Pesticide effects upon the circadian time structure in the thyroid, adrenal and testis in rats.

An aspect of environmental toxicology, namely the changes in the mammalian time structure induced by chronic exposure to potentially toxic agents used widely in agriculture as pesticides, is reported. Effects of pesticides upon thyroid, adrenal and testis have been described till now, without regard to their time structure. In the present study, the circadian rhythms of RNA, DNA and protein, in these glands were explored by single cosinor analysis, for alterations of their rhythm parameters, after chronic exposure of rats to pesticides. Four herbicides, a fungicide and two insecticides were tested. A wide variety of rhythm alterations were found. It has to be emphasized that several of the changes encountered after chronic exposure of the animals to pesticides, e.g., the form of acrophase alterations, the changes in amplitude or the free-running of several of the rhythms studied, are temporal alterations only, not linked to any changes in mean or mesor. If the circadian rhythms of the functions studied and the predominantly temporal aspects of these changes are ignored, the pesticide effects could remain undetected. The different directions and degress of phase alteration found in the three circadian rhythms studied within the same gland lead to a condition of internal desynchronization within thyroid or adrenal. Of interest is the almost complete lack of effect of these pesticides on the same circadian rhythms in the testis. The data presented indicate that the study of pesticide effects and the effects of other potentially noxious environmental agents upon the mammalian organism, clearly demands the observation of the exposed organism's time structure. Chronotoxicology appears to be essential for increased sensitivity in detecting adverse effects of potentially noxious agents. Early recognition of alterations in the human time structure induced by environmental agents may allow the prevention of clinically manifest damage and disease before it occurs.