Nongenomic effects of progesterone on spermatozoa: Mechanisms of signal transduction and clinical implications

Progesterone (P) is one of the physiological stimuli of human sperm acrosom e reaction. It is present in high levels at the site of fertilization (cumu lus oophorus) and has been described to affect several sperm functions incl uding motility, capacitation and acrosome reaction. The effects of the ster oid, which is present in high levels in the cumulus matrix that surrounds t he oocyte, are mediated by an increase of intracellular calcium concentrati ons, efflux of chloride, stimulation of activity of phospholipases and phos phorylation of proteins. These effects are due to activation of a rapid/non genomic pathway. Two different types of receptors for P, distinct from the genomic ones, have been recently identified on the surface of human spermat ozoa. The affinities of P for these receptors are respectively in the nano- and in the micromolar range. Sperm responsiveness to progesterone is impai red in subfertile patients and is strictly correlated to the ability of fer tilizing the oocyte. In addition, the determination of sperm responsiveness is predictive of fertilizing: 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.