MAGNOLOL DECREASES BODY TEMPERATURE BY REDUCING 5 HYDROXYTRYPTAMINE RELEASE IN THE RAT HYPOTHALAMUS

1. The effects of magnolol, isolated and purified from the cortex of Magnolia officinalis Rehd. et Wils, on thermoregulation and hypothalamic release of 5-hydroxytryptamine (5-HT) by in vivo microdialysis were assessed in normothermic rats and in febrile rats treated with interleukin-1β. 2. Intraperitoneal administration of magnolol (25–100 mg/kg) produced a decrease in colon temperature, an increase in foot skin temperature, a decrease in metabolic rate and a decrease in the endogenous release of 5-HT in the rat hypothalamus. 3. Depletion of rat brain 5-HT, produced by intracerebro-ventricular pretreatment with 5,7-dihydroxytryptamine, attenuated the magnolol-induced hypothermia, cutaneous vasodilation and decreased metabolism. 4. Intracerebroventricular administration of (±)-2,5-dimethoxy-4-iodoamphetamine (a 5-HT₂ receptor agonist; 5–10 μg/5 μL) increased basal colon temperature and reversed the magnolol-induced hypothermia. 5. The increases in both colon temperature and hypothalamic 5-HT release produced by interleukin-1β injection were attenuated by treatment with magnolol. 6. The data suggest that magnolol decreases body temperature (due to increased heat loss and decreased heat production) by reducing 5-HT release in rat hypothalamus.