CARDIOVASCULAR AND RENAL NERVE RESPONSES TO STATIC MUSCLE-CONTRACTIONOF DECEREBRATE RABBITS

The purpose of this study was to determine whether the biphasic arteri al blood pressure responses elicited by static muscle contraction of d ecerebrate rabbits are mediated, at least in part, by an initial decre ase and a subsequent increase in sympathetic outflow. Renal sympatheti c nerve activity (RSNA) was used as an index of sympathetic outflow. S tatic contraction of the triceps surae muscle (n = 14) initially decre ased 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 w as 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) a lso 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 a nd 46 +/- 15%). These data suggest that the initial depressor and subs equent presser responses elicited by skeletal muscle contraction and s tretch are mediated, at least in part, by biphasic changes in sympathe tic outflow.