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The present study was performed to investigate the role of type 1A ANG II (A[T.sub.1A]) receptors in regulating sodium balance and blood pressure maintenance during chronic dietary sodium variations in A[T.sub.1A] receptor-deficient (-/-) mice. Groups of A[T.sub.1A] (-/-) and wild-type mice were placed on a low (LS)-, normal (NS)-, or high-salt (HS) diet for 3 wk. A[T.sub.1A] (-/-) mice on an LS diet had high urinary volume and low blood pressure despite increased renin and aldosterone levels. On an HS diet, (-/-) mice demonstrated significant diuresis, yet blood pressure increased to levels greater than control littermates. There was no effect of dietary sodium intake on systolic blood pressures in wild-type animals. The pressure-natriuresis relationship in A[T.sub.1A] (-/-) mice demonstrated a shift to the left and a decreased slope compared with wild-type littermates. These studies demonstrate that mice lacking the A[T.sub.1A] receptor have blood pressures sensitive to changes in dietary sodium, marked alterations of the pressure-natriuresis relationship, and compensatory mechanisms capable of maintaining normal sodium balance across a wide range of sodium intakes. kidney; pressure-natriuresis relationship; angiotensin II; plasma renin concentration; aldosterone