Human spermatozoa capacitated with progesterone or a long incubation show accelerated internalization by an alkyl ether lysophospholipid.

Objective: To evaluate changes that occur in sperm plasma membranes during capacitation, the internalization of [(3)H]lyso-platelet activating factor ([(3)H]lyso-PAF) across the plasma membrane of human spermatozoa was measured as a function of incubation time or exposure to progesterone (P).

Design: In vitro cell culture study using human spermatozoa.

Setting: Department of Obstetrics and Gynecology, School of Medicine, the University of Tokushima, Japan.

Patient(s): Semen were obtained from three fertile healthy volunteers.

Intervention(s): The internalization of [(3)H]lyso-PAF across the plasma membranes of human spermatozoa that were incubated for an extended period or exposed to P was measured at 5, 20, 60, and 120 minutes after the addition of the phospholipid probe using the modified albumin back-exchange method.

Main Outcome Measure(s): The percentage of capacitated and acrosome-reacted sperm and the proportion of internalization of lyso-PAF across the plasma membrane.

Result(s): A 6-hour incubation period significantly increased the percentage of capacitated spermatozoa and the proportion of internalization of [(3)H]lyso-PAF across the plasma membrane of human spermatozoa compared with controls (capacitated spermatozoa, 20.3 +/- 10.6% vs. 8.5 +/- 1.8%; internalization 120 minutes after the addition of the phospholipid probe, 25.6 +/- 2.5% vs. 11.6 +/- 3.0%) (mean +/- SEM). Exposure to P significantly increased the percentage of capacitated spermatozoa compared with controls (19.6 +/- 6.8% vs. 11.0 +/- 2.4%) and also significantly accelerated the internalization of [(3)H]lyso-PAF compared with controls (internalization 120 minutes after the addition of the phospholipid probe, 26.2 +/- 1.8% vs. 21.4 +/- 1.1%).

Conclusion(s): The administration of P or a long incubation increased the proportion of internalization and consequently induced capacitation in human spermatozoa.