Comparison of testosterone and insulin-like peptide 3 secretions in response to human chorionic gonadotropin in cultured interstitial cells from scrotal and retained testes in dogs.

Levels of testosterone and insulin-like peptide 3 (INSL3) secretions in response to different doses of human chorionic gonadotropin (hCG) in cultured interstitial cells were compared between retained and scrotal testes in dogs. Retained (n=10) and scrotal (n=9) testes were obtained from small-breed dogs. The testicular tissues were dispersed in Dulbecco's Modified Eagle Medium with Ham's nutrient mixture containing 2000 PU/ml dispase II and 10% fetal bovine serum. The cells were plated with differing concentrations (0-10 IU/ml) of hCG for 18 h in multiwell-plates. Testosterone and INSL3 in the same spent medium were measured by enzyme-immunoassays (EIA). A new EIA with a reliable detection range of 0.025-5 ng/ml was developed in order to measure canine INSL3 in culture medium. Dose-dependent stimulation of testosterone by hCG was observed in the cells of both retained and scrotal testes. The incremental rate of testosterone secretion was significantly lower at 0.1, 1 and 10 IU/ml hCG in the cells of retained testes than in scrotal testes, however. INSL3 secretion was significantly stimulated at 10 IU/ml hCG relative to unstimulated controls comprising cells of scrotal testes; no such stimulation was observed in the cells of retained testes. At 10 IU/ml hCG, the incremental rate of INSL3 was significantly lower in the cells of retained testes than scrotal testes. These results suggest that LH-induced secretory testosterone and INSL3 responses are lower in the interstitial cells of retained testes than of scrotal testes. Furthermore, the high concentrations of LH may acutely stimulate INSL3 release in scrotal testes of dogs, but not in retained testes.