Regulation of the transport of immunoglobulin G into the male rat reproductive tract.

The net movements of IgG in the rat testis and epididymis were studied using physiological techniques in conditions of anticipated subnormal organ concentrations of testosterone (T). The volume of extracellular fluid accessible to IgG per gram whole testis (Veq, microliter/g) did not change but that per gram interstitial tissue decreased in intact rats treated with T to suppress gonadotrophin secretion. Estimates of surface areas of the exchange vessels (S, cm2/g whole tissue) did not change in any of the organs studied. The speed at which equilibrium between tissue extracellular fluid and serum was reached (magnitude of K, min-1), lymph flow (QL, microliter/g/min) and estimates of microvascular permeability (P, nm/min) to IgG decreased in the testis of T-treated intact rats. In these animals, magnitude of K and P were higher than normal in the cauda. After castration, magnitude of K and P decreased to near zero in the caput and corpus regions. The changes in magnitude of K and P due to castration could partly be prevented by T supplementation in the caput, but not in the corpus, where Veq was supra-normal after T treatment. This difference in endothelial response between caput and corpus indicates differences in control of endothelium and epithelium along the length of the epididymal duct. In the testis of efferent duct-ligated (EDL) rats, P was lower than that in the intact rats, whereas in the corpus epididymidis of EDL rats, Veq and P were higher than normal. The supra-normal Veq values in the corpus epididymidis of EDL and castrated T-treated rats suggest that the epithelial barrier leaks in the corpus when luminal testosterone is low. It is concluded that during testosterone administration to normal rats, the testicular and epididymal epithelial barrier remains intact, that trans-endothelial transport of IgG and extracellular fluid volume decrease in the testicular interstitium and that in conditions of low serum T, the endothelium of microvessels in the caput and corpus epididymidis forms a barrier to IgG.