Hepatic microsomal monooxygenase activities in natural populations of the Mallard DuckAnas platyrhynchos, the Tufted DuckAythya fuligula and the Great Crested GrebePodiceps cristatus.

Birds from three waterfowl species were collected over a period of three years, mainly near the river Rhine in France. Cytochrome P-450 content and monooxygenase activities were measured in liver microsomes of 71 Mallard DucksAnas platyrhynchos, 57 Tufted DucksAythya fuligula and 64 Great Crested GrebesPodiceps cristatus. The monooxygenase activities were estimated by measuring the dealkylation of substituted alkoxycoumarins, substituted alkylresorufins, and the metabolism of the insecticide parathion to its neurotoxic metabolite, paraoxon. A very high dispersion of values was shown, with no indication of season- or sex-related differences. It was concluded that the cytochromes P-450 in the studied populations of these waterfowl species are not induced, even if some individuals exhibit elevated cytochrome P-450 and enzymatic activities. Correlations were found between some enzymatic activities which suggested that the regulation of monooxygenase activities is widely different between birds and rodent laboratory species.