Long-term control of renal blood flow: what is the role of the renal nerves?

We have developed a system for long-term continuous monitoring of cardiovas cular parameters in rabbits living in their home cage to assess what role r enal sympathetic nerve activity (RSNA) has in regulating renal blood flow ( RBF) in daily life. Blood pressure, heart rate, locomotor activity, RSNA, a nd RBF were recorded continuously for 4 wk. Beginning 4-5 days after surger y a circadian rhythm, dependent on feeding time, was observed. When average d over all days RBF to the innervated and denervated kidneys was not signif icantly different. However, control of RBF around these mean levels was dep endent on the presence of the renal sympathetic nerves. In particular we ob served episodic elevations in heart rate and other parameters associated wi th activity. In the denervated kidney, during these episodic elevations, th e increase in renal resistance was closely related to the increase in arter ial pressure. In the innervated kidney the renal resistance response was si gnificantly more variable, indicating an interaction of the sympathetic ner vous system. These results indicate that whereas overall levels of RSNA do not set the mean level of RBF the renal vasculature is sensitive to episodi c increases in sympathetic nerve activity.