Modified Characteristics of the Aortic Baroreceptor Activities in the Spontaneously Hypertensive Rat

The characteristics of the aortic baroreceptor reflex activities in the Spontaneously Hypertensive Rat (SHR) were studied by electrophysiological approach-es. After systemic blood pressure was reduced by hyperventilation to a sufficiently low level (50 to 60mmHg), mixture solution of noradrenaline and angiotensin was infused intravenously so that a variety of systemic blood pressure levels which caused a full range of the. aortic baroreceptor firing could be obtained. The aortic baroreceptor activities were. recorded simultaneously with systemic blood pressure, and the firing rates of the former were. plotted against the various levels of the latter. These experimental procedures were carried out both on SHR and control rats, and the results were compared between the two groups. The results could be summarized as follows. 1. The mean blood pressure-firing rate curve in SHR showed a shift to the higher blood pressure level. 2. The range of blood pressure within which the aortic baroreceptors showed a response was significantly expanded in SHR in comparison with controls. 3. Natural blood pressure in SHR was above the value which was postulated to represent the greatest reflex producing point of the mean blood pressure-firing rate curve, while in controls their normal blood pressure was below or around the point. These findings indicate that the aortic baroreceptor function in SHR was reset to the higher blood pressure. Besides, it is suggested that SHR will not be favoured with so effective a buffer action of baroreceptors as in controls against an abnormal blood pressure-raising disturbance such as stress.