Caloric intake and Na+-K+-ATPase: differential regulation by alpha 1- and beta-noradrenergic receptors

Abstract

This study examined the effects of diet and treatment with noradrenergic receptor antagonists on weight gain and indices of Na+-K+-adenosine triphosphatase (ATPase) activity in the rat. When rats were fed a palatable cafeteria diet, their caloric consumption increased by about 80%, but they did not gain weight significantly. Ouabain binding and K+-p-nitrophenylphosphatase (NPPase) activity were increased in brown adipose tissue and soleus. These indices remained elevated after the rats were returned to a regular diet. When rats were fasted for 3 days, they lost weight, and the indices of Na+-K+-ATPase activity were markedly reduced in brown adipose tissue and soleus. After refeeding the fasted rats gained weight three times more rapidly than nonfasted rats with similar food intake. Indices of Na+-K+-ATPase activity remained as low as they had been when the rats were fasting. There was a consistent negative correlation between weight gain per calorie eaten and brown adipose tissue NPPase activity. Changes in Na+-K+-ATPase could therefore be involved in the effects of overfeeding and fasting on metabolic efficiency. Desmethylimipramine binding was increased by cafeteria diet and decreased by fasting, consistent with changes in sympathetic nervous system activity. Treatment with prazosin, an alpha 1-noradrenergic receptor antagonist, reduced Na+-K+-ATPase in either control or cafeteria diet-fed rats but did not alter the effect of cafeteria diet feeding. By contrast, treatment with propranolol, a beta-receptor antagonist, prevented the increase in Na+-K+-ATPase during cafeteria diet feeding.(ABSTRACT TRUNCATED AT 250 WORDS)