Effects of Progesterone on Intracellular Free Ca~(2+) Concentration in the Spermatozoa of Fertile Men and Patients with Unexplained Infertility

HUO Yong-wei; WANG Li-rong; TIAN Hong; XU Yong-jun; ZHAO Xiao-ge; QIU Shu-dong

Abstract：Objective: To investigate the difference in the responsiveness of intracellular free Ca~(2+) concentration ([Ca~(2+)]_i) to progesterone in the spermatozoa of normal fertile men and patients with unexplained infertility. Methods: Nine normal fertile men and 10 patients with unexplained infertility were selected in this study. After swim-up separation of the motile fraction and 2-hour in vitro capacitation, the spermatozoa were loaded with the fluorescent calcium indicator Fluo-3/AM (8.85 μmol/L) for 40 minutes away from the light, and then the sperm suspension was mixed with equal amount of 20% gelatin to immobilize the spermatozoa. The basal intracellular free [Ca~(2+)]_i and that induced by 10 μmol/L progesterone in the individual sperm were assessed by laser scanning confocal microscopy. Results: The infertile patients had a significantly lower basal level of [Ca~(2+)]_i in the capacitated sperm than the fertile men (P<0.01). The sperm from the normal controls responded to progesterone by exhibiting a rapid but transient rise in [Ca~(2+)]_i, with the peak level significantly higher than the basal level (P<0.05), while those from the infertile patients by showing a slight increase, with no significant difference between the peak and basal levels (P>0.05). Both the peak of the progesterone-induced [Ca~(2+)]_i and its increase amplitude expressed as the difference between the peak and basal levels were significantly higher in the normal fertile group than in the infertile patients (P < 0.01). Conclusion: The responsiveness of [Ca~(2+)]_i to progesterone is reduced in the spermatozoa of patients with unexplained infertility, which suggests a functional defect in the non-genomic sperm membrane progesterone receptor responsible for calcium influx.