AJP - Endocrinology and Metabolism, Vol 259, Issue 2 E162-E169, Copyright © 1990 by American Physiological Society
Lighting conditions affect serum and pituitary TSH in male rats
M. L. Laakso, T. Porkka-Heiskanen, D. Stenberg, G. Johansson and P. T. Mannisto
Department of Physiology, University of Helsinki, Finland.
It has been reported that periodicity of lighting plays a role in the
regulation of the function of the hypothalamus-anterior pituitary-thyroid
axis in the rat. We studied whether other properties of lighting influence
the levels of pituitary and serum thyrotropin (TSH) in adult male rats. The
animals were reared 7 days under various lighting conditions, then trunk
blood and adenohypophyses were collected at different times of the day, and
TSH was measured radioimmunologically. In natural lighting conditions the
diurnal variation of plasma and pituitary TSH levels was abolished, and the
overall levels of plasma TSH were higher and those of pituitary TSH lower
than in ordinary laboratory lighting conditions. The intensity of lighting
affected the serum TSH levels; daytime serum TSH decreased in the rats
under low daytime illuminances and in those under nighttime twilight
instead of darkness. Changing the rate of the lighting transition at dawn
and dusk had no influence on the TSH patterns. We conclude that, in
addition to periodicity, other features of lighting affect the daily
secretion patterns of TSH.
