Circadian Variations of Thyroid Hormone Levels of Nonpregnant Uniparous Fat-tailed Iranian Ewes in Summer (original) (raw)

2008, Turkish Journal of Veterinary & Animal Sciences

Circadian variations in serum triiodothyronine (T3), thyroxine (T4), free triiodothyronine (fT3), and free thyroxine (fT4) 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 T3, T4, fT3, and fT4 were measured by radioimmunoassay. There were statistically significant differences in thyroid hormone concentrations (T3, T4, fT3, and fT4) at different hours of the day. The results revealed that serum T3, T4, fT3, and fT4 levels were highest at 1800 (P < 0.05). Significant 24 h periodicity in the serum levels of T3, T4, fT4 and fT3 was observed in nonpregnant uniparous Iranian ewes. It is concluded that circadian rhythm was observed in serum thyroid hormones.