Evaluation of the effect of 17αOH‐progesterone and 17β‐oestradiol on human sperm ability to fuse with oocytes: comparison and possible interference with the effect of progesterone

The demonstration of a stimulatory effect of progesterone (P) on the sperm/oocyte fusion has provided the most relevant biological evidence of the effect of P on sperm functions involved in fertilization. Some evidence exists that 17alpha-hydroxyprogesterone (17alphaOH-P) and 17beta-oestradiol (17beta-E2), could also exert non-genomic effects on human spermatozoa and a role for 17beta-E2 as a possible physiological modulator of P action on spermatozoa has been suggested. This study aimed to determine the effect of the exposure of human spermatozoa to 17alphaOH-P and 17beta-E2 on sperm/oocyte fusion as well as the possible interference of 17beta-E2 with the effect of P. The effect of steroids on sperm/oocyte fusion was assessed by means of the hamster egg penetration test (HEPT). The exposure of capacitated sperm suspensions to scalar doses of 17alphaOH-P produced a significant enhancement of penetrations/oocytes with a dose/response effect. It was equal to 75.3% of that produced by equimolar doses of P. Conversely, 17beta-E2 (from 100 nM to 50 microM) did not produce any significant effect when added either before or after capacitation. Moreover, the sperm pre-incubation with 17beta-E2 did not interfere with the stimulatory effect of P. These results support a physiological role for 17OH-P in the process of fertilization, but not a role for 17beta-E2 as a possible physiological modulator of P action on spermatozoa.