Remodeling of Wall Mechanics and the Myogenic Mechanism of Rat Intramural Coronary Arterioles in Response to a Short-Term Daily Exercise Program: Role of Endothelial Factors

Abstract

Purpose: Exercise elicits early adaptation of coronary vessels enabling the coronary circulation to respond adequately to higher flow demands. We hypothesized that short-term daily exercise induces biomechanical and functional remodeling of the coronary resistance arteries related to pressure. Methods: Male rats were subjected to a progressively increasing 4-week treadmill exercise program (over 60 min/day, 1 mph in the final step). In vitro pressure-diameter measurements were performed on coronary segments (119 ± 5 μm in diameter at 50 mm Hg) with microarteriography. The magnitude of the myogenic response and contribution of endogenous nitric oxide and prostanoid production to the wall mechanics and pressure-diameter relationship were assessed. Results: Arterioles isolated from exercised ani mals – compared to the sedentary group – had thicker walls, increased distensibility, and a decreased elastic modulus as a result of reduced wall stress in the low pressure range. The arterioles of exercised rats exhibited a more powerful myogenic response and less endogenous vasoconstrictor prostanoid modulation at higher pressures, while vasodilator nitric oxide modulation of diameter was augmented at low pressures (< 60 mm Hg). Conclusions: A short-term daily exercise program induces remodeling of rat intramural coronary arterioles, likely resulting in a greater range of coronary autoregulatory function (constrictor and dilator reserves) and more effective protection against great changes in intraluminal pressure, contributing thereby to the optimization of coronary blood flow during exercise.

Long-term exercise results in morphological and biomechanical changes in coronary resistance arterioles in male and female rats

“…The inner diameter decreased, and the wall thickness to diameter ratio increased in trained animals. Several observations have described lumen distension and thinner walls in vessels as effects of long-term physical exercise [11,12,[26][27][28][29], while others, similarly to us, have found thicker walls and decreased lumens [14,30,31]. A possible explanation is that different segments of the resistance artery network The elevated wall thickness to lumen diameter ratio may be advantageous in providing better control of the vascular lumen and segmental hemodynamic resistance.…”

“…The elevation of endothelium-dependent vasorelaxation by long-term exercise has been described in some earlier publications both in male and female animals [12,14,39,40]. During exercise training, wall shear stress is elevated and acts on the endothelial cell layer, inducing acute and chronic adaptation mechanisms, such as enhanced endothelial NO release or decreased endothelin levels in vascular smooth muscle cells [14].…”

“…*P < 0.05 vs. MSE, $ P < 0.05 vs. MEx regarding how the contractility of coronaries is affected by long-term exercise; specifically, some studies have found increased sensitivity to vasoconstrictor agonists [34], while others have found unaltered [35] and reduced [36,37] agonist-induced contractions for different coronary specimens. Elevated myogenic tone in trained animals has been described previously [12,14,38].…”

“…A paper on the effects of a moderate chronic treadmill exercise program on intramural coronary arterioles in male rats was recently published. In the low intraluminal pressure range, the distensibility and endotheliumdependent modulation of myogenic tone were augmented, whereas at higher pressures, wall thickness increased, wall stress was reduced, the myogenic response increased, and the effect of intrinsic constrictor prostanoids was diminished [14].…”

Biomimetic human small muscular pulmonary arteries

“…Figure 2A Figure 2B demonstrates the design space for the flexural stiffness  of tubular structures with thickness varying from 0.5 to 2 m and Young's modulus varying from 1 to 200 GPa. For in vivo hSMPA, thicknesses of 10 to 30 m and Young's moduli of 15 to 500 kPa have been reported in the literature (40)(41)(42)(43). The inserted plane in Fig.…”