Effects of central stimulation on reflex bradycardia in the spontaneously hypertensive rat.

In order to determine the role of the posterior hypothalamus (PH) in the regulation of blood pressure in the hypertensive state an experimental model was utilized. Bolus intra-aortic administration of noradrenaline elicited a dose-related pressor response and subsequent reflex bradycardia in the awake, freely moving spontaneously hypertensive (SHR), renal hypertensive and Wistar Kyoto rats. The reflex bradycardia was greater in the Wistar Kyoto rats than in the two hypertensive models indicating that there is a decrease in baroreceptor sensitivity in the hypertensive state. PH stimulation elicited pressor and tachycardic responses in each group of animals. Moreover, the reflex bradycardia elicited by infusion of noradrenaline was attenuated during PH stimulation. A greater attenuation of the reflex bradycardia occurs in the SHR compared to the other groups at similar stimulation parameters. Evidence is presented to indicate that the PH may be important in the alteration of baroreceptor sensitivity in the SHR.