Hypothalamic Histamine Neurons Activate Lipolysis in Rat Adipose Tissue

The contribution of hypothalamic histamine neurons to the central regulation of peripheral lipid metabolism was investigated in rats using in vivo microdialysis system. A bolus infusion of l-histamine at doses of 10–10³ nmol/rat into the third cerebral ventricle (i3vt) dose-dependently increased glycerol concentration in the perfusate from the epididymal adipose tissue. I3vt infusion of 10² nmol/rat thioperamide, an autoinhibitory H₃ receptor antagonist that activates histamine neurons to increase synthesis and release of neuronal histamine, convincingly mimicked histamine action in the augmented lipolysis. Intraperitoneal pretreatment with propranolol, a β-adrenoceptor antagonist, abolished the thioperamide-induced lipolytic action. An electrophysiological study demonstrated that efferent sympathetic nerves innervating the epididymal fat were activated after the i3vt infusion of thioperamide. Hypothalamic histamine neurons thus regulate peripheral lipid metabolism through the accelerating lipolytic action by activation of sympathetic β-adrenoceptor.