Significance of renin-angiotensin system during and after surface-induced simple hypothermia in open-heart surgery.

The present studies were performed to investigate the metabolic role of the lungs in the renin-angiotensin system under hypothermia by measuring plasma renin activity, plasma angiotensin I (A I), plasma angiotensin II (A II), plasma aldosterone and plasma angiotensin converting enzyme activity on 14 patients who underwent open-heart surgery with surface-induced simple hypothermia. In addition, dog experiments were performed, in which changes of renal blood flow and angiotensin metabolism in lungs and kidneys under hypothermia were studied in vivo. The following results were obtained: 1) During and after open-heart surgery with surface-induced simple hypothermia, the homeostasis in the renin-angiotensin system is still maintained. 2) An increase of A II may play an important role in maintaining blood pressure under hypothermia. 3) Under hypothermia, the conversion of A I to A II in the kidneys may contribute to an increase of plasma A II.