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Abstract
Sperm flagellar activity is modulated by cAMP. In target tissues, vasoactive intestinal peptide (VIP) stimulates adenyl cyclase activity, which elevates intracellular cAMP levels and activates protein kinase activity. This study investigated the effects of VIP on motility of sperm from 17 subjects. Motile activities, monitored before (0 min, baseline) and for 40 min after incubation with VIP (0.2 mug/mL cell suspension), were analyzed by computer-assisted semen analysis. The data (mean +/- SEM) are expressed as percentages of baseline values and changes were compared by trend analysis for interval level measures by repeated measures analysis of variance orthogonal polynominal contrasts. The addition of VIP significantly increased motile sperm concentration (110 +/- 17% [10 min], 132 +/- 15% [20 min], 152 +/- 18% [30 min], 125 +/- 18% [40 min]; p <. 02) and sperm with rapid straight-line motility (V > 25 mum/s) (167 +/- 20%, 174 +/- 19%, 173 +/- 23%, 141 +/- 16%; p <. 02). Mean track speed (mum/s) was increased (125 +/- 12%, 134 +/- 9%, 129 +/- 12% and 126 +/- 12%; p <. 02), while mean progressive velocity, amplitude of head displacement, and beat frequency were not affected by VIP. These results indicate that VIP stimulates sperm motile activity by cAMP-mediated phosphorylation of axonemal proteins.