Phytosterols or plant sterols (PS) enter the ecosystem via pulp mill effluents. They are also consumed by the general population of developed countries in natural remedies and margarines to lower elevated serum cholesterol levels. This study screened the endocrine and enzymatic parameters of the field vole (Microtus agrestis) for the effects of subchronic PS exposure at three doses (0, 5, or 50 mg of PS kg-1 day-1). PS at 5 or 50 mg kg-1 day-1 decreased the relative liver weight of the voles. The kidney glycogen phosphorylase activity decreased at 5 or 50 mg kg-1 day-1, but the liver glycogen Phosphorylase activity increased at 5 mg kg-1 day-1. The plasma estradiol and testosterone concentrations of males were higher due to PS supplement at 5 mg kg-1 day-1. This can be due to increased sex steroid synthesis from PS precursors. Biotransformation enzyme activities were not affected. PS caused multiple, previously unreported effects that were more pronounced at a low dose. As 5 mg PS kg-1 day-1 is the recommended dose for various health products, a thorough risk assessment of the effects and interactions of PS is warranted.
Use of coupled oscillator models to understand synchrony and travelling waves in populations of the field vole Microtus agrestis in northern England
