Self-Priming Effect of Luteinizing Hormone-Human Chorionic Gonadotropin (hCG) upon the Biphasic Testicular Response to Exogenous hCG. I. Serum Testosterone Profile*

Abstract

The present study was conducted to investigate whether the early (2–8 h) testicular response to a single dose of exogenous hCG depends on previous exposure to LH activity. Four different groups of subjects were studied: 1) four normal adult men [Tanner stage-G5 (T-G5)] and one late pubertal subject (T-G4); 2) normal prepubertal (T-Gl) and early- and midpubertal boys (T-G2 and T-G3) (n = 4–6 each); 3) five patients with hypogonadotropic hypogonadism (HH); and 4) two patients with the complete form of the androgen insensitivity syndrome. Each subject received an im injection of hCG (40IU/ kg) on day 1 and blood samples were drawn before and 1-8, 24, 48, and 72 h after injection. At 96 h, a second dose of hCG was given (80 lU/kg) and blood samples were obtained at the same times as after the first hCG dose. Serum testosterone (T) was measured by RIA. The first dose of hCG evoked a biphasic response of serum T in groups T-G2 to T-G5 as well as in the two patients with the complete form of the androgen insensitivity syndrome. The early peak was at 2–7 h, whereas the late T peak was at 48–72 h after injection. In T-Gl children and in patients with HH, the early response did not occur [T-Gl, from 129 ± 43 (SEM) to 288 ± 127 pg/ml (P < 0.05); HH, 79 ± 18 to 107 ± 12 (P > 0.05) pg/ml], and the late peak was attenuated as compared with the pubertal boys. There were not significant differences in the responses of the T-Gl and the HH groups. After the second dose, all groups had biphasic T responses, although they varied in magnitude. These results demonstrate that previous exposure to LH activity is an obligatory prerequisite for the early peak of the hCG-mediated biphasic testicular response, and that a single dose of hCG has a priming effect that is sufficient to ensure a biphasic response to a second dose of hCG given 96 h later.