Sodium and fluid balance during hypotensive response to alpha-methyldopa.

1. Detailed observations on sodium and fluid balance during treatment with alpha-methyldopa were made in five hypertensive patients. The initial fall in blood pressure concurred with a decline in fluid and sodium excretion. Sodium balance increased 100-300 mEq. In one patient with serve hypertension the sodium balance was incompletely restored, the relationship with blood pressure indicating a negative feedback loop. In the other patients sodium balance reverted to baseline, while the hypotensive response was maintained. This is probably due to a decrease in renal arteriolar tone. 2. Parallel systemic and renal vasodilatation may account for the discrepancy between a significant increase in blood volume and insignificant long-term changes in the fluid and sodium status.