Effect of progestogens and androgens upon spermatogenesis and steroidogenesis in dogs

Two different progestogens, mixed testosterone esters, and a combination of progestogen and androgens were evaluated for their effect on semen quality and peripheral plasma testosterone and LH concentration in dogs. Megestrol acetate (2 mg kg-1) given orally for 7 days, and medroxyprogesterone acetate (10 mg kg-1) given subcutaneously produced no change in semen quality compared with that of control dogs. Higher doses of megestrol acetate (4 mg kg-1) produced minor secondary sperm abnormalities, whereas 20 mg medroxyprogesterone acetate kg-1 produced a rapid and significant decrease in sperm motility, morphology and output. The effect of progestogen was probably mediated by action upon the epididymis, since semen quality declined rapidly, morphological changes were the result of more secondary sperm abnormalities, and there was no suppression of plasma LH concentration. Mixed testosterone esters (5 mg kg-1) produced a significant decline in semen quality, which occurred 3 weeks after treatment and persisted for 3 months. There was an increase in the number of primary sperm abnormalities, and it was thought that the effect was probably related to suppression of gonadotrophin resulting in an effect on spermatogenesis. The combination of mixed testosterone esters (5 mg kg-1) and medroxyprogesterone acetate (20 mg kg-1) produced a rapid and profound decrease in semen quality. It was postulated that the effect of this combination of treatment on semen quality was mediated directly by the progestogen upon the epididymal phase of development, and the androgen causing suppression of gonadotrophins. Indeed a reduction in the plasma LH concentration was noted, and both primary and secondary sperm abnormalities were present. The dog appears to differ from other species in the sensitivity of the pituitary-hypothalamus to progestogen feedback. Gonadotrophin suppression does not occur even when high doses of progestogens are used and there are no significant effects on libido. However, combinations of progestogens and androgens may provide a clinically useful method of reversible contraception in the dog.