Abstract
The influence of urapidil, clonidine, prazosin and propranolol on autonomic nerve activity was determined in anaesthetized cats and rats. The effects of these drugs on blood pressure and heart rate were also evaluated. Impulse output was recorded in the splanchnic and vagus nerve of the cat, and in the cervical sympathetic trunk of the rat. Urapidil increased activity in sympathetic and parasympathetic nerve fibres in cats at low doses without affecting blood pressure and heart rate. At higher doses which lowered blood pressure, urapidil reduced sympathetic impulse output in cats and rats while vagal output was increased. The α 1-adrenoceptor blocking agent, prazosin, did not affect activity in sympathetic and parasympathetic nerve fibres while the β-adrenoceptor blocking agent, propranolol, increased activity in these nerves in cats. The α-adrenoceptor agonist, clonidine, reduced sympathetic impulse output at all doses tested in both rats and cats. The results provide evidence that urapidil, in addition to its peripheral α- and β-adrenoceptor blocking properties, affects cardiovascular regulation by a central action. Blockade of α- or β-adrenoceptors in the brain is probably not responsible for the central effect of urapidil.
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