Differential Effects of Chronic Testosterone Treatment on the Onset of Puberty in Male Rats

Summary

Immature male rats were daily injected with 5 or 10 μg testosterone propionate (TP)/100 g b.w. from day 5 after birth through day 30 or through the day at which spermatozoa appeared in preputial smears (SpA). The age and body weight at preputial separation (PS) and SpA as well as the testes weight on the day of SpA were recorded. Reduced testicular weights as compared to the controls injected with oil were found in all experimental groups. Whereas daily injections of 5 μg TP/100 g b.w. did not alter the age and body weight at PS and SpA, administration of the higher TP dose from day 5 through day 30 resulted in highly significant delay of PS and SpA. This effect was almost completely abolished if treatment was continued to the day of SpA. In otherwise untreated males, however, injections of 10 μ TP/100 g b.w. from day 30 through the day of SpA did not advance the spontaneous onset of puberty.

The findings suggest that slight elevation of the circulating testosterone level during infancy causes impairment of testicular functions resulting in retardation of spermatogenesis and, presumedly, long-lasting reduction of testosterone secretion. The effect can be abolished by substitution of testosterone during the late prepubertal phase, but spontaneous sexual maturation can probably not be accelerated in this way.

Key words

Sexual maturation - Spermatogenesis - Testosterone - Rat