Endocrine Abstracts

The aim of this work was to study the condition of the reproductive system after long-term administration of letrozole followed by its withdrawal in young males and against the background of involutive changes in aging males in a comparative aspect. The experiments were carried out on Wistar rats with an initial age of 5 months and 15 months, which have been gavaged by letrozole every other day at a dose of 1 mg/kg body weight for 3 months and then 2 months after its discontinuation. The blood plasma testosterone and estradiol levels were measured by immunoassays. The spermatozoa concentrations in epididymal washes were determined. The testicles and accessory sexual glands were weighed, and morphology of gonads and ventral prostate have been studied. The results of the study were compared with those of control animals of corresponding age. As the result of letrozole treatment, the ratio of testosterone and estradiol levels in blood plasma of aged rats increased. The spermatozoa content in epididymis rose up by 28% at average. The histological study revealed functional activation of Leydig cells, a significant retardation of involutive changes of their number and morphology. Some Leydig cells demonstrated the signs of functional exhaustion. Letrozole caused an increase of relative weights of the coagulation gland by an average of 40%, seminal vesicles by 31%, and ventral prostate by 33% compared with those of control animals. Two months after letrozole withdrawal, there were no any signs of difference between letrozole-treated and control animals. In young rats, the effects of letrozole were almost not detectable. Letrozole administration to male rats with age-related involution of the reproductive system increases testosterone/estradiol ratio in blood plasma, the spermatozoa content in epididymises and the weights of androgen-dependent accessory sexual glands. This is accompanied by slowing down of age-related changes of the gonad and prostate gland morphology. Letrozole-induced reproductive effects are reversible. Keywords: letrozole, reproductive organs, male, rats.