Muscle release of the amino acid 3-methyl-histidine (3MH) is a sensitive index of myofibrillar protein overdegradation (MPO). We hypothesized that patients with chronic heart failure (CHF) could have increased muscle release of 3MH, which in turn reflects MPO, and that serum electrolyte sodium (Na⁺) and potassium (K⁺) levels may be associated with this 3MH muscle release.

Thirty-one overweight outpatients (body mass index, 27 ± 4.4 kg/m²; 22 men and 9 women; age, 56 ± 8.7 y) with clinically stable CHF were studied. After a 24-hour meat-free diet and overnight fasting, patients underwent blood sampling from a cannulated arm vein (V) and concomitantly from the arterial artery (A) to determine plasma 3MH levels and to calculate the A-V difference. Serum levels of Na⁺ and K⁺ in the venous blood were determined, and the Na⁺/K⁺ ratio was calculated. Ten healthy subjects who were matched for gender, age, and body mass index served as controls and underwent the same protocol as the patients with CHF.

The patient group had higher arterial (P = 0.02) and venous (P = 0.005) 3MH levels but a similar A-V 3MH difference (P = 0.28) as compared with the controls. Within the CHF group, 67.7% of patients released 3MH, which resulted in a negative A-V value (P < 0.02 as compared with controls). In patients with CHF, the A-V 3MH difference correlated positively with the serum K⁺ level (r = 0.62; P = 0.0002) and negatively with Na⁺/K⁺ ratio (r = −0.55; P = 0.002). No association was found between the A-V 3MH difference and the Na⁺ level.

The study demonstrated the existence of MPO in resting overweight patients with CHF, thereby suggesting that low serum levels of K⁺ may contribute to MPO.