Identification of Sperm Stimulating Factor of Rabbit Oviduct Fluid.

Rabbit spermatozoa are stimulated to respire at a greater rate in oviduct fluid than in calcium-free Krebs-Ringer phosphate solution. From experiments involving dialysis, heating, and acid neutralizing of oviduct fluid, it appears that bicarbonate may be the sole stimulating factor present. 2. Bicarbonate stimulates maximally the respiration of rabbit sperm at 2.36 × 10-3 M and rooster, bull, and human sperm at 3.54 × 10-3 at pH 7.0. The respiration rate for human sperm of ZO2 = 13.7 is the highest rate so far reported suggesting that reports that human sperm do not respire or respire at a very slow rate were due to improper bicarbonate concentrations. 3. Bicarbonate appears to stimulate respiration by increasing the concentration of tricarboxylic acid cycle intermediates. 4. Stimulation of respiration of sperm may be important in essential processes in the female tract.