In swim-up-selected spermatozoa of 38 normozoospermic patients, capacitated 
spermatozoa exhibited enhanced pentose phosphate pathway (PPP) activity and 
increased expression of glucose-6-phosphate dehydrogenase (G6PD). The G6PD 
inhibitor DHEA and the inhibitors of NADPH oxidase apocynin and diphenylene 
iodonium (DPI) prevented both superoxide generation and capacitation in human 
spermatozoa, but whereas DPI and DHEA inhibited PPP, apocynin did not influence 
it, suggesting that PPP activation during capacitation is not a response to 
increased oxidative stress but exerts a role by supplying reducing equivalents 
to oxygen.