Hemodynamics in hypertension and heart failure

Acute hypertension selectively potentiates constrictor responses of large coronary arteries to serotonin by altering endothelial function in vivo

We tested the hypothesis that acute coronary artery hypertension may damage vascular endothelium and alter vasomotor responses to humoral agents. We examined effects of intracoronary infusion of the endothelium-dependent agent serotonin and two endothelium-independent agents, angiotensin II and methoxamine, on large coronary artery diameter in the blood perfused dog heart. Responses were examined before and 30 minutes after brief periods of coronary hypertension (200 mm Hg for 10 seconds to 15 minutes). In open-chest anesthetized dogs, the left anterior descending coronary artery was perfused at constant pressure. Coronary diameter (D) was measured with piezoelectric crystals. At a control perfusion pressure of 80 mm Hg, serotonin produced dose-dependent constriction of the large coronary artery (mean +/- SEM; delta D = -22 +/- 10 microns at 5 micrograms/min; -108 +/- 50 microns at 50 micrograms/min). Increasing perfusion pressure to 200 mm Hg increased flow 515 +/- 79% and coronary diameter 509 +/- 9 microns. After 15 minutes of hypertension, when coronary diameter had returned to baseline values, the constriction of the large artery to serotonin was potentiated (delta D = -89 +/- 33 microns at 5 micrograms/min; -207 +/- 45 microns at 50 micrograms/min; p less than 0.05). Hypertension for 1-5 minutes potentiated constrictor responses of large coronary arteries for at least 2 1/2 hours. Removal of endothelium prevented effects of hypertension on constrictor responses of large arteries to serotonin. Hypertension did not alter constrictor responses to angiotension II (1 and 2.5 micrograms/min) or methoxamine (50 and 100 micrograms/min) or the dilator response to acetylcholine (40 micrograms/min). Acute hypertension altered endothelial morphology. There were small endothelial craters following 10 seconds of hypertension, and disruption of endothelial junctions with leukocyte adherence following 1-15 minutes of hypertension. We conclude that acute hypertension alters constrictor responses of large coronary arteries to serotonin by impairing endothelial function and not by directly affecting vascular smooth muscle. These effects of acute hypertension on vascular reactivity are selective in that they do not involve non-endothelium-dependent agents or the endothelium-dependent agent, acetylcholine. The effect of hypertension also persists long after pressure is restored to normotensive levels.

[Regional blood flow in congestive cardiac failure and inhibition of angiotensin converting enzyme]

In congestive cardiac failure myocardial deficiency is accompanied by neurohormonal dysfunction with reflex stimulation of the sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS). These two systems act synergistically, resulting in peripheral vasoconstriction with increased vascular resistance and therefore greater demand on left ventricular haemodynamics. The role of the RAAS is better understood when angiotensin-converting enzyme inhibitors (ACEI) are used. The vasodilatation produced by these inhibitors mostly affects those vascular beds that depend on the vasopressor effect of angiotensin II, and primarily the renal vascular system: glomerular filtration is improved, and sodium excretion is increased. The RAAS has little influence on the other regional blood flows, so that the administration of ACEI is not followed by cutaneous, muscular or visceral vasodilatation. However, the cerebral blood flow remains normal or even increases despite the fall in systemic arterial pressure, and the coronary output is preserved. Angiotensin-converting enzyme inhibitors produce a strong, though selective, vasodilatation without reflex tachycardia, benefiting primarily the kidneys. The resulting increase in sodium excretion contributes to the long-term effect of ACEI in the treatment of congestive cardiac failure.