The effect of varying doses of hCG on the in vivo uptake by rat testis and serum testosterone response.

The in vivo uptake of human chorionic gonadotropin (hCG) in the rat testes and mode of the early testosterone response were studied after a single intravenous injection of varying doses of hCG. The uptake of hCG by the testes was parallel up to 6 h with all hormone doses, decreased thereafter to low level by 24 h with low hormone doses but continued to increase up to 24 h with the highest dose of hCG. The clearance rate of hCG from the blood was independent of the hormone dose used. Serum testosterone peaked gradually earlier when the hCG dose increased, and the highest hCG dose caused a slightly biphasic response with maxima at 1 and 12 h, the former peak being more pronounced. These results suggest that the in vivo uptake of hCG in the testes is modulated by the hormone dose used and that the mode of early serum testosterone response to varying hCG doses is dose dependent.