Selective expression of a progesterone receptor on the human sperm surface.

OBJECTIVE

To visualize progesterone (P) binding sites on the sperm surface, examine the relationship between hormone binding and hormone action (acrosome reaction), and determine the size of the hormone-responsive sperm subpopulation.

DESIGN

Kinetic analysis of P binding was combined with the assessment of the hormone effect using a fluorescent acrosomal marker.

SETTING

Private hospital, medical research center, and a university-based andrological laboratory.

PATIENTS, PARTICIPANTS: Sperm samples were from healthy volunteers with normal spermiogram values.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Progesterone binding was analyzed by fluorescence microscopy and flow cytometry using P coupled to fluorescein isothiocyanate-labeled bovine serum albumin. Tetramethylrhodamine isothiocyanate-labeled Pisum sativum agglutinin was used as acrosomal marker in double-labeling experiments.

RESULTS

After in vitro capacitation, only few spermatozoa (approximately 10%) were able to bind P to the cell surface, but most of these cells subsequently generated the acrosome reaction in response to hormone binding.

CONCLUSIONS

The expression of P receptor sites on the human sperm surface is a major factor controlling the P-induced acrosome reaction. Further studies are warranted to explore if defective expression of the receptor can compromise fertility.