naloxone and Malaria

The effect of morphine on immunomodulation and host defense have been investigated during Plasmodium berghei infection in BALB/c mice. A single low (5.0 mg/kg) subcutaneous dose of morphine strongly suppressed (sometimes completely eliminated) the parasitaemia, whereas a high dose (80.0 mg/kg) exerted mild potentiating effect. Mice treated with the low dose showed a significant (p < 0.05) increase in the total number of circulating leukocytes, the number (pool-size) of peritoneal macrophages, and the phagocytic activity of peritoneal macrophages, in vitro. Conversely, in mice treated with the high dose, all these parameters were diminished. Silica (3.0 mg/mouse), administered intravenously, abrogated the morphine-induced protective effects but did not affect its potentiation of the infection. Naloxone pretreatment (4.0 mg/kg) completely blocked the protective effects of morphine, suggesting the mediation via naloxone-sensitive opiate-receptors; paradoxically, it did not affect the potentiating effects. These observations indicate that morphine exerted a dose-dependent, biphasic effect on the course of P. berghei infection in mice, apparently by modulating the macrophage-mediated protective mechanisms.

Topics: Adjuvants, Immunologic; Animals; Dose-Response Relationship, Drug; Female; Leukocytes; Macrophages; Malaria; Male; Mice; Mice, Inbred BALB C; Morphine; Naloxone; Plasmodium berghei; Silicon Dioxide

Topics: Drug Tolerance; Gastric Lavage; Glucose; Humans; Hypotension; Malaria; Naloxone; Narcotics; Opioid-Related Disorders; Plasma Substitutes; Receptors, Opioid; Sexually Transmitted Diseases; Substance Withdrawal Syndrome; Substance-Related Disorders; Tetanus; Tuberculosis