The Cardiotoxic Action of the Pyrethroid Insecticide Deltamethrin, the Azole Fungicide Prochloraz, and Their Synergy on the Semi-Isolated Heart of the Bee Apis mellifera macedonica

The contraction of the isolated heart of the bee in physiological solution can be monitored for hours, making this preparation suitable for the investigation of the cardiotoxic action of certain compounds. The results of this study have shown that exposure of the semi-isolated heart of the bee to 1,0.1. and 0.01(mu)M deltamethrin causes a temporal increase in the frequency and the force of spontaneously generated contractions, which is followed by a decrease in both parameters. The decrease is dose dependent. The action of deltamethrin was not reversible. The fungicide prochloraz applied at the same concentration levels as deltamethrin has an immediate chronotropic and inotropic effect on the semi-isolated heart of the bee, but its effects are more intense than those caused by deltamethrin. Comparison of the dose-response curves clearly shows that prochloraz is more cardiotoxic than deltamethrin. When prochloraz and deltamethrin are combined there is an increase of over 100 times in the cardiotoxicity of deltamethrin and an increase of 10 times in the toxicity of prochloraz. Our suggestion is that this synergistic action could be caused by the action of the two compounds on the same target site, which in the heart of the bee may be gap junctional intercellular communication, a vital physiological mechanism for the functioning of the heart in both vertebrates and invertebrates.