Mechanisms of hypertension during the acute and intermediate phases of the one clip, two kidney model in the dog

The acute and intermediate onset phases of one-clip, two-kidney hypertension were studied in 6 conscious dogs. Mean arterial pressure (MAP), cardiac output (CO), total peripheral resistance (TRP), serum renin concentration (SRC), plasma aldosterone (PA) and cumulative sodium and water balance were studied prior to unilateral renal artery constriction, at 2, 10, an 24 hr postconstriction, and daily thereafter for 5 days. At 2 hr postconstriction, MAP, CO, TRP, and SRC were elevated, with unchanged fluid balance. At 10 and 24 hr there was a further rise in CO accompanied by positive fluid-sodium balance, with a slight decrease in MAP, TRP, and SRC. During days 2 and 3, MAP, CO, TRP, and SRC remained elevated and stable in the presence of decreasing fluid-sodium balance to preconstriction levels. During days 4 and 5, MAP, SRC, and fluid-sodium balance remained unchanged, TRP demonstrated a secondary increase, whereas CO decreased to preconstriction values. Sequential changes in PA parallel those of SRC, but were significant only at 2 hr postconstriction. These changes suggest that the increased CO is not totally dependent on fluid-sodium balance, and that CO is not the sole determinant of elevated MAP. The temporal relation between MAP and SRC throughout the study is consistent with renin-mediated hypertension. The secondary rise of TRP may be due to total body autoregulation and/or increased vascular reactivity to high levels of circulating angiotension. A unitary renin-angiotensin mechanism, therefore, may be responsible for the induction and maintenance of hypertension in this model.