Investigation of distal aortic compliance and vasodilator responsiveness in heart failure due to proximal aortic stenosis in the guinea pig

Hypotension and syncope are recognized features of chronic aortic stenosis. This study examined vasomotor responses and dynamic compliance in isolated abdominal aortae after chronic constriction of the ascending aorta. Guinea pigs underwent constriction of the ascending aorta or sham operation. Sect ions of descending aorta were removed for studies of contractile performanc e and compliance. Dynamic compliance was measured using a feedback-controll ed pulsatile pressure system at frequencies of 0.5, 1.5 and 2.5 Hz and mean pressures from 40 to 100 mmHg. Chronic (149 +/- 6 days) aortic constrictio n resulted in significant increases in organ weight/body weight ratios for left ventricle (58%), right ventricle (100%) and lung (61%). The presence o f heart failure was indicated by increased lung weights, left ventricular e nd-diastolic pressure and systemic vascular resistance, reduced cardiac out put and increased levels of plasma atrial natriuretic peptide (166%), adren aline (x 20), noradrenaline (106%) and dopamine (x 3). Aortic rings showed similar constrictor responses to phenylephrine and angiotensin II, but maxi mal vasodilator responses to acetylcholine and isoprenaline were significan tly increased (144% and 48% respectively). Dilator responses to sodium nitr oprusside, forskolin and cromokalim were unchanged. Compliance of all vesse ls decreased with increasing pulsatile frequency and to a lesser extent wit h increased mean pressure, but were similar in aortic-constricted and contr ol groups. Chronic constriction of the ascending aorta resulted in heart fa ilure and increased vasodilator responses to acetylcholine and isoprenaline in the distal aorta while dynamic compliance was unchanged. We hypothesize that increased endothelium-mediated vasodilatation may contribute to hypot ension and syncope in patients with left ventricular outflow obstruction.