Apoptotic cell death and fertility in three unilateral cryptorchid rat models

Three rat strains have been studied, using a sensitive apoptotic detection method for germ-cell degeneration, to resolve the controversy regarding the effect of cryptorchidism on the contralateral descended testis (CDT). Sprague Dawley and Buffalo rats were made cryptorchid by operation at 20–22 days of age, while trans-scrotal (T-S) rats were a congenitally unilateral cryptorchid strain. Sham operated rats or normal T-S littermates were used as controls. Experiments were performed over a period ranging from 2 weeks to 18 months. Testis weight was assayed, as was the detection of apoptosis by agarose gel laddering and immunohistochemistry by using the TUNEL method. Labeled cells in 150 cross-sectioned testis tubules were counted on the TUNEL stained slides and the mean number of labeled cells per tubule was calculated. Paternity studies on Sprague Dawley and T-S rats were carried out at 12 and 24 weeks of age to assess fertility by the resultant number of pregnancies and litter sizes. Both Sprague Dawley and T-S rat models showed a biphasic distribution of apoptosis levels. This biphasic distribution was not observed in Buffalo rats as they were only studied at later time points (12–20 weeks). A significant effect on either testis weight or apoptosis in the CDT compared with the control descended testis (P ≥ 0.1) has not been found in these three cryptorchid models, and the present results are discussed with reference to observations of other researchers in rodents and humans. While the cryptorchid testis showed a high level of labeled apoptotic cells per tubule in all rat strains, fertility was not affected and remained the same as controls at 12 and 24 weeks. There was, however, a marked strain difference in fertility in T-S as compared with Sprague Dawley rats. After 24 weeks of cryptorchidism, both control and cryptorchid T-S rats had a 44% pregnancy incidence compared with a 90% pregnancy incidence in Sprague Dawley rats. In addition, litter size in T-S control and cryptorchid rats were small compared with those of Sprague Dawley rats at 12 and 24 weeks. Received: 11 January 2000 / Accepted: 21 April 2000