Oseltamivir, an anti-influenza virus drug, induces marked hypothermia in normal mice. We have proposed that the hypothermic effect arises from inhibition of the nicotinic acetylcholine receptor function of sympathetic ganglion neurons which innervate the brown adipose tissue (a heat generator). It has been reported that local anesthetics inhibit nicotinic acetylcholine receptor function by acting on its ionic channels, and that bupropion, a nicotinic antagonist, induces hypothermia. In this study, we compared the effects of oseltamivir, procaine and bupropion on body temperature, cardiovascular function and neuromuscular transmission. Intraperitoneal administration of oseltamivir (100 mg/kg), procaine (86.6 mg/kg) and bupropion (86.7 mg/kg) lowered the core body temperature of normal mice. At lower doses (10-30 mg/kg oseltamivir, 8.7-26 mg/kg procaine and bupropion), when administered subcutaneously, the three drugs antagonized the hypothermia induced by intraperitoneal injection of nicotine (1 mg/kg). In anesthetized rats, intravenous oseltamivir (30-100 mg/kg), procaine (10 mg/kg) and bupropion (10 mg/kg) induced hypotension and bradycardia. Oseltamivir alone (100 mg/kg) did not inhibit neuromuscular twitch contraction of rats, but at 3-30 mg/kg it augmented the muscle-relaxing effect of d-tubocurarine. Similar effects were observed when lower doses of procaine (10-30 mg/kg) and bupropion (3-10 mg/kg) were administered, suggesting that systemic administration of oseltamivir inhibits muscular nicotinic acetylcholine receptors. These results support the idea that the hypothermic effect of oseltamivir is due to its effects on sympathetic ganglia which innervate the brown adipose tissue, and suggest that oseltamivir may exert non-selective ion channel blocking effects like those of ester-type local anesthetics.
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