Leydig cell responsiveness to single and repeated human chorionic gonadotropin administration.

A single im injection of 1500 IU hCG significantly increased plasma testosterone levels for at least 96--120 h in normal men (n = 7), patients with isolated gonadotropin deficiency (n = 6), and boys with delayed puberty (n = 7); the maximum values [1315 +/- 309, 370 +/- 177, and 963 +/- 249 ng/100 ml (mean +/- SD), respectively] were achieved after 72 h in each group. Repeated daily injections of 1500 IU hCG for 3 days increased plasma testosterone levels in the same subjects at 72 h after the start to levels (1342 +/- 412, 407 +/- 199, and 1052 +/- 449 ng/100 ml, respectively) similar to those found in the single dose experiment. The levels achieved at 24 and 48 h also did not differ significantly in the two experiments. The data indicate the lack of additional leydig cell stimulation by repeated hCG injections given within 48 h after a single dose.