Circadian and 30 minutes variations in serum TSH and thyroid hormones in normal subjects.
Ten normal young males were investigated in order to examine diurnal and short-term variations in serum TSH and serum thyroid hormones. In five subjects blood samples were obtained every 30 min during a 24 h period of daily life. A synchronous diurnal rhythm was found for free T3 and serum TSH with low levels in the day-time and higher levels at night. The mean increase from day to night was 15 and 140 per cent, respectively. There was a tendency to a similar rhythm in free T4, but the increase of 7 per cent fell short of statistical significance. In the other five men blood samples were obtained every 5 min in a 6 to 7 h period starting within the interval from 19.15 to 22.00 h. A significant regular variation with a cycle-length of half an hour was found in TSH, free T3 and free T4. This rhythm accounted for a significant part of the total variation in the levels of TSH, free T3 and free T4. The mean amplitude of the short-term variation is 13, 15 and 11 per cent of the mean level of the respective hormones. The data suggest a pulsatile release of hormones from the thyroid gland governed by a pulsatile TSH secretion.
D000328:Adult; D002940:Circadian Rhythm; D006801:Humans; D008297:Male; D011863:Radioimmunoassay; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine