Adaptation of the left ventricle to exercise-induced hypertrophy

Abstract

Cardiac functional and structural adaptations to exercise-induced hypertrophy were studied in 68 pigs. Pigs were exercise trained on a treadmill for 10 wk. Sequential measurements were made of cardiac dimensions, [left ventricular end-diastolic diameter (EDD), changes in diameter (delta D%), wall thickness (WTh), wall thickening (WTh%), left ventricular pressure (LVP), time derivative of pressure (dP/dt), stroke volume, total body O2 consumption (VO2), blood gases, and systemic hemodynamics] at rest and during moderate and severe exercise. Postmortem studies included morphometric measurements of capillary density, arteriolar density, mitochondria, and myofibrils. All of the exercise-trained pigs showed significant increases in aerobic capacity. Maximum O2 consumption (VO2 max) increased by 37.5% in group 1 (moderate exercise training) and 34% in group 3 (heavy exercise training). Cardiac hypertrophy ranged from less than 15% in a group (n = 8) subjected to moderate exercise training to greater than 30% in a group (n = 11) subjected to heavy exercise training. Before training, exercise was characterized by a decreasing EDD during progressive exercise; this was reversed after exercise training. Stroke volume and end-diastolic volumes during exercise showed a highly significant increase after exercise training and hypertrophy. Morphometric measurements showed that mitochondria and cell membranes increased with increasing myocyte growth in all exercise groups, but there was only a partially compensated adaptation of capillary proliferation. Arteriolar number and length increased in all exercise groups. Intrinsic contractility as measured by delta D%, WTh%, or left ventricular dP/dt did not increase with exercise training and in some instances decreased. Therefore, left ventricular adaptation to strenuous exercise in the pig heart is primarily one of changes in left ventricular dimensions and a compensated hypertrophy. Exercise-induced increases in EDD and stroke volume can be accounted for by decreases in peripheral resistance and increased cardiac dimensions.

Calcineurin and Calcium/Calmodulin-dependent Protein Kinase Activate Distinct Metabolic Gene Regulatory Programs in Cardiac Muscle

“…In support of this latter notion, a recent report utilizing NFAT reporter mice demonstrated that NFAT activity, an indirect measure of a select target of Cn signaling, is activated in pathological but not exercise-induced cardiac hypertrophy (31). Our results would predict that Cn acts through PPAR␣ and MEF2 during developmental and physiological forms of cardiac hypertrophic growth in which mitochondrial energy production keeps pace with cardiac growth (32)(33)(34).…”

Regional myocardial downregulation of the inhibitory guanosine triphosphate-binding protein (Gi alpha 2) and beta-adrenergic receptors in a porcine model of chronic episodic myocardial ischemia.

“…A 30-s collection in the basal state was followed by a 30-s collection during exercise at a heart rate of 220 bpm. Radioactive microspheres were injected at rest and during moderate treadmill exercise to establish transmural myocardial blood flow deficits in the ischemic bed ( 1,2,14). Data analyses were conducted upon the mean values obtained from 10 continuous cardiac cycles of the acquired data.…”

“…End-systole was taken as the point 20 ms before peak negative dP/dt. Percent wall thickening (%WTh) was calculated as: end-systolic wall thickness (mm) -end-diastolic wall thickness (mm) x 100. end-diastolic wall thickness (mm) Myocardial blood flow was determined by the radioactive microsphere technique as previously reported (1,2,14). Transmural samples from the relevant beds were divided into inner (endocardial), outer (epicardial), and middle thirds, and blood flow to each third as well as transmural flow were determined.…”

Effects of Exercise Intensity and Pre-Exercise Feeding on Splanchnic Tissue Blood Flow

“…The increase in MAP between REST and N-MAX (19 mmHg) was comparable to that reported for pigs (1) and man (4,30), but less than other reported increments of 31-37 mmHg for pigs (23,32,39).…”

“…of pre-exercise feeding on gastrointestinal (GI) BF. sion matrix calculations on the isotopic spectra and overlap ratios (39).…”