Impaired arterial baroreceptor reflex and cardiopulmonary vagal reflex in conscious spontaneously hypertensive rats.

The activity of baroreceptor reflexes and cardiopulmonary reflexes was examined in conscious spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) rats. The baroreceptor heart rate reflex, elicited by phenylephrine- and nitroprusside-induced changes in blood pressure, had a reduced range and lower heart rate plateau in SHR than in WKY rats, which suggests impaired vagal control of the heart rate in SHR. Cardiopulmonary receptor reflex activity was assessed by intravenous injections of phenyldiguanide which evoke the Bezold-Jarisch reflex. Phenyldiguanide elicited dose-dependent bradycardic and hypotensive responses in WKY rats, but these were significantly attenuated in SHR. This is the first demonstration of impaired Bezold-Jarisch responses in conscious SHR and provides evidence of both impaired vagally mediated arterial baroreceptor activity and impaired cardiopulmonary receptor activity in this rat strain.