In acute insulin deficiency the absence of its effect on glucose metabolism results in hyperglycemia. The extracellular accumulation of glucose leads to hyperosmolarity. The transport maximum of glucose is exceeded in the kidney so that glucose is excreted in the urine. This results in anosmotic diuresis withrenal loss of water (polyuria), Na+, and K+, dehydration, and thirst. Despite the renal loss of K+, there is no hypokalemia because the cells give up K+ as a result of reduced activity of Na+-K+ -2 Cl–cotransport and of Na+-K+-ATPase. The extracellular K+ concentration, which is therefore more likely to be high, disguises the negative K+balance. Administration of insulin then causes a life-threatening hypokalemia. Dehydration leads to hypovolemia with corresponding impairment of the circulation. The resulting release of aldosterone increases the K+ deficiency, while the release of epinephrine and glucocorticoids exacerbates the catabolism. The reduced renal blood flow diminishes the renal excretion of glucose and thus encourages the hyperglycemia.