Baroreflex sensitivity during the development of spontaneous hypertension in rats.

1. Baroreflex sensitivity was studied in relation to the development of spontaneous hypertension in rats (SH rats), with normotensive Wistar-Kyoto (WKY) rats as controls. Conscious, freely moving animals were studied at different times, ranging from 4 to 20 weeks after birth. 2. The youngest SH rats (4-6 weeks; n = 10) already had significantly (P less than 0.01) higher mean arterial blood pressure (112 +/- 2 mmHg) than WKY rats of corresponding age (95 +/- 4 mmHg; n = 10). Baroreflex sensitivity did not differ at this age (0.37 +/- 0.04 vs 0.38 +/- 0.05 ms/mmHg). 3. Mean arterial pressure increased rapidly in SH rats during further development, reaching a value of 166 +/- 3 mmHg in 12-20 week old animals (n = 25). In equally old WKY rats blood pressure was significantly (P less than 0.001) lower (110 +/- 6 mmHg, n = 25). Baroreflex sensitivity did not change during development of SH rats (0.40 +/- 0.03 ms/mmHg in 12-20 weeks old SH rats), whereas it increased two- to three-fold in WKY rats (0.93 +/- 0.08 ms/mmHg, P less than 0.001). 4. It is concluded that an increase in baroreflex sensitivity is part of the development of a normotensive cardiovascular system, whereas in SH rats responsiveness of the baroreceptor reflex remains depressed during the development and stabilization of hypertension.