title: Mechanical efficiency of isolated in situ perfused hearts of the eel Anguilla australis.
abstract: Administration of exogenous Ach to isolated in situ saline-perfused hearts of Anguilla australis via the perfusate, resulted in reduction in cardiac frequency (F). This reduction in F became significant at Ach concentrations of 10(-11) M or greater. A weak inotropic effect of Ach at the lowest concentration tested (10(-13) M) was also observed. Maximum power output of preparations was 2.94+/-0.26 mW gVM(-1). The mechanical efficiency of A. australis hearts working at 25 and 50% of maximum power under different conditions of stroke volume (SV) and F was investigated. Cardiac frequency was manipulated using a combination of temperature and Ach administration. Stroke volume was manipulated by regulating input pressure of the perfusate supplying the preparations (pre-load). Values of MEF from preparations generating flow under conditions of low F/ high SV (treated with Ach 10(-7) M) were significantly greater than under conditions of high F/ low SV (untreated). The MEF of preparations appears to be related to inotropic state. The negative inotropy and increased mechanical efficiency produced by Ach appears to be the opposite of the so-called 'oxygen-wasting' effect produced by the positive inotropic agents, the catecholamines. This effect of Ach may be related to the dependence of teleost myocardium on extracellular Ca(2+) for excitation-contraction coupling during the cardiac cycle.
authors.affiliation: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand. gdavidso@cyllene.uwa.edu.au
authors.forename: G W
authors.initials: GW
authors.lastname: Davidson
authors.forename: P S
authors.initials: PS
authors.lastname: Davie
mesh_terms: D000109:Acetylcholine / Q000008:administration & dosage / Q000494:pharmacology; D000811:Anguilla / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D010101:Oxygen Consumption; D010477:Perfusion; D013318:Stroke Volume
chemical_list: D000109:Acetylcholine; D002118:Calcium