Increasing vasoconstrictor response to ergonovine with oxidative injury in canine coronary artery

Elevated oxidative stress and endothelial dysfunction in right coronary artery of right ventricular hypertrophy

Remodeling of right coronary artery (RCA) occurs during right ventricular hypertrophy (RVH) induced by banding of the pulmonary artery (PA). The effect of RVH on RCA endothelial function and reactive oxygen species (ROS) in vessel wall remains unclear. A swine RVH model (n = 12 pigs) induced by PA banding was used to study RCA endothelial function and ROS level. To obtain longitudinal coronary hemodynamic and geometric data, digital subtraction angiography was used during the progression of RVH. Blood flow in the RCA increased by 82% and lumen diameter of RCA increased by 22% over a 4-wk period of RVH. The increase in blood flow and the commensurate increase in diameter resulted in a constant wall shear stress in RCA throughout the RVH period. ROS was elevated by ∼100% in RCA after 4 wk of PA banding. The expressions of p47(phox), NADPH oxidase (NOX1, NOX2, and NOX4) were upregulated in the range of 20-300% in RCA of RVH. The endothelial function was compromised in RCA of RVH as attributed to insufficient endothelial nitric oxide synthase cofactor tetrahydrobiopterin. In vivo angiographic analysis suggests an increased basal tone in the RCA during RVH. In conclusion, stretch due to outward remodeling of RCA during RVH (at constant wall shear stress), similar to vessel stretch in hypertension, appears to induce ROS elevation, endothelial dysfunction, and an increase in basal tone.

The mystery of coronary artery spasm

Coronary artery spasm is an important cause of chest pain and myocardial ischaemia. It can be defined as an exaggerated contractile response of epicardial coronary artery smooth muscle to various stimuli but the underlying mechanism is not well understood. Recent studies have shown that the loss of endothelial vasodilatory function in conjunction with an increase in vascular smooth muscle constrictor sensitivity to calcium are the likely predisposing conditions for coronary spasm. This review highlights current understanding of the pathophysiology, predisposing factors, diagnostic and therapeutic approaches for coronary spasm.

Coronary vasospasm and the regulation of coronary blood flow

Under physiologic conditions, epicardial arteries contribute minimally to coronary vascular resistance. However, in the presence of endothelial dysfunction, stimuli that normally produce vasodilation may instead cause constriction. Examples include neural release of acetylcholine or norepinephrine, platelet activation and production of serotonin and thrombin, and release of local factors such as bradykinin. This shift from a primary endothelial-mediated vasodilator influence to one of endothelial dysfunction and unchecked vasoconstriction is precisely the milieu in which coronary vasospasm is observed. This condition, which typically occurs during periods of relatively sedentary activity, is associated with focal and transient obstruction of an epicardial arterial segment resulting in characteristic echocardiographic changes and symptoms of myocardial ischemia. This review highlights the current understanding of mechanisms regulating the coronary circulation during health and examines the pathophysiologic changes that occur with coronary spasm. Genetic and other predisposing conditions are addressed, as well as novel therapies based on recent mechanistic insights of the coronary contractile dysfunction associated with coronary spasm.

Negative NO3- difference in human coronary circulation with severe atherosclerotic stenosis

To examine whether or not the levels of NOx (nitrite; NO2- and nitrate; NO3-) in coronary circulating blood reflect endothelial dysfunction due to coronary atherosclerosis, NOx levels in plasma obtained from ostium of left coronary artery and coronary sinus of patients who complained of chest pain were evaluated in relation to their coronary angiographic findings. Prior to the study, a HPLC-Griess system for NOx measurement was critically evaluated. This system has a detection limit of 0.1 microM of NO2- and NO3- by 10 microl of loading and was able to distinguish a difference of 0.1-0.2 microM of these substances. Heparin (1 U/10 microl) did not affect the detective and discriminative abilities. NO3- difference, calculated from sino-arterial difference of NO3-, was almost zero (-0.2 +/- 0.2 microM) in patients with either normal coronary arteries or mild organic coronary stenosis (< or = 20% narrowing), while a significant negative value (-5.9 +/- 1.7 microM) was obtained from patients with significant stenosis (> or = 70% narrowing) in the left coronary arteries. These results demonstrate reliable ability on the HPLC-Griess system in evaluating NO2- and NO3- in biological samples, and that the negative NO3- difference through coronary circulation may reflect endothelial dysfunction in the patients with coronary atherosclerosis with severe organic stenosis.

The development of enhanced arterial serotonergic hyperresponsiveness in mineralocorticoid hypertension

OBJECTIVE

To demonstrate that the receptor in the rat mesenteric artery mediating contraction in response to 5-hydroxytryptamine switches from a 5-hydroxytryptamine-2A to a 5-hydroxytryptamine-2B receptor after 4 weeks of deoxycorticosterone and salt (1.0% NaCl plus 0.2% KCl) therapy, and, as an extension of these studies, to test the hypothesis that this switch occurs prior to the development of hypertension.

DESIGN

Rats were administered deoxycorticosterone-salt therapy or no therapy for 1, 3, 5, 7, or 28 days. Additionally, four groups of rats (sham-normal salt, sham-high salt, deoxycorticosterone-normal salt, and deoxycorticosterone-high salt) were administered therapy for 4 weeks (28 days) to distinguish between the roles of salt and blood pressure in serotonergic responsiveness.

METHODS

Superior mesenteric arteries were mounted in tissue baths for measurement of isometric contractile force; systolic blood pressure was measured by a tail-cuff method.

RESULTS

Systolic blood pressure was first elevated by deoxycorticosterone-salt therapy relative to that in sham controls on day 5. Contraction in response to phenylephrine was minimally altered after 7 days of deoxycorticosterone-salt therapy. By day 3, the tryptophan metabolite and putative 5-hydroxytryptamine-2B receptor agonist kynuramine contracted hypertensive arteries to a greater maximum (percentage of contraction induced by phenylephrine for rats administered deoxycorticosterone-salt therapy 48.5 +/- 16.0%) than that observed for arteries in sham-treated rats (9.7 +/- 6.2%); this was also observed for the ergot alkaloid ergonovine (deoxycorticosterone-salt 67.1 +/- 18.5% and sham treatment 14.5 +/- 9.1%); however, increase in reactivity to 5-hydroxytryptamine began on day 5. Ketanserin (a 5-hydroxytryptamine-2A antagonist with a low affinity for 5-hydroxytryptamine-2B receptor; 30 nmol/l) competitively inhibited contraction in response to 5-hydroxytryptamine of mesenteric arteries from sham-treated and deoxycorticosterone-salt-treated rats on days 1, 3, and 5 but had less effect on arteries in deoxycorticosterone-salt-treated rats by day 7, signifying that a change to a non-5-hydroxytryptamine-2A receptor had occurred. Sensitivities to 5-hydroxytryptamine and to ergonovine of deoxycorticosterone-treated rats fed a normal or high-salt diet for 28 days tended to increase, as did those of sham-treated rats fed a high-salt diet (with normal blood pressure). Contraction in response to phenylephrine was changed in arteries only from animals whose systolic blood pressure had been increased (deoxycorticosterone-normal salt and deoxycorticosterone-high salt groups).

CONCLUSIONS

These experiments support the hypothesis that the switch to ketanserin-insensitive 5-hydroxytryptamine-2 receptors likely occurs coincident with or just after the initial increase in blood pressure in the deoxycorticosterone-salt-treated rat.