PRESSURE NATRIURESIS AND CORTICAL AND PAPILLARY BLOOD-FLOW IN INBRED DAHL RATS

The present study examined whether alterations in papillary blood flow, renal interstitial pressure (RIHP), and the pressure-natriuretic (PN) response are associated with the development of hypertension in inbred Dahl salt-sensitive (Dahl-S) rats. The PN responses were compared in 18- to 20-wk-old, Inactin-anesthetized, inbred Dahl salt-sensitive (S/Jr) and salt-resistant (R/Jr) rats fed a low- (0.3%) and a high- (8.0%) sodium chloride diet. Cortical and papillary blood flows were measured using laser-Doppler flowmetry. Neural and hormonal influences on the kidney were controlled by renal denervation and by fixing plasma norepinephrine, vasopressin, corticosterone, and aldosterone levels by intravenous infusion. The slope of the PN relationship in S/Jr rats maintained on a low-salt diet was 62% lower than that observed in R/Jr rats; however, whole kidney, cortical, and papillary blood flows and RIHP were not significantly different at any perfusion pressure studied. Glomerular filtration rate (GFR) was 25% lower in S/Jr rats than in R/Jr animals maintained on a low-salt diet. The slopes of the PN responses were similar in S/Jr and R/Jr rats exposed to a high-salt diet, but the entire relationship was shifted toward higher pressures by 20 mmHg in the S/Jr rats. Control cortical and papillary blood flows measured at control mean arterial pressures of 126 +/- 3 and 167 +/- 5 mmHg in R/Jr and S/Jr rats, respectively, were not significantly different. However, cortical and papillary blood flows were 25% lower in the S/Jr than in the R/Jr rats exposed to a high-salt diet when compared at equivalent renal perfusion pressures. These results indicate that the PN relationship and GFR are altered before exposure to a high-salt diet in S/Jr rats; however, the resetting of the PN relationship is not associated with changes in renal cortical or papillary blood flow or RIHP.