A COMPARISON OF THE EFFECTS OF DOXAZOSIN AND TERAZOSIN ON THE SPONTANEOUS SYMPATHETIC DRIVE TO THE BLADDER AND RELATED ORGANS IN ANESTHETIZED CATS

The effects of i.v. infusion of the alpha(1)-adrenoceptor antagonists doxazosin and terazosin (2 mg kg(-1) h(-1)) on spontaneous hypogastric , renal and inferior cardiac nerve activity, spontaneous bladder contr actions, blood pressure, heart rate and femoral arterial flow were inv estigated separately in alpha-chloralose-anaesthetized cats. Both drug s caused a reduction in hypogastric nerve activity associated with no overt changes in spontaneous bladder contractions. Doxazosin was more potent than terazosin, in that there was a significant reduction in hy pogastric nerve activity after 20 min (0.67 mg kg(-1)) of infusion, wh ile for terazosin this occurred after 40 min (1.33 mg kg(-1)). Both dr ugs also caused significant falls in blood pressure of 34 +/- 3 mm Hg and 33 +/- 4 mm Hg after 60 min. This was associated with no change in heart rate for doxazosin while terazosin caused an initial and signif icant increase in heart rate of 20 +/- 3 beats min(-1) by 5 min, decli ning by 30 min to 1 +/- 5 beats min(-1). This terazosin-induced tachyc ardia was associated with a significant increase in cardiac nerve acti vity of 128 +/- 22%. Both drugs caused increases in renal nerve activi ty however only for doxazosin was this increase significant. Femoral a rterial conductance was also increased by both drugs, however, for dox azosin this increase was immediate and larger over the infusion period . These results demonstrate that alpha(1)-adrenoceptor antagonists can reduce sympathetic drive to the bladder and related organs.