Circadian variations in serum triiodothyronine (T_3), thyroxine (T_4), free triiodothyronine (fT_3), and free thyroxine (fT_4) levels were investigated in Iranian ewes. For that purpose, blood samples were collected from the jugular veins of 15 adult clinically healthy Iranian nonpregnant uniparous ewes every 6 h (0600, 1200, 1800, and 0000) during 6 days in summer with a mean ambient temperature of 40 °C. Serum T_3, T_4, fT_3, and fT_4 were measured by radioimmunoassay. There were statistically significant differences in thyroid hormone concentrations (T_3, T_4, fT_3, and fT_4) at different hours of the day. The results revealed that serum T_3, T_4, fT_3, and fT_4 levels were highest at 1800 (P < 0.05). Significant 24 h periodicity in the serum levels of T_3, T_4, fT_4 and fT_3 was observed in nonpregnant uniparous Iranian ewes. It is concluded that circadian rhythm was observed in serum thyroid hormones.
Circadian rhythm, triiodothyronine, thyroxine, nonpregnant uniparous ewes
NAZIFI, SAEED; SAEB, MAHDI; HASANKHANI, MAHDI; ANSARI-LARI, MARYAM; GHAFARI, NARJES; and HASANSHAHI, FATEMEH (2008) "Circadian Variations of Thyroid Hormone Levels of Nonpregnant Uniparous Fat-tailed Iranian Ewes in Summer," Turkish Journal of Veterinary & Animal Sciences: Vol. 32: No. 2, Article 13. Available at: https://journals.tubitak.gov.tr/veterinary/vol32/iss2/13