Ascorbic acid does not affect the age-associated reduction in maximal cardiac output and oxygen consumption in healthy adults

Maximal aerobic capacity ((V) over dot O-2 max) decreases progressively with age, primarily because of a reduction in maximal cardiac output ((Q) over dot (max)). This age-associated decline in V. O2 max may be partially mediated by the development of oxidative stress that can suppress beta-adrenergic-receptor responsiveness and, consequently, reduce (Q) over dot(max). To test this hypothesis, (V) over dotO(2 max) ( indirect calorimetry) and (Q) over dot(max) (open-circuit acetylene breathing) were determined in 12 young ( 23 +/- 1 yr, mean +/- SE) and 10 older ( 61 +/- 1 yr) adults following systemic infusion of either saline ( control) and/or the powerful antioxidant ascorbic acid ( acute: bolus 0.06; drip 0.02 g/kg fat-free mass) and following chronic 30-day oral administration of ascorbic acid ( 500 mg/day). Plasma ascorbic acid concentration was not different between young and older adults and was increased similarly, independent of age [ change (Delta) acute = 1,055 +/- 117%; Delta chronic = 62 +/- 19%]. Oxidized low-density lipoprotein concentration was greater ( P < 0.001) in older ( 57 +/- 5 U/l) compared with young ( 34 +/- 3 U/ l) adults and was reduced in both groups ( P < 0.02) following acute ( Delta = - 6 +/- 2%) but not chronic ( P = 0.18) ascorbic acid administration. Control ( baseline) (V) over dot O-2 max and (Q) over dot(max) were positively related ( r = 0.76, P < 0.001) and were lower ( P < 0.05) in older ( 34 +/- 2 ml . kg(-1) . min(-1); 16.1 +/- 1.1 l/min) compared with young (43 +/- 3 ml . kg-1 . min(-1); 20.2 +/- 0.9 l/min) adults. Following ascorbic acid administration, neither (V) over dot O-2 max ( young acute = 41 +/- 2; young chronic = 42 +/- 2; older acute = 34 +/- 2; older chronic = 34 +/- 2 ml . kg(-1) . min(-1)) nor (Q) over dot (max) ( young acute = 20.1 +/- 0.9; young chronic = 19.1 +/- 0.8; older acute = 16.2 +/- 1.1; older chronic = 16.6 +/- 1.4 l/min) was changed. These data suggest that ascorbic acid administration does not affect the age-associated reduction in (Q) over dot(max) and (V) over dot O-2 max.