Circannual variations of TSH circadian rhythm parameters in the rat.
We had previously observed a circadian rhythm for serum TSH in male Sprague-Dawley rats (under a 12-hour light-dark cycle, light off at 19.00 h). In the present work the parameters of this previously observed TSH rhythm were determined over a year on a monthly basis. A circadian rhythm was detected for each month except April. From month to month, the amplitudes and acrophases of these rhythms were not significantly different, and a circannual rhythm was only established for the mean TSH concentration over the 24-hour period (mean hormonal value). We conclude that there is a constant circadian pattern for serum TSH fluctuations superimposed on a small basal circannual rhythm of the mean hormonal value.
D000818:Animals; D002940:Circadian Rhythm; D008297:Male; D010507:Periodicity; D051381:Rats; D011919:Rats, Inbred Strains; D012621:Seasons; D013972:Thyrotropin / Q000097:blood*
D013972:Thyrotropin