Enlargement of the processus vaginalis during testicular descent in rats.

The role of the processus vaginalis (PV) during inguinoscrotal testicular descent remains controversial. Some authors propose passive dragging of the PV by the migrating testis, while others suggest active elongation. In addition, the exact site of growth is unknown. Our aim was to determine whether the PV actively proliferates at its tip or stretches passively during the inguinoscrotal phase of descent in the rat. Gubernacula were removed from Sprague-Dawley (SD) rats and congenitally-cryptorchid TS mutants. Animals (at days 3, 7, 10, and 11) were treated with bromo-uridine deoxyribose (BUdR) 2 h before death. BUdR incorporation into newly-synthesised DNA served as a marker for cell division. The gubernacula were processed for haematoxylin and eosin and immunoperoxidase staining. Three sites were examined: (1) the tip of the PV on either side of the gubernacular bulb; (2) the proximal gubernacular cord; and (3) the proximal parietal PV. At each site, 50 adjacent cells were counted and the number of positive cells recorded. The highest BUdR labelling in SD rats was at the tip (site 1) on day 3 (17/50) compared with sites 2 (11/50) and 3 (9/50) (P < 0.05). Labelling decreased by 7 and 11 days to similar levels in all three sites. In TS rats, labelling rates were lower at day 3 and were highest at the tip at day 11. These results suggest active growth of the caudal tip of the PV during testicular descent. In normal rats, the growth rate slows as the testis approaches the scrotum. By contrast, in TS rats growth continued longer. We propose that the PV elongates actively from the tip to allow the intraperitoneal testis to leave the abdomen in a special peritoneal diverticulum.