Gonadotropin receptors in human corpora lutea of the menstrual cycle and pregnancy

Hyperglycosylated hCG

Hyperglycosylated hCG (hCG-H) is a glycosylation variant of the hormone hCG. Here we review all that is known about this independently functioning molecule. As discussed, it is a very different molecule to the hormone hCG. First, hCG-H is produced by cytotrophoblast cells while regular hCG is made in syncytiotrophoblast cell. Second, it is an autocrine acting directly on the cells which produce it, while regular hCG is an endocrine acting on maternal corpus luteal cells. Third, hCG-H has minimal biological activity in promoting progesterone production compared to regular hCG. Fourth, hCG-H functions unlike regular hCG as an invasion promoter, whether invasion as in choriocarcinoma and testicular germ cell malignancies, or as in implantation of pregnancy. These functions seemingly occur through action on cytotrophoblast cell TGFbeta receptors. Fifth, hCG-H is an essential component for successful human implantation to prevent early pregnancy loss and spontaneous abortion. Sixth, hCG-H is critical for promoting the midtrimester hemochorial implantation, and for preventing preeclampsia. Seventh, measurements of hCG-H have advantages over measurements of regular hCG or total hCG, in detecting pregnancy, pregnancy outcome (failing or term pregnancy), predicting preeclampsia in pregnancy, or as a tumor marker for gestational trophoblastic diseases.

Immune cells contribute to systemic cross-talk between the embryo and mother during early pregnancy in cooperation with the endocrine system

In early pregnancy, human chorionic gonadotropin (HCG) stimulates the corpus luteum to produce progesterone that in turn maintains human embryo implantation in the uterus. This inevitable communication through blood circulation can be called 'systemic cross-talk between the embryo and mother'. Despite considerable evidence suggesting that the human corpus luteum cannot be maintained by HCG alone, no other responsible soluble factors have been proposed. We found that peripheral blood mononuclear cells (PBMC) derived from pregnant women promoted progesterone production by human luteal cells and propose that both hormones and immune cells participate in this systemic cross-talk. This systemic cross-talk by immune cells is believed to operate in embryo implantation. Splenocytes derived from pregnant mice promoted endometrial differentiation and embryo implantation in vivo. Human PBMC derived from women early in pregnancy promoted invasion of murine embryos in vitro. In addition, recombinant HCG increased the effects of human PBMC on murine embryo invasion. Human chorionic gonadotropin also increased chemokine production by human PBMC through a lectin-glycan interaction, which is a primitive pathway in the immune system. Furthermore, chemokines were shown to induce human trophoblast invasion. These findings suggest that the immune system positively contributes to systemic cross-talk between the embryo and mother in cooperation with the endocrine system. (Reprod Med Biol 2006; 5: 19-29).

Functional Luteinizing Hormone/Chorionic Gonadotropin Receptors in Human Adrenal Cortical H295R Cells

Previous studies have suggested that activation of normal human adrenal and adrenal tumor luteinizing hormone (LH)/chorionic gonadotropin (hCG) receptors results in an increased secretion of steroid hormones. Since it is not feasible to test this suggestion on normal human adrenal cells, we used human adrenal cortical carcinoma H295R cells, which are similar in some respects to normal adrenal cortical cells. These cells contained LH/hCG receptor transcripts and receptor protein that can bind (125)I-hCG in a hormone-specific manner. Culturing the cells with highly purified hCG resulted in a time- and dose-dependent significant increase in dehydroepiandrosterone sulfate (DHEAS) secretion as compared with the controls. The DHEAS response was hormone as well as steroid specific. Since hCG treatment did not increase DHEA secretion, we suspected that the hCG might increase DHEA sulfotransferase (ST). Consistent with this possibility, hCG treatment increased steady-state DHEA-ST mRNA levels. The hCG effects require its receptors, as inhibition of their synthesis by treatment with antisense phosphorothioate oligodeoxynucleotides (ODN) made from the LH/hCG receptor sequence resulted in loss of DHEA-ST and DHEAS responses. The findings that 1) hCG treatment increased cAMP levels and activated protein kinase A (PKA), 2) 8-bromo cAMP mimicked hCG, and 3) blocking PKA activation prevented hCG as well as 8-bromo cAMP from increasing both DHEA-ST mRNA and DHEAS levels suggested that cAMP/PKA signaling was involved in the hCG actions. In conclusion, H295R cells contain LH/hCG receptors, which are coupled to increasing DHEAS secretion through upregulating the ST enzyme mRNA level. This action is mediated by the cAMP/PKA signaling pathway. These findings support the concept that adrenal function in normal and pathological conditions could be influenced by LH and hCG.

Macrophages in human reproductive tissues contain luteinizing hormone/chorionic gonadotropin receptors

PROBLEM

To determine whether macrophages in human reproductive tissues contain luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptor mRNA and receptor protein that can bind 125I-hCG.

METHOD OF STUDY

Macrophages isolated from term pregnancy human decidua were used for LH/hCG receptor detection by in situ hybridization for receptor mRNA and immunocytochemistry for a macrophage marker, CD68, performed alone and in combination, reverse transcription-nested polymerase chain reaction, Western and ligand blotting. The LH/hCG receptor presence in macrophages in late luteal phase human endometria and corpora lutea was determined by sequential performance of in situ hybridization and immunocytochemistry.

RESULTS

The macrophages present in term pregnancy human decidua and late luteal phase human endometria and corpora lutea contain LH/hCG receptors.

CONCLUSIONS

This is the first demonstration of macrophages present in human reproductive tissues containing LH/hCG receptors. The receptor presence suggests that LH and hCG may regulate macrophage functions in gonadal as well as in non-gonadal target tissues.

Human chorionic gonadotropin/luteinizing hormone receptor expression in the adult rat spinal cord

The adult and fetal rat brain contains human chorionic gonadotropin/luteinizing hormone (hCG/LH) receptors, that are functional in mediating the neurotropic, neuroendocrine and behavioral actions of gonadotropins. We hypothesized that the spinal cord also contains these receptors. We have now demonstrated by in situ hybridization, immunohistochemistry, and topical autoradiography that the adult rat spinal cord expresses hCG/LH receptors. Positive cells included motoneurons, interneurons and/or glia in the intermediate and ventral gray matter, interneurons and/or glia in the dorsal gray matter, and oligodendrocytes or astrocytes in the white matter. The receptors were able to bind an appropriate ligand, (125)I-hCG. The functional significance of these receptors in the spinal cord is unknown, but we can speculate that they may be neurotrophic in function.

Immortalized hippocampal cells contain functional luteinizing hormone/human chorionic gonadotropin receptors

We used immortalized HN33p cells as surrogates for hippocampal neurons to investigate the functional importance of luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors. The use of various detection techniques demonstrated that HN33p cells contain LH/hCG receptor transcripts and receptor protein that can bind 125I-hCG. Culturing them with highly purified hCG resulted in a significant, although modest, dose-and time-dependent and hormone specific increase in steady state 5-lipoxygenase (5-LO) mRNA and protein levels. The studies on signaling revealed that treatment of HN33p cells with hCG resulted in a robust dose- and a time-dependent significant increase in media cyclic AMP levels. In addition, treatment with a protein kinase (PK)A inhibitor, isoquinolinesulfonamide (H-89), but not with a PKC inhibitor, bisindolylmaleimide (Bis), prevented hCG from increasing the 5-LO protein levels. Pretreatment of HN33p cells for 48 hrs with 2 microM antisense, but not sense, phosphorothioate oligodeoxy-nucleotides (ODN) synthesized from mouse LH/hCG receptor sequence resulted in a dramatic decrease in LH/hCG receptor protein levels. In the antisense, but not in sense, ODN-treated cells, hCG was unable to increase cyclic AMP and 5-LO protein levels, suggesting that receptors are required for hCG to work in HN33p cells.

Localization of receptors for luteinizing hormone/chorionic gonadotropin in neural retina

Although the expression of the luteinizing hormone (LH)/human chorionic gonadotropin (CG) receptor gene has been traditionally thought to be restricted to gonadal tissue, recent studies have shown that LH/CG receptors are present in many regions of the central nervous system (CNS), as well as in peripheral tissues. We now report the characterization of LH/CG receptor gene expression in the neural retina, a component of the CNS. Transcript levels in the retina are approximately equal to levels present in the cerebral cortex, but are at least 100 fold lower than the levels in testis. The density of LH/CG receptor transcripts, receptor protein and 125I-CG binding is the highest in the photoreceptor cells and then decreased throughout the inner retina. Our study is the first to demonstrate the presence of LH/CG receptors in the neural retina. This finding raises the possibility that photoreceptor cells have the potential to mount cellular responses to LH/CG that may impact on visual processing, and poses an intriguing connection to the proposed role of gonadotropins in the progression of proliferative retinopathy.

A novel regulation of the oviductal glycoprotein gene expression by luteinizing hormone in bovine tubal epithelial cells

The hypothesis that bovine oviductal epithelial cells contain luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors and LH may regulate the oviductal glycoprotein (OGP) gene expression was tested. The results showed that bovine oviductal epithelial cells contain an 80 kDa LH/hCG receptor protein which can bind [(125)I]hCG. Culturing these cells with highly purified hCG, used as a surrogate hormone for LH, resulted in a dose and time dependent increase in a 95 kDa protein and a 2.3 kb transcript of OGP. The maximal increase of 100% was obtained with 10 ng/ml hCG and after three days of culture. LH, but not other hormones in the glycoprotein hormone family, isolated subunits of hCG, estradiol-17beta or progesterone, mimicked hCG, suggesting that the effect is hormone specific and requires the conformation of native hormone. The increase in steady state OGP mRNA levels by hCG is not due to an increase in the transcription rate of the gene. It is rather due to a significant increase in the half-life of OGP transcripts from 23 h in the control to 28 h after treatment with hCG. In summary, we conclude that LH and hCG can increase the synthesis of OGP by decreasing the degradation of its transcripts in bovine oviductal epithelial cells. Since OGP may play important roles in fertilization and growth and development of early embryo, higher LH levels present during the periovulatory period may directly participate in the early pregnancy events through increasing the synthesis of OGP.

The presence of luteinizing hormone/human chorionic gonadotropin receptors in lactating rat mammary glands

Previous studies have implied that mammary glands might contain luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors. But no one ever previously investigated them. We now demonstrate, by using several techniques, that lactating rat mammary glands contain LH/hCG receptor mRNA transcripts and receptor protein which can bind 125I-hCG. Primarily mammary epithelial cells, and to a lesser extent the interductal stromal cells, contain the receptor transcripts and the receptor protein. These findings support the concept that mammary glands are also the targets of direct regulation by LH/hCG.

Novel expression of luteinizing hormone/chorionic gonadotropin receptor gene in rat prostates

The reverse transcription-polymerase chain reaction (RT-PCR) amplified an expected 255 bp luteinizing hormone/chorionic gonadotropin (LH/CG) receptor sequence from rat prostates. Northern blotting demonstrated that prostates contain 4.3, 3.3, 2.6, 1.8, 0.8 and 0.2 kb LH/CG receptor transcripts. Western immunoblotting and ligand blotting demonstrated that prostates also contain an 80 kDa receptor protein which can bind 125I-labeled hCG and this binding was inhibited by excess unlabeled hCG. In situ hybridization and immunocytochemistry revealed that while the receptors are most abundant in epithelial cells, they are scarcely found in the stroma. The ventral lobe contained more receptors than the lateral lobe and the receptors in peripheral acini of the ventral lobe are higher which progressively decreased towards central acini. In summary, prostate glands express LH/CG receptor gene. The cellular, topographical and lobular distribution of receptors suggest that LH may directly regulate prostate functions.

Lymphocytes from pregnant women express human chorionic gonadotropin/luteinizing hormone receptor gene

Previous studies have indicated that human chorionic gonadotropin (hCG) has immunoregulatory properties and alters the functions of human lymphocytes. However, it has not been determined whether the gene encoding the receptors for hCG/luteinizing hormone (LH) is expressed in human lymphocytes. Total peripheral mononuclear lymphocytes isolated from blood samples of pregnant women by Ficoll-Paque gradient centrifugation contained mRNA transcripts encoding the hCG/LH receptors and a 50 kDa receptor protein which can bind 125I-hCG. T-Lymphocytes isolated from total mononuclear cell fractions also contained these receptor mRNA transcripts as well as the receptor protein. The levels of receptor transcripts and receptor protein are lower in lymphocytes than in ovarian tissue. These findings suggest that the immunoregulatory actions of hCG are probably mediated by specific receptors in T-lymphocytes from pregnant women.

Influence of corpus luteum age on the steroidogenic response to exogenous human chorionic gonadotropin in normal cycling women

OBJECTIVE

The null hypothesis of this study is that the patterns of steroid secretion exhibited by the human corpus luteum in response to exogenous human chorionic gonadotropin stimulation are independent of corpus luteum age at the time of treatment.

STUDY DESIGN

Twenty-five normally cycling women in whom the midcycle urinary luteinizing hormone surge (luteal day 0) was identified and from whom blood samples were obtained daily from cycle day 11 until menses were prospectively randomized to receive no treatment (group I, n = 5) or exogenous human chorionic gonadotropin 5000 IU administered intramuscularly on luteal day 0 (group II, n = 5), +4 (group III, n = 5), +8 (group IV, n = 5), or +12 (group V, n = 5). Serum concentrations of estrone, estradiol, progesterone, 17-hydroxyprogesterone, and androstenedione were measured by specific radioimmunoassays in all subjects; serum human chorionic gonadotropin concentrations were determined by immunoradiometric assay in treated subjects.

RESULTS

Serum human chorionic gonadotropin levels (mean +/- SEM) were virtually identical among treatment groups (p greater than 0.05). Luteal phase duration (mean +/- SEM) was prolonged (p less than 0.05) only in group V (18.4 +/- 0.5 days) compared with untreated subjects (group I 13.8 +/- 0.7 days). In all groups estrone and 17-hydroxyprogesterone concentrations closely paralleled those of estradiol and progesterone, respectively. Steroid data and progesterone/estradiol ratios (mean +/- SEM) in groups I and II were indistinguishable and were combined (control, n = 10). Group III subjects exhibited patterns of steroid secretion similar to groups I and II, although progesterone was moderately increased after human chorionic gonadotropin treatment. In groups IV and V, progesterone increased (p less than 0.05) 1 day after human chorionic gonadotropin and remained elevated for 5 to 6 days; a 4-day rise (p less than 0.05) in estradiol began 3 days after treatment, and androstenedione rose modestly in parallel. Progesterone/estradiol ratios in groups III through V increased (p less than 0.05) approximately twofold after human chorionic gonadotropin treatment and remained elevated for 4 to 5 days.

CONCLUSION

The human corpus luteum exhibits distinct age-dependent patterns of steroid secretion in response to exogenous human chorionic gonadotropin stimulation, an observation that may have clinical implications regarding the empirical use of exogenous human chorionic gonadotropin in support of luteal function.

Role of luteal cell nucleus in the expression of gonadotropin action

Gonadotropin receptors are not only present in cell membranes, but also in nuclei of bovine and human luteal cells. hCG/hLH can directly regulate several nuclear functions. To further investigate the role of luteal cell nucleus in the expression of gonadotropin action, the effect of enucleation of luteal cells on gonadotropin receptors and gonadotropin response was studied. Luteal cytoplasts were prepared by colchicine treatment of purified whole luteal cells followed by centrifugation at 37 C in a Percoll gradient. The cytoplasts were 85 to 90% pure with a recovery of about 57%. Cytoplasts were viable as determined by trypan blue exclusion (87%) and metabolically competent as determined by 3H-leucine incorporation into proteins. On the day of preparation, the viability and metabolic competency of cytoplasts were similar to control cells, i.e. untreated and colchicine treated whole luteal cells. In addition, cytoplasts and control cells showed a similar decline in number and viability during storage at 4 C. While control cells continue to be metabolically competent, cytoplasts showed a dramatic decline by 48 h of storage at 4 C. Neither the cytoplasts nor control cells degraded 125I-hCG. The kinetics of 125I-hCG association and dissociation, specificity and affinity of binding to cytoplasts were similar to control cells. However, the number of available gonadotropin receptors in cytoplasts was significantly lower than in control cells. Cytoplasts contained lower progesterone levels and more importantly, they could not be stimulated by 10 nM hCG or 10 mM dibutyryl cyclic AMP to produce more progesterone. Controls cells, on the other hand, contained higher progesterone levels and responded to hCG and dibutyryl cyclic AMP stimulation. In summary, removal of nuclei from luteal cells results in a partial loss of gonadotropin receptors and complete loss of steroidogenic response to hCG and dibutyryl cyclic AMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of the human ovarian LH/hCG receptor and comparison of the properties of mammalian LH/hCG receptors

Methods previously published by us [Wimalasena et al., J Biol Chem 260: 10689-10697, 1985; Wimalasena et al., J Biol Chem 261: 9416-9420, 1986] were utilized to solubilize the human corpus luteal leuteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor with 3-[(3-cholamide-propyl)dimethylammonio]-1-propanesulfonate (CHAPS) and to purify the receptor by two steps of hCG-Sepharose affinity chromatography. The specific binding capacity (SBC) of the purified human receptor was 7510 pmol/mg protein, and KA = 2.2 x 10(9) M-1 when iodo hCG was competed by hCG; the yield was 4-7% of starting activity. When hLH was used in competition with hCG, specific binding capacity was 7900 pmol/mg protein and KA 1.0 x 10(9) M-1. Silver staining and autoradiography demonstrated a single protein of Mr 78,000 under reducing and Mr 58-62 x 10(3) under nonreducing conditions. Rat ovarian LH/hCG receptor was purified by similar methods and the KA of 3.5 x 10(10) M-1 for hCG was substantially different from the KA for hLH which was 2.1 x 10(9) M-1. Mr of the rat protein was 78-82 x 10(3) (reduced) and 58-62 x 10(3) (nonreduced) when analyzed by silver staining and autoradiography. For the first time, human LH/hCG receptor has been purified to apparent homogeneity, and its Mr of 78,000 was essentially identical to the Mr values of purified rat and porcine receptors.

Masked gonadotropin-binding sites in human corpora lutea during menstrual cycle and pregnancy

To evaluate the possible existence of masked receptors for luteinizing hormone (LH)/human chorionic gonadotropin (hCG) in the human corpus luteum, we examined the effect of neuraminidase pretreatment on the specific binding of (125I)hLH to luteal particulates obtained from 11 patients during the menstrual cycle and 4 patients during early pregnancy. The pretreatment with neuraminidase significantly enhanced the specific binding of hLH to corpora lutea at the different stages of the luteal phase. Scatchard analyses revealed that neuraminidase increased the number of LH binding sites without altering the affinity for LH. Furthermore, the specific binding of hLH to human corpora lutea during pregnancy significantly increased after the pretreatment with neuraminidase. The data suggest that distinct populations of receptors for LH/hCG are masked within the human luteal cells.

The nature of reversible and not readily reversible bovine corpus luteum plasma membranes bound human chorionic gonadotropin

125I-human chorionic gonadotropin (125I-hCG) bound to plasma membranes of bovine corpora lutea consisted of reversible and not readily reversible fractions. The not readily reversible fraction progressively increased as the length and the temperature of preincubation were increased. The not readily reversible fraction was, however, completely eluted after any time or temperature of preincubation. Although the not readily reversible and reversible bound 125I-hCG were precipitated equally well with 10% trichloroacetic acid, the not readily reversible bound 125I-hCG was able to rebind much higher to fresh plasma membranes compared to reversible bound 125I-hCG. These findings suggest that while not readily reversible bound 125I-hCG was intact, the reversible bound 125I-hCG was somewhat altered during the binding reaction.

Morphological and biochemical characterization of small and large bovine luteal cells during pregnancy

Small (15-18 microns) and large (18-45 microns) luteal cells were obtained from bovine corpora lutea of pregnancy by centrifugal elutriation of enzymatically dispersed luteal cells. Small luteal cells accounted for about 85% and large luteal cells for 8-12% of total luteal cell population. Small luteal cells were characterized by a low cytoplasmic/nuclear ratio with cytoplasm containing mitochondria, lysosomes, lipid droplets, dense granules and endoplasmic reticulum. Large luteal cells possessed a higher cytoplasmic/nuclear ratio with cytoplasm containing more abundant mitochondria, lipid droplets, dense granules and lysosomes compared to small luteal cells. Some of the mitochondria were very long. Both small and large luteal cells contained scarce amounts of Golgi elements. Dense granules were found close to the nucleus in both cell types. The nucleus of both cell types was acentric, irregular in shape and contained a well-defined nucleolus. The highly condensed chromatin in small luteal cells was found at the nuclear periphery and in the central region. Dispersed chromatin was found throughout the nucleus with condensed chromatin at the nuclear periphery of large luteal cells. Macrophages and fibroblasts were occasionally found in small luteal cell preparations, but their morphology was quite distinct from both small and large luteal cells. Scanning electron microscopy revealed that the majority of the small and large luteal cells were spherical or slightly elongated in shape. Small luteal cells displayed the presence of blebs, ruffles and short microvilli. Large luteal cell surface contained ruffles and randomly distributed clusters of blebs of different sizes, predominantly spherical in shape with a smooth surface. Finger-like projections were also occasionally seen. Small luteal cells contained significantly lower amounts of protein, but the ratios between protein and DNA were similar in both cell types. The basal, human chorionic gonadotropin (hCG)- or cyclic AMP-stimulated progesterone production, the apparent dissociation constants for [125I]hCG binding and the apparent total number of available sites per cell were similar in small and large luteal cells. The activities of enzymes that are involved directly or indirectly in progesterone biosynthesis and those involved in general cellular metabolism and biosynthesis were also similar in small and large luteal cells with one exception. That is, the activities of 5'-nucleotidase and NADH cytochrome c reductase were significantly higher in small compared to large luteal cells.

Internalization of 125I-human choriogonadotropin in bovine luteal slices. A biochemical study

Various intracellular organelles as well as outer cell membranes of bovine corpora lutea intrinsically contain gonadotropin receptors (Rao et al., J biol chem 256 (1981) 2628 [5]). In order to investigate whether exogenously added human choriogonadotropin (hCG) can internalize and bind to the intracellular sites, bovine luteal slices that had been carefully checked with respect to structural and functional integrity were incubated with 0.1 nM 125I-hCG. Following incubation, specific radioactivity was found to be associated with various intracellular organelles, but not with cytosol. The order of radioactivity uptake by subcellular organelles following a 2-h incubation was: Golgi medium greater than Golgi heavy greater than Golgi light greater than plasma membranes = rough endoplasmic reticulum greater than mitochondria-lysosomes- greater than nuclei. The 5'-nucleotidase activity and electron microscopic examination of the fractions revealed that the presence of radioactivity in the intracellular organelles cannot be attributed solely to plasma membrane contamination. The internalization and intracellular binding of 125I-hCG was time and temperature-dependent. Only excess unlabeled hCG and hLH (but not hCG subunits, FSH and PRL) competed with 125I-hCG for internalization in luteal slices. Very little or no 125I-hCG added was internalized in liver or kidney slices; luteal, liver and kidney slices accumulated neither 125I-BSA nor 125I. The radioactivity eluted from various luteal subcellular organelles was able to rebind to fresh corresponding organelles and came off Sepharose 6B columns in a position corresponding to native 125I-hCG. The gel filtration profile of detergent-solubilized radioactivity revealed that 125I-hCG was macromolecular bound. The degraded and altered 125I-hCG was found in the incubation media.

Decrease of various luteal enzyme activities during prostaglandin F2 alpha-induced luteal regression in bovine

Luteal gonadotropin receptors decrease in cows, sheep and rats within 24 h following an injection of a luteolytic dose of prostaglandin (PG) F2 alpha. But it is not known whether this decrease is the specific event, or a reflection of general decline in luteal cell structure, function and metabolism. In order to investigate this possibility, 15 of 21 heifers were given on day 9 of the estrous cycle, a single 500 micrograms injection of Cloprostenol (CO), a synthetic PGF2 alpha analog. These heifers were ovariectomized in groups of 5 at 12, 24 and 36 h after CO. For controls, a group of 6 heifers were ovariectomized just prior to injection of the others. Serum progesterone levels decreased whereas LH levels increased (P less than 0.05) by 12 h with no additional changes observed at 24 or 36 h. The luteal plasma membranes [125I]hCG specific binding, as well as 5'-nucleotidase (5'-NE) activity, decreased by 12 h and continued to decline (P less than 0.05) until 24 h (binding) or 36 h (5'-NE). Scatchard analysis showed that the decrease in [125I]hCG binding was due to a decrease in receptor number rather than a decrease in receptor affinity. The activities of cytochrome c oxidase in mitochondria, NADH cytochrome c reductase in rough endoplasmic reticulum and galactosyl transferase in Golgi decreased while NAD pyrophosphorylase in nuclei virtually disappeared following the injection of CO. The beta-N-acetyl-D-glucosaminidase (a lysosomal hydrolase) activity in the homogenate increased by 12 h and continued to increase up to 36 h.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple way to determine nonspecific effects of plasma and serum components in radioreceptor assays and radioimmunoassays for human chorionic gonadotropin

A simple approach is validated for the determination of nonspecific effects of human plasma and serum in the radioreceptor assays and radioimmunoassays for human chorionic gonadotropin (hCG). The approach is based on the findings that, despite differences in the degree of inhibition of 125I-hCG binding to its receptors and antibodies by nonhormonal components in different dilutions of pool plasma and serum, the standard curves (plotted as the percentage of control for each serum or plasma dilution) are superimposable. The approach consists of (1) running a single standard curve with no pool plasma or serum, (2) including a set of "correction" tubes which contain pool plasma or serum diluted correspondingly to the dilution of the unknown samples in the assay, (3) dividing the counts per minute found in the correction tubes into the counts per minute of the unknown samples and multiplying by 100, and (4) using this value to obtain the amount of hCG in the unknown samples by comparison with the no pool plasma or serum standard curve.

Gonadotropic hormone binding to human ovarian tumors

A variety of normal human ovarian tissues as well as benign and malignant human ovarian neoplasms have been examined in vitro for the presence of gonadotropin binding sites and gonadotropin-stimulable cAMP production, in order to determine whether gonadotropic hormones have an effect on ovarian tumors. Binding of either FSH or hCG, or both, was demonstrated in several tumors from each of the histologic subgroups of primary ovarian tumors, including epithelial, sex cord-stromal, and germ cell types. Cyclic AMP stimulation was found in one tumor of sex cord-stromal origin, in two of epithelial origin, in two of germ cell origin, and in one tumor-like condition, pregnancy luteoma. Additional biochemical studies are needed to characterize receptor sites and to relate them to histologic features, growth behavior in vivo, and serum gonadotropin levels.

Properties of LH/hCG receptors in porcine corpus luteum homogenates and subcellular fractions, and factors influencing the recovery of membrane-bound hormone

An evaluation of several techniques commonly used to separate bound from free hormone was made for the binding of radiolabelled human chorionic gonadotropin to mid-luteal pig corpus luteum homogenates and subcellular fractions. Compared to millipore filtration with 0.22 or 0.45-mu HAWP filters, centrifugation of homogenates at 2 500 x gav or 1 000 x gav for 15 min recovered only 50 and 33% respectively of the total bound hormone present. This discrepancy was accentuated further when hormone binding to post-nuclear subcellular fractions was studied. Centrifugation of a nuclear fraction at 2 500 x gav for 15 min recovered 70% of the membrane-bound receptors present (as measured by filtration), whereas centrifugation of mitochondrial, lysosomal and microsomal fractions under these conditions recovered only 46, 16 and 4% respectively. Divalent metal ions influenced hormone binding in 2 ways: (i) Specific bonding of hCG was greatest in the absence of metal ions and in the presence of low levels of chelating agents. Increasing concentrations of magnesium and calcium ions appeared to interfere with the interaction of hormone and receptor. (ii) Divalent metal ions reduced the recovery of particle-bound hormone by centrifugation, at both high and low speeds. The results illustrate the pitfalls of using low-speed centrifugation to recover membrane-bound hormone-receptor complexes when small membrane vesicles are present.

The presence of gonadotropin binding sites in the intracellular organelles of human ovaries

The nuclei (N), plasma membranes (PM), mitochondria-lysosomes, rough endoplasmic reticulum, and combined (light, medium, and heavy) Golgi (G) fractions were isolated from human ovaries. The purities of these fractions were evaluated by assays of appropriate marker enzymes, which revealed that some fractions were very pure but that others had minor contamination. When tested, all of the fractions exhibited 125I-labeled human chorionic gonadotropin (125I-hCG)-specific binding. This intracellular 125I-hCG binding was not due to PM contamination because: (1) N, which had no detectable 5'-nucleotidase (5'-NE) activity, a marker for PM, exhibited 125I-hCG-specific binding; (2) the G, which had only a fraction of the 5'-NE activity of PM, exhibited as much binding as PM; and (3) the ratios between specific 125I-hCG binding and 5'-NE activity in other fractions were not the same as for PM. They should have been the same if PM contamination was responsible for the 125I-hCG binding observed in other organelles. In conclusion, our results demonstrate that gonadotropin-binding sites are present in various intracellular organelles as well as in PM of human ovaries.

Chorionic gonadotropin concentration in early human pregnancy: comparison of specific and nonspecific assays

Daily blood samples were collected during 10 menstrual cycles in which conception had occurred, and changes in circulating concentrations of human chorionic gonadotropin (hCG) were measured simultaneously in specific and nonspecific radioimmunoassays. The hCG concentration profiles were not identical, and the fundamental differences could not be related to differences in technique. Both specific and nonspecific parameters of hCG concentration rose exponentially for the first 2 to 3 weeks following first detection and were thus amenable to linear regression analysis. Doubling times were significantly different at 2.3 and 1.8 days, respectively. Extrapolation of the regression data gave a (theoretical) plasma concentration of 3 IU/liter at 9.5 days after the luteinizing hormone peak using the specific assay but at only 5.5 days using the nonspecific assay. This difference is sufficiently large to suggest the presence of other forms of hCG or its subunits about the time of implantation and during early pregnancy.

Gonadotropin and prostaglandins binding sites in nuclei of bovine corpora lutea

Highly purified nuclei isolated from bovine corpora lutea showed marked enrichment of NAD pyrophosphorylase, a marker for this organelle. Rough endoplasmic reticulum and lysosomal markers were undetectable, whereas plasma membrane and Golgi markers were detectable but not enriched in nuclei. These highly puridied nuclei exhibited specific binding with 125I-labeled human choriogonadotropin, [3H]prostaglandin E1 and [3H]prostaglandin F2 alpha. However, these bindings were only 15.4% (human choriogonadotropin), 7.9% (prostaglandin E1) and 8.9% (prostaglandin F2 alpha) of the plasma membrane binding observed under the same conditions. Washing of nuclei and plasma membranes twice with buffer containing 0.1% Triton X-100 resulted in gonadotropin and prostaglandin F2 alpha binding site and 5'-nucleotidase (EC 3.1.3.5) losses from nuclei that were different from those observed for plasma membranes. More importantly, the washed nuclei exhibited 44% (human choriogonadotropin), 21--26% (prostaglandins) of original specific binding despite virtual disappearance of 5'-nucleotidase activity. The nuclear membranes isolated from nuclei, specifically bound 125I-labeled human choriogonadotropin and [3H]prostaglandin F2 alpha to the same extent or significantly more ([3H]prostaglandin E1, P less than 0.05) than nuclei themselves, despite the marked losses of chromatin. In summary, our data suggest that gonadotropin and prostaglandins bind to nuclei and that this binding was intrinsic and was primarily associated with the nuclear membrane.

Gonadotropin receptors of human corpus luteum during menstrual cycle and pregnancy

Specific high-affinity low-capacity binding of human chorionic gonadotropin (hCG) and lutropin (hLH) was demonstrated in the plasma membrane fractions of human corpora lutea. The number of binding sites for both hormones increased from early to late luteal phase, whereas regressing corpus luteum from proliferative phase did not bind either hormone. On the basis of apparent dissociation constants the affinity of the receptor for hLH is highest during early luteal phase and decreases toward the end of the cycle, which may reflect an increasing insensitivity of the corpus luteum to circulating hLH. By contrast, the affinity of the receptor for hCG is highest in the midluteal phase. There are gonadotropin binding sites in the human corpus luteum also during pregnancy, but they are saturated by endogenous hCG. Evidence for this was obtained by elution of hCG with 0.15M sodium chloride at pH 2.3 from washed plasma membrane fractions of luteal tissue from six to 16 week's gestation. After acid treatment and neutralization these preparations showed specific binding for 125I-labeled hCG, but not for 125I-labeled hLH. Our results demonstrate a shift in the balance of affinity of the gonadotropin receptor from hLH to hCG during the course of luteal phase, and during pregnancy the binding sites appear to be available for hCG only.