AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 2 151-R160, Copyright © 1986 by American Physiological Society
Propylthiouracil causes phase delays and circadian period lengthening in male and female hamsters
L. P. Morin, M. L. Gavin and J. E. Ottenweller
The thyroid neuroendocrine axis has been implicated in the control of
circadian rhythmicity. The present work examined the ability of a thyroid
hormone-inhibiting agent, propylthiouracil (PTU), to modulate phase and
period of the hamster wheel-running circadian rhythm. The circadian period
(tau) of blind male hamsters was lengthened by approximately 0.2 h when
they were fed a diet containing 0.6% PTU. Removal of the PTU reversed the
change in tau. Pinealectomy did not alter the tau response to PTU. Blind
ovariectomized female hamsters showed changes in tau during and after PTU
treatment that were similar to those of males. Males were also tested with
0.3, 0.6, or 1.2% PTU diets, and a dose-response relationship was
established. Under 14:10 light-dark (LD 14:10) conditions, the phase of
activity onset relative to lights off (psi) was not affected by 0.6% PTU.
In LD 6:18, mean psi was 16.7 h, but this shortened to 13.3 h during PTU,
returning to 16.0 h after PTU removal. In intact males under LD 14:10, the
three PTU diet concentrations failed to differentially suppress thyroxine
and triiodothyronine levels. Food intake and body weight were
differentially reduced by the PTU treatments. A 0.5% quinine hydrochloride
diet also reduced food intake and body weight but did not change tau. The
inconsistency between the dose-tau response and the dose-thyroid hormone
response suggest that PTU may affect circadian rhythmicity independent of
its action on the thyroid neuroendocrine axis.
