title: Factors confounding blockade of cardiac afferents by intrapericardial procaine in conscious rabbits.
abstract: Intrapericardial procaine has been used by several groups to block cardiac afferent nerves to study effects of cardiogenic reflexes. In eight conscious rabbits, procaine (17-113 mg ipc; median 32) blocked cardiac efferents. Procaine (17-113 mg ipc; median 39) abolished the reflex depressor effects of the cardiac C-fiber excitant 1-phenylbiguanide (PBG), and in four of eight rabbits prevented the hypotensive phase 2 of acute central hypovolemia, which has been attributed to a signal from the heart. However, in three of the rabbits respiratory incoordination and blood gas abnormalities developed. In another study of four rabbits, procaine (165-335 mg ipc; median 235) invariably caused phrenic nerve blockade and underventilation. In three rabbits, after intrapericardial (250 mg) or subcutaneous (50 mg) procaine, plasma procaine levels rose to 9.4 and 4.8 micrograms/ml, respectively. During intravenous infusion of procaine, the PBG chemoreflex was abolished at plasma levels > 3.1 micrograms/ml, and phase 2 of acute hypovolemia at levels > or = 4.3 micrograms/ml. There is a narrow margin between a dose of intrapericardial procaine that blocks cardiac nerves and one that can produce confounding effects from phrenic nerve blockade or absorption into the bloodstream.
authors.affiliation: Department of Surgery, University of Melbourne, Victoria, Australia.
authors.forename: R G
authors.initials: RG
authors.lastname: Evans
authors.forename: I P
authors.initials: IP
authors.lastname: Hayes
authors.forename: J
authors.initials: J
authors.lastname: Ludbrook
authors.forename: S
authors.initials: S
authors.lastname: Ventura
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D006324:Heart Arrest, Induced; D006329:Heart Conduction System / Q000187:drug effects*; D006470:Hemorrhage / Q000503:physiopathology; D007267:Injections; D007275:Injections, Intravenous; D007279:Injections, Subcutaneous; D009475:Neurons, Afferent / Q000187:drug effects*; D010496:Pericardium; D011343:Procaine / Q000008:administration & dosage / Q000494:pharmacology*; D011817:Rabbits; D012121:Respiration, Artificial
chemical_list: D011343:Procaine