بررسي اثرات سيستم H2- هيستامينرژيك و سيستم هاي موسكاريني كولينرژيك بر ميزان اخذ آب در موش هاي صحرايي نر بالغ نژاد WISTAR

Effect of H2- Histaminergic and muscarinic cholinergic systems on water intake in adult male rats

Introduction: Histamine can be found in a restricted population of neurons originating from the tuberomammillary nucleus and projecting diffusely to several brain areas. The three subtypes of histamine receptors (Hi, H2 and H3) are distributed in almost all parts of the brain of mammalian species. Central histaminergic neurons have been implicated in many physiological processes, such as circadian rhythms, thermoregulation, learning and memory and cardiovascular and neuroendocrine regulation. It is unclear whether endogenous histamine is involved in the regulation of water balance. Furthermore, in addition to its well- documented modulation of food intake, the cholinergic system also plays a role in water intake. Aim: The present study investigated the effects of H2-histaminergic receptors and muscarinic cholinoceptors on water intake in adult male rats. Materials and Methods: Intraperitoneally (i.p.) injections were carried out in all experiments after 24-h deprivation of water. After deprivation, the volume of consumed water was measured for 1 h. Results: Administration of pilocarpine, a muscarinic cholinoceptor agonist (1-10 mg/kg wt.), and histamine (1-5 mg/kg wt.) increased, while scopolamine, a muscarinic cholinoceptor antagonist <0.01-1 mg/kg wt.) and ranitidine, a histamine H2 receptor antagonist (10-50 mg/kg wt.) decreased water intake in isolated rats. Blockade of histamine H2 receptors attenuated the histamine-mduced response. Pretreatment with ranitidine attenuated the pilocarpine-induced response. However, pharmacological blockade of muscarinic cholinoceptors b\ scopolamine did not potentiate the inhibitory effect induced by ranitidine. Conclusion: It is concluded that H2-histaminergic and muscarinic cholinergic systems may interact on water intake in rats.