ABSTRACT

Progesterone (P) is one of the physiological stimuli of human sperm acrosome reaction. It is present in high  levels at the site of fertilization (cumulus oophorus) and has been described to affect several sperm functions including motility, capacitation and acrosome reaction. The effects of the steroid are mediated by an increase of intracellular calcium concentrations, efflux of chloride, stimulation of activity of phospholipases and phosphorylation of proteins. These effects are due to activation of a rapid/nongenomic pathway, as expected for cells lacking of transcription/ transduction mechanisms. The involvement of a progesterone receptor(s) different from the genomic one has been recently demonstrated. Indeed, two P binding proteins, with different molecular weights respect to the genomic receptor, have been recently identified on the surface of human spermatozoa by ligand and western blot analysis. By binding experiments using radioactive P, two different receptors for P, with affinities in the nano- and in the micromolar range have been also identified. Since sperm responsiveness to P is impaired in subfertile patients and is strictly correlated to the ability of fertilize the oocyte, we believe that the effects of the steroid are physiologically relevant. In addition, the determination of sperm responsiveness to P is predictive of fertilising ability with a positive predictive value of 90% and can be clinically useful for the preliminary assessment of the male partner to select the appropriate assisted reproductive technique.