Effect of n-propyl thiouracil on muscle

Abstract

Ingestion of a 0.03% solution of n-propyl thiouracil caused the development of a hypothyroidic condition in rabbits. Concurrent with this development, changes were observed in the texture and properties of skeletal muscle. Electron microscopy indicated a definite degenerative change in the myofibrillar organization of the back muscle. The enzymatic activity of the contractile protein, myosin B, isolated from the back muscle of the rabbits was altered by the n-propyl thiouracil treatment. The changes in enzymatic activity which occur were most readily seen on the addition of an enzymatic activity activator such as ethylenediamine tetraacetate at high ionic strength or magnesium chloride at low ionic strength. Both activators increased the enzymatic activity of the myosin B from the n-propyl thiouracil treated animals to a greater extent than the myosin B from the control animals. The maximum velocity of the enzymatic reaction derived from Michaelis Menton kinetics for the myosin B from the rabbits treated with the goitrogen was greater than the values obtained with the control animals. The absolute values of the adenosine triphosphatase activity of the myosin B decreased with age but the relative differences between the myosin B from the control and n-propyl thiouracil treated animals remained constant.