Cardiac sympathetic control of heart excitation rhythm in conscious cats

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In this study we examined whether cardiac sympathetic nerve activity (CSNA) conveys neural information specific for the heart, rather than other organs such as the kidneys. To solve this, we measured CSNA,mean arterial blood pressure (MAP), and heart rate (HR) for 24 hour using freely moving conscious cats in combination with autonomic blockades. CSNA,MAP,and HR were sampled at 400 Hz and their mean values over 6 s were sequentially calculated over a 24 hour period. A multivariate correlation analysis was performed fro the 24-hour data. The frequency distribution histograms of CSNA and HR over a 24 hour period were multimodal, while the distribution of AP was unimodal. CSNA had a significant positive correlation with HR,which was blunted by propranolol but not by atropine. CSNA also had a positive correlation with MAP,whose coefficient (0.3-0.4) was smaller than the relationship between CSNA and HR (correlation coefficient, 0.7). If renal sympathetic nerve activity (RSNA) should be related to changes in renal hemodynamics and/or renal function rather than cardiac function, the relationships between RSNA,HR,and MAP must be changed from the relationships between CSNA,HR,and MAP.IN fact, although RSNA had a significant positive correlation with HR,the correlation coefficient (0.4) was smaller than the relationship between CSNA and HR.In conclusion, cardiac sympathetic nerve activity, which conveys neural information specific for the heart rather than the other organs such as the kidneys, is one of the predominant determinant of cardiac excitation rhythm during a 24 hour period. The sympathetic nervous sytem seems to perform a differential and specific control of the physiological function of individual organs.