I seem to recall a ratty experiment in which lab rats had electrodes inserted into pleasure centres in the brain. They could stimulate the centre through pressing a bar. (Which is what lab rats do best.)
IIRC, the rats pleasured themselves to death, eschewing food and drink, in order the stimulate the pleasure centres.
Most animals don't have sex for very long at a time; I wouldn't be surprised if the pleasure wiring overrides any ability to feel any other urges, because of the rarity (and importance) of its activation. I imagine it would be quite different in the human case; things frequently "interrupt" people.