Pressure natriuresis and angiotensin II in reduced kidney mass, salt-induced hypertension

In normal subjects, high sodium intake causes little change in mean arterial pressure (MAP). However, MAP is sodium sensitive after reduction of kidney mass. The present study examined the role of increased renal artery pressure and decreased angiotensin II (ANG II) formation in maintaining sodium balance during high sodium intake in dogs with reduced kidney mass. In seven dogs with pressure natriuresis intact, increasing sodium intake from 36 to 466 meq/day for 7 days raised MAP from 91 ± 2 to 106 ± 2 mmHg. Sodium excretion increased promptly and cumulative sodium balance increased by only 80 ± 26 meq after 7 days of high sodium intake. When renal perfusion pressure was servo-controlled to prevent pressure natriuresis, comparable increases in sodium intake raised MAP from 88 ± 2 to 128 ± 4 mmHg after 7 days. Sodium excretion rose to match intake, but cumulative sodium balance increased by 226 ± 34 meq after 7 days. In dogs in which ANG II levels were held constant by converting enzyme inhibition and constant ANG II infusion (2 ng·kg^-1·min^-1 iv), raising sodium intake for 7 days elevated MAP from 126 ± 2 to 146 ± 4 mmHg after 7 days while increasing cumulative sodium balance by 212 ± 29 meq. When renal perfusion pressure was servo-controlled and ANG II levels held constant, raising sodium intake elevated MAP from 125 ± 3 to 166 ± 11 mmHg and increased cumulative sodium balance by 399 ± 128 meq. These data indicate that pressure natriuresis and decreased ANG II formation are important in minimizing sodium retention and hypertension during high sodium intake. However, other mechanisms can increase sodium excretion independent of pressure natriuresis and suppression of ANG II during salt-induced hypertension.