Exercise-induced cardiac hypertrophy: a correlation of blood flow and microvasculature

Abstract

The effects of exercise conditioning on the myocardium were studied in seven instrumented pigs strenuously exercised for 12 wk by treadmill running. Data were compared with eight instrumented untrained pigs. O2 consumption measured during maximum exercise effort was significantly elevated in the trained pigs (71.7 +/- 4.0 vs. 56.3 +/- 3.0 ml X ml-1 X kg-1). Absolute right and left ventricular mass increased by 20 and 13%, respectively, in response to exercise. Myocyte cross-sectional area increased by 21% in the trained hearts compared with the untrained hearts. Transmural left ventricular myocardial blood flow (ml X min-1 X g-1) was not significantly different at rest, during maximum exercise, or during exercise with adenosine infusion. However, training caused an elevation of the regional epicardial blood flow noted during exercise and exercise with adenosine. In the trained pigs mean aortic pressure during maximum exercise with adenosine infusion was not significantly different compared with untrained pigs. Coronary resistance during exercise with adenosine infusion was the same in both animal groups. In the trained group capillary numerical (no./mm2) and length (mm/mm3) densities were reduced, whereas arteriolar numerical and length densities were significantly increased compared with the untrained group. Measurements of capillary luminal surface density (mm2/mm3) in the trained group were unchanged compared with the untrained group. These results suggest that strenuous exercise does not stimulate the production of new capillaries, but this is modified by the ability of existing capillaries to increase their luminal surface area to parallel increases in myocyte growth. The arteriolar data suggest that exercise promotes the formation of new arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological Society Symposium – the Athlete's Heart

“…3). Treadmill training for 3 months or more also enhanced the maximum coronary blood flow capacity in dogs (Laughlin, 1985) and increased the number of coronary resistance arterioles of 35-75 mm in diameter in pigs (Breisch et al 1986). In humans, the coronary flow reserve, that is, the ratio of maximum (using dipyridamole to dilate vessels) to resting coronary arterial blood flow (Strauer, 1992) has been used to assess expansion of the resistance vasculature with greater values found in athletes (5.9) compared to sedentary controls (3.7; Hildick-Smith et al 2000).…”

“…The majority of studies in which young animals such as rats and guinea pigs were trained by swimming or running reported increases in myocardial capillary density or capillary/fibre ratio irrespective of whether cardiac hypertrophy occurred; however, in adult rats, dogs or pigs the results showed no change or a decrease despite the fact that all studies involved training for many weeks or months (Breisch et al 1986;Laughlin & Tomanek, 1987). The issue remained unresolved until a seminal study by White et al (1998) that examined in detail the time course of exercise-induced adaptations in the coronary microvasculature.…”

Effects of gradual coronary artery occlusion and exercise training on gene expression in swine heart

“…The miniature swine model of treadmill running produces physiological cardiac hypertrophy with little or no alteration in major biochemical parameters associated with calcium handling, contractile function, or metabolism (8). Indices of swine heart function and blood flow are either maintained, or augmented by exercise training (9,10). Furthermore, exercise training improves blood flow and endothelium-dependent vasorelaxation to collateral-dependent areas in which major coronary arteries are compromised (3,11).…”

“…Furthermore, exercise training improves blood flow and endothelium-dependent vasorelaxation to collateral-dependent areas in which major coronary arteries are compromised (3,11). Although exercise training does not cause detectable shifts in cardiac biochemical parameters such as myosin ATPase activity, sarcoplasmic reticulum Ca 2+ -ATPase activity, and enzyme activities of the glycolytic and oxidative pathways (8) that are typically observed in rodents, exercise training does induce significant cardiac hypertrophy of 15-30% that enhances cardiac reserve, improves myocardial blood flow, and augments myocardial function (3,(8)(9)(10)(11). Whether or not exercise training alters the expression of hypertrophy-associated genes that reflect the physiological phenotype in the porcine heart as it does in the rodent heart has not been reported.…”

Exercise Training Enhances Vasodilation Responses to Vascular Endothelial Growth Factor in Porcine Coronary Arterioles Exposed to Chronic Coronary Occlusion

“…[1][2][3][4] CCO creates a proangiogenic environment that is dependent on the presence of growth factors and appropriate receptors. 1,5 Indeed, increased myocardial release of vascular endothelial growth factor (VEGF) has been demonstrated after coronary artery occlusion. 6 Furthermore, a significant body of evidence indicates that impaired endothelial function and altered vasomotor responsiveness of collateral-dependent vasculature contribute to abnormal regulation of coronary tone distal to CCO.…”