Thyroxine and Propylthiouracil Effects on Alpha- and Beta-adrenergic Receptor Number, Atpase Activities, and Sialic Acid Content of Rat Cardiac Membrane Vesicles

TLDR: Several sarcolemmal constituents which have been shown to influence myocardial contractility were measured in membrane vesicle preparations from the hearts of animals in the three thyroid states to identify biochemical changes which might correlate with known functional changes occurring in these thyroid states.

Abstract: Summary: Membrane vesicle preparations from the hearts of euthyroid, hyperthyroid, and hypothyroid rats were analyzed in an attempt to identify biochemical changes which might correlate with known functional changes occurring in these thyroid states. Several sarcolemmal constituents which have been shown to influence myocardial contractility were measured in membrane vesicle preparations from the hearts of animals in the three thyroid states. These constituents included the apparent number of alpha- and beta-adrenergic receptors (judged from specific binding of radiolabeled adrenergic antagonists) and Na-, K--ATPase activity. As a control for the recovery of sarcolemma in the preparations, the sialic acid content was measured in all preparations. The activity of K-, Ca2--ATPase, a sarcoplasmic reticulum enzyme which regulates intracellular ionized Ca2- concentration, was also measured. Membrane vesicles of the thyroxine-treated hyperthyroid rats showed a decrease (41%, p