Abstract
Central nervous interactions between baroreceptor and chemoreceptor control mechanisms were studied by many researchers (reviewed by Iriki and Korner, 1979) . But the central interaction between baroreceptor control and thermoregulation has not yet been investigated precisely, in spite of the precise investigation about the responses of regional circulation and of undergoing regional sympathetic nervous activities to thermal stimulations. This experimental series was aimed to elucidate the central interaction of circulatory and thermal regulatory mechanisms.
Methods: Renal sympathetic nerve activity (RSNA) of unanesthetized rabbits was recorded using chronically implanted electrode. The integrated activities in every 2 seconds, simultnaeously recorded with direct recording, were used for the indicator of the RSNA. The mean arterial pressure (MAP) was elevated or fallen 5, 10 and 20 mmHg from resting MAP by means of previously implanted aortic and vena caval perivascular balloons. Rectal and ear temperatures were recorded simultaneously.
The RSNA baroreflex curve was estimated by the response of RSNA to the change of MAP in neutral (25°C), cold (15°C) and warm (35°C) environments. The condition of cold environments was selected when the ear cutaneous vessels were constricted but no shivering could be detected, and in warm environments the ear cutaneous vessels were markedly dilated but no significant increase of respiratory rate (panting) was presented. Renal sympathetic baroreflex functions in various conditions were compared by the calculating of median arterial pressure, RSNA range and reflex gain of the renal baroreflex curves.
Results and discussions: Within the zone of vasomotor control of physical thermoregulation, i. e. the zone without shivering or panting, the resting MAP in warm environments was lower than that of cold, and no signifcant difference of RSNA at resting MAP at both conditions could be detected. Concerning the parameters of RSNA baroreflex curves, all three curve parameters in warm condition were significantly lower than those in cold. That means the existence of significant central interaction on renal sympathetic motoneuron pool between baroceptor inputs and thermal inputs. Warm receptor inputs have inhibitory effect on the central interaction.
When the panting was presented in hot environments, the central interaction of both inputs on the baroreflex control of RSNA was also significant, but its direction was contraverse to those in warm environments without panting. It could be clarified by the increase of all three curve parameters in hot comparing those in cold.
