Kinetics of Human Chorionic Gonadotropin-Induced Steroidogenic Response of the Human Testis. I. Plasma Testosterone: Implications for Human Chorionic Gonadotropin Stimulation Test*

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Abstract
The profiles of plasma testosterone and hCG in normal adult men were studied after the administration of 6000 IU hCG under three different protocols. In the first protocol, seven subjects received a single im injection. Plasma testosterone increased sharply (1.6 ± 0.1-fold) within 4 h. Then testosterone decreased slightly and remained at a plateau level for at least 24 h. A delayed peak of testosterone (2.4 ± 0.3-fold) was seen between 72–96 h. Thereafter, testosterone declined and reached the initial levels at 144 h. In the second protocol, six subjects received two iv injections of hCG at 24-h intervals. The initial increment of plasma testosterone after the first injection was similar to that seen in the first protocol despite the fact that plasma hCG levels were 5–8 times higher in this case. At 24 h, testosterone levels were again lower than those observed at 2–4h and a second iv injection of hCG did not induce a significant increase. The delayed peak of plasma testosterone (2.2 ± 0.2-fold of control) was seen about 24 h later than that in the first protocol. Four subjects were studied in the third protocol, which consisted of four iv injections of hCG on days 0, 5, 10, and 15. Basal testosterone levels on days 5, 10, and 15 were significantly higher (P < 0.001) than those of control. Moreover, the hCG injection on days 5 and 10 produced, within 2–4 h, a significant increment of plasma testosterone (P < 0.01). These results suggest that in man, as in other species, hCG might induce a testicular steroidogenic desensitization. Moreover, our data raise question of the rational of daily hCG injection as used in the current protocols investigating human testicular function.

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