Role of renin in adaptation to sea water in euryhaline fishes.

The role of the renin-angiotensin system as an aldosterone stimulating factor in the mammal is well-established (1, 2). A high salt intake diminishes the demand to conserve sodium in the body, and the secretion of aldosterone is decreased by the control of renin angiotensin system. Decreased renin activity on a high salt diet has been shown in the mammal (3-5). In 1942, Friedman, Kaplan, and Williams found the absence of renin in the kidney of marine fish, but detected it in the fresh water fish (6). If this be true, renin-angiotensin would play a role in salt adaptation of the fish. We kept Japanese eels in both fresh and sea water for 3 to 11 weeks, and determined the renin content of the kidney, to see if eury halinity is controlled by renin in eels. We found a decrease in renin of those kept in sea water, and suggested that the renin-angiotensin system plays a part in salt adaptation (7). The purpose of this paper is to give details of these studies on Japanese eels and other euryhaline fishes adapted to sea water.