SEXUAL DEVELOPMENT OF MALE WISTAR RATS

1. Sexual development was investigated in male Wistar rats from 22 to 97 days of age by morphometric, biochemical and radioimmunological met hods. 2. The first significant increase of plasma testosterone (T) occ urred from 40 to 50 days of age and a progressive enhancement was obse rved thereafter to a maximum at 76 days (5.4 +/- 0.9 ng/ml). From that time onward, plasma T was gradually depressed to adult levels at 97 d ays of age (2.0 +/- 0.3 ng/ml). Plasma prolactin increased in parallel to T, reaching a maximum at 76 days (9.2 +/- 0.9 ng/ml) and attaining a lower plateau by 83 to 97 days of age (5.0 +/- 0.5 ng/ml). A small but significant increase was observed in plasma luteinizing hormone fr om 22 to 83 days of age. Plasma follicle stimulating hormone was high at 22 days, increased to a maximum at 40 days (15.4 +/- 0.6 ng/ml) and fell slowly to a lower plateau by 76 to 97 days of age. 3. Fructose c ontent in the ventral prostate increased abruptly from 50 to 63 days o f age (148.8 +/- 19.8 mug) and no significant change was observed ther eafter. A progressive increase in the seminal vesicle fructose content was observed from 40 to 63 days (45.6 +/- 2.8 mug) when a plateau was reached. 4. The evolution of the germinal epithelium was investigated in cross-sections of seminiferous tubules analyzed at random for the presence of the most advanced germ cell and also for sperm production (estimated by the number of spermatids in stages 15 to 18 of spermioge nesis). Spermatocytes I were the most advanced germ cells in the testi s of 22-day-old animals. At 40 days, spermatogenesis evolved to sperma tids in the maturation phase (stages 15 to 18 of spermiogenesis) and a t 50 days of age mature spermatids (stage 19 of spermiogenesis) were f ound in the testes, although in small amounts. From 63 days of age on, a progressive increase in the amount of stage 19-spermatids was obser ved. Sperm production increased up to 97 days of age. 5. The present r esults show that male Wistar rats were pubertal between 40 and 50 days of age (180-200 g body weight) and fully mature between 83 and 97 day s of age (about 400 g body weight).