Low renal papillary plasma flow in both Dahl and Kyoto rats with spontaneous hypertension

Abnormally low plasma flow to renal papilla characterizes Dahl hypertension. When eating a normal Na diet (0.3% NaCl) both hypertension-sensitive (S) rats and hypertension-resistant (R) rats, 16 weeks old, have fairly normal blood pressure (BP), averaging 144 and 129 mm Hg, respectively. However, even in this barely hypertensive state, 18 S rats had a 31% lower papillary plasma flow (Lilienfield method) than 22 R rats, 19.2 ml/100 g of papilla per min compared to 25.6 (P less than 0.001). When a high (8%) NaCl diet was fed for 7 days, R rats increased papillary plasma flow from 25.6 on 0.3% NaCl to 33.8 on 8% NaCl, a 32% rise (P less than 0.001). S rats increased papillary flow from 20.4 to 24.8, a 22% rise (P less than 0.05). When a high (8%) NaCl diet was fed for 4 weeks, R rats increased papillary plasma flow from 25.7 ml/100 g per min on 0.3% NaCl to 29.5 ml/100 g per min on 8% NaCl, a 15% rise (P less than 0.025). S rats increased papillary flow from 17.7 to 20.0 ml/100 g per min (not significant). S rats on 8% NaCl had a papillary flow 32% lower than R rats on 8% NaCl (P less than 0.001). BP of S rats rose to 162 mm Hg after 4 weeks on 8% NaCl; in R rats, BP did not rise at all. S rats on 0.3% NaCl have a low papillary flow even in a borderline hypertensive state. When challenged with 8% NaCl, R rats increased papillary flow, an adaptation possibly important for the natriuresis. S rats failed to achieve this same high papillary flow. Lacking this adaptation, hypertension may then conceivably occur in S rats to accomplish natriuresis through a "pressure natriuresis" mechanism. Papillary flow also decreased by 11% in 26 Kyoto 17-week-old spontaneously hypertensives (BP, 182 mm Hg) compared to 24 Kyoto normotensives (BP, 118 mm Hg), 29.5 vs 33.2 ml/100 g per min (P less than 0.001). Thus, low papillary flow exists in both hypertensions.