The role of a renal thirst factor in drinking induced by extracellular stimuli.

1. Rats in normal fluid balance drank water 1-2 hr after complete ligation of the inferior vena cava either above or below the renal veins. At the same time there was a fall in urine flow and excretion of electrolyte, especially after caval ligation above the renal veins, so that the animals ended the initial 6 hr period in positive fluid balance.2. Caval ligation was relatively ineffective as a stimulus to drinking after bilateral nephrectomy, but was effective in rats made anuric by ureteric ligation.3. Rats subjected to caval ligation and offered a choice between water and 1.8% saline (w/v) drank water, despite the increasing hypotonicity of the body fluids thereby resulting.4. During the secondary polydipsia, which generally occurred on about the third day after caval ligation as renal function was recovering, there was an increased preference for 1.8% saline.5. Constriction of the aorta above the renal arteries, or constriction of both renal arteries, also caused drinking, oliguria and the development of positive fluid balance.6. Constriction of the aorta below the renal arteries, or after nephrectomy, was ineffective as a stimulus to drinking.7. Saline extracts of renal cortex caused rats in normal water balance to drink. Activity was destroyed by boiling the extract for 10 min. Renal medullary and hepatic extracts were without effect on drinking.8. It proved impossible to separate dipsogenic and pressor activities of renal extracts during the different stages of fractionation which lead to the production of renin; disappearance of one activity was invariably accompanied by disappearance of the other.9. Dipsogenic and pressor actions were greater in nephrectomized rats than in normal rats.10. Both extractable dipsogenic factor and extractable pressor activity were reduced by treating the rat with DOCA and saline for several weeks beforehand.11. The renal dipsogen therefore has similar properties to renin. It may prove to be identical with renin, particularly in view of the fact that angiotensin also stimulates drinking.12. Adrenalectomy did not affect drinking induced by renin or by caval ligation.13. It is concluded that the renin angiotensin system may play a role in the genesis of the thirst which follows certain extracellular stimuli.