Circadian variations of T3 and T4 in euthyroid subjects
Cucinotta, D.; Longo, G.; Saitta, A.; Squadrito, G.
Bollettino della Societa Italiana di Biologia Sperimentale 54(19): 1867-1873
1978
ISSN/ISBN: 0037-8771 PMID: 753273 Document Number: 130066
Eight normal healthy volunteers were subjected to periodic blood samplings and the values of triiodothyronine (T3) and thyroxine (T4) determined over a 28 h period. The existence of a bioperiodicity in thyroid hormone release could not be determined, due to the limited available data. There were oscillations, mostly irregular and incapable of being correlated from case to case. There was almost always a minimum level at 0400 h and a maximum at 2000 h for T3, and generally an increase in T4 in the early hours of the morning. The latter could be correlated with the peak of TSH (thyroid stimulating hormone of the pituitary). In the case of T3 there is a certain contraposition in relation to TSH and that for cortisolemia.