Central and Baroreflex Control of Sympathetic Nerve Activity to the Heart and Kidney in a Daily Life of the Cat

Abstract

We measured simultaneously and continuously the sympathetic nerve activity to the heart (CSNA) and kidney (RNA) together with heart rate (HR) and arterial blood pressure (AP) in conscious cats. The time course and magnitude of their responses to behavioral stimuli and norepinephrine iv administration were analyzed quantitatively. The increases in CSNA and RNA occurred almost simultaneously with the onset of standing, walking or eating behavior. The abrupt increases in CSNA and RNA were not preceded by a decrease in AP so it was unlikely to have been a reflex initiated by baroceptors. Rather, the increases in CSNA and RNA were followed by increases in HR and AP. The lag time ranged from 2 to 10 sec. Relative response magnitude of CSNA differed significantly from that of RNA. Thus, when AP increased spontaneously by behavioral stimuli, there was always preceding nonuniform increases in CSNA and RNA. On the other hand, when AP was elevated by norepinephrine iv administration, CSNA and RNA were inhibited proportionally to a rise in AP due to baroreflexes. At rest, the baroreflex effect on CSNA was greater than that on RNA. Cardiac-related discharges of CSNA and RNA, which were induced reflexly by baroceptor input, occurred dominantly at rest. However, with excitement or at the onset of body movements, they were diminished significantly. Our results suggested that AP adjustment associated with various behavior was made directly by a nonuniform central activation of the sympathetic nerve activity to the heart and blood vessels and partly by a central modulation of the baroceptor input.