Effects of age and luteinizing hormone antiserum on human chorionic gonadotropin-stimulated testosterone secretion in young male rats.

The steroidogenic capacity of young male rats of different ages was studied. Two days prior to sacrifice at 5, 10, 15, 20, 25 and 30 days of age, the rats in treatment groups were given intramuscularly either human chorionic gonadotropin (HCG) at 20 I.U. twice daily/rat or luteinizing hormone (LH) antiserum (AS) at 0.25 ml twice daily/rat. Either saline or normal sheep serum (NSS) was given to control rats. The serum and testicular testosterone concentrations in the control rats averaged 0.85 +/- 0.03 ng/ml and 1.35 +/- 0.06 ng/mg testicular protein, respectively. At day-15 the serum and testicular testosterone concentrations in the HCG-treated rats had significantly increased to 9.30 +/- 0.85 ng/ml and 11.92 ng/mg of testicular protein, respectively. At the same age, the HCG-induced higher levels of serum and testicular testosterone concentrations were significantly reduced to 2.80 +/- 0.70 ng/ml and 6.02 +/- 1.00 ng/mg protein by concomitant administration of LH/AS and HCG. Our results suggest that the testosterone production in response to HCG stimulation is age-related. It was also determined that neutralization of circulating gonadotropin in LH/AS-treated rats decreased the sensitivity of Leydig cells to gonadotropin stimulation. This in vivo model should provide an excellent opportunity for the investigation of the testicular function in developing young males.