Seminiferous tubules and daily sperm production in older adult men with varied numbers of Leydig cells.
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Previous studies of adult men have failed to reveal a relationship between numbers of Leydig cells in the testes and rates of sperm production, perhaps because of a functional excess of these cells in younger men. Hence, a possible relationship between Leydig cell numbers and sperm production was sought in 50 older men, aged 50-90 years, in whom the Leydig cell population had been depleted by age-related attrition. When these men were sorted by increasing numbers of Leydig cells per man into two, three, or five groups, no difference could be found between or within these groups when daily sperm production per man (DSP); seminiferous tubular volume, diameter, or length; or seminiferous epithelial volume was examined. Furthermore, no significant correlation could be detected between Leydig cell numbers and DSP in these 50 men. The only relationship between numbers of Leydig cells and spermatogenesis appeared to be a threshold effect, in that men with fewer than 60 million Leydig cells (4 in this study) had drastically reduced DSP. Men with few Leydig cells tended to have larger Leydig cells, and the increased size was due to more cytoplasm instead of nucleoplasm. There were weak but significant positive correlations between total Leydig cell cytoplasm per man and DSP and between average size of a Leydig cell and DSP. These findings suggest that a relationship may exist between sperm production and the amount of cytoplasm containing testosterone-producing organelles in surviving Leydig cells of older men.