1. Selected organ-ablation experiments were performed in dogs in an attempt to identify the source of the natriuretic hormone postulated to participate in the natriuresis of blood volume expansion.
2. An isolated dog kidney perfused with blood from the femoral artery of deoxycorticosterone-loaded dogs subjected to acute volume expansion with equilibrated blood served as the bioassay system for the natriuretic factor. Four groups were studied after the following procedures: group I, no ablation; group II, thyroparathyroidectomy; group III, hypophysectomy; group IV, adrenalectomy.
3. In all groups, the administration of equilibrated blood promoted a significant increase in sodium chloride excretion in the isolated kidney. The natriuresis was unrelated to changes in glomerular filtration rate, renal blood flow, renal arterial pressure, plasma protein concentration or packed cell volume. In the absence of volume expansion, sodium chloride excretion in the isolated kidney did not change or decreased.
4. These results argue against the thyroid, parathyroid, adrenal and pituitary glands as the source of natriuretic hormone.