Effect of PDE4-specific inhibitors (Rolipram and RS23544) on sperm motion parameters. Bovine caudal epididymal spermatozoa were incubated for 15 min at 37°C with Rolpiram, RS23544, 2-chloroadenosine, or vehicle control. Data have been normalized against baseline preincubation values (equal to 100%). VCL, Curvilinear velocity, VSL, progressive velocity, ALH, amplitude of lateral head displacement, LIN, linearity. Asterisks indicate significance difference from baseline value (100%) by P < 0.05, (n = 3).