AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 6 1970-R1975, Copyright © 1994 by American Physiological Society
Intrapericardial blocking agents have extracardiac effects in dogs
S. W. Mittelstadt, K. P. O'Hagan, L. B. Bell and P. S. Clifford
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226.
The purpose of this study was to determine if intrapericardial infusion of
hexamethonium, propranolol, or atropine affected extracardiac receptors in
anesthetized dogs. Intrapericardial hexamethonium (> or = 25 mg)
decreased renal sympathetic nerve activity (RSNA) in a dose-dependent
fashion. After 250 mg, RSNA began to decrease in 65 +/- 7 s. Whereas vagal
stimulation caused a muscarinic receptor-mediated increase in tracheal
smooth muscle tone (as indicated by a 9.6 +/- 1.1 mmHg increase in
endotracheal cuff pressure), the increase in cuff pressure (1.8 +/- 0.4
mmHg) was attenuated after intrapericardial tropine (4 mg). When the ansa
and vagus were stimulated simultaneously, beta-adrenergic receptor-mediated
smooth muscle relaxation opposed the muscarinic receptor-mediated
constriction resulting in an increase in cuff pressure of only 3.6 +/- 0.9
mmHg. After intrapericardial propranolol (8 mg), simultaneous ansa and
vagal stimulation caused a 7.0 +/- 1.6 mmHg increase in cuff pressure,
demonstrating that intrapericardial propranolol blocked beta-adrenergic
receptor-mediated relaxation of tracheal smooth muscle. These results show
that hexamethonium, atropine, and propranolol infused intrapericardially
have extracardiac effects.
