Seasonal variations in aldrin epoxidase (MFO) activity of yellow-legged herring gulls: the relationship to breeding and PCB residues.

Abstract

The hepatic mixed function oxidases (MFO) constitute a defense mechanism which enables the organism to make xenobiotics more polar and thus render them more readily excretable. The degree of induction of this system is an expression of its exposure to xenobiotics, but it is also a function of endogenous physiological mechanisms. These two forms of induction may lead to mutual interference: foreign compounds may stimulate hepatic hydroxylation and affect the metabolism of steroid hormones; the later may in turn stimulate the activity of the MFO system favoring the degradation of the xenobiotics. Induction and detoxication processes of endogenous and exogenous compounds have been observed in mammals in laboratory experiments. Relationships between MRO activity, the reproductive cycle and variations in tissue levels of liposoluble xenobiotics, have been reported for marine organisms. In birds, seasonal variations of MFO levels have been observed, but the relationship between these enzyme variations and the levels of contaminants in the animal tissues has never been made clear. The authors aim to clarify this relationship by determining the levels of PCBs residues and aldrin epoxidase activities in Yellow-legged Herring gull (Larus cachinnans) specimens from different areas of Italy collected during two phases of the annual cycle, namelymore » those of reproduction (spring) and of sexual inactivity (autumn). This species was chosen because of its wide distribution, its opportunistic feeding habits and its adaptive capacity in polluted environments.« less