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Influence of the Pineal Gland and Circadian Rhythms in Circulating Levels of Thyroid Hormones of Male Hamsters
Author(s) -
Vriend Jerry
Publication year - 1984
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1984.tb00191.x
Subject(s) - medicine , pinealectomy , endocrinology , radioimmunoassay , triiodothyronine , melatonin , hormone , pineal gland , thyroid , hamster , biology , circadian rhythm
Thyroxin (T4) and triiodothyronine (T3) were measured by radioimmunoassay in serum of hamsters sacrificed at 4‐hr intervals throughout the daily light‐dark cycle (14L/10D). Both T4 and T3 concentrations increased significantly during the L period of the daily cycle and decreased during the D period of the cycle; A.M. versus P.M. differences in free thyroxin indices (FTI) were also studied using the T4 and T3 uptake assays of Nuclear Medical Laboratories (Dallas, Texas). The free thyroxin index was significantly greater in serum samples of hamsters sacrificed at 7 P.M. than at 7 A.M. (lights on at 6:30 A.M.). Serum taken at 7 P.M. had less unsaturated binding sites than serum taken at 7 A.M. No significant A.M. versus P.M. differences in free thyroxin index were found in blind hamsters, although blind hamsters had significantly lower T4 and FTI than controls. Placing melatonin in the drinking water at a dose of 80 μg/ml did not significantly influence hormone levels. The greatest difference in hormone concentrations between control and blinded hamsters was found in P.M. samples. Blind hamsters had FTIs that were 48% of P.M. controls. Pinealectomy prevented the effects of blinding on T4 levels and FTIs.