pH and bicarbonate in the ductuli efferentes testis of the rat

The pH and bicarbonate concentrations of luminal fluids in the efferent duc ts of the rat were estimated from pH measurements of samples in vitro under conditions of controlled temperature and carbon dioxide tension. The pH of scrotal blood was estimated to be more acidic than systemic blood (mean pH = 7.44) at either of the putative scrotal carbon dioxide tensions (5% and 7%, pH, respectively, = 7.42 and 7.28). For PCO2 tensions of 5% and 7%, res pectively, the data indicated that the pH in the efferent ducts was signifi cantly higher (distal initial zone pH = 7.55 or 7.41; coni vasculosi pH = 7 .66 or 7.51; p < 0.01) than in fluid entering (rete testis fluid, pH = 7.34 or 7.20) or leaving the ducts (zone 1a of the epididymal duct 7.26 or 7.11 ). Bicarbonate concentrations were also significantly higher (p < 0.01) in the efferent ducts (35.4 +/- 4.7 mM, distal initial zone; 45.2 +/- 7.6 mM, coni vasculosi) than in fluids entering (22.9 +/- 3.6 mM) or leaving (20.4 +/- 4.9 mM) the ducts. Estimates of the reabsorption of bicarbonate and flu id indicated that 96% of the testicular output of bicarbonate was reabsorbe d in the efferent ducts, but there was also some secretion of bicarbonate i nto the ducts. It is concluded that luminal pH and bicarbonate levels in th e efferent ducts of the rat are high relative to those found in the epididy mis where low pH and bicarbonate contributes to sperm quiescence during sto rage. Nevertheless, the high rate of bicarbonate reabsorption in the effere nt ducts is a major contributor to the establishment of the low pH and bica rbonate milieu of the epididymis.