The current study was designed to evaluate the role of angiotesin II (ANG II) in the regulation of renin mRNA and angiotensinogen mRNA levels. We investigated the changes in renin mRNA levels in the kidney and angiotensinogen mRNA levels in the liver induced by ANG II infusion and by inhibition of the endogenous renin-angiotensin system with enalapril or saralasin in rats. mRNAs for angiotensinogen and renin were measured by densitometric analysis of Northern blot hybridization. After a 4-h intravenous infusion of ANG II (0.2 micrograms.kg-1.min-1), angiotensinogen mRNA level in the liver increased 2.5-fold to the control level, and renin mRNA level in the kidney decreased by 45%. Four hours after treatment with a single dose of enalapril (3 mg/kg po), angiotensinogen mRNA level in the liver decreased by 50%, and renin mRNA level in the kidney increased 1.5-fold to the control level. These mRNA levels returned to control levels 8 h after treatment. After a 4-h infusion of saralasin (2.5 micrograms.kg-1.min-1) in the low-sodium state, angiotensinogen mRNA level in the liver decreased by 45%, and renin mRNA level in the kidney increased twofold to the control level. These findings suggest that ANG II is one of the factors that regulate angiotensinogen mRNA level in the liver and renin mRNA level in the kidney.