Once Is Enough

You may want to make love all night long, but your body most likely
doesn't, studies show.

Studies at two German universities found that the hormone prolactin
may dampen sexual arousal after orgasm, perhaps signaling to the body
that it's had enough. Researchers, led by Michael Exton, Ph.D., a
biological psychologist at the University of Essen's Institute of Medical
Psychology, asked 10 women to masturbate until achieving orgasm, then
examined them afterward. He discovered a surge in the hormones
adrenaline, nonadrenaline and prolactin that occurred during arousal and
orgasm--but prolactin's rise was the most dramatic and prolonged.

Prolactin has been linked to functions in both men and women,
including sperm and breast milk production. Exton believes it regulates
dopamine, a neurotransmitter that plays a role in movement control,
pleasure and pain, and likens it to a built-in switch for turning on and
off sexual desire. "The prolactin surge may possibly signal the brain and
reproductive organs that 'once is enough,'" he says.

Women are not alone in releasing prolactin after orgasm--Exton's
previous research on men and animals has uncovered a similar dynamic. He
believes that because women seem more capable of having multiple orgasms
than men, prolactin response to sexual arousal may vary individually, a
theory that begs further research.