“…16.21] as well as on NaVK+-ATPase activ ity in the basolateral cell membrane [22,23,31,32], Enhancement ofN a+ reabsorption by these cells stimulated by a steroid hormone such as aldosterone has been found to be correlated with an increase in the activity of NaVK^-ATPase [12]. Enhanced ATPase ac tivity clearly requires an increased delivery of adenosine triphosphate (ATP) produced by mitochondrial enzymes involved in the citric acid cycle and in oxidative phosphorylation [9, 10, 13], Among these enzymes, citrate synthase seems to be a key enzyme which is able to accelerate the cycle [2,[25][26][27][28]33], The activity of the enzyme is decreased in rat and rabbit kidney after adrenalectomy [9,16]; aldosterone administration restores normal activity within 90 min [17,18], Spironolac tone blocks the effect of aldosterone on citrate synthase in this situation after adren alectomy. Although these results suggest that citrate synthase is an aldosterone-induced protein [11], this interpretation has been questioned by others, because in cell mono layer cultures from toad kidney and urinary bladder [6][7][8] aldosterone increases Na+ transport without any detectable change in citrate synthase activity.…”