Canine pituitary-testicular function in relation to toxicity testing.

The physiological onset and establishment of adult pituitary-testicular function has been characterised for Beagle dogs. Testicular measurements, circulating prolactin, luteinising hormone and testosterone concentrations, semen analyses and the histological appearance of testicular biopsies, suggest that male Beagles attain sexual maturity between 35 and 41 weeks of age. The assessment of testicular toxicity is discussed and attention drawn to possible approaches for investigating primary mechanisms of toxic action on the canine testis. Expected values for testicular size, hormone levels and semen characteristics are reported.