Abstract

Angiotensin I-converting enzyme (ACE) plays a pivotal role in whole body fluid balance and the degradation of bradykinin. A common allelic variant with a 287 base pair insert has been identified on the ACE gene. The homozygous insertion genotype (II) corresponds with lower basal serum ACE concentrations compared to the heterozygous (WI) and homozygous wild type genotypes (WW). Higher circulating levels of ACE may decrease vasodilation; affecting blood flow and sweat loss during exercise. A genotype-independent rise in ACE activity following 20 min of exercise has been reported, but the response to prolonged exercise is unknown. The aim was to examine the influence of ACE genotype on the serum ACE response to exercise in the heat. Healthy Caucasian males (n=45, 18–45 y) completed 60 min of cycle exercise at (mean ± SD) 62 ± 5% VO_2max in 30.5 ± 0.3°C, with fluid ad libitum. Fluid intake and sweat loss were recorded. Venous blood samples were drawn pre, mid, and postexercise for the determination of serum ACE concentration and ACE genotype. Basal serum ACE concentrations were dependent on ACE genotype (WW: 215 ± 57 ng.ml^-1; WI: 158 ± 28 ng.ml^-1; II: 106 ± 29 ng.ml^-1, P<0.001). Serum ACE concentrations increased at 30 min of exercise to 231 ± 55 ng.ml^-1, 166 ± 29 ng.ml^-1 and 115 ± 30 ng.ml^-1 for WW, WI and II, respectively (P<0.001), and remained elevated post exercise. Serum ACE response was not influenced by ACE genotype (P= 0.321). No differences were found for mean fluid intake (WW: 613 ± 388 ml; WI: 753 ± 385 ml; II: 862 ± 421 ml, P= 0.31), or sweat loss (WW: 1013 ± 257 ml; WI: 1048 ± 254 ml; II: 1257 ± 675 ml, P= 0.28). Serum ACE concentration increased independently of ACE genotype within 30 min exercise at 30.5°C. Coupled with the lack of genotype effect on sweat loss and fluid intake, these results suggest ACE genotype plays little role in fluid balance during exercise.