H3 RECEPTOR-MEDIATED INHIBITION OF THE NEUROGENIC VASOPRESSOR RESPONSE IN PITHED RATS

In pithed rats, the H-3 agonist R-(-)-alpha-methylhistamine (R-alpha-MeHA) inhibited the electrically induced increase in blood pressure without affecting the vasopressor response to exogenous noradrenaline. The effect of R-alpha-MeHA was not affected by the H-1 and H-2 antagonists dimetindene and ranitidine, but attenuated by the H-3 antagonist thioperamide. At higher doses, R-alpha-MeHA itself increased basal blood pressure; this effect was not affected by the H-1, H-2 and H-3 antagonists. In conclusion, the neurogenic vasopressor response can be modulated via H-3 receptors, probably located presynaptically on postganglionic sympathetic nerve fibres.