Stereological evaluation of human spermatogenesis after suppression by testosterone treatment: heterogeneous pattern of spermatogenic impairment.

Testosterone (T) treatment suppresses gonadotropin levels in normal men and is a promising reversible contraceptive that induces azoospermia in approximately 70% of subjects and oligospermia in the remainder; however, the basis of this variable response is unclear. This study aimed to investigate this reported variable response by examining the spermatogenic process and quantitating germ cell number in men after T-induced gonadotropin withdrawal. Ten normal fertile men (31-46 yr), already planning to undergo vasectomy, either received T enanthate (200 mg, i.m., weekly) for 19-24 weeks (n = 5; TE group) or proceeded directly to surgery (n = 5; controls), at which time a unilateral testicular biopsy was taken, and germ cell numbers were estimated using the optical disector stereological method. In response to TE treatment, serum T levels rose 2-fold, and FSH/LH levels became undetectable. Sperm counts fell to azoospermia in 4 men and to 21 million/mL in the fifth man. The mean number of type A spermatogonia per 100 Sertoli cells was unchanged, but type B spermatogonia fell markedly to 10% of the control values, and later germ cell types decreased to 11-18% of the control values. The pattern of germ cell suppression varied widely and showed no relationship with sperm count or the time to azoospermia. Despite the presence of elongated spermatids (1.4-20% of the control), four men remained azoospermic. Two TE subjects with similar early germ cell complements and elongated spermatid numbers had sperm counts of zero and 21 million/mL; the latter man demonstrated marked variability in germ cell numbers between adjacent tubules. We conclude that 1) the principal spermatogenic lesion in TE-treated men is the marked (90%) inhibition of type A-->B spermatogonial maturation. Other sites are also affected, particularly the release and/or survival of elongated spermatids during transit; and 2) a steady state in germ cell number may not be established even after 4-5 months of TE treatment. The findings suggest that TE treatment does not adequately or consistently withdraw hormonal support for spermatogenesis, leading to variable between- and within-individual patterns of germ cell suppression.