Manipulating thyroid hormone levels alters development of skeletal muscle mitochondria in nestling red-winged blackbirds

Thyroid hormones are key regulators of development and metabolism in vertebrates. Red-winged blackbirds are an altricial species that exhibit an increase in plasma 3,3’, 5-triiodo-L-thyronine (T3) levels during the first 5 days post-hatch (dph), begin to develop endothermic metabolic responses by 7 dph, and fledge within 10 days of hatching. To better understand the role thyroid hormones play in the endothermic metabolic development in an altricial species, we treated nestling red-winged blackbirds on 2, 3, and 5 dph with either methimazole to induce hypothyroidism or supplemental T3 to induce hyperthyroidism. We examined mitochondria function in breast and thigh skeletal muscle at 5, 7 and 9 dph in permeabilized muscle fibers. Hypothyroid conditions prior to day 5 post-hatching induced lower oxygen flux during oxidative phosphorylation through complexes I and II than controls in both breast and thigh skeletal muscles of 7 and 9 dph nestlings. Elevating thyroid hormones during the first 5 dph resulted in greater leak respiration but no change in oxidative phosphorylation respiration later in the nestling period. These data suggest that thyroid hormone levels play a role in development of skeletal muscle mitochondrial function and may be a foundational mechanism by which endothermic capacity is achieved by neonate altricial birds. NSF 1146758 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.