THE CONCENTRATION OF SODIUM,POTASSIUM PUMPS IN CHRONIC OBSTRUCTIVE LUNG-DISEASE (COLD) PATIENTS - THE IMPACT OF MAGNESIUM DEPLETION AND STEROID TREATMENT

Objectives. To evaluate the concentrations of magnesium (Mg), potassiu m (K) and sodium,potassium pumps (Na,K pumps) in skeletal muscle in pa tients with chronic obstructive lung disease (COLD) treated with or wi thout diuretics. Design. An open cross-sectional study. Setting. COLD patients admitted to the Medical Department of Vejle Hospital, Denmark . Subjects. Thirty-six consecutive COLD patients and 23 age- and sex-m atched controls. Main outcome measures. Biopsies of skeletal muscle we re performed in patients and controls for measurements of Mg, K and Na ,K pumps. In a parallel animal experiment the influence of medical tre atment on the concentration of Na,K pumps in skeletal muscle was evalu ated by infusing 10-week-old rats for 14 days with vehicle, terbutalin e, or dexamethasone. Results. In the patients, mean muscle Mg and K co ncentrations were reduced by 22 and 14%, respectively (P < 0.001), but in those patients who received diuretics muscle Mg and K were further reduced (by 31 and 27%, respectively, of the control values). The con centration of Na,K pumps was increased by 31% (P < 0.001), with a maxi mum increase of 61% (P < -0.001) in 12 intensive care patients receivi ng high dosages of glucocorticoids. Linear regression analysis showed a positive correlation between daily glucocorticoid intake and the con centration of Na,K pumps in the biopsy specimens from each patient (r= 0.38, P=0.02). In the experimental study, dexamethasone induced 27-34% increase in the concentration of Na,K pumps (P < 0.01) in three diffe rent muscles, whereas there was no significant change following terbut aline infusion. Conclusions. COLD patients show reduced concentrations of Mg and K in skeletal muscle, associated with an upregulation of th e Na,K pump concentration. It is plausible that this upregulation may be caused by glucocorticoid treatment. The clinical benefits of glucoc orticoids may in part be due to an increase irt the activity and capac ity of the Na, K pump and thereby in a possible enhancement of muscle force.