AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 1 1-R5, Copyright © 1988 by American Physiological Society
Propylthiouracil, but not other antithyroid treatments, lengthens hamster circadian period
L. P. Morin
Department of Psychiatry and Behavioral Science, State University of New York, Stony Brook 11794.
Two experiments were performed to evaluate the role of the thyroid gland as
a mediator of circadian rhythms in the hamster. In experiment 1, the
antithyroid drug propylthiouracil (PTU) lengthened the circadian period
(tau), increased thyroid weight, and eliminated detectable thyroxine (T4)
and triiodothyronine (T3) from blood. A low-iodine diet greatly reduced T4
levels but had no effect on T3 or tau. Treatment with 500 microCi of 131I
failed to alter any parameter of physiology or rhythmicity measured. In
this experiment, some animals in the low-iodine and PTU groups had greatly
reduced testes sizes, and testes size was inversely correlated with change
in tau. In experiment 2, T4 and T3 levels detected 11 wk after surgical
thyroidectomy were significantly less than those found in sham-operated
animals, but concentrations of the two hormones varied widely across the
thyroidectomized group. Thyroidectomy did not increase tau either 4 or 11
wk after surgery, nor was there evidence from individuals that level of
thyroid function was associated with change in tau. The results from these
experiments suggest that diminished thyroid function is not causal of
lengthened circadian period.
