Circadian Clocks: Showtime for the Adrenal Cortex

Extract

THE LAST 10 yr have seen remarkable advances in understanding the control and interrelationships of circadian rhythms in the brain and peripheral organ systems of mammals and of their critical importance to human health. Disturbances in circadian timekeeping have been linked to cardiovascular disease, hypertension, metabolic syndrome, gastrointestinal disorders, affective disorders, and cancer (1). The adrenal gland, and the adrenal cortex in particular, has increasingly been seen as a critical source of signals to coordinate and temporally program metabolic activities throughout the body. For many years the prominent circadian oscillations in steroidogenesis and glucocorticoid secretion of the adrenal cortex were thought to be a consequence of similar circadian rhythms in ACTH secretion. However, evidence of functional neural innervation of the adrenal cortex (2, 3) and findings of nycthemeral rhythms in adrenal responsiveness to ACTH that could be altered extremely rapidly (4, 5) led to the recent demonstration of direct neural control of adrenal rhythms (6, 7). In this issue of Endocrinology, a study by Valenzuela and Torres-Farfan and colleagues (8) takes another step in advancing understanding of the regulation of adrenocortical rhythms by demonstrating the presence of an intrinsic circadian oscillator in the adrenal cortex of the capuchin monkey (Cebus apella) and by showing that expression of its clock genes are influenced by melatonin, another major role-player in the circadian rhythm story (9).