Immunomodulation by morphine in Plasmodium berghei-infected mice.
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.
Singh
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Division of Microbiology and Pharmacology, Central Drug Research Institute, Lucknow, India.
Singh
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Dutta
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Srimal
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RC
D000276:Adjuvants, Immunologic / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D007962:Leukocytes / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects; D008288:Malaria / Q000097:blood / Q000188:drug therapy* / Q000276:immunology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D010962:Plasmodium berghei; D012822:Silicon Dioxide / Q000494:pharmacology
D000276:Adjuvants, Immunologic; D009270:Naloxone; D012822:Silicon Dioxide; D009020:Morphine