Response of Immature, Mature Nonbreeding and Mature Breeding Ferret Testis to Exogenous LH Stimulation

Abstract

Mature male ferrets undergo an annual period of sexual inactivity during which they resemble immature ferrets in their low plasma testosterone levels (< 0.2-5 ng/ml) and reduced testis and epididymal size. Plasma testosterone concentrations in immature, mature nonbreeding and mature breeding male ferrets were compared after stimulation with [ovine] LH [luteinizing hormone] administered by i.m. injection at doses of 10 and 100 .mu.g/kg body wt. Mature breeding animals showed a variable response depending on their plasma testosterone concentrations prior to injection. Animals with high preinjection levels of testosterone (25-30 ng/ml) showed little response, suggesting that their testes were already being maximally stimulated. The mature nonbreeding animals responded to both the low and high dose of LH with elevated plasma concentrations of testosterone consistent with those found in sexually active males (15-27 ng/ml). The higher dose of LH produced a higher and more sustained response than the lower. Immature ferret testes showed a small transitory response to both 10 and 100 .mu.g of LH, but their plasma testosterone concentrations did not approach those found in sexually active ferrets. Increase in responsiveness of the ferret testis to LH may be an important factor in puberty, while variation in level of LH secretion may be responsible for annual recrudescence of mature males.