Male infertility in the hereditary polydactyly (PD) rat

In the PD strain of rats, male pd homozygotes never sire, whereas male heterozygotes and female hetero- and homozygotes are fertile. In order to investigate the cause of infertility, pd/pd males were examined for their reproductive ability and gross and histological changes in the reproductive organs. Mating ability of pd/pd males was comparable to that of pd/+ males when a 2 week cohabitation procedure was employed. Cryptorchidism, which is considered to be a cause of infertility, was observed in 63% of the 12 week old pd/pd males. However, this abnormality frequently was observed unilaterally and the incidence of bilateral cryptorchidism was only 13%. Although the relative weights of descended testes and epididymides were comparable between the pd/pd and pd/+ males at 3 and 6 weeks of age, the values at 9 and 12 weeks of age were significantly lower in pd/pd males than in pd/+ males. A marked difference was not noted in relative weight changes of the seminal vesicles and prostate between the pd/pd and pd/+ males. Histological examination revealed defects in spermatogenesis in both descended and undescended testes in pd/pd males. The changes first appeared at 9 weeks of age and included vacuolation of nuclei of spermatocytes and spermatids, degeneration of spermatids, and occasionally multinucleated giant cells in the seminiferous tubules. In accessory sexual organs such as the epididymides, seminal vesicles, and prostate, no histological abnormalities were detected. These findings indicate that the substantial cause of infertility in pd/pd males is a disorder of spermatogenesis through which functionally normal spermatozoa are not produced.