Correlations and otherwise between blood pressure, cardiac mass and resistance vessel characteristics in hypertensive, normotensive and hypertensive/normotensive hybrid rats.

We have measured heart weight and properties of 150-200 microns mesenteric resistance vessels from spontaneously hypertensive (SHR), Wistar-Kyoto (WKY), two-kidney, one clip Goldblatt renal hypertensive (RHR) and outbred Wistar rats, as well as in SHR/WKY F2-hybrid rats. All rats were 14-weeks-old. In the SHRs, WKYs, RHRs and Wistars the mean blood pressures (measured intra-arterially) were, respectively: 136, 111, 164 and 100 mmHg. In the SHR/WKYs the systolic blood pressures (measured regularly over a two-week period by the tail cuff method) were normally distributed between the values obtained from control SHRs and WKYs. Relative heart weight and resistance vessel media thickness/lumen diameter ratio correlated (P less than 0.001) with blood pressure between SHRs, WKYs, RHRs and Wistars; however, no significant correlation was seen in SHR/WKYs. By contrast, the calcium sensitivity of the resistance vessel noradrenaline response did correlate (P less than 0.01) with blood pressure in the SHR/WKYs, but did not correlate between the pure strains (calcium sensitivity of the SHR and Wistar vessels was similar, but higher than that of the WKY vessels; induction of renal hypertension did not affect calcium sensitivity). The results suggest that although the cardiac enlargement and increased resistance vessel media/lumen ratio of 14-week SHRs may be advantageous for these animals, these structural abnormalities may not be primary causes of the hypertension. Furthermore, the results indicate that it is the WKYs which are abnormal in having a low calcium sensitivity of their resistance vessels, but suggest also that this reduced sensitivity may be associated with mechanisms which help to keep the WKYs normotensive.