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

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).

In vitro cell culture study using human spermatozoa.

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

Semen were obtained from three fertile healthy volunteers.

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.

The percentage of capacitated and acrosome-reacted sperm and the proportion of internalization of lyso-PAF across the plasma membrane.

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%).

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