AJP - Regulatory, Integrative and Comparative Physiology, Vol 233, Issue 5 230-R238, Copyright © 1977 by American Physiological Society
Cortisol-mediated synchrinization of circadian rhythm in urinary potassium excretion
M. C. Moore-ede, W. S. Schmelzer, D. A. Kass and J. A. Herd
Conscious chair-acclimatized squirrel monkeys (Saimiri sciureus) studied
with lights on (600 lx) from 0800 to 2000 h daily (LD 12:12) display a
prominent circadian rhythm in renal potassium excretion. The
characteristics of this rhythm were reproduced in adrenalectomized monkeys
by infusing 5 mg cortisol and 0.001 mg aldosterone, or 5 mg cortisol alone,
between 0800 and 0900 h daily. When the timing of cortisol adminisration
(with or without aldosterone) was phase-delayed by 8 h, the urinary
potassium rhythm resynchronized by 80% of the cortisol phase shift, but
only after a transient response lasting 3-4 days. With the same daily dose
of adrenal steroids given as a continuous infusion throughout each 24 h,
urinary potassium excretion showed free-running oscillations no longer
synchronized to the light-dark cycle. These results indicate that the
cirdacian rhythm of plasma cortisol concentration acts as an internal
mediator in the circadian timing system, synchronizing a potentially
autonomous oscillation in renal potassium excretion to environmental time
cues and to other circadian rhythms within the animal.
