VARIATIONS IN THE WEIGHT OF THE ADRENAL GLANDS OF THE FIELD VOLE, MICROTUS AGRESTIS

Abstract

SUMMARY 1. Mean weights are given for the adrenal glands of 1167 male and 806 female voles from naturally fluctuating populations at Lake Vyrnwy, Wales, during 1952–58. 2. Although the mean standardized adrenal weights of both males and females varied from year to year, no consistent relationship with population trend could be found, except that females from expanding populations tended to have the heaviest adrenals. 3. The adrenal weights increased seasonally each year from low values in the spring to maxima in midsummer and decreased again to low values in the autumn. 4. This fluctuation was exhibited not only by breeding animals but also by those that were sexually immature. It therefore seems unlikely that the seasonal enlargement is entirely a direct effect of gonadal activity, though it may be due to changes in social behaviour during the breeding season. 5. In each month the adrenals of pregnant or lactating females were heavier than those of nulliparous animals of the same body weight.