Cardiovascular and renal nerve responses to static muscle contraction of decerebrate rabbits

The purpose of this study was to determine whether the biphasic arterial blood pressure responses elicited by static muscle contraction of decerebrate rabbits are mediated, at least in part, by an initial decrease and a subsequent increase in sympathetic outflow. Renal sympathetic nerve activity (RSNA) was used as an index of sympathetic outflow. Static contraction of the triceps surae muscle (n = 14) initially decreased mean arterial blood pressure (MAP) -20 +/- 3 mmHg and heart rate (HR) -15 +/- 5 beats/min (nadir values). After this initial decrease, MAP increased 12 +/- 2 mmHg (peak increase) above baseline and there was a tendency for HR to be elevated (6 +/- 3 beats/min). The changes in RSNA during muscle contraction (n = 6) mirrored the nadir and peak responses of MAP (-50 +/- 9 and 32 +/- 11%). Muscle stretch (n = 11) also evoked similar nadir and peak responses of MAP (-20 +/- 5 and 9 +/- 1 mmHg), HR (-17 +/- 7 and 3 +/- 3 beats/min), and RSNA (-43 +/- 9 and 46 +/- 15%). These data suggest that the initial depressor and subsequent pressor responses elicited by skeletal muscle contraction and stretch are mediated, at least in part, by biphasic changes in sympathetic outflow.