alpha 1-adrenoceptor stimulation is able to reverse halothane-induced cardiac depression in isolated rat hearts.
BACKGROUND
Stimulation of myocardial alpha 1-adrenoceptors has been shown to exert positive inotropic effects through a cyclic AMP-independent mechanism. The purpose of this study was to examine if alpha 1-adrenoceptor stimulation is able to attenuate myocardial depression produced by exposure to halothane, and to test if alpha 1-adrenoceptor stimulation alters myocardial oxygen supply-demand balance in hearts exposed to halothane.


METHODS
The effects of phenylephrine were examined in 7 isolated perfused rat hearts. Variables measured were: heart rate, isovolumetric peak left ventricular pressure (LVP), LV dP/dt, coronary arterial flow, myocardial O2 delivery (DO2), myocardial O2 consumption (MVO2) and the ratio of DO2/MVO2. Each heart was exposed to phenylephrine cumulatively 0.1 microM, 0.3 microM, 1 microM and 3 microM under the administration of 1% halothane in the presence of propranolol 1 microM.


RESULTS
Halothane 1% decreased the heart rate by 9 +/- 3%, LVP by 37 +/- 3%, and LV dP/dt by 35 +/- 2%. Phenylephrine restored these decreases to the baseline levels. Phenylephrine maintained or further enhanced the reductions in coronary flow and DO2 produced by halothane, resulting in a decrease in the DO2/ MVO2 ratio.


CONCLUSIONS
alpha 1-adrenoceptor stimulation is capable of restoring direct cardiac depressant effects of halothane with a possible impairment of the oxygen supply-demand balance.
Okuyama
T
T
Department of Anesthesiology and Critical Care Medicine, Kyuslm University, Japan.
Hoka
S
S
Okamoto
H
H
Kawasaki
T
T
Yamaura
K
K
Takahashi
S
S
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003326:Coronary Circulation / Q000187:drug effects; D003864:Depression, Chemical; D006221:Halothane / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*
D018685:Anesthetics, Inhalation; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine; D002118:Calcium; D006221:Halothane