Relaxin and prostaglandin E2 (PGE2) are in human semen and affect sperm movement. One study looked at how relaxin and PGE2 impact human sperm activity. PGE2 boost sperm movement best at 25 micrograms/ml. Relaxin and PGE2 don’t change sperm movement in fresh semen but can help washed sperm move better. Relaxin improves motility in stored sperm, but PGE2 doesn't. When used together, relaxin and PGE2 don’t affect washed or stored sperm motility, showing they counteract each other. Seemingly, certain components in fresh semen sustain optimal sperm movement. Both relaxin and PGE2 in seminal fluid with active sperm suggest other elements regulate their effects on sperm movement.