Erythrocyte Li⁺/Na⁺ and Na⁺/H⁺ exchange, cardiac anatomy and function in insulin‐dependent diabetics

It has been proposed that an increased activity of cell membrane Na + /H + exchange, mirrored by increased erythrocyte Li + /Na + exchange, may facilitate cell hypertrophy and hyperplasia. Patients with insulin‐dependent diabetes mellitus may develop a specific cardiomyopathy with systolic and diastolic abnormalities and increased thickness of the left ventricle. Therefore, we have investigated the relationships between erythrocyte Li + /Na + and Na + /H + exchange and echocardiographic parameters in 31 male insulin‐dependent diabetics (aged 17–68), in good metabolic control. Three had untreated mild hypertension. In all patients the urinary albumin excretion rate was less than 200 μg min ‐1 . Ten patients had a Li + /Na + countertransport higher than 0.37 mmol 1 ‐1 cell h ‐1 the upper normal limit for our laboratory (0.49 ± 0.10, mean ± SD). In comparison with the patients with normal counter‐transport, they had increased interventricular septum thickness and relative wall thickness (h/r). End diastolic volume and cardiac index were reduced while blood pressure and urinary albumin excretion rate were similar. In the whole study group, interventricular septum thickness was significantly correlated to Li + /Na + exchange ( r = 0.61, P < 0.001) and Na + /H + exchange ( r = 0.35, P <0.05), independently of the effect of age and blood pressure. Posterior wall thickness was correlated to Li + /Na + exchange ( r = 0.38, P <0.05) and h/r to Li + /Na + exchange ( r = 0.41, P < 0.05) and to Na + /H + exchange ( r = 0.44, P <0.05). Li + /Na + exchange was negatively correlated to cardiac index ( r =—0.37, P <0.05). Urinary albumin excretion rate was negatively correlated to posterior wall thickness ( r =— 0.40, P < 0.05) and h/ r ( r =—0.44, P <0.05), and positively to cardiac index ( r = 0.40, P <0.05) and it did not influence the correlations between erythrocyte Na + transport and echocardiographic parameters. An increased activity of the erythrocyte Li + /Na + and Na + /H + exchange may, therefore, indicate high risk of developing cardiac hypertrophy in male insulindependent diabetics. A widespread abnormality of cell Na + /H + exchange is likely to contribute to the development of cardiac hypertrophy and diabetic cardiomyopathy in these patients.