Secretion of the rat cauda epididymidis.

A method has been developed to study the mechanism of epididymal secretion in the anesthetized rat in vivo. Secretion of the cauda epididymidis was affected by altering the intraluminal calcium ion concentration. Removal of calcium caused a rise and high calcium (10 X normal) caused a fall in the rate of secretion. Exocytosis did not seem to be operative in the epididymidis. The perfusate collected from the cauda epididymidis stimulated the forward motility of the washed caudal epididymal spermatozoa. This effect was concentration-dependent. At low concentration the perfusate stimulated the forward motility and at high concentration it caused a fall. A similar relationship between concentration and effect was noted for the epididymal plasma. When the diluted perfusate was used as the stimulant, there was a time lag of 15 min before any stimulation of forward motility was observed. However, the effect of the diluted epididymal plasma was immediate. The effect of the perfusate but not the plasma was inhibited by pretreatment of the sperm with cyclohexamide (10(-4) M). This difference in the action of the two fluids was discussed in relation to the proteins present in the fluids as revealed by SDS polyacrylamide gel electrophoresis.