grs-21), a cyclic AMP analogue (8-Br-cAMP) was found to increase SCP2 mRNA and protein levels within 24 h of treatment. P450scc mRNA was also induced whereas actin mRNA levels were not affected. The 8-Br-cAMP stimulation of SCP2 mRNA accumulation was completely inhibited by actinomycin D and cycloheximide. The cyclic AMP analogue also increased SCP2 mRNA levels in a non-steroid hormone producing transformed rat granulosa cell line Gs-8. We conclude that SCP2 gene expression in the ovary is correlated with the state of differentiation of granulosa cells. Gonadotropic hormones which stimulate luteinization of the cells increase SCP2 gene expression. These actions of gonadotropins appear to be mediated at least in part by cyclic AMP through a mechanism requiring ongoing RNA and protein synthesis. However, SCP2 gene expression is not obligatorily coupled to steroidogenic activity, as cyclic AMP analogues can increase SCP2 mRNA in a line of transformed ovarian granulosa cells incapable of synthesizing hormones.

Similarity between the amino-terminal portion of mammalian 58-kD sterol carrier protein (SCPx) and Escherichia coli acetyl-CoA acyltransferase: evidence for a gene fusion in SCPx

A computer analysis of the amino acid sequences of rat and human 58-kD sterol carrier protein and Escherichia coli acetyl-CoA acyltransferase reveals that the two proteins have a segment of about 350 residues with strong sequence similarity. The ALIGN comparison scores for the rat and human sterol carrier proteins and the E. coli enzyme are 8.25 and 8.8 SD, respectively. The catalytically active cysteine of E. coli acetyl-CoA acyltransferase (cysteine 91) aligns with cysteine 93 and cysteine 94 on human and rat 58-kD sterol carrier protein, respectively.

E-cadherin expression during the differentiation of human trophoblasts

The morphologic and functional differentiation of human trophoblast cells culminates in the formation of the terminally differentiated multinucleated syncytial trophoblast. In culture, isolated mononuclear cytotrophoblasts aggregate and then fuse to form syncytia, recapitulating the in vivo process. In the present studies, we investigated the expression of the Ca(2+)-dependent cell adhesion molecule (CAM), E-cadherin, during the morphologic differentiation of trophoblastic cells. Cytotrophoblasts were isolated from human chorionic villi, and JEG-3 and BeWo choriocarcinoma cells, cytotrophoblastic cell lines which under standard culture conditions are not fusion competent, were obtained by dispersion of ongoing cultures. Cultures were terminated at timed intervals and E-cadherin was analyzed by immunocytochemistry and electron microscopy using specific antibodies. In addition, E-cadherin expression was investigated by western and northern blotting. During the aggregation of cytotrophoblasts, E-cadherin was localized on the cell surface at points of cell-cell contact and could not be demonstrated following cellular fusion. In contrast, it remained on the surface of aggregated JEG-3 and BeWo cells throughout the duration of culture. Western blot analysis revealed a time-dependent increase in E-cadherin (120 × 10(3) Mr) which coincided with maximal aggregate formation at 24 h in both normal cytotrophoblasts and JEG-3 cells. A marked reduction of E-cadherin in fusing cytotrophoblasts was subsequently observed as syncytial trophoblasts became the predominant cellular form in culture. In agreement with the immunohistochemical observations, there was no change in E-cadherin levels in the non-fusing JEG-3 cells. Northern blotting demonstrated a significant reduction in the 4.5 kb transcript in fusion-competent cells over the 96 h of culture. Exposure of the normally non-fusing BeWo cells to 1.5 mM 8-bromo cyclic AMP induced cellular fusion and syncytium formation. This process was accompanied by a disappearance of E-cadherin from the cell surface as assessed by immunocytochemistry and western blotting and a parallel reduction in the abundance of the E-cadherin mRNA. Immunoneutralization experiments using an antiserum directed against the extracellular domain of cadherins inhibited syncytium formation in normal trophoblasts compared to an antiserum against the E-cadherin cytoplasmic tail, which had no effect upon aggregation and fusion of these cells. We conclude that E-cadherin exists in a dynamic state in fusion-competent cytotrophoblasts and that down regulation of its gene expression coincides with cellular fusion. In addition, this process appears to be cyclic AMP-mediated in BeWo choriocarcinoma cells.(ABSTRACT TRUNCATED AT 400 WORDS)

cDNAs encoding members of a family of proteins related to human sterol carrier protein 2 and assignment of the gene to human chromosome 1 p21----pter

Sterol carrier protein 2 (SCP2) is believed to play a key role in intracellular lipid movement. Here we report the cloning and nucleotide sequences of cDNAs encoding SCP2-related proteins of 58.85 kD and 30.8 kD and the assignment of the SCP2 gene to human chromosome 1 p21-pter. The SCP2-related proteins share common deduced carboxyl amino acid sequences with SCP2 and the cDNAs have a common 3' untranslated nucleotide sequence. The mRNAs encoding these proteins increased in a coordinate fashion as human placental cytotrophoblasts differentiated into syncytiotrophoblasts in culture. Our observations document the existence of a family of related proteins encoded by the human SCP2 gene.

Cloning and expression of a cDNA encoding human sterol carrier protein 2

We report the cloning and expression of a cDNA encoding human sterol carrier protein 2 (SCP2). The 1.3-kilobase (kb) cDNA contains an open reading frame which encompasses a 143-amino acid sequence which is 89% identical to the rat SCP2 amino acid sequence. The deduced amino acid sequence of the polypeptide reveals a 20-residue amino-terminal leader sequence in front of the mature polypeptide, which contains a carboxyl-terminal tripeptide (Ala-Lys-Leu) related to the peroxisome targeting sequence. The expressed cDNA in COS-7 cells yields a 15.3-kDa polypeptide and increased amounts of a 13.2-kDa polypeptide, both reacting with a specific rabbit antiserum to rat liver SCP2. The cDNA insert hybridizes with 3.2- and 1.8-kb mRNA species in human liver poly(A)+ RNA. In human fibroblasts and placenta the 1.8-kb mRNA was most abundant. Southern blot analysis suggests either that there are multiple copies of the SCP2 gene in the human genome or that the SCP2 gene is very large. Coexpression of the SCP2 cDNA with expression vectors for cholesterol side-chain cleavage enzyme and adrenodoxin resulted in a 2.5-fold enhancement of progestin synthesis over that obtained with expression of the steroidogenic enzyme system alone. These findings are concordant with the notion that SCP2 plays a role in regulating steroidogenesis, among other possible functions.

2-hydroxyestradiol enhanced progesterone production by porcine granulosa cells: dependence on de novo cholesterol synthesis and stimulation of cholesterol side-chain cleavage activity and cytochrome P450scc messenger ribonucleic acid levels

2-Hydroxyestradiol (2-OH-E2) stimulates progestin secretion by granulosa cells, but the intracellular locus of the stimulatory effect has not been clarified. The objectives of the present studies were to 1) determine the role of de novo sterol synthesis in the effect of 2-OH-E2 on progestin biosynthesis, and 2) examine the effects of 2-OH-E2 on cholesterol side-chain cleavage (SCC) activity and the level of messenger RNA (mRNA) for P450scc. Inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase with lovastatin (5 micrograms/ml) or mevinolin (5 micrograms/ml) reduced FSH- and 2-OH-E2-stimulated (but not E2-stimulated) progesterone production. Mevalonate (20 mM) enhanced basal progesterone production and reversed the inhibitory effect of lovastatin but did not affect progesterone biosynthesis in the presence of 2-OH-E2. As an index of the activity of cholesterol SCC enzyme, granulosa cells were exposed to 25-hydroxycholesterol (10 micrograms/ml) for 24 h and progesterone secretion monitored. Conversion of 25-hydroxycholesterol into progesterone was stimulated 2- to 3-fold by maximally effective concentrations of 2-OH-E2, E2, and FSH. 2-OH-E2 and/or E2 further enhanced 25-hydroxycholesterol conversion in the presence of FSH, LH, and epinephrine. Aminoglutethimide, an inhibitor of SCC, reduced 2-OH-E2- and 2-OH-E2 plus FSH-stimulated progesterone production by 97% and 95%, respectively. 2-OH-E2 also increased basal (by 2 to 3-fold) and FSH-stimulated (to 3.5-fold of FSH-treated controls) levels of mRNA for cytochrome P450scc. Collectively, our studies support the hypothesis that 2-OH-E2-enhanced progesterone biosynthesis by porcine granulosa cells is dependent on de novo cholesterol synthesis and is associated with increased levels of the mRNA encoding cytochrome P-450scc, which leads to increases in basal and gonadotropin-induced SCC activity.

A cDNA encoding a rat mitochondrial cytochrome P450 catalyzing both the 26-hydroxylation of cholesterol and 25-hydroxylation of vitamin D3: gonadotropic regulation of the cognate mRNA in ovaries

A cDNA expression library prepared from rat liver RNA was screened with a polyclonal antibody specific for mitochondrial vitamin D3 25-hydroxylase and a cDNA for rabbit liver mitochondrial cytochrome P450c26 (CYP 26), yielding cDNA clones with identical sequences. The deduced amino acid sequence derived from a 1.9-kb full-length cDNA was 73% identical to that of rabbit cytochrome P450c26. A monoclonal antibody was used to demonstrate that the product of the 1.9-kb cDNA clone was targeted to the mitochondrial compartment when expressed in COS cells. Mitochondrial membranes containing the expressed protein showed both vitamin D3 25-hydroxylase and cholesterol 26-hydroxylase activities when reconstituted with ferredoxin reductase and ferredoxin, demonstrating that the same P450, designated as P450c26/25, can catalyze both reactions. Northern blot analysis revealed that the P450c26/25 cDNA hybridizes with a 2.4-kb RNA from rat liver and unstimulated ovaries. Treatment of rats with pregnant mare's serum gonadotropin resulted in a fivefold increase in the 2.4-kb mRNA as well as the appearance of a 2.1-kb mRNA species in the ovaries. Our findings document the presence of a regulated bifunctional mitochondrial cytochrome P450 capable of catalyzing the 25-hydroxylation of vitamin D3 and the 26-hydroxylation of cholesterol.

Generation of regulatory oxysterols: 26-hydroxylation of cholesterol by ovarian mitochondria

De novo synthesis of cholesterol and low-density lipoprotein (LDL) receptor levels are suppressed in the presence of cholesterol. Recent evidence suggests that a cholesterol metabolite (possibly a hydroxysterol), not cholesterol per se, is the effector that inhibits transcription of genes encoding enzymes involved in sterol synthesis and LDL receptors. We found that 26-hydroxycholesterol inhibits human ovarian cell sterol synthesis, and that luteinized human granulosa cells contain 26-hydroxylase messenger RNA (mRNA). We proceeded to characterize the enzyme generating 26-hydroxycholesterol in the rat ovary. Mitochondria derived from ovaries of PMSG-human CG (hCG) primed immature rats (day 3 post-hCG) metabolized [3H] cholesterol into [3H]26-hydroxycholesterol in the presence of nicotinamide adenine dinucleotide phosphate and aminoglutethimide (100 micrograms/ml), added to inhibit metabolism of sterols by the cholesterol side-chain cleavage system. The identity of the product was confirmed by chromatography in several systems; recrystallization to constant specific activity and mass spectrometry. Negligible 26-hydroxylase activity was detected in other ovarian subcellular fractions. 26-Hydroxycholesterol formation progressed at a linear rate for up to 40 min and was linearly related to mitochondrial protein added to the incubation mixture. 26-Hydroxylase was markedly stimulated (5-fold) by calcium (0.2 mM). Maximal rates of 26-hydroxycholesterol formation observed were 1 pmol/min.mg protein. This activity is substantially lower than cholesterol side-chain cleavage measured in the absence of aminoglutethimide. Ketoconazole (1-100 microM) inhibited 26-hydroxylase in a dose-dependent manner. Pregnenolone (1-1000 microM) and progesterone (1-100 microM) inhibited 26-hydroxylase in a dose-dependent manner, with appreciable inhibitory effects in the 1-10 microM range. We suggest that 26-hydroxycholesterol is an intracrine regulator that controls cellular sterol metabolism. Formation of 26-hydroxcholesterol in ovarian cells may be regulated by steroidogenic activity in such a way as to ensure availability of steroid hormone precursors. When steroidogenesis is active, 26-hydroxylase is inhibited by products of the side-chain cleavage system, allowing increased de novo sterol synthesis and LDL uptake. With reduced steroidogenic activity and less demand for cholesterol, 26-hydroxylase is not blocked, permitting formation of 26-hydroxycholesterol with attendant reduction in sterol synthesis and LDL receptor gene expression.

Characterization of a cDNA encoding rat sterol carrier protein2

Sterol carrier protein2 (SCP2) is a 13.2-kD protein that is thought to be involved in the intracellular transport of cholesterol. Using synthetic oligonucleotides based on the protein sequence of SCP2, a clone (SP43) was isolated from a rat liver cDNA library. The DNA sequence revealed that the cDNA could encode a polypeptide of 273 amino acids (28.9 kD) or 143 amino acids (15.3 kD) in which the carboxy-terminal 123 amino acids are identical to the SCP2 protein. RNA blot hybridization revealed that a variety of rat tissues contain a homologous RNA of a size similar to SP43 (approximately 1.5 kb). Levels of SCP2 mRNA increased in parallel with cytochrome P450scc mRNA in the immature gonadotropin-primed rat ovary. The isolation of a cDNA clone encoding SCP2 will facilitate studies on its role in cholesterol metabolism.

Cloning and sequence of cDNA for human placental cytokeratin 8. Regulation of the mRNA in trophoblastic cells by cAMP

A 1735 bp cDNA for human placental cytokeratin 8 is described which encompasses the entire coding sequence as well as 33 and 250 base pairs of 5'- and 3'-untranslated region, respectively. The level of cytokeratin 8 mRNA in various fetal tissues and placentae of different gestational ages was determined as were the effects of 8-bromo-cAMP on cytokeratin 8 mRNA in primary cultures of cytotrophoblasts and JEG-3 choriocarcinoma cells. Cytokeratin 8 mRNA was abundant in fetal small intestine, placenta, pancreas, lung, liver, and kidney. Levels of cytokeratin 8 mRNA in placenta increased slightly during pregnancy. 8-Bromo-cAMP suppressed cytokeratin 8 mRNA in primary cultures of cytotrophoblasts, whereas the cAMP analog increased mRNA levels in JEG-3 cells, revealing differential regulation of this mRNA in normal and transformed trophoblastic cells.

Aggregation of dispersed human cytotrophoblastic cells: lessons relevant to the morphogenesis of the placenta

The syncytial trophoblast of the human placenta forms by the fusion of mononuclear cytotrophoblast cells. Cytotrophoblast cells only fuse with other trophoblastic cells, indicating a specificity to this interaction. To explore the cellular aggregation which precedes fusion, we examined the association of cytotrophoblast cells isolated from term placentae and JEG-3 choriocarcinoma cells, a cytotrophoblast-like cell line, in suspension culture. Cytotrophoblast cells were isolated by dispersion of chorionic villi in trypsin-DNase in Ca2+/Mg2(+)-free medium. JEG-3 cells were released from culture flasks by trypsinization in Versene-EDTA buffer. In suspension culture, each cell type aggregated forming tissue-like masses over a 24-hr period. Transmission electron microscope analysis demonstrated the formation of numerous desmosomes between the aggregated cells. In outgrowth culture, the aggregates created in suspension were maintained as microvilli-covered multicellular structures with hollow cores. The extent of aggregation was dependent upon the concentration of cells in the incubations with greater aggregation occurring with higher cell densities. Aggregation of both cytotrophoblast cells and JEG-3 cells progressed rapidly during the initial 10 hr of incubation and then continued at a slower rate. Aggregation took place in serum-containing and serum-free medium, but was impeded in Ca2+/Mg2(+)-free medium. Incubation of JEG-3 and cytotrophoblast cells in the presence of the protein synthesis inhibitor, cycloheximide, prevented aggregation, whereas the inhibitor of N-linked glycosylation, tunicamycin, did not. The inhibitor of RNA synthesis, actinomycin D, had no effect on the aggregation of the cells during the initial 6 hr of aggregation. These findings suggest that trypsin treatment in Ca2+/Mg2(+)-poor medium removed a protein(s) from the trophoblast cell surface which must be resynthesized for cell-cell association to take place.

Regulation of the gene for estrogenic 17-ketosteroid reductase lying on chromosome 17cen----q25

17-Ketosteroid reductase (17KSR), also known as 17 beta-hydroxysteroid dehydrogenase, catalyzes the reversible interconversion of estradiol to estrone and of androstenedione to testosterone. Using a recently cloned human placental 17KSR cDNA, we show that the 1.4-kilobase mRNA for this enzyme is detected only in tissues producing estrogens, and a 2.4-kilobase mRNA is detected in some estrogenic tissues and some androgenic tissues. This tissue distribution suggests that the interconversion of androstenedione and testosterone may be mediated by a different enzyme. Southern blotting studies show that the mRNA for this estrogenic 17KSR is encoded by two very similar genes localized to chromosome 17cen----q25 by analysis of DNA from mouse/human somatic hybrid cell lines. 8-Br-cAMP increases the abundance of estrogenic 17KSR mRNA as well as mRNAs for other steroidogenic enzymes in JEG-3 choriocarcinoma cells. By contrast, cAMP decreases estrogenic 17KSR mRNA in primary cultures of human cytotrophoblasts and human granulosa cells, a pattern of tropic regulation that differs from other steroidogenic enzyme mRNAs.

Control of low density lipoprotein receptor gene expression in steroidogenic cells

Low density lipoprotein (LDL)-carried cholesterol is a primary substrate for steroid hormone synthesis by luteinized human granulosa cells. Chorionic gonadotropin and 8-bromo-cAMP both increase LDL receptor levels in granulosa cells by stimulating accumulation of the receptor mRNA. LDL and 25-hydroxycholesterol reduce LDL receptor expression, but this suppressive effect is partially overcome by 8-bromo-cAMP. Using fusion gene constructs containing the LDL receptor gene promoter transfected into JEG-3 cells, a cyclic AMP responsive enhancer could not be identified in the LDL receptor gene upstream promoter in transfection studies. We suggest that the LDL receptor gene in human steroidogenic cells is under negative control by a sterol effector, but that a cyclic AMP triggered process overcomes, to some extent, the sterol-mediated suppression. The detailed mechanisms by which sterol and cyclic AMP modulate LDL receptor gene expression remain to be elucidated.

Control of low density lipoprotein receptor gene promoter activity. Ketoconazole inhibits serum lipoprotein but not oxysterol suppression of gene transcription

We have examined the effects of ketoconazole, a drug which inhibits enzymes involved in cholesterol biosynthesis and metabolism, on the suppressive effects of serum lipoproteins and 25-hydroxycholesterol on low density lipoprotein (LDL) receptor gene promoter activity. A LDL receptor promoter-chloramphenicol acetyltransferase (CAT) fusion gene construct (pLDLR-CAT 6500) was transfected into JEG-3 choriocarcinoma cells, and the transfected cells were cultured in the absence or presence of serum, LDL, or serum and 25-hydroxycholesterol. Serum, LDL, and serum + 25-hydroxycholesterol reduced chloramphenicol acetyltransferase activity in cells transfected with pLDLR-CAT 6500, whereas these treatments had no effect upon enzyme activity in cells transfected with a control construct (pSV2CAT). Ketoconazole (50 microM) overcame the effects of serum and LDL on suppression of pLDLR-CAT 6500 expression, but could not override the combination of serum + 25-hydroxycholesterol. Ketoconazole had no significant effect on expression of pSV2CAT. The drug inhibited cholesterol side chain cleavage enzyme in the cells, but appeared to have no impact on the ability of cells to take up LDL-carried lipids. Our observations are consistent with the idea that serum lipoprotein cholesterol is metabolized to an effector substance which acts to suppress LDL receptor gene transcription. The generation of this effector seems to be sensitive to ketoconazole.

Plasminogen activator inhibitor types 1 and 2 in human trophoblasts. PAI-1 is an immunocytochemical marker of invading trophoblasts

Trophoblast implantation, vascular remodeling, and maintenance of intervillous blood flow may depend on the regulated production of proteolytic enzymes such as plasminogen activator (PA). Since the functional activity of plasminogen activators is determined not only by the quantity of protease but also by levels of specific plasminogen activator inhibitors (PAI), we examined trophoblasts both in vitro and in vivo for the presence of two PAIs, PAI-1 and PAI-2. Cytotrophoblasts were isolated from first trimester or term placentae, cultured, and immunocytochemically stained using specific anti-PAI antibodies. The antiserum against PAI-1 demonstrated prominent cell-surface staining and some cytoplasmic staining. The antiserum generated against PAI-2 revealed a cytoplasmic localization, with some trophoblasts staining intensely, whereas others had no apparent reactivity. We also found that cultured cytotrophoblasts contain the mRNAs for PAI-1 and PAI-2. Immunohistochemical analysis of tissue sections from 8-, 16-, and 40-week implantation sites using antisera against PAI-1 demonstrated weak staining of villous syncytiotrophoblasts but prominent cytoplasmic staining of trophoblasts invading the decidua and myometrium. Antisera against PAI-2 stained the cytoplasm of villous syncytiotrophoblasts, but no staining was evident in villous cytotrophoblasts or in invading trophoblasts. We conclude that 1) human trophoblasts can express both PAI-1 and PAI-2 in vitro and in vivo and 2) prominent PAI-1 immunostaining defines invading trophoblasts, whereas PAI-2 is the predominant PAI accumulated in villous syncytiotrophoblasts. Thus, the various trophoblast forms have distinctive patterns of PAI expression.

Characteristics of premenstrual syndrome

To characterize the symptoms associated with premenstrual syndrome (PMS), the menstrual symptom calendars of 100 women diagnosed with PMS were factor-analyzed. Scores on 18 symptoms were recorded daily for one menstrual cycle prior to the women's first clinic visits. Two factors were found to predominate throughout the cycle: The first included emotional and behavioral symptoms and the second included physical and cognitive symptoms. The two factors were constant throughout all the phases of the menstrual cycle. Emotional symptoms clustered together throughout the menstrual cycle and were the dominant symptoms on factor I. However, they loaded (correlation of the variable with the factor) on factors I and II during the postmenstrual phase. Behavioral symptoms loaded on factor I throughout the menstrual cycle; however, they were prevalent predominantly in the later half of the intermenstrual and the premenstrual phases. Physical symptoms loaded predominantly on factor II and were less prevalent than the emotional symptoms. The cognitive symptoms loaded on factor II during the premenstrual phase. These findings are relevant for defining PMS criteria for women who seek treatment.

Regulation of human trophoblast function by glucocorticoids: dexamethasone promotes increased secretion of chorionic gonadotropin

Steroid hormones are thought to play a role in controlling placental endocrine function. Since maternal free cortisol levels increase during gestation, and glucocorticoid receptors have been identified in placental tissue, we examined the effects of glucocorticoids on the production of CG by cultured human cytotrophoblasts. Treatment of cytotrophoblasts with 1 microM dexamethasone increased CG secretion by 6- to 10-fold over a 72-h period, whereas progesterone (1 microM) had no effect. The stimulatory effects of dexamethasone were blocked by the glucocorticoid antagonist RU 486, indicating a requirement for the glucocorticoid receptor. Intracellular accumulation of the CG alpha-subunit in response to dexamethasone was demonstrated by immunocytochemistry, and Northern blot analyses revealed that dexamethasone treatment increases CG alpha- and beta-subunit mRNA levels. Dexamethasone also enhanced the stimulatory effects of 8-bromo-cAMP on CG secretion. We conclude that glucocorticoids as well as cAMP modulate human trophoblast endocrine functions.

Hepatic lipase in the rat ovary. Ovaries cannot synthesize hepatic lipase but accumulate it from the circulation

Hepatic lipase is proposed to have a role in steroidogenesis through its involvement in the metabolism of high density lipoproteins. We examined the activity, synthesis, distribution, and uptake of this enzyme and assessed the content of its mRNA in luteinized ovaries. We found that during peak steroidogenesis, ovaries of pregnant mare's serum gonadotropin-human chorionic gonadotropin-treated immature rats contained heparin-releasable hepatic lipase-like activity which was neutralized in a dose-dependent manner by purified antibodies to hepatic lipase isolated from post-heparin perfusates of rat livers. Quantitative immunoelectron microscopy revealed that ovarian hepatic lipase occurred along endothelial cells and was 3-fold more abundant in blood vessels of corpora lutea than those of stroma. However, hepatic lipase was not synthesized by the ovary since radiolabeled enzyme was not immunoisolated from the medium of dispersed luteinized granulosa cells incubated with [35S]methionine whereas it was present in the medium of control cells (hepatocytes). Similarly, hepatic lipase mRNA was detectable in liver but not ovaries or kidneys by Northern or slot blot analyses or by the polymerase chain reaction. Finally, 125I-labeled hepatic lipase injected into tail veins was quickly cleared from the systemic circulation, accumulating in liver, ovaries, kidneys, and spleen. Subsequent heparin injection caused rapid reappearance of radioactivity in the bloodstream and a marked decline of radiolabel in liver and ovaries but a modest decrease of that in kidneys and none in spleen. Exogenous 125I-bovine serum albumin also accumulated in all four organs but was not displaced from liver or ovaries by subsequent administration of heparin. Taken together, these data suggest that steroidogenically active ovaries possess but do not synthesize hepatic lipase. Instead, hepatic lipase originating elsewhere, presumably in the liver, is accumulated from the circulation at heparin-sensitive sites in ovarian blood vessels.