Isolated blood-bathed tissues which were superfused with renal venous blood during various manipulations of the visceral organs of dogs showed no detectable pharmacologically active substances, except a noradrenaline-like substance which was liberated under some conditions of manipulation. 2. An acetylcholine-like substance was liberated into renal venous blood during experimental manipulation of visceral organs in dogs during infusion of physostigmine; the acetylcholine activity was detected with the dorsal muscle of the leech. 3. The amount of liberated acetylcholine-like substance depended on the strength of visceral stimulation as judged by the changes in the hepatic portal venous pressure. Strong reflex stimulation produced the release not only of acetylcholine but also of noradrenaline. 4. Physostigmine augmented and prolonged the reflexly induced renal vasodilator and diuretic responses, and these were abolished by atropine. It was suggested that the reflex involves a cholinergic nervous mechanism. 5. In some dogs there was a high output of acetylcholine from the kidney during visceral stimulation, and this was accompanied by a decrease in urine flow. The reason was not known. 6. Prostaglandin E1 administered into the renal artery produced similar vasodilator and diuretic responses to acetylcholine, but the onset of the effects were slower and they persisted longer than those produced by acetylcholine.
