Maturation of the Diurnal Rhythm of Corticosterone in Female Domestic Fowl

Abstract

The purpose of this study was to examine the maturation of the avian corticosterone diurnal rhythm in relation to other indices of adrenocortical maturation. Female chickens were studied at 1, 5, 11, 17, 23, and 55 weeks of age. Blood samples were drawn at 4-hr intervals during a 24-hr (14 hr light: 10 hr dark) photoperiod. The diurnal rhythm in corticosterone concentration was not apparent until 11 weeks of age. At this age, unlike at 17 weeks of age, the maximal corticosterone concentration occurred during the light period. This indicates that although a rhythm is present at 11 weeks, a phase shift apparently occurs before the adult-like diurnal rhythm is attained. Injection of adrenocorticotropin (ACTH) produced an increase in the circulating corticosterone concentration in chickens at all ages. These results indicate 1) a phase shift must occur between the time of the initial emergence of a diurnal corticosterone rhythm and the attainment of the characteristic adult-like diurnal rhythm, and 2) the avian adrenal cortex is capable of responding to an ACTH stimulus with an increase in circulating corticosterone before the central nervous system rhythmically controls the pattern of circulating ACTH or corticosterone.