EFFECTS OF K-STEROIDS ON NA+, K+-PUMP CONCENTRATION IN SKELETAL-MUSCLE(, MG2+ DEFICIENCY AND ADRENAL)

Animal studies have shown that deficiency of K+ is associated with a r eduction in the concentration of Na+, K+ pumps in skeletal muscle, and that this reduction is closely correlated with the reduction in the m uscle K+ concentration. Furthermore. animals deficient in Mg+ show a d ownregulation oi the Na+, K+-pump concentration. but this seems to be secondary to the concomitant K+ deficiency. which often accompanies Mg 2+ deficiency. Measurements on skeletal muscle biopsies from patients who had been in long-term treatment with diuretics showed that 55% had reduced concentrations of both K+ and Mg2+, and that this was associa ted with a reduction in the concentration of Na+, K+ pumps. Furthermor e. the Na+, K+-pump concentration correlated significantly with both m uscle K+ and Mg2+, suggesting that the downregulation of the Na+, K+ p umps was related to the loss of K+, as predicted from the animal exper iments. In accordance with this. normalization of muscle K+ and Mg2+ i n response to oral Mg2+ supplementation. resulted in a restoration of the Na+, K+ pumps. Apart from thyroid hormone, which is another major regulator for the Na+, K+-pump concentration. other hormones may be of importance. It is well known that adrenal steroids control the synthe sis of Na+, K+ pumps in the kidney and heart. Recently. treatment with dexamethasone was found to increase the Na+, K+-pump concentration in rat skeletal muscle. The increase was found in EDL. soleus. gastrocne mius and diaphragm muscles. and amounted to 23-52%. in contrast. treat ment with aldosterone induced a decrease in the Na+, K+-pump concentra tion. which was closely correlated to the reduced K+ content of the mu scles. The results indicate that in skeletal muscle. high doses of glu cocorticoids upregulate the concentration of Na+, K+ pumps, whereas mi neralocorticoids induce a downregulation which is secondary to the con comitant K+ deficiency.