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 l eft main coronary artery (LMCA) in young (Y - 5 months) and old (O - 2 7.5 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 w orkload of 15% grade, 1 hr/day, 5 d/wk at speeds of 36 and 15 m/min fo r the Y and 0 rats, respectively. Aging resulted in a 40% increase in left ventricle (LV) weight which was proportional to the increased bod y weight of the old animals. Exercise training produced a mild (approx imately 10%) but significant left ventricular hypertrophy (LVH) in bot h trained groups. Cross-sectional area of the LMCA lumen and wall, wal l thickness, and areas of collagen (C), elastin (E), and collagen-to-e lastin ratio (CIE) of the LMCA wall were determined morphometrically i n all four groups. A method for pinpointing the coronary ostium for us e as a reference point was also developed. LMCA lumen area almost doub led (p < .001) across the measured age difference, but was unaffected by training. With aging, the increase in LMCA wall area bordered on si gnificance (p < .053), while wall thickness, C area, and the CIE 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 adaptatio n of this vessel to elevated resistances further downstream in the cor onary circulation so that tissue perfusion can be maintained. However, exercise training-induced LVH in either age group does not result in any additional increase in lumen size of the LMCA.