Thermogenesis in the avian body and the role of the pineal in thermoregulation.
In the absence of the brown adipose tissue, maintenance of body temperature (Tb) in birds is generally believed to be by shivering thermogenesis (ST), though evidence for nonshivering thermogenesis (NST) is becoming available. In ST, glycogen utilization by the anaerobic white muscle fibers forms the main energy process, while the aerobic red fibers appear to be largely involved in NST. Winter pigeons maintained on a 12 h photophase (PP) and 12 h scotophase (SP) had higher Tb during PP in both warm (25 degrees C) and cold (3 degrees C) acclimated birds. In pinealectomized (Px) pigeons Tb was higher than in controls during PP and SP without affecting the circadian thermal rhythm. This hyperthermic effect (HE) of pinealectomy was nullified with subcutaneous implantation of melatonin. These warm acclimated winter Px pigeons when examined for Tb next winter, did not show HE. Summer Px pigeons did not show HE as did the winter Px pigeons, indicating seasonal difference. No significant difference in circulating levels of T3 and T4 was seen in the summer as well as winter warm acclimated Px pigeons. These results suggest that the HE observed in warm acclimated Px winter pigeons was not mediated by the thyroid and that the pineal has no influence on the thyroid in the warm acclimated birds. The slightly higher HE seen in cold (3 degree C) acclimated Px pigeons may well be due to the influence of the thyroid.
D000222:Adaptation, Physiological; D000818:Animals; D001717:Birds / Q000502:physiology*; D001833:Body Temperature Regulation; D003080:Cold Temperature; D006003:Glycogen / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D010870:Pineal Gland / Q000502:physiology*; D012768:Shivering
D006003:Glycogen