A comparison of the effects of doxazosin and alfuzosin with those of urapidil on preganglionic sympathetic nerve activity in anaesthetised cats.

Preganglionic sympathetic nerve activity, blood pressure, heart rate and femoral arterial conductance were recorded in anaesthetised, paralysed cats. Urapidil, doxazosin and alfuzosin were infused i.v. for 1 h into different animals at the rate of 2 mg kg-1 h-1. All three drugs caused a fall in thoracic preganglionic sympathetic nerve activity along with blood pressure. Although urapidil had a greater hypotensive action than doxazosin and alfuzosin its sympathoinhibitory action was delayed and weaker. Since all three drugs are alpha 1-adrenoceptor antagonists it appears that antagonism at this receptor type may cause central sympathoinhibition as well as a decrease in total peripheral resistance. However, the different effects of urapidil suggest that its action on central sympathetic tone and therefore its hypotensive action cannot be due entirely to its ability to block alpha 1-adrenoceptors.