[Developmental changes in plasma gonadotropins and testosterone and in testicular lutropin receptors in normal and cryptorchid rats]

Testis weight, ventral prostate weight, plasma gonadotropins and testosterone and testicular LH receptors were assessed throughout sexual maturation in the 23 to 84 day old rat. Intact, sham-operated and cryptorchid rats (operated at day 21) were studied. In the intact rats, plasma FSH rose to a peak at day 33, and fell to a plateau from day 50 throughout adult life. Plasma LH showed a sharp peak at day 42. Testis LH receptor content increased continually with age, reaching a plateau at day 49, but there was no change in the affinity constant (Ka = 2.4 +/- 0.5 X 10(10) M-1) measured at four time intervals. These observations suggested that the peak of FSH initiated an increase in testicular LH receptors, and that the LH peak enhanced it. In the cryptorchid rats, FSH showed a maximum between days 30 and 40. After day 33, FSH was higher in the cryptorchid rats than in the controls. The pattern of plasma LH was different in controls and cryptorchids; in the latter group, LH was often higher than in the controls. Testicular LH receptors increased continually between days 23 and 84, but Ka remained constant (Ka = 2.2 +/- 0.9 X 10(10) M-1) during that period. When compared with the control rats, the cryptorchid animals showed an increased concentration of testicular LH receptors at day 84, but this concentration decreased at days 35, 49 and 84; plasma testosterone also declined at days 23 and 49. These data suggested that the Leydig cell function of the cryptorchid rats was altered.