The effect of small doses of antidiuretic hormone on renal excretion of sodium and water in saline loaded acutely hypophysectomized rats.

Small doses of vasopressin (200 micronU min-1 kg-1) did not influence the loss of ability of acutely hypophysectomized rats to react by natriuresis to the extracellular fluid volume expansion with saline, inspite of restoring their arterial blood pressure to normal. It is concluded that the level of antidiuretic hormone efficient enough to concentrate urine is not a decisive factor in the homeostatic mechanism promoting the 'volume' natriuresis.