[Nycthemeral variations of thyroxine levels in the quail: effect of ambient temperature].
Plasma T4 levels were determined at 2 hr intervals in male quail reared under 18 L6-24 : 6D and 26 +/- 1 degrees C. Low thyroxinemia (4.7 -5.7 mg/ml) was observed during the light phase of the photoperiod. T4 levels were sharply increasing during the first part of the dark period, up to a peak (9.2 ng/ml) at 3 a.m., and decreased again by the last part of the night. Exposure to 4 degrees C for 30 min resulted in different effects on thyroxinemia according to the time of the day. During the light phase (i.e., low resting T4 levels), cold- induced thyroxinemia was significantly increased (50% approximately). Similar effects were observed during the last part of the night. On the contrary, no thyroid response to cold could be detected during the beginning of the dark period, when basal thyroxine concentrations were sharply increasing. Participation of feed back mechanisms in such a phenomenon is suggested.U
D000818:Animals; D003624:Darkness; D008027:Light; D010507:Periodicity; D011784:Quail; D013696:Temperature; D013974:Thyroxine / Q000097:blood*
D013974:Thyroxine
Variations nycthémérales de la thyroxinémie chez la caille: influence de la température ambiante.