Since waterlogging, increased vascular water and sodium contents, could contribute to the development of deoxycorticosterone acetate (DOCA)-salt hypertension, we have examined the effect of dietary potassium supplementation on the water and sodium contents of abdominal aorta after short-term (one week) treatment with DOCA while receiving a 1% NaC1 solution to drink. Supplementation with 1% KC1 solution could counteract the blood-pressure rising action of DOCA-salt, associated with the inhibition of sodium retention. In addition, treatment with DOCA-salt was associated with increases in water (83.1 +/- 3.0% wet weight) and sodium (118.7 +/- 2.8 microEq/g dry weight) contents of the aorta compared with those of the control rats (69.7 +/- 0.3% wet weight and 103.0 +/- 4.0 microEq/g dry weight, respectively). In contrast, 1% KC1 supplementation could attenuate the increase in water (73.2 +/- 1.5% wet weight) and sodium (110.3 +/- 2.3 microEq/g dry weight) contents of the aorta in DOCA-salt rats. Taken together, these results suggest that potassium supplement not only attenuates the sodium retention but also moderates the "waterlogging" in the vascular wall in DOCA-salt rats, thus leading to the antihypertensive action of potassium supplement in the early stage of DOCA-salt hypertension.