In the previous paper (1), the present authors reported a new perfusion method, in which the kidney of a recipient dog with intact innervation was perfused with the donor's blood using an artificial heart-lung apparatus. That method revealed a good response of renal vessels to various vasoactive substances as well as good hemodynamic conditions for about one hour, following by a gradual increase of renal vascular resistance. Such an increase in renal vascular resistance of the perfused dog kidney was also observed by several investigators (2-5), who used perfusion methods somewhat different from the authors' method. But the mechanism for the increase has been left unclarified. In the present study, it was observed that renin was liberated from the perfused kidney, and angiotensin was produced due to interaction of renin and its substrate in the perfusion circuit. The angiotensin thus formed constricted renal vessels, resulting in an increase in renal vascular resistance.
