hCG Secretion Research Articles

Characterization of cell types within a chorionic gonadotropin-secreting, mechanically dissociated human placental cell population in perifusion.

A cell perifusion system was established to examine human placental endocrine regulation by locally synthesized peptides. First-trimester and term trophoblast cells were mechanically dissociated. Cells were plated on microcarrier beads and cultured for 7-14 days. Cells on beads were loaded in chambers, perifused with culture media and effluent was assayed for chorionic gonadotropin (hCG). Mechanical dissociation of placental tissue produced cell preparations with 85-95% viability. Staining with Masson trichrome, cytokeratin and beta-hCG antibodies suggested that greater than 50% of the cells were trophoblast. Perifused trophoblast cells secreted hCG in a continuous non-pulsatile fashion, independent of exogenous hormonal stimuli. hCG secretion from first-trimester trophoblast cells remained stable in static culture for 14 days. GnRH perifusion (10(-8) M) for 15-120 s transiently increased hCG secretion from first-trimester trophoblast cells. Longer GnRH exposure stimulated greater hCG secretion. Each of 3 consecutive pulses of 8-bromo-cyclic adenosine-3',5'-monophosphate (cAMP, 10(-9) M) administered at 2-hour intervals stimulated transient hCG secretion from first-trimester and term placental cells. cAMP stimulated hCG secretion more potently from first-trimester than from term placental cells.

Human chorionic gonadotropin secretion from the early human placenta: in vitro regulation by progesterone and its antagonist.

Local actions of placental neurohormones and sex steroids have been proposed to play a role in the regulation of human chorionic gonadotropin (hCG) release from the human placenta. Accordingly, we utilized an in vitro perifusion system and cultures of placental explants to investigate short- and long-term effects of progesterone and its respective antagonist on hCG secretion from the human first-trimester placenta. Tissue slices (100 mg) obtained from legal pregnancy terminations of 9-12 weeks of gestation were continuously perifused and the effluent collected in fractions of 2-20 min. After initial perifusion periods of 30-140 min, either progesterone, a progesterone antagonist (ZK 98-299), or both were added to the perifusion medium at final concentrations of 10(-4)-10(-9) mol/l. Administration was either continuous or intermittent in 10-min pulses. Furthermore, 50-mg pieces of placental explants were cultured in multiwell tissue culture plates for up to 5 days. During the perifusion studies, hCG (determined by enzyme immunoassay) was released in a pulsatile fashion. This hCG pulsatility was decreased in response to both progesterone and progesterone antagonist at all concentrations tested. In contrast, intermittent administration of either treatment increased the hCG secretion. Secretion of hCG was not affected when progesterone and its antagonist were co-administered at equimolar concentrations. These observations demonstrate the diverging effects of progesterone and its antagonist on hCG secretion from the human first-trimester placenta in vitro, depending on the experimental conditions. Thus, progesterone-modulated hCG secretion appears to be regulated in a complex manner, its fine tuning involving other, as yet uninvestigated intraplacental factors.

Growth factors in the biology of human trophoblast and their clinical relevances in early pregnancy maintenance

We have shown highly increased expression of myc product and PDGF in cytotrophoblast of early placenta. This suggests that myc protein and PDGF may be linked to trophoblast proliferation. On the other hand, simultaneous expression of EGF and EGF receptor in cytotrophoblast of 4- to 5-week placenta and in syncytiotrophoblast of 6- to 12-week placenta implies that EGF may act in an autocrine manner in the first trimester placenta. EGF has been found to exert gestational age dependent dual action on the placenta: one is to stimulate the proliferation of cytotrophoblast in very early (4–5 week) placenta and the other is to stimulate the ability to secrete hCG and hPL in early (6–12 weeks) placenta. Furthermore, we have demonstrated that optimal concentration of thyroid hormone exerts stimulatory effects on progesterone, estradiol, hCG, and hPL secretion by cultured early placental tissues. Indeed, serum T 4 , T 3 , free T 4 and free T 3 levels in patients with a clinical diagnosis of threatened abortion who subsequently aborted were significantly lower compared to patients who did not abort. These findings suggest that thyroid hormone may play an important role in maintaining early pregnancy in threatened abortion through acting as a physiological amplifier of trophoblast endocrine function.

Gestational age-dependent dual action of epidermal growth factor on human placenta early in gestation.

In order to better understand the role of epidermal growth factor (EGF) in the regulation of placental growth and function, effects of EGF on proliferative activity and differentiated function of trophoblast were examined. Explants from very early (4-5 week) placentas and early (6-7 week, 8-9 week, 10-12 week) placentas were respectively cultured under a serum-free condition in the absence or presence of EGF (100 micrograms/L) for the first 48 h, and the cultures were continued for subsequent 72 h without EGF. The proliferative potential and differentiated function of trophoblast were assessed by immunohistochemical Ki-67 staining and by determining the ability to secrete human CG (hCG) and human placental lactogen (hPL), respectively. Quantitative estimates of proliferative activity based on mean percentage of Ki-67 positive nuclei showed that EGF stimulated proliferative potential of cytotrophoblast in very early (4-5 week) placental explants. The EGF stimulation of trophoblast proliferation was apparent at a 12-h EGF-treated period. By contrast, early (6-12 week) placental explants did not respond to EGF with increase in trophoblast proliferation. Instead, in early placental explant culture EGF stimulated hCG and hPL secretion with a lag period of 72 h, whereas very early placental explants did not respond to EGF with increase in hCG and hPL secretion. These results suggest that EGF exerts gestational age-dependent dual action on the first-trimester placenta: one is to stimulate trophoblast proliferation in 4-5 week placenta and the other is to stimulate differentiated trophoblast function in 6-12 week placenta.

Rapid stimulation of human chorionic gonadotropin secretion by interleukin-1 beta from perifused first trimester trophoblast.

Placental trophoblast has been implicated as a major source of interleukin-1 beta (IL-1 beta), a cytokine that mediates immunological responses in the body. This study evaluated the effect of IL-1 beta on hCG secretion from 8- to 12-week-old placental trophoblast. Physically dissociated trophoblast cells collected from multiple placentae were cultured on carrier beads and loaded into chambers in a perifusion system. Medium was perifused through the chambers, and effluent was collected and assayed for hCG. Basal hCG secretion was not dependent on exogenous IL-1 beta or GnRH, but varied between mixed placental preparations and increased with duration of culture. Therefore, hCG secretion was expressed as a percentage of mean basal hCG secretion for any given chamber. IL-1 beta (10(-9) M) stimulated a rapid and transient hCG secretory response. hCG release increased by approximately 150% (P less than 0.05; n = 5) in response to the cytokine, but lower concentrations (10(-10) and 10(-11) M) were ineffective (P greater than 0.05; n = 3 each). GnRH stimulated hCG secretion by approximately 80% (P less than 0.05; n = 6). The hCG secretory profiles in response to IL-1 beta and GnRH were similar. Combined treatment with equimolar (10(-9) M) IL-1 beta and GnRH increased hCG secretion by approximately 150% (P less than 0.05; n = 5), stimulating hCG secretion as effectively as either hormone alone (P greater than 0.05). The stimulatory effect of GnRH on hCG secretion was blocked by the concomitant presence of a GnRH antagonist, Nal-Glu-GnRH (P less than 0.05; n = 5). However, simultaneous treatment with IL-1 beta and Nal-Glu-GnRH did not affect IL-1 beta-stimulated hCG secretion (100.5 +/- 3.6 vs. 162.9 +/- 10.2%; P less than 0.05; n = 7). The data suggest that IL-1 beta and GnRH stimulated a near-maximal physiological hCG secretory response, possibly through different receptor types. Alternatively, these two hormones may share a common signal transduction pathway, or IL-1 beta may influence a step distal to the coupling of GnRH to its receptor in the placental trophoblast.

Prophylactic effect of bestatin on the onset of invasive mole--clinical and fundamental studies.

This study was performed to determine whether bestatin (Ubenimex) has clinical prophylactic effects on the onset of invasive mole and a direct inhibitory effect on the growth of hydatidiform molar cells. A total of 49 patients with hydatidiform mole treated at Nagoya University Hospital from 1984 to 1990 were randomly divided into two groups, a bestatin administered-group and a bestatin non-administered group. Patients in the bestatin group were given 30 mg of bestatin orally and daily for three months just after their molar deliveries. There was no significant difference in age, gravidity, parity and gestational weeks between the two groups. There was also no significant difference in the duration of human chorionic gonadotropin (hCG) negative conversion in patients without invasive mole between the two groups. However, the incidence of invasive mole in the bestatin group (2/25, 8%) was significantly lower than that of the non-bestatin group (7/24, 29.2%). Nevertheless, there was no significant difference between the two groups in such immunological parameters as PHA skin test, PPD skin test, PHA stimulation index (PHA-SI), white blood cell (WBC) count lymphocytes % per WBC, OKT 3% per lymphocytes, OKT 4% per lymphocytes, OKT4/OKT8 and Leu 11% per lymphocytes. In vitro studies were performed with primary cultured hydatidiform moles. The result was that bestatin inhibited the secretion of hCG and 3H-thymidine uptake of hydatidiform molar cells. Thus, a possibility was suggested that bestatin directly inhibits the growth of hydatidiform molar cells and prevents the onset of invasive mole.

The influence of mercury on the secretion of human chorionic gonadotropin in superfused young placental tissue.

The effect of mercury (Hg), as HgCl2, in levels ranging from 0.75 to 12 micrograms/ml medium, on the secretion of human chorionic gonadotropin (hCG) was examined in first-trimester placental explants, after 6 or 24 hr incubation, employing both static and dynamic systems (the latter by superfusion). Later the unbound Hg was washed for 45 min. with fresh medium devoid of Hg, followed by superfusion with the latter medium for 75 min., during which time samples were collected for hCG assay. For the superfusion experiments the parameters used for evaluating the hCG secretion pattern were: mean peak amplitude, pulse frequency and the area under the hCG secretion curve (AUC). The results observed after 24 hr incubation indicate that in the dynamic system the hCG secretion increased significantly, and this increase was dose-dependent. There was also a dose-related increase in mean total hCG secreted by the explants exposed to Hg. Maximal hCG secretion was observed after 24 hr exposure of explants to 6 micrograms of the metal/ml. Both the mean peak amplitude and AUC parameters showed a statistically-significant increase for this dose level. At 12 micrograms/ml, the pulsatile secretion of hCG decreased, but the value for the mean hCG secretion was still higher than that observed for 0.75 and 3 micrograms/ml. After 6 hr incubation, however, there were no significant changes from the control, as judged by all of the above parameters. The levels of hCG secreted by the explants into the media in the static system were not significantly different from their respective controls, for both incubation periods and Hg levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The expression of human chorionic gonadotropin/human luteinizing hormone receptors in human gestational trophoblastic neoplasms.

Normal human placental trophoblasts have recently been shown to contain receptors for hCG/hLH. The present studies investigated the expression of these receptors in hyperplastic and anaplastic trophoblasts in gestational trophoblastic neoplasms. The results demonstrated that both hydatidiform moles and choriocarcinomas contained receptor messenger RNA (mRNA) and receptor protein. A variety of nontrophoblast tumors, on the other hand, contained neither receptor mRNA nor receptor protein. Choriocarcinomas contained more receptor mRNA and receptor protein than hydatidiform moles which in turn contained more than normal human placenta. Midluteal phase human corpus luteum contained more receptor mRNA than normal human placenta and about the same as choriocarcinomas. The hyperplastic and anaplastic trophoblasts in hydatidiform moles and choriocarcinomas contained more receptor immunostaining than the normal trophoblasts in the same tissue or those from normal placentas from about the same gestational age. The receptor immunostaining increased as the degree of trophoblast hyperplasia increased in hydatidiform moles. Anaplastic trophoblasts of choriocarcinomas contained a similar amount of receptor immunostaining as severely hyperplastic trophoblasts of hydatidiform moles. Invading anaplastic trophoblasts of choriocarcinoma contained greater amount of receptor immunostaining than the surrounding endometrial stromal and myometrial smooth muscle cells. In summary, this is the first study to our knowledge demonstrating the expression of hCG/hLH receptor gene in gestational trophoblastic neoplasms. The increased receptor expression in these neoplasms suggests that hCG, via its receptors, could play a fundamental and previously unsuspected autocrine role in the regulation of trophoblast transformation, growth, invasion, and high hCG secretion.

Effects of calcitonin on human trophoblastic cells in culture: absence of autocrine control

The purpose of this work was to investigate the effects of calcitonin (CT) on trophoblastic cells with respect to cAMP levels and human chorionic gonadotrophin (hCG) secretion in cultured cells from first-trimester and term placentas and in a choriocarcinoma cell line (JEG-3). The expression of the CT gene was investigated to elucidate a putative autocrine control of CT during pregnancy. The addition of salmon CT (10 −10 M and above) resulted in concentration-dependent increases in cAMP secretion by normal trophoblastic cells from term and first-trimester placentas. Moreover, CT was found to increase cAMP secretion preferentially in completely differentiated cells, i.e. after 4–7 days in culture. Addition to the culture medium of JEG-3 cells slightly increased cAMP secretion only at a concentration of 10 −8 M. The basal level of hCG in the medium was found to be higher in the first-trimester than in the term trophoblast culture, but salmon CT induced an increase in hCG secretion by term placenta cells only. CT gene expression in our experimental model was investigated to elucidate a putative autocrine control of CT action during pregnancy. It was not found to be expressed in syncytiotrophoblast cells from either first-trimester or term placenta cells by the method used. Our data demonstrate the absence of autocrine control of CT effects in trophoblastic cells, and suggest that CT is likely to exert its effect preferentially on differentiated cells.

Luteinizing hormone-releasing hormone (LHRH)- and (hydroxyproline9)LHRH-stimulated human chorionic gonadotropin secretion from perifused first trimester placental cells.

(Hydroxyproline9)LHRH [(Hyp9)LHRH] has been isolated from human, sheep, rodent, and frog hypothalamus. (Hyp9)LHRH is the major LHRH moiety in fetal rat hypothalamus. This study compared 1) synthetic LHRH-stimulated hCG secretion from term trophoblast vs. first trimester placental cells and 2) the ability and specificity with which synthetic LHRH and (Hyp9)LHRH could stimulate hCG secretion from 8- to 12-week gestation placenta. Physically dissociated cells from multiple placentae were pooled, plated on microcarrier beads, and perifused in 1.5-ml chambers (1.5 x 10(6) cells/chamber). Effluent fractions were analyzed for hCG. Each chamber was its own control. Basal hCG secretion did not depend upon exogenous LHRH stimulation. The amplitude of LHRH-stimulated hCG pulses was greater from first trimester placental than term trophoblast cells (mean +/- SEM, 6.99 +/- 1.47 vs. 0.50 +/- 0.05 mIU/ml perifusate; peak minus basal; n = 4 chambers; P less than 0.01). LHRH and (Hyp9)LHRH (10(-9) M) increased hCG secretion from first trimester placental cells (5.02 +/- 1.29 vs. 8.64 +/- 1.61 and 4.36 +/- 0.58 vs. 7.44 +/- 1.01 mIU/ml; n = 15 and 9, respectively; P less than 0.01). At the concentrations used, LHRH and (Hyp9)LHRH seemed to stimulate hCG secretion equipotently (P greater than 0.05). Simultaneous perifusion with an LHRH antagonist, (Nal-Glu)LHRH blocked the hCG secretory response to LHRH or (Hyp9)LHRH (equimolar 10(-9) M concentrations; n = 5; P less than 0.05). (Nal-Glu)LHRH alone (10(-9) M) did not affect hCG secretion (n = 5; P greater than 0.05). The results suggested that first trimester placental cells are more responsive to LHRH than are term trophoblast cells. (Hyp9)LHRH is a potential physiological secretagogue of hCG.

Effects of diacylglycerol and gonadotropin-releasing hormone on human chorionic gonadotropin release by cultured trophoblast cells

The effect of activation of calcium- and phospholipid-dependent protein kinase (protein kinase C) on human chorionic gonadotropin (hCG) release by cultured trophoblast cells was studied and a role of protein kinase C in the GnRH-mediated hCG release was also evaluated. Both GnRH and 1-oleoyl-2- acetylglycerol (OAG), a protein kinase C activator, stimulated h CG release after 3 h incubation in a dosedependent manner with ED 50 of 55 nmol/l and 4.0 nmol/l, respectively. A tumor-promoting phorbol ester, 12-0-tetradecanoylphorbol-13-acetate (TPA) also stimulated hCG release while two non-tumor-promoting compounds, phorbol and 4α-phorbol, failed to stimulate hCG release. hCG release by maximal effective dose of GnRH (10 μmol/l or OAG (1 μmol/l) was further stimulated when cells were incubated with same concentrations of GnRH and OAG. OAG-stimulated hCG release was completely inhibited by a protein kinase C inhibitor, H-7, with ID 50 of 23 nmol/l while H-7 did not affect GnRH-mediated hCG release. These results indicate that GnRH-stimulated hCG release is not mediated by protein kinase C pathway, however, the secretion of hCG is also regulated by the mechanism that involves protein kinase C activation.

Herpes simplex virus infection of cultured human term trophoblast.

Mononuclear trophoblast cells were isolated from term placentas of uncomplicated pregnancies, purified to homogeneity by negative immunomagnetic separation using monoclonal antibodies to the major histocompatibility complex, and challenged with herpes simplex virus (HSV). The cultures were highly susceptible to virus-induced cytopathic effect as evidenced by cytopathic alteration and inhibition of human chorionic gonadotropin (hCG) secretion. Both HSV I and II underwent a full replicative cycle in the trophoblast, although the production of progeny virus was 10-100 times less than that obtained with placental fibroblasts or choriocarcinoma cells. The permissiveness was independent of in vitro syncytial differentiation of the trophoblast. The results suggest that the trophoblast layer may be involved in intrauterine HSV infection.

Antibodies to hCG inhibit progesterone production from human syncytiotrophoblast cells.

The placenta holds the key position for the remarkable endocrine alterations during pregnancy. It elaborates two major hormones, the chorionic gonadotropin (CG) and progesterone in addition to many other factors. Several agents like GnRH (Siler-Khodr and Khodr, 1981), EGF (Takemori et al, 1981; Morrish and Siy, 1985; Huot et al, 198 1) and CAMP (Hilf and Merz, 1985; Handwerger et al, 1973) have been suggested as being involved in the regulation of hCG secretion. However, the regulation of progesterone secretion by the human trophoblasts is largely unknown. Androgens and estrogens have been reported to influence placental progesterone production but only in a permissive manner (Grimshaw, Mitchell and Challis, 1983; Wunsch et al, 1986). The gonadotropins (LH/hCG) are known stimulators of luteal progesterone synthesis (Stock et al, 1971; Hanson, Powell and Stevans, 1971), but the role ofthese hormones in the synthesis of progesterone by placenta needs to be ascertained. The purpose of the present study was to elucidate the role of hCG on progesterone production by the human placenta. The trophoblast cell culture system has been chosen particularly for this purpose as defined cell populations can be manipulated and their morphological and functional capacities observed over the days of culture.

Secretion of human chorionic gonadotropin in superfused young placental tissue exposed to cadmium.

The effect of various concentrations of cadmium (Cd) in levels ranging from 0.75 to 12 micrograms/ml medium, on the secretion of human chorionic gonadotropin (hCG) in first-trimester placental explants, after 6 or 24 h incubation, employing both static and dynamic systems was examined. Later the unbound Cd was washed for 45 min with fresh medium devoid of Cd, followed by superfusion with the latter medium for 75 min, during which time samples were collected for hCG assay. For the superfusion experiments the parameters used for evaluating the hCG secretion pattern were: mean peak amplitude (MPA), pulse frequency (PF) and the area under the hCG secretion curve (AUC). The results indicate that in the dynamic system the hCG secretion increased significantly, and this increase was dose dependent. There was also a dose-related increase in mean total hCG secreted by the explants exposed to Cd. Maximal hCG secretion was observed after 24 h exposure of explants to 6 micrograms of the metal/ml. Both the MPA and AUC parameters showed a statistically significant increase for this dose level. At 12 micrograms/ml, the pulsatile secretion of hCG decreased, the value for the mean hCG secretion being comparable to that observed for 0.75 micrograms/ml. After 6 h incubation, however, there were no significant changes from the control, as judged by all of the above parameters. The levels of hCG secreted by the explants into the media in the static system were not significantly different from their respective controls, for both incubation periods and Cd levels. These results indicate that Cd may affect the normal placental function, as reflected in its hCG secretion pattern.

Gestational age dependent, rapid and delayed effect of epidermal growth factor upon human chorionic gonadotropin secretion by the first trimester explants

EGF is believed to play an important role in the regulation of placental function. We have examined in detail, the effect of 50–200 ng/ml EGF on first trimester (7–13 gestational weeks) placental human chorionic gonadotropin (hCG) secretion using both static (explants and isolated cells) and kinetic (superfusion of explants) culture methods. In 7–9 week explants, short (1–4 minutes) pulses of EGF increased both the rate and amplitude of spontaneous hCG pulses. This effect was dose dependent and the concentration of 50 ng/ml was the most effective. Addition of 50 ng/ml EGF for 90 minutes in superfusion caused an initial increase followed by a significant decrease in spontaneous pulsatile hCG secretion. hCG secretion was not affected by a subsequent addition of a one minute pulse of 50 ng/ml EGF, reflecting desensitization. A gestational age dependent delayed effect of EGF wsas documented. At 7–9 weeks, following overnight preincubation with 50 ng/ml EGF, there was a significant increase in hCG pulse parameters as calculated by PULSAR. In contrast, at >10 weeks, the growth factor effect was inhibitory. In explants cultured for 24 hours, the same trend was noted at 7–9 weeks. EGF caused a two-fold increase while >11 week, the effect was markedly inhibitory. In isolated trophoblastic cell cultures, EGF added daily for the first week increase in hCG secretion until the fifth day. However, apparently no morphological changes were associated with this increase. In conclusion, EGF has a gestational dependent rapid, long term, and delayed effect on hCG secretion in the first trimester. The involvement of EGF in control of hCG secretion is strongly suggested.

Evidence for a modulation of human chorionic gonadotropin (hCG) subunit messenger ribonucleic acid levels and hCG secretion by gamma-aminobutyric acid in human first trimester placenta in vitro.

The cytotrophoblasts are the site of production of liberins and statins in human placenta, whereas the syncytiotrophoblasts synthesize tropic hormones. These placental cell layers seem to interact like the hypothalamus and pituitary. In the central nervous system, gamma-aminobutyric acid (GABA)-ergic neurons represent one important control mechanism that seems to influence the lutropin biosynthesis indirectly (via gonadoliberin) and directly. It was the objective of the present study to find out whether GABA also may influence the biosynthesis and secretion of hCG by human first trimester placenta. Already one single pulse of GABA (1 h; 0.01-100 microM) stimulated hCG secretion significantly (P less than 0.0001). GABA also induced a marked increase in the mRNA levels of both subunits, with an optimum at 10 microM. The effect on hCG secretion was mimicked by the GABA-A receptor agonist muscimol (P less than 0.002), but under the experimental conditions used (multiple pulses; 1 microM), only the beta mRNA was increased. The GABA-A receptor antagonist bicuculline (two pulses; 10 microM) suppressed basal hCG secretion (P less than 0.001) and abolished the episodic secretion pattern observed in the control cultures. Applying a combination of equimolar amounts of GABA and bicuculline, hCG secretion and the episodic secretion pattern were similar as in control cultures. The data seem to suggest a regulation of hCG biosynthesis in human first trimester placenta in which GABA is involved, probably acting via GABA-A-like receptor sites.

The human first-term placenta in vitro: regulation of hCG secretion by GnRH and its antagonist.

Gonadotropin releasing hormone (GnRH) has been proposed to play a role in the regulation of human chorionic gonadotropin (hCG) release from the human placenta. To test this assumption, we utilized an in vitro perifusion system, together with cultures of placental explants, to investigate short- and long-term effects of GnRH and its respective antagonist on the hCG secretion from the early human placenta. Tissue slices of human placenta (100 mg), obtained from first-trimester terminations of pregnancies, were continuously perifused and the effluent collected in fractions of 2-20 min. After initial perifusion periods of 30-40 min, either GnRH, a GnRH antagonist (SB-75; Asta Pharma, Frankfurt, Germany) or both compounds at equimolar concentrations were added to the perifusion medium at final concentration of 10(-4)-10(-8) mol/l). Administration was effected either continuously or intermittently in 10-min pulses. Further, 50-mg pieces of placental tissue explants were cultured in tissue culture plates for up to 6 days. During the perifusions, hCG (determined by enzymeimmunoassay) was found to be released spontaneously in a pulsatile fashion. Pulse amplitudes and frequencies of this episodic hCG secretion were increased in response to GnRH, but not affected by GnRH antagonist. Also, GnRH stimulated the hCG secretion during cultures of placental explants. When pharmacological doses of GnRH (10(-4) mol/l) were utilized, this stimulatory effect of GnRH was no longer evident, while perifusion with medium containing GnRH antagonist at identical concentrations stimulated the hCG secretion, indicating an intrinsic agonistic activity of the antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor necrosis factor-alpha inhibits human chorionic gonadotropin secretion.

The placenta is a major source of tumor necrosis factor-alpha (TNF alpha) and is rich in TNF alpha receptors. TNF alpha inhibited hCG secretion by normal chorionic villi at 6 weeks gestation, but chorionic villi contain the heterogenous cell population. To investigate the direct effects of TNF alpha on trophoblasts, the NUC1 choriocarcinoma cell line was used as an in vitro placental cell model. TNF alpha also inhibited hCG secretion by NUC1 cells at concentrations from 1-100 U/mL. TNF alpha at concentrations of 1, 10, and 100 U/mL significantly decreased hCG secretion for 24 h to 88%, 81%, and 71% of the control level, respectively. The expression of hCG beta mRNA was also decreased to 23% of the control level after 24 h of TNF alpha treatment (100 U/mL). Inhibition occurred after 12 h of TNF alpha treatment (100 U/mL). Two measurements, trypan blue dye exclusion and 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide reduction, revealed that these inhibitory effects were not due to the cytotoxic activity of TNF alpha on NUC1. In conclusion, TNF alpha reduces hCG secretion in vitro.

Effects of Prolactin on Secretion and Synthesis of Human Chorionic Gonadotropin in Human Term Placentas in vitro: Short-Term Increase in Secretion, Followed by Medium-Term Suppression of Synthesis and Secretion

We studied the influence of human prolactin on the secretion and de novo synthesis of human chorionic gonadotropin (hCG) in the human term placenta in culture. Placental tissue from 14 patients with uncomplicated pregnancies and deliveries was prepared mechanically, with addition of a Percoll gradient step. hCG levels were determined in the culture media and in the cytosolic fraction of cells by means of an enzyme immunoassay with coated beads. The amount of newly synthesized hCG was measured by the extent of incorporation of 35S-methionine into the hCG molecule. Our results showed that human prolactin had two different effects in vitro: between 1/2 and 1 h, prolactin slightly increased secretion of hCG into the culture medium without affecting de novo synthesis; after 2 h, prolactin began to cause a significant decrease in both secretion and de novo synthesis of hCG over several hours. It appears that both effects are receptor mediated, for ovine prolactin failed to produce any response. We conclude that prolactin is one of the main factors regulating the synthesis and secretion of hCG in the human trophoblast at term.

Evidence for a modulation of human chorionic gonadotropin (hCG) subunit messenger ribonucleic acid levels and hCG secretion by gamma- aminobutyric acid in human first trimester placenta in vitro

Evidence for a modulation of human chorionic gonadotropin (hCG) subunit messenger ribonucleic acid levels and hCG secretion by gamma- aminobutyric acid in human first trimester placenta in vitro