To investigate the effect of chronic daily administration of different doses of tadalafil on the structure of the seminiferous tubules and on spermatogenesis.

Sixty adult male Wistar rats were included; they were divided into four groups: a control group (group I) and groups II, III, and IV that received daily tadalfil in doses of 0.45, 0.9, and 1.8 mg/kg for 12 weeks (equivalent to human doses of 5, 10, and 20 mg daily), respectively. The epididymis was processed for evaluation of sperm parameters, serum testosterone was measured, Johnsen score for rats was calculated, and testicular histopathological and ultrastructural examinations were performed.

Serum testosterone was significantly lower in group IV than in groups I and II. Moreover, posttreatment values in group IV were significantly lower than pretreatment values. A significant decline in sperm motility and morphology was detected in groups III and IV compared to groups I and II. Sperm count was significantly lower in group IV compared to the other groups. Johnsen score was significantly lower in groups III and IV compared to groups I and II and in group IV compared to group III. In addition, histopathological and ultrastructural degenerative changes in rat testes were detected; these changes were dose dependent and increased with increasing the dose of tadalafil.

Chronic daily oral administration of tadalafil to male albino rats demonstrates a dose-dependent alteration to testicular histology and semen parameters. The influence of these changes on the actual fertility of these animals remains to be determined.