Short-term exposure to insulin-like growth factors stimulates testosterone production by testicular interstitial cells

The effect of short-term exposure to the insulin-like growth factors (IGF-I and IGF-II) on testosterone production by rat testicular interstitial cells in primary culture has been examined. Both peptides, when present during a 1-h pre-incubation period, increased human chorionic gonadotropin (hCG)-stimulated testosterone release over the following 16-h period. The effect of exposure to IGFs was most marked on maximally hCG-stimulated testosterone release. Maximal stimulation following IGF exposure was 80-85% above that seen without IGFs, and the IGF effect was half-maximal at 1.5-2 micrograms/l of IGF-I or IGF-II. Pre-incubation with IGFs did not alter the concentration of hCG (0.1 microgram/l) at which half-maximal stimulation of testosterone release was seen. Increasing cell density had a marked effect on the testosterone production rate per 10(5) cells, and the stimulatory effect of IGFs was only seen at relatively high cell density (2.8 X 10(5) cells/ml). Varying the period of pre-incubation with IGFs between 0.5 and 16 h, it was found that a 1-h period gave maximal stimulation. We conclude that a short exposure to IGFs is capable of increasing hCG-stimulated steroidogenesis in Leydig cells, and postulate that this effect may be part of an intratesticular paracrine control mechanism.