Objective: To compare the function of a novel nongenomic progesterone (P) receptor on the human sperm surface (mediating the P-induced acrosome reaction) in spermatozoa from fertile donors and from infertile patients. To examine the possible implication of defective P receptor function as an etiologic factor in unexplained male infertility.
Design: Progesterone binding and P effects were assessed in sperm from infertile patients and compared with corresponding parameters for sperm from healthy donors.
Setting: Private hospital, medical research center, and a university-based andrological laboratory.
Patients, participants: Sperm samples were from infertile patients (no pathology detected in their wives) attending our infertility clinic and from healthy sperm donors.
Interventions: None.
Main outcome measures: Progesterone binding sites were visualized with a fluorescein-labeled protein-P conjugate. Indo 1-AM (a fluorescent indicator of intracellular free Ca2+) was used to measure P-induced Ca2+ influx. Progesterone-induced acrosome reaction was monitored after acrosomal staining with Pisum sativum agglutinin.
Results: Among 8 patient sperm samples with normal spermiogram values (of 53 examined), 5 showed a reduced percentage of P-binding spermatozoa and an abnormal response to the hormone in terms of Ca2+ influx and the acrosome reaction.
Conclusions: Defective function of a sperm surface P receptor is described in some cases of male infertility. The observed fluorescence microscopic patterns of hormone binding may be used to further investigate receptor activity in unexplained male infertility.