Malaria Parasite Infection and Chloroquine-Induced Pruritus: The Role of Opioid-Peptides

Abstract

Pruritus or itch is associated with malaria infection and/or chloroquine chemotherapy. This study examined the relationship between parasitaemia and chloroquine (CQ) on body scratching (BS) in healthy (un-infected) and malaria-infected rats. The malaria parasite induced a significant (p< 0.001) increase in body scratching (28.3 ± 4.6) compared to un-infected rats (7.7 ± 1.0). Intraperitoneal administration of CQ (20 mg/kg, i.p) increased the frequency of body scratching (28.7 ± 8.1) compared to control animals (7.5 ± 1.0, p < 0.001). The -opioid receptor antagonist, naltrexone (0.25mg/kg i.p given 15 minutes prior) blocked both parasite and CQ (20mg/kg)–induced body scratching. In morphine tolerant rats, the frequency of BS was significantly reduced (12.7 ± 3.7, p<0.001) compared to that induced by parasite infection (28.0 ± 4.6) and CQ (20 mg/kg i.p, 28.7 ± 8.1) in morphine naïve animals. Promethazine (1mg/kg i.p) and dexamethasone (1 mg/kg) 15 min did not alter parasite-induced body scratching, whereas promethazine (1mg/kg i.p) abolished CQ-induced scratching in uninfected rats. The study indicated that both CQ and malaria parasite-induced scratching are mediated by opioid receptors, and that histaminergic and corticosteroid systems are not involved in parasite-induced body scratching, whereas, the histaminergic system was implicated in CQ-induced itching.

Keywords: Rats, parasitaemia, chloroquine, opioids, antihistamine, naltrexone

West African Journal of Pharmacology and Drug Research Vol. 22/23 2007: pp. 31-38