Another suggests that the alkalosis is due to renal compensatory mechanisms used to correct volume loss. Extracellular fluid (ECF) volume contraction is associated with decreased blood volume and decreased renal perfusion pressure. Three compensation mechanisms engage as a result:
renin secretion is increased,
production of angiotensin II is increased, and
secretion of aldosterone is increased.
Increases in angiotensin II cause increased Na+-H+ exchange in the proximal tubule and increased HCO3− (bicarbonate) reabsorption in the proximal tubule due to increased luminal H+. Increased aldosterone secretion stimulates the H-ATPase of alpha-intercalated cells of the collecting duct, which causes 1) increased distal tubule H+ secretion, worsening the metabolic alkalosis, and 2) increased generation of "new" bicarbonate within these same cells, which will be reabsorbed.
Additionally, increased aldosterone secretion causes increased distal tubule K+ secretion, in turn causing the hypokalemia seen with contraction alkalosis. Aldosterone also induces H+-eflux and K+ influx from cells through the K+-H+ exchanger, which could be a possible mechanism for the development of hypokalemia.
Finally, it has been suggested that the term "contraction alkalosis" is actually a misnomer, and that the alkalosis observed during volume contraction is actually attributable entirely to chloride depletion, which leads to a failure of pendrin, a chloride/bicarbonate exchanger in the collecting duct.[3]