A tryptophan to arginine (Trp64Arg) mutation in the β₃-adrenergic receptor (β₃ AR) gene was related to an abdominal fat obesity, i.e. visceral fat obesity in Japanease subjects. This study were to investigate the relationships between a Trp64Arg mutation in the β₃AR gene and body composition using ultrasound methods or expiratory gas responses during exercise. Five Trp64Arg heterozygotes (group AT) and 6 normal homozygotes (group TT) men were studied that participated in a maximum graded treadmill test and measured a preperitoneal fat tissue thickness (PFTT) for assessment of visceral fat obesity used to measure the B-mode ultrasound anatomy. A mutation in the β₃AR gene was analyzed by polymerase chain reaction and pin-point sequencing methods. The maximum graded treadmill test using a walking protocol was developed to obtain the ventilatory threshold (VT), performed untill an acute exhaution. Minute oxygen consumption (VO₂) was measured continuously during the maximum graded exercise test. Data were analyzed at rest, VT, and peak time. Statistical analysis demonstrated a significant negative correlation (p<0.05) between PFTT and VO₂max (ml/kg/min) or VO₂@VT (ml/kg/min) in group AT, but not in group TT. It was significant correlation with absolute value of the VO₂@VT (l/min), though PFTT in group AT was no significant correlation with the absolute value of VO₂max (l/min). In addition, PFTT was not signifcantly correlated with resting energy expenditure, but it was significantly correlated with energy expenditure at VT (p<0.05) in group AT. These data suggested that visceral fat obesity in a mutation of the β₃AR gene may be related to the aerobic capacity, and it was especially related to fat consuming capacity during exercise rather than resting energy expenditure. Therefore, a mutation in the β 3AR gene in human may have not became obesity, if they maintained high VT level with a habits of fitness sports or physical exercise.

DESCENTE SPORTS SCIENCE Vol.21/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE