Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC201
The influence of bradykinin receptor B2 genetic variation on voluntary fluid intake and fluid balance
A. Yau1, A. Moss1, L. J. James2, J. J. Ashworth1, G. H. Evans1
1. School of Healthcare Science, Manchester Metropolitan University, Manchester, United Kingdom. 2. School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom.
The regulation of fluid within the human body is vital for normal physiological and psychological function. Thirst is a strong predictor of voluntary fluid intake, and bradykinin, a component of the kallikrein-kinin system, has been shown to be dipsogenic. Allelic variation of the bradykinin receptor B2 (B2R) gene on which bradykinin exerts its effect, is associated with differences in receptor activity. The homozygous wild type (MM) genotype is associated with greater receptor activity than the heterozygous insertion (MP) and the homozygous insertion (PP)  thus theoretically promoting greater thirst sensation. Previous research with ultra endurance athletes has associated the B2R allelic variant with greater percentage body mass loss (BML) during competition . The purpose of this study was to investigate the influence of B2R genetic variation on voluntary fluid intake and fluid balance in healthy males during moderate intensity exercise. Forty-five healthy Caucasian males aged 18-45 yr completed 60 minutes of cycle exercise at (mean ± S.D) 62 ± 5% VO2max in a room heated to 30.5 ± 0.3°C. Fluid was provided ad libitum during the cycle. Venous blood samples were collected pre, mid, and immediately post-cycle. Fluid intake, BML and sweat loss were recorded. Heart rate, oxygen uptake, ratings of perceived exertion and subjective feeling of thirst were measured at regular intervals. All participants were genotyped for the B2R nine base pair repeat insert sequence within exon one using polymerase chain reaction and gel electrophoresis (MM, n= 13; MP, n= 17; PP, n= 15). No significant differences between genotypes were found with mean voluntary fluid intake (MM: 599 ± 322 mL; MP: 745 ± 374 mL; PP: 870 ± 459 mL, P= 0.20; one-way ANOVA), percentage BML (MM: 0.50 ± 0.49%; MP: 0.41 ± 0.64%; PP: 0.37 ± 0.77%, P= 0.87; one-way ANOVA), or sweat loss (MM: 986 ± 254 mL; MP: 1089 ± 401 mL; PP: 1195 ± 521 mL, P= 0.41; one-way ANOVA). Mean serum osmolality and plasma volume over time were also not significantly different between genotypes (interaction P= 0.42 and P= 0.69, respectively; two-way mixed ANOVA). Mean thirst perception in the PP group, on the other hand, was significantly higher (P<0.05; two-way mixed ANOVA) than both MM and MP genotypes at 30, 45 and 60 minutes. This significantly higher thirst perception and slight trend of greater fluid intake with lesser percentage BML in the PP group were the reverse of what was hypothesised. These data suggest that voluntary fluid intake and fluid balance in healthy male participants undertaking 60 minutes of moderate intensity exercise in the heat are not predominantly influenced by B2R genetic variation. Differences in subjective feelings or perception of the exercise environment may play an influential role in determining thirst and fluid intake during exercise.
Where applicable, experiments conform with Society ethical requirements