Restoration of sodium balance in hypophysectomized rats after acute sodium deficiency

Abstract

Like intact rats, hypophysectomized (hypex) rats showed appropriate increases in thirst and sodium appetite when they became sodium deficient following subcutaneous formalin treatment. Decreased water and sodium losses in urine permitted renal retention of ingested fluids and restoration of intravascular fluid volume and sodium concentration. The only apparent effect of hypophysectomy was to decrease the rate of saline intake. Consequently, hypex rats remained hypovolemic longer (11–20 hr) than did intact rats (6–10 hr). Urinary potassium/sodium ratios suggested that aldosterone levels in hypex rats were not increased as much as in intact rats by the formalin treatment. Since both groups of rats increased saline intake when mineralocorticoid levels were increased, it is possible that formalin treatment did not provide as strong a stimulus for sodium appetite in hypex rats as in intact rats. Nevertheless, although pituitary hormones may potentiate sodium appetite and generally defend the animal against stress, it must be concluded that the pituitary gland is not vital to sodium metabolism at either a behavioral or a physiological level.