Effects of environmental temperature on thyroid hormones in the barn owl (Tyto alba)

Abstract

The basic patterns of thyroid hormones [thyroxine (T4) and 3,3',5-triiodothyronine (T3)] and the T4 and T3 responses induced by thyrotropin releasing hormone (TRH) are reported in captive female barn owls (Tyto alba) during the non-breeding period. The main findings of the study, conducted on a total of 10 owls, are as follow: (1) The thyroid gland of barn owl can be stimulated by the classical TRH stimulation test. (2) T3 response was much more pronounced both under cold (around 10 °C) and warm (around 20 °C) conditions, whereas T4 response ranged so widely that we could not point out any significant change in it. (3) Basal T3 plasma level was significantly (p = 0.036) higher in birds exposed to cold temperature, and they responded to TRH treatment with a lower plasma T3 elevation than the birds kept in a warm chamber. This pattern, however, cannot be explained by increased food intake, but is in agreement with the fact that enhanced T3 level may account for higher avUCP mRNA expression, which results in higher heat production on the cell level. From the results it is concluded that altering T3 plasma level plays a significant role in cold-induced thermoregulation.

Up-regulation of avian uncoupling protein in cold-acclimated and hyperthyroid ducklings prevents reactive oxygen species production by skeletal muscle mitochondria

“…Further, fatty acids may also contribute to the activation of avUCP expression by analogy with mammals in which the expression of muscle UCPs mainly depends on NEFA activation of PPARs (peroxisome proliferator-activated receptors) through their interaction with the UCP promoter [51]. Because CA ducklings also present slight hyperthyroidism compared to controls (Table 1), in agreement with data in mammals and birds [23,52,53], we cannot rule out the possibility that the increased expression of avUCP in the cold also involves changes in thyroid status [54,55]. …”

Mitochondrial function is enhanced by thyroid hormones during zebra finch development

“…They affect cellular differentiation, proliferation [4] and metabolic regulation [5], all of which are essential for growth. At the cellular level, understanding the interaction between TH and mitochondria is crucial because their secretion is flexibly adjusted to environmental conditions, such as climatic conditions or food availability [1,2,[6][7][8]. Aerobic mitochondrial metabolism-and hence ATP production-determines an organism's energy metabolism [9] and thus the ability to adjust to different ecological conditions [10].…”

“…These studies are vital for understanding the effects of environmental challenges on life-history outcomes. For example, it is still not clear how an organism’s metabolism is adjusted to changing environmental conditions, like rising temperatures or a lack of nutrient availability—both of which have been shown to influence TH-secretion [ 1 , 2 , 6 , 7 , 40 ]—and what the consequences are for fitness and life-history outcomes. Growth is a valuable trait to study because growth patterns in early life can determine survival, especially in young passerines [ 41 ].…”