Adrenal response in a wild Microtus population: seasonal aspects
Adrenal response was determined during a 13-month period in a population of southern Manitoba meadow voles (Microtus pennsylvanicus) as a preliminary part of a study to determine the effects of chronic ionizing radiation on free-living mammals. Livetrapped voles were subjected to behavioral tests, killed, and their isolated adrenals superfused and stimulated with ACTH. Superfusates were assayed fluorometrically for corticosterone. Peaks of adrenal response occurred during spring in both adult males and females, followed by a significant decline into early summer. Subadult males exhibited a peak response in early summer. Corticosterone levels of adults were generally higher than those of juveniles in the same season. Levels of nonpregnant adult females were higher than those of pregnant voles. Observed differences over the annual cycle were attributed to the behavioral and hormonal states of various age and sexual components of the population.