BLOOD-PRESSURE AND HEART-RATE DEVELOPMENT IN YOUNG SPONTANEOUSLY HYPERTENSIVE RATS

The course of hypertension development in young spontaneously hyperten sive rats (SHR) was studied by the measurement of changes in systolic blood pressure (BP), body weight, and heart rate (KR) at 2, 3, 4, and 6 wk of age. To achieve this, we compared inbreeding lines of SHR and Wistar-Kyoto rats (WKY) to determine if differences in BP, body weight , or HR were present among inbreeding lines of the same strain or betw een strains. The effect of these differences on the eventual level of BP was then assessed. We found that BP began to diverge between SHR an d WKY at 4 wk of age. Significant differences in systolic BP (24 mmHg) between SHR inbreeding lines at 4 wk of age did not affect the BP at 8 wk (172 vs. 170 mmHg). Pulse pressure was significantly higher in SH R than in WKY at 4 wk of age. HR was elevated in SHR over age-matched WKY at 3 wk of age and positively correlated to the level of BP attain ed by individual animals at 6 wk (P = 0.037). Moreover, WKY inbreeding lines showing elevated HR developed higher BP (145 vs. 127 mmHg) at 1 0-12 and 20 wk of age. The prehypertensive tachycardia in SHR was inve stigated further and found to result from an increased intrinsic HR. B ecause HR at 3 wk is a genetic trait that can be partitioned into inbr eeding lines, and inbreeding lines most expressive of this trait showe d the highest eventual BP, we conclude that prehypertensive tachycardi a may be an important first step during hypertension development in SH R. Moreover, early elevations in HR are highly predictive (r = 0.41) o f hypertension occurrence in the animal population studied.