Spermatogenesis in Asian men appears to be more susceptible to suppression by steroidal contraceptives administered in clinical trials than spermatogenesis in Caucasian men. The objective of this study was to determine whether ethnic differences exist in testicular structure and spermatogenic potential that might predispose Asians to a high sensitivity to steroidal contraceptives. Testes from 12 Chinese men were compared to those from 8 Hispanic men and 12 non-Hispanic Caucasian men of ages 29+/-3, 30+/-2, and 29+/-3 years, respectively. Testes were fixed by vascular perfusion with glutaraldehyde, further fixed in osmium, embedded in Epon, and evaluated by stereology using 0.5-microm sections stained with toluidine blue. Homogenates of fixed testes were evaluated for the number of Sertoli cells and the daily sperm production based on pachytene primary spermatocytes (PDSP) or spermatids with spherical nuclei (DSP). Paired parenchymal weight was less (P < 0.05) in Chinese men than in Hispanic or Caucasian men. The PDSP per gram of parenchyma was lower (P < 0.05) and the DSP per gram tended to be lower in Chinese men than in other groups. The histologic appearance, volume density, and length per man of seminiferous tubules were the same among the ethnic groups; however, the diameter of seminiferous tubules was less (P < 0.05) in Chinese than in Hispanic or Caucasian men. The PDSP per man and the DSP per man were lower (P < 0.05) in Chinese than in Hispanic or Caucasian men. The number of Sertoli cells per gram was higher (P < 0.05) in Chinese or Caucasian men than in Hispanic men, but the number of Sertoli cells per man was lower (P < 0.05) in Chinese men than in Hispanic or Caucasian men. Sertoli cell function, measured as the number of germ cells accommodated by a single Sertoli cell, was lower (P < 0.05) in Chinese men than in Caucasian men. The volume density of Leydig cell cytoplasm was greatest (P < 0.05) in Chinese men, but the number of Leydig cells was similar among the ethnic groups. Hence, smaller testes coupled with reduced Sertoli cell number and function and reduced daily sperm production could predispose Asian men to have a heightened negative response of testes to steroidal contraceptives, as compared to Caucasian men. Dampening (by exogenous androgens) of any physiological benefit to spermatogenesis that a high volume density of Leydig cell cytoplasm may bestow on the human testis (that Asian men may have evolved to require) would exacerbate ethnic differences in the spermatogenic response to hormonal contraceptives.
PIP: Multicenter studies conducted by the World Health Organization suggest that the efficacy of spermatogenesis suppression by hormonal contraception differs across racial and ethnic groups. For both androgens alone and androgens in combination with a progestin, the suppression of spermatogenesis to persistent azoospermia occurred in about 90% of Asian men compared to 60-70% of Caucasians. The present study investigated ethnic differences in testicular structure that may affect the sensitivity of the testis to gonadotropin suppression and the spermatogenic potential of the testis. Testes of 12 healthy Asian men from China who died of sudden traumatic injuries and of 8 Hispanic and 12 Caucasian men from the US who died of the same cause were obtained at autopsy and analyzed. Both paired testicular weight and paired testicular parenchymal weight were significantly lower in Chinese men than Hispanic or Caucasian men. Pachytene primary spermatocytes per gram of parenchyma and spermatids with spherical nuclei also were lower in Chinese men than in the other groups. The histologic appearance, volume density, and length per man of seminiferous tubules were the same across ethnic groups, but the volume of seminiferous tubules per man was significantly lower in Chinese men. The number of Sertoli cells per gram was significantly higher in Chinese and Caucasian men than in Hispanic men, but the number of Sertoli cells per man and Sertoli cell function were significantly lower in Chinese men than the other two groups. The volume density of Leydig cell cytoplasm was greater in Chinese men, but the number of Leydig cells was similar across groups. It is postulated that smaller testes, coupled with the reduced number and function of Sertoli cells and reduced daily sperm production, contribute to an inherently lower spermatogenic potential in Asian men, which predisposes them to a heightened negative spermatogenic response to steroidal contraceptives.