CENTRAL INJECTION OF PHYSOSTIGMINE ATTENUATES EXERCISE-INDUCED PRESSOR-RESPONSE IN CONSCIOUS CATS

The effects of intracerebroventricular administration of physostigmine , a cholinesterase inhibitor, on the cardiovascular responses evoked b y static voluntary exercise were investigated using conscious cats. Fo ur cats were trained to press a bar (200-650 g) with one forelimb for at least 20 s. The changes in mean arterial pressure (MAP), heart rate (HR), and developed force during the first five trials in 30 min by e ach individual cat were averaged, and a mean of the four values was th en calculated. After the cats exercised for 30 min, either artificial cerebrospinal fluid (CSF) or physostigmine (5 mu g) was administered i ntracerebroventricularly. Before physostigmine, exercise trials by the cats increased MAP and HR by 17 +/- 3 mmHg and 42 +/- 4 beats/min, re spectively. Administration of physostigmine did not alter the resting MAP and HR but attenuated the MAP and HR responses to exercise (5-30 m in postphysostigmine: MAP = 8 +/- 3 mmHg, HR = 25 +/- 7 beats/min; 30- 60 min postphysostigmine: MAP = 4 +/- 3 mmHg, HR = 19 +/- 8 beats/min) . Intracerebroventricular administration of CSF had no effect on the c ardiovascular responses to static exercise. Pretreatment with the musc arinic antagonist, atropine (25 mu g icv), blocked the attenuating eff ects of subsequent intracerebroventricular administration of physostig mine. These results demonstrate that stimulation of central muscarinic receptors attenuates the cardiovascular responses to static exercise by conscious cats. In addition, the present study suggests that there is no tonic effect of central muscarinic receptors on the cardiovascul ar responses to voluntary exercise.