Quantification of Human Spermatogenesis: Germ Cell Degeneration during Spermatocytogenesis and Meiosis in Testes from Younger and Older Adult Men1

Abstract

Germ cell degeneration during spermatocytogenesis and meiosis was investigated to explain the age-related decline in daily sperm production (DSP). Numbers of Types A-dark, A-pale, and B-spermatogonia, potential daily sperm production per g parenchyma (PDSP) based on type B-spermatogonia, early primary spermatocytes, and late primary spermatocytes, and DSP per g based on early spermatids were determined in 15 men aged 20 to 48 yr (mean ± SEM, 33 ± 2 yr) and 15 men aged 52 to 90 yr (65 ± 3 yr). Testes obtained within 15 h of death (largely due to trauma or heart failure) were perfused vascularly with glutaraldehyde. The number of each cell type per g parenchyma was calculated as the product of the percentage of nuclei in the parenchyma times a correction factor for section thickness and nuclear diameter divided by the volume of a single nucleus of that cell type. Paired testicular weight was lower (p < 0.01) in older men (33 ± 3 g) than in the younger men (49 ± 3 g). Younger and older men had similar numbers of A-dark, A-pale, and B-spermatogonia per g parenchyma. PDSP based on late primary spermatocytes and DSP based on early spermatids were lower (p < 0.01) in older men than in younger men. In younger men, PDSP was similar (p > 0.05) between B-spermatogonia and late primary spermatocytes, whereas DSP measured at the spermatid level was abruptly lower than that estimated from younger cell types. Older men showed reduction in PDSP between early and late primary spermatocytes, with further reduction occurring in DSP at the spermatid level. Hence, age-related differences in germ cell degeneration that result in lower rates of sperm production in older men occurred in meiotic prophase during the transition of early (leptotene) primary spermatocytes to late (pachytene) primary spermatocytes or among the late primary sperm atocytes themselves.