The Impacts of ACE Activity according to ACE I/D Polymorphisms on Muscular Functions of People Aged 65

Abstract

Objective: To investigate associations between angiotensin-converting enzyme (ACE) polymorphisms and muscle fatigability in 65-year-old Koreans.

Method: The study participants were 49 Koreans aged 65 years. ACE insertion/deletion (I/D) polymorphisms were determined by polymerase chain reaction and serum ACE activity, by spectrophotometry. Body mass index (BMI), body fat mass (BFM), and lean body mass (LBM) were determined. To evaluate muscle fatigability, dynamic Electromyography was used to measure maximum voluntary isometric contractions (MVICs) of ankle plantar flexor muscles. Patients were seated with their hips flexed at 90°, knees fully extended, and ankles at 0°. Continuous submaximal VICs (40% MVIC) were then performed, and contraction duration and EMG frequency changes during the initial 2 min were measured. A self-reported physical activity questionnaire was used to evaluate effects of ACE activity levels on muscle fatigability.

Results: Among the 49 volunteers, 15 showed II genotype; 22, ID genotype; and 12, DD genotype. Serum ACE activity levels were significantly higher in DD genotype subjects than in II genotype subjects (p<0.05). Furthermore, the duration of submaximal isometric contractions was longer in II and ID genotype subjects than in DD genotype subjects (p<0.05). Dynamic EMG showed significantly lower mean frequency changes in II genotype subjects than in DD genotype subjects (p<0.05). However, LBM, BFM, and BMI were independent of ACE genotypes.

Conclusion: ACE II genotype subjects showed significantly higher resistant to muscle fatigue than that by DD genotype subjects. However, body composition and BMI showed no correlations with ACE I/D polymorphisms.

Keywords: Angiotensin converting enzyme; Body composition; Muscle fatigue; Polymorphism.

Fig. 1

Detection of I/D polymorphism of the angiotensin-converting enzyme gene in 2% agarose gel electrophoresis (M-size marker, II type: 29, 36, 38/ID type: 26, 28, 30, 32, 33, 35, 37/DD type: 23, 24, 34).

Fig. 2

Experimental design for measurement of fatigability. (A) Experimental protocol. After a 5 min warm up (W) exercise and a 5 min rest period, the maximal voluntary contraction (MVC) of plantar flexion was evaluated. Three full plantar flexion (C) efforts of 3 s duration were performed, separated by 10 s rest (R) periods. Next, after a 5 min rest period, the subject was required to maintain a submaximal isometric plantar flexion at 40% of the MVC until exhaustion (E). (B) Apparatus used for determination of MVC (1) and submaximal isometric contraction (2) of plantar flexor muscles. (1) Subjects were strapped in a sitting position on an examination chair and performed plantar flexions in the right limb at full force. (2) Assessments of the maintenance of fixed submaximal force output were performed on the same apparatus, but with plantar flexion in both limbs. Subjects observed their efforts on a digital voltmeter and attempted to maintain the output from the wall as close as possible to 40% of MVC.

Fig. 3

Muscle endurance and handgrip strength in different ACE genotypes in the whole group.

Fig. 4

Endurance time and frequency change according to ACE polymorphism in the gender division. There was a significant difference between the 3 ACE genotypes by Kruskal-Wallis test (Endurance time: p=0.001, frequency change: p=0.031). The endurance time of the II genotype was significantly longer than that of the DD genotype in males alone, and in all subjects together (p<0.05/3) (A, C, E). The frequency change of the DD genotype was significantly greater than that of the II genotype in males alone, and in all subjects together (p<0.05/3) (B, D, F). However, frequency change in the ID genotype was not statistically different from the II and DD genotypes, although the median value was different among the 3 genotypes. Data are presented as box-plots, where the horizontal line represents the median value.