PHENYL BIGUANIDE DOES NOT INHIBIT LOCOMOTION IN CONSCIOUS RABBITS

Stimulation of cardiopulmonary vagal C fibers with phenyl biguanide (P BG) reflexly inhibits locomotion in addition to causing depression of blood pressure (BP), heart rate (HR), and respiration in cats and rats . We investigated whether PEG caused somatomotor inhibition during exe rcise in the rabbit, a species in which it is known that the hemodynam ic and respiratory responses to PEG are mediated by cardiac rather tha n by pulmonary receptors. In eight New Zealand White rabbits, BP, HR, and hindlimb electromyographic (EMG) responses to 60 and 120 mu g/kg P EG and saline vehicle were evaluated during two separate S-min exercis e bouts at 10 m/min at 0% grade. During exercise, 60 mu g/kg PEG decre ased BP (-27 +/- 4 mmHg) and HR (-95 +/- 16 beats/min) but did not inh ibit locomotion as suggested by the EMG response (+112 +/- 8% of prein fusion EMG). Hemodynamic and EMG responses to 120 mu g/kg PEG were sim ilar to 60 mu g/kg PEG. Saline infusion during exercise had no effect on HR, BP, or locomotion(+114 + 8% of preinfusion EMG). Locomotion is not inhibited by PEG in rabbits, which suggests that PBG-induced refle x somatomotor inhibition observed in other species is primarily mediat ed by pulmonary rather than by cardiac receptors.