Differences in the regulation of steroidogenesis and tropic hormone receptors between the scrotal and abdominal testes of unilaterally cryptorchid adult rats.

Rats were made unilaterally cryptorchid by cutting the gubernaculum testis at birth. At 100 days age, the rats were injected with 600 IU/kg hCG. A biphasic testosterone response was seen in the scrotal (Scr) testis in response to hCG, with maxima at 1 h and 3 days after injection. The acute peak of testosterone was of similar magnitude in the abdominal (Abd) testis, but the secondary peak was not present. The response of testicular progesterone concentration to hCG stimulation showed a maximum at 1 day in both gonads, but it was 10- to 20-fold higher (P less than 0.01) in the Abd testis. The content of LH, FSH, and PRL receptors per testis was decreased on the Abd side. After hCG injection, the loss of available LH receptors was faster in the Abd testis. Likewise, the recovery of binding was faster in the Abd testes; at day 10 of the experiment, it was 102 +/- 5% of the starting levels compared to 52 +/- 4% on the Scr side (P less than 0.01). hCG did not affect FSH binding of the Scr testes, but induced a transient drop of 25-35% on day 1 on the Abd side (P less than 0.05). Thereafter, on days 3-10, the FSH binding of the Abd testes was 20-40% higher than on the Scr side (P less than 0.05-0.01). In PRL binding, similar heterologous down-regulation of 50-80% was found in both testes between 12-24 h. Thereafter, the Abd testis PRL receptors showed a transient elevation of 25-70% (P less than 0.05-0.01) on day 3, which was not seen in the Scr testes. In conclusion, the Abd testis displays a dramatically enhanced blockade of C21 steroid side-chain cleavage upon gonadotropin stimulation. The kinetics of changes in testicular LH receptors after hCG stimulation is faster in the Abd testis. Only Abd testes displayed hCG-induced changes in FSH binding and transient up-regulation of PRL receptors. The altered tropic regulation of Leydig and Sertoli cells of the Abd testis are indicative of direct functional changes in these cells in the elevated intra-Abd temperature and/or of changes in the paracrine component of testicular regulation.