Effects of testosterone and levonorgestrel combined with a 5alpha-reductase inhibitor or gonadotropin-releasing hormone antagonist on spermatogenesis and intratesticular steroid levels in normal men.

A similar high testicular:serum gradient exists for E2 and T in normal men, and 8 wk of gonadotropin suppression markedly reduces iTT, with 5alpha-reduced androgens and E2 levels decreasing to a much lesser degree.