Dopamine is behind a lot of the desire we associate with eating and sexual intercourse. Similarly, all addictive drugs trigger dopamine (the "craving neurochemical") to stimulate the pleasure/reward center. So do gambling, shopping, overeating and other, seemingly unrelated, activities. Go shopping: dopamine. Smoke a cigarette: dopamine. Computer games: dopamine. Heroin: dopamine. Orgasm: dopamine. They all work somewhat differently on the brain, but all raise your dopamine.
You , sexy man, make my dopamine levels go all silly. ;)