1. The renal artery was constricted leaving the opposite kidney intact in ten conscious and seven anaesthetized dogs. Intravenous infusion of exogenous renin was done in seven conscious dogs; in four of these the renal artery was constricted 15–17 days later. The following variables were measured in all animals before and after renal artery constriction: plasma renin concentration, blood pressure, cumulative sodium balance, plasma volume, extracellular fluid volume and plasma non-protein nitrogen. Before and after renal artery constriction in the conscious dogs cardiac output, stroke volume, total peripheral resistance and cardiac rate were also measured. In a few dogs angiotensin responsiveness and plasma concentration of renin substrate were also measured.
2. There was no significant difference between the regression of change in blood pressure on change in plasma renin concentration within 2 h from renal artery constriction in the conscious dogs and that observed during intravenous infusion of renin. Comparing the changes of these variables with the ones previously obtained with renal artery constriction to the lone remaining kidney, for a given increase of plasma renin concentration the rise of blood pressure was lower when the contralateral kidney was untouched. The changes of the other variables in the conscious dogs may be divided into three phases: a first phase lasting hours, in which, besides the changes described above, there was an increase of total peripheral resistance while the other variables remain unchanged: a second phase, 24 h after constriction, in which blood pressure, total peripheral resistance and plasma renin clearance decreased while plasma volume, cardiac output and extracellular fluid volume slightly increased; however, only the plasma volume change was statistically significant: and a third phase 6–7 days after constriction, when all the variables returned towards normal values, except that the blood pressure and total peripheral resistance remained significantly higher. Sodium balance remained at equilibrium throughout the study period. It is suggested that these results are compatible with the ‘autoregulation theory’ of renal hypertension.
3. Renal artery constriction in the anaesthetized animals caused a slight but significant sodium retention that very likely influenced the sequence of the events. On the second day after constriction, the plasma renin concentration was significantly increased, whereas the highest values of blood pressure, plasma volume and extracellular fluid volume occurred on the seventh day after constriction.