AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 1 393-R399, Copyright © 1997 by American Physiological Society
Central injection of physostigmine attenuates exercise-induced pressor response in conscious cats
A. Ally, G. A. Hand and J. H. Mitchell
Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-9034, USA.
The effects of intracerebroventricular administration of physostigmine, a
cholinesterase inhibitor, on the cardiovascular responses evoked by static
voluntary exercise were investigated using conscious cats. Four 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 each individual cat were
averaged, and a mean of the four values was then calculated. After the cats
exercised for 30 min, either artificial cerebrospinal fluid (CSF) or
physostigmine (5 micrograms) was administered intracerebroventricularly.
Before physostigmine, exercise trials by the cats increased MAP and HR by
17 +/- 3 mmHg and 42 +/- 4 beats/min, respectively. Administration of
physostigmine did not alter the resting MAP and HR but attenuated the MAP
and HR responses to exercise (5-30 min 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 cardiovascular responses to static exercise.
Pretreatment with the muscarinic antagonist, atropine (25 micrograms icv),
blocked the attenuating effects of subsequent intracerebroventricular
administration of physostigmine. 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
cardiovascular responses to voluntary exercise.
