Chronobiology and the Kidney

Abstract

The kidney plays a critical role in maintaining a stable internal environment by balancing output and intake, circadian variations in the contents of intracellular and extracellular fluids, the levels of some pharmaceuticals and total body water volume. Variations in the quantities of daytime and night-time urine were recorded in early observations of humans and later studied in manipulated light/dark environments, in clinical disorders and in laboratory animals. Circadian variations in the transfer of substances from the gastrointestinal tract and in metabolism influence the volume and content of urine. The nephron tubules are responsible for transferring solutes and water, modifying glomerular filtrate as it transits through them. In both health and many disorders, changes are necessary to balance intake and output, and circadian variations result from the influence of clock genes. Exogenous changes from an erect to supine position, during sleep and due to extrinsic events may modify intrinsic circadian rhythms, as can illness. Renal transplantation can change day-to-night variability. The circadian timing of medication can modify renal responses. Benefits, toxicity and side effects may change with the timing of administration of medication. A “best” circadian timing for medications prescribed for renal conditions and times of administration that result in modified side effects are often found.