EFFECTS OF INTRACEREBROVENTRICULARLY INFUSED HISTAMINE AND SELECTIVE H-1, H-2 AND H-3 AGONISTS ON FOOD AND WATER-INTAKE AND URINE FLOW IN WISTAR RATS

The actions of intracerebroventricularly infused histamine and selecti ve histamine H-1, H-2 and H-3 receptor agonists on food and water inta ke and urine flow were studied in rats. It was found that 100-800 nmol es of histamine significantly suppressed feeding. The H-1 agonist 2-(3 -trifluoromethylphenyl)histamine (FMPH) decreased food intake, whereas the H-2 agonist dimaprit was without effect. Histamine- and FMPH-indu ced suppressions of feeding were attenuated by blockade of H-1 but not by H-2 receptors. The results clearly demonstrate that activation of brain H-1 receptors decreases food intake. In subsequent studies, we f ound that both metoprine and thioperamide, which increase histaminergi c activity through different mechanisms, also reduced food intake. Thi s finding indicates that the brain histaminergic system is associated with feeding behavior. The same is true with body water homeostasis. H istamine caused a long-lasting diuresis. Also dimaprit and metoprine i ncreased urine flow and the blockade of H-2 receptors abolished the di uretic responses to histamine and dimaprit. On the other hand, the H-3 agonist (R)-alpha-methylhistamine elicited drinking and this effect c ould be prevented by thioperamide pretreatment. The results imply that activation of H-3 receptors predominantly provokes drinking, whereas central H-2 receptors mediate the diuretic effect of histamine. (C) 19 98 Elsevier Science B.V. All rights reserved.