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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 alpha 1-adrenoceptor blocking agent,
prazosin, did not affect activity in sympathetic and parasympathetic nerve fibres
while the beta-adrenoceptor blocking agent, propranolol, increased activity in these
nerves in cats. The alpha-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 alpha- and beta-adrenoceptor blocking properties,
affects cardiovascular regulation by a central action. Blockade of alpha- or beta-adrenoceptors
in the brain is probably not responsible for the central effect of urapidil.