Characterization of cyclic adenine dinucleotide phosphate ribose levels in human spermatozoa

Objective: To determine the presence of the Ca2+-releasing pyridine nucleotide derivative, cyclic adenine dinucleotide phosphate ribose (cADPR), in human spermatozoa and to investigate its role in progesterone-induced Ca2+ oscillations in spermatozoa. Design: Biochemical investigation on human spermatozoa from healthy volunteers. Setting: Healthy volunteers in an academic research environment. Patient(s): Ten volunteers. Intervention(s): None. Main Outcome Measure(s): The cADPR levels. Result(s): Human spermatozoa contain micromolar concentrations of cADPR that do not change significantly during sperm capacitation. An active synthetic machinery for cADPR is present in human spermatozoa, whereas degradation activity is minimal. Although progesterone-induced Ca2+ oscillations are dependant on the ryanodine receptor, they are unaffected by cADPR antagonists. Conclusion(s): It appears that cADPR does not to play a role in Ca2+ oscillations in spermatozoa, but the presence of high concentrations of cADPR suggests that, instead, it may be introduced into the egg at fertilization and play a role in the Ca2+ transient immediately following sperm-egg fusion.