Reversal of early thyroid hormone action on mitochondria by bovine serum albumin in vitro.

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Abstract
Pretreatment of hypothyroid rats with 2.6 [mu]g L-thyroxine [T4]/m for 30 min. lowered the excessive respiratory control in their liver mitochondria to normal levels, and raised mitochondrial hormone content 55-fold. Adding 6-12 rag of bovine serum albumin to the mitochondrial assay mixtures completely reversed the action of the injected hormone, and removed 70% of the hormone from the mitochondria. The reversibility of the hormone action on respiratory control was evidence that synthesis of protein components of mitochondria was not involved in the early functional changes; that those changes were due in part to the presence of the hormone and perhaps in part to the release of endogenous mitochondrial components that can decrease respiratory control and that are bound by albumin; and that measurements of mitochondrial function in the presence of enough albumin would reveal only irreversible and secondary effects of the hormone.