Luminal acidification by the perfused rat cauda epididymidis.

1. Acid secretion by the rat cauda epididymidis was studied by microperfusion of the epididymal duct and by measuring the pH of the perfusate at a constant pCO(2) using a micro pH sensitive electrode. The rate of acidification was expressed as the rate of fall of intraluminal bicarbonate per cm duct per min.2. When the cauda epididymal duct was perfused with normal bicarbonate solution, the luminal bicarbonate concentration fell at a rate of 0.59 +/- 0.39 n-equiv cm(-1) min(-1) (mean +/- s.e.,n = 22).3. The rate of luminal acidification was independent of the perfusion rate but was dependent on the concentration of bicarbonate in the perfusion fluid. The rate of fall of luminal bicarbonate increased with increasing bicarbonate concentration and showed saturation at an intraluminal bicarbonate concentration of 25 m-mole/l.4. Acidification was abolished in the absence of intraluminal sodium ions. This may suggest a linked sodium reabsorption and hydrogen ion secretion.5. Acidification of the luminal fluid was studied under different acid-base conditions. In animals undergoing metabolic acidosis, the rate of acidification was enhanced, and conversely in animals undergoing metabolic alkalosis, the rate was depressed.6. Intravenous infusion of acetazolamide into rats at a dose rate of 20 mg/kg.hr markedly inhibited the acidification process. This effect was still observed in animals undergoing metabolic acidosis. Acetazolamide (10(-5)m) applied luminally was found to have no effect but higher concentration (10(-4)m) was found to inhibit acidification by 50%.7. The role of acidification of the epididymal fluid in sperm maturation was discussed.