Diuretics and arteriolar resistance and arterial compliance in human hypertension.

Differences exist between short- and long-term haemodynamic effects of diuretics. In the short term, plasma volume depletion is accompanied by increased peripheral vascular resistance and decreased cardiac output. In the long term cardiac output returns toward normal, peripheral resistance falls to below pretreatment values and blood volume remains lower than before therapy. This long-term decrease in volume may contribute to the chronic antihypertensive effects of diuretics. Many studies have reported that arterial compliance is increased after antihypertensive drug administration. However, it is important to known whether such action is a primary pharmacological effect or mediated by the reduction in blood pressure. Two different methods using pulse wave velocity measurements have been applied to determine the pressure-dependence of compliance before and after thiazide administration. In the first method, blood pressure was controlled as a variable by changing transmural pressure of the forearm encased in a rigid plastic tube. In the other method arterial compliance in the brachial artery was evaluated using a simple non-linear arterial model. Both methods demonstrated that the decrease in blood pressure with thiazide therapy was associated with increased arterial compliance. However, by measuring arterial compliance at the same pressure, its isobaric values were found to be unchanged. The implication is that the increase in compliance of the peripheral artery observed with diuretics is due to the decline in blood pressure rather than to a change in the intrinsic properties of the arterial wall.

Comparative long-term vasoactive effects of atenolol and carteolol on the properties of the small and large arteries of the upper extremities in human essential hypertension.

The long-term effects of selective (atenolol) and nonselective (carteolol) beta-blockers on brachial artery diameter velocity and flow and on vascular resistance (pulsed Doppler) were compared in two groups of 10 hypertensive patients at respective daily doses of 100 and 20 mg. The drugs decreased mean blood pressure (p less than 0.01) with similar magnitude, although systolic blood pressure was decreased more by atenolol than by carteolol (p less than 0.05). Heart rate was decreased by atenolol (p less than 0.01) but was unchanged by carteolol. The drugs did not change brachial circulation when the hand circulation was present. During hand exclusion (wrist occlusion) comparison from baseline showed that atenolol decreased velocity and flow (p less than 0.01, p less than 0.05) and increased resistance (p less than 0.05), whereas carteolol decreased resistance (p less than 0.05); after 3 months of treatment, velocity and flow were higher (p less than 0.01, p less than 0.001) and resistance was lower (p less than 0.01) with carteolol than with atenolol. Thus, hand exclusion demonstrated opposite drug effects on arterioles--dilation for carteolol and constriction for atenolol.