Studies of cardiovascular responses to some endogenous pressor and hypotensive agents in conscious stroke-prone spontaneously hypertensive rats of different ages.

The effects of the endogenous pressor agents noradrenaline (NA), and angiotensin II (Ang II), and of the hypotensive agents acetylcholine (ACh) and adenosine (ADS), on blood pressure and heart rate in conscious and unrestrained stroke-prone spontaneously hypertensive rats (SHR-SP) and normotensive Wistar Kyoto rats (WKY) of different ages (4-9 weeks old) were investigated. Pressor responses to NA were enhanced in 7- and 9- week-old SHR-SP compared with those in WKY, but pressor responses to Ang II in SHR-SP were not different from those in WKY at all ages. The bradycardias following pressor responses to NA and Ang II were markedly attenuated in SHR-SP, especially older ones. Hypotensive responses to ACH were enhanced in SHR-SP, particularly at 9 weeks of age. However, hypotensive responses to ADS were attenuated in SHR-SP, especially at 7 weeks of age. Transient fall of heart rate due to ADS was also attenuated in 7- and 9- week-old SHR-SP. These alterations of hemodynamic or cardiovascular responses in SHR-SP became more evident in the established stages of hypertension. These results suggest intimate relationships of the enhanced pressor responses to NA, attenuated bradycardias following pressor effects with NA or Ang II, and the attenuated hypotensive responses to ADS with the development or the maintenance of hypertension in SHR-SP.