Age-Related Alterations of Isolated Rat Leydig Cell Function: Gonadotropin Receptors, Adenosine 3', 5'-Monophosphate Response, and Testosterone Secretion
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Abstract:
Decreased serum testosterone has been reported in old male rats, but in vivo studies have shown decreased gonadotropin levels and normal testis response to 120 min or more of gonadotropin stimulation, leaving doubt as to whether an aging defect exists in the Leydig cell per se. We compared the function of Leydig cells from old Wistar rats (22-25 months) with cells from mature rats (6-9 months) in vitro. The cells from old rats showed a 77% diminution in testosterone secretory response to hCG after incubation with various concentrations of hCG for 120 min. Cells from old animals reached a maximum response at a hCG concentration of 0.2 ng⁄ml, and cells from mature rats reached a maximum response at a hCG concentration of 0.5 ng⁄ml. Testosterone secretory response to 0.2 and 0.5 ng/ml hCG was also diminished in the old animals after incubations ranging from 60-180 min Leydig cells from old rats had 27% fewer gonadotropin receptors than mature rats (P < 0.001); however, total intracellular cAMP and protein-bound cAMP increases after hCG were not significantly different. Our findings point to the development of an intrinsic Leydig cell defect with age in the strain of rats studied, not reversible by hCG stimulation up to 3 h in vitro. They also suggest that the alteration responsible for the testosterone secretory hyporesponsiveness of Leydig cells from old rats is probably not attributable to a reduction in gonadotropin receptors or deficient cAMP production.Keywords:
Gonadotropin
Human chorionic gonadotropin
Cyclic adenosine monophosphate
OBJECTIVE: We investigated the variation in human chorionic gonadotropin results found with different commercial kits. Levels of human chorionic gonadotropin and related molecules were determined in pregnancy serum and urine and compared with the specificities of different laboratory, office, and home test kits. STUDY DESIGN: Total human chorionic gonadotropin (nicked + nonnicked), nonnicked human chorionic gonadotropin, free β subunit, and β core fragment were measured in 242 serum samples and 125 urine samples from early pregnancies. RESULTS: In serum, in the 2 weeks after the missed period when most pregnancy tests are performed, median levels of total, nonnicked, and β human chorionic gonadotropin (total + free β + β core) were similar (≤12% difference). Individual values, however, varied significantly. For nonnicked human chorionic gonadotropin, values ranged from 41 % to 145% and for β from 101 % to 145% of the total human chorionic gonadotropin level. In urine individual nonnicked values varied from < 1 % to 148% and β values from 102% to 547% of the total human chorionic gonadotropin level. A survey of 29 kits revealed that 10 were types detecting total human chorionic gonadotropin, five detecting nonnicked only, and 14 were β assays. CONCLUSIONS: Results from total, nonnicked, and β human chorionic gonadotropin kits are not necessarily interconvertible. Individual variations in levels of nicked human chorionic gonadotropin, free β and 2 core, and differences in their recognition by immunoassays causes discordant results. OBJECTIVE: We investigated the variation in human chorionic gonadotropin results found with different commercial kits. Levels of human chorionic gonadotropin and related molecules were determined in pregnancy serum and urine and compared with the specificities of different laboratory, office, and home test kits. STUDY DESIGN: Total human chorionic gonadotropin (nicked + nonnicked), nonnicked human chorionic gonadotropin, free β subunit, and β core fragment were measured in 242 serum samples and 125 urine samples from early pregnancies. RESULTS: In serum, in the 2 weeks after the missed period when most pregnancy tests are performed, median levels of total, nonnicked, and β human chorionic gonadotropin (total + free β + β core) were similar (≤12% difference). Individual values, however, varied significantly. For nonnicked human chorionic gonadotropin, values ranged from 41 % to 145% and for β from 101 % to 145% of the total human chorionic gonadotropin level. In urine individual nonnicked values varied from < 1 % to 148% and β values from 102% to 547% of the total human chorionic gonadotropin level. A survey of 29 kits revealed that 10 were types detecting total human chorionic gonadotropin, five detecting nonnicked only, and 14 were β assays. CONCLUSIONS: Results from total, nonnicked, and β human chorionic gonadotropin kits are not necessarily interconvertible. Individual variations in levels of nicked human chorionic gonadotropin, free β and 2 core, and differences in their recognition by immunoassays causes discordant results.
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The ovulatory response of immature rats to varying doses of human chorionic gonadotropin (hCG), 1–100 IU or pregnant mare serum gonadotropin (PMSG), 3–60 IU, was studied at 24, 48 and 72 h after injection of the gonadotropin. Both hCG and PMSG induced ovulation by 24 h in the absence of significant increases in ovarian weight; the highest percentage ovulation at 24 h was seen with 50 IU hCG. At 48 h, 100 IU hCG or 60 IU PMSG produced a higher percentage of ovulations than the same doses at 24 h. This was in contrast to the unchanged or decreased response seen with lower doses of either gonadotropin. The doses of hCG or PMSG which produced relatively few ovulations at 48 h yielded high percentages of ovulations at 72 h, while doses of the gonadotropin giving a relatively high percentage ovulations at 48 h produced lower percentages at 72 h. These data indicate that the ovulatory response of immature rats to exogenous gonadotropins may involve more than a single mechanism.
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Of more than 500 boys with bilateral cryptorchidism who presented during a 10-year period 28 prepubertal patients less than 11 years old who had no palpable testes after human chorionic gonadotropin therapy were studied to assess the ability of serum gonadotropin levels to identify patients with anorchism. Of the boys 21 had a normal testosterone response to human chorionic gonadotropin therapy and all of them had testes at exploration. The serum luteinizing hormone levels ranged from 2 to 6 mIU per ml., with a mean of 3.7 mIU per ml., and the serum follicle-stimulating hormone levels ranged from 1.6 to 6.2 mIU per ml., with a mean of 3.7 mIU per ml. Seven patients showed no testosterone response to human chorionic gonadotropin and all but 1 underwent exploration, at which time no testes were found. Of these 7 patients 6 had elevated gonadotropin levels that averaged 3 standard deviations above the mean. For comparison, 2 pubertal patients with nonpalpable gonads and 3 castrated prepubertal boys also were studied. From the study we concluded that in boys with nonpalpable gonads 1) abnormally elevated serum gonadotropin levels before puberty are indicative of anorchism, 2) neither exploration nor human chorionic gonadotropin stimulation tests are essential for diagnosis in these select patients, 3) serum gonadotropin levels alone are not sufficient for a definitive diagnosis after puberty and 4) all boys with normal serum gonadotropin levels must undergo exploration regardless of the outcome of a human chorionic gonadotropin stimulation test.
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By means of two assay systems, a beta chain human chorionic gonadotropin radioimmunoassay and a radioreceptor gonadotropin assay, a chorionic gonadotropin-like substance was demonstrated in extracts of liver and colon obtained at autopsy from three patients who died of nonneoplastic disease. In contrast to placental chorionic gonadotropin, colon and liver chorionic gonadotropin was not bound to concanavalin A-Sepharose columns, indicating that this substance possessed little or no carbohydrate. Previous workers demonstrated that desialylated human chorionic gonadotropin possesses little or no bioactivity in vivo but retains full radioreceptor and radioimmunoassay activity in vitro. Our data suggest that the genome responsible for the human chorionic gonadotropin production is not completely suppressed in adult nonendocrine tissues, and that the chorionic gonadotropin produced by colon and liver has little or no bioactivity in vivo because of its low carbohydrate content. Since many normal tissues produce chorionic gonadotropin, bioactivity may be modulated by regulation of carbohydrate content.
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Intraperitoneal injection of human chorionic gonadotropin in the rat induces a dose-dependent frequency of ovarian hyperemia. The occurrence of such hyperemia can be inhibited by pre-injection (3 hours) of antisera from rabbits immunized with gonadotropin extracts. It is demonstrated that the retained capacity of gonadotropin to induce hyperemia following antisera injections is greater when the gonadotropin is from patients with choriocarcinoma than when the gonadotropin is from pregnant women or U.S.P. standard human chorionic gonadotropin. This differential shows up consistently for pools of urinary extracts and for extracts from individual patients with choriocarcinoma prior to therapy and does not seem to be related to the source of gonadotropin used for rabbit immunization. The data are interpreted as indicating that there is a variant of chorionic gonadotropin in the urine of choriocarcinoma patients. Further work would be necessary before the present findings could be employed usefully in the detection of choriocarcinoma.
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