The use of rabbits in male reproductive toxicology.

The rabbit is the smallest and least expensive laboratory animal in which serial semen samples can be obtained for morphologic, biochemical, and fertility evaluation. The female rabbit has a predictable reproductive cycle and can be artificially inseminated with a known amount of sperm during fertility testing. These advantages make the rabbit an extremely valuable model for studying the effects of chemicals or other stimuli on the male reproductive system. Quantitative evaluation of the testis, semen, and accessory reproductive organs is important in order to detect subtle effects of a chemical on reproductive capacity. Evaluation of testis size, serum hormone concentrations, and the number, morphology, motility, and fertility of sperm in the ejaculate can be performed serially in the live rabbit. Weights of testes and accessory reproductive organs, estimates of daily sperm production, and histomorphometric data on the seminiferous epithelium can be obtained after sacrifice. Multinucleated spermatids, focal tubular hypospermatogenesis, swelling of spermatocytes, and cytoplasmic vacuoles in Sertoli's cells occur commonly in testes of control rabbits. These changes may be confused with toxic lesions. The incidence of multinucleated spermatids may be increased by stress associated with handling or the environment. Histomorphometric evaluation may be required to prove that a test compound has an adverse effect on the male reproductive system.