Plasma from patients with the pruritus of cholestasis induces opioid receptor-mediated scratching in monkeys.

The medullary dorsal horn is a site of action of opiates in producing facial scratching. Extracts of plasma (0.4 microliter) from 4 patients with the pruritus of cholestasis induced facial scratching when microinjected into the medullary dorsal horn of monkeys. This extract-induced scratching could be abolished or prevented by administering the opioid receptor antagonist, naloxone. Neither saline nor an extract of plasma from a nonpruritic cholestatic patient induced scratching when similarly administered. We infer that plasma of patients with the pruritus of cholestasis contains a factor which induces pruritus by a central opioid receptor-mediated mechanism.