Effects of age and exercise training on size and composition of the rat left main coronary artery

This study evaluated the effects of age and exercise training on the left main coronary artery (LMCA) in young (Y-5 months) and old (O-27.5 months) female Fischer 344 rats. Both age groups were divided into trained (T) and weight-matched sedentary (S) control groups. Training consisted of 10 weeks of treadmill running progressing to a maximum workload of 15% grade, 1 hr/day, 5 d/wk at speeds of 36 and 15 m/min for the Y and O rats, respectively. Aging resulted in a 40% increase in left ventricle (LV) weight which was proportional to the increased body weight of the old animals. Exercise training produced a mild (approximately 10%) but significant left ventricular hypertrophy (LVH) in both trained groups. Cross-sectional area of the LMCA lumen and wall, wall thickness, and areas of collagen (C), elastin (E), and collagen-to-elastin ratio (C/E) of the LMCA wall were determined morphometrically in all four groups. A method for pinpointing the coronary ostium for use as a reference point was also developed. LMCA lumen area almost doubled (p < .001) across the measured age difference, but was unaffected by training. With aging, the increase in LMCA wall area bordered on significance (p < .053), while wall thickness, C area, and the C/E ratio were unchanged. Our results indicate that there is a disproportionate increase in the cross-sectional area of the rat LMCA with respect to LV mass changes with aging. This finding presumably reflects adaptation of this vessel to elevated resistances further downstream in the coronary circulation so that tissue perfusion can be maintained.(ABSTRACT TRUNCATED AT 250 WORDS)