[Cardiovascular effects of urapidil].

The cardiovascular effects of urapidil have been investigated in the anesthetized rat. The mechanism of the hypotensive action of this drug has been tested in vitro on the isolated rat aorta and in vivo by intracerebroventricular injections. The peripheral vasoconstrictor effect has been studied in the pithed rat. In the pithed rat, the thoracic part of the spinal cord was electrically stimulated in order to induce a tachycardia. The reduction of this tachycardia by a drug is due to its inhibitory effect on cardiac sympathetic nerves endings. Intravenous urapidil produces a significant hypotension without change in heart rate. Directly injected into the brain cavities, urapidil produces a hypotensive effect only at very high doses (1 mg/kg). This hypotensive action of urapidil appears therefore to be mainly of peripheral origin. Urapidil antagonizes competitively the contraction of the aorta induced by norepinephrine. The drug has alpha-blocking properties which explain its hypotensive action. On the other hand, urapidil provokes a weak vasoconstrictor effect in the pithed rat and induces a presynaptic inhibition in the heart which may explain the lack of heart rate change during the hypotensive effect of the drug. Urapidil may therefore also stimulate post or presynaptic alpha 2-adrenoceptors.