title: Hormetic effects of gamma radiation on the stress axis of natural populations of meadow voles (Microtus pennsylvanicus).
abstract: We tested the hypothesis that low doses of gamma radiation have beneficial, hormetic effects on the stress axis (the hypothalamic-pituitary-adrenocortical axis) of free-ranging meadow vole populations (Microtus pennsylvanicus). Voles were exposed to chronic gamma radiation from a 137Cs field irradiator. In isolated populations, voles received one of three treatments over a four-year period: Controls (0.19-0.42 microGy/h--levels that were 2-5x above background levels [0.1 microGy/h] and live-trapped in all years--1982--1985), low doses (22.6 microGy/h--50-200x background, live-trapped from November 1982--April 1985), or high doses (3,840 microGy/h--40,000x background, live-trapped from November 1983--April 1985). Voles exposed to a low dose had levels of free and total corticosterone that were significantly higher than those in the control or high-dose groups. Differences in response to radiation between the sexes were apparent for maximum corticosterone-binding capacity, with females exposed to low doses having higher binding capacity than control or high-dose females, whereas males exposed to low doses had lower binding capacity than control or high-dose males. Low-dose voles had higher counts of neutrophils than either the controls or high-dose voles; hematocrit was greater in the controls than in irradiated voles. These results indicate that voles display a hormetic response to radiation, wherein low doses of an otherwise harmful agent produce a beneficial effect. The stimulation of the stress axis resulting in the increased secretion of glucocorticoids, which may protect against the excessive actions of the immune and inflammatory responses, may be a key mechanism producing this effect.
authors.affiliation: Department of Life Sciences, University of Toronto at Scarborough, Scarborough, Ontario M1C 1A4, Canada. boonstra@utsc.utoronto.ca
authors.forename: Rudy
authors.initials: R
authors.lastname: Boonstra
authors.forename: Richard G
authors.initials: RG
authors.lastname: Manzon
authors.forename: Steve
authors.initials: S
authors.lastname: Mihok
authors.forename: Julie E
authors.initials: JE
authors.lastname: Helson
mesh_terms: D000308:Adrenocortical Hyperfunction; D000818:Animals; D003411:Arvicolinae / Q000254:growth & development*; D003345:Corticosterone / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D004781:Environmental Exposure; D005260:Female; D005720:Gamma Rays / Q000009:adverse effects*; D006400:Hematocrit; D008297:Male; D011157:Population Dynamics; D013312:Stress, Physiological; D013997:Time Factors
chemical_list: D003345:Corticosterone