Quantitative study of testis histology and plasma androgens at onset of spermatogenesis in the prepuberal laboratory-born macaque (Macaca fascicularis).

Laboratory-born Macaca fascicularis underwent successive testicular biopsies and peripheral blood sampling during the peripuberal age. Testicular fragments were studied quantitatively on seminiferous cord or tubule histological cross sections. Plasma testosterone, androstenedione, and dihydrotestosterone were quantified by RIA. Enlargement of the diameter of seminiferous cords or tubules resulted from the increasing number of spermatocytes and the formation of the lumen. The number of Sertoli cells per cord or tubule cross section decreased abruptly at the onset of full spermatogenesis, and, as the tubules lengthened, the total number of these cells per testis remained constant. The number of A spermatogonia per cross section did not vary; consequently the total number per testis increased. The first spermatocytes appeared at 3-4 yr of age at a body weight of 3.24 +/- 0.15 kg, and full spermatogenesis was attained between 3 years, 8 months and 4 years, 4 months at a body weight of 3.5-3.8 kg. Plasma levels of androstenedione did not exhibit a clear pattern of variation, whereas plasma dihydrotestosterone and testosterone reached high levels with great fluctuations at the time full spermatogenesis was established. No relation between plasma testosterone level and the initiation of meiosis was observed.