CHANGES IN CALMODULIN CONCENTRATION AND CYCLIC 3',5'-NUCLEOTIDE PHOSPHODIESTERASE ACTIVITY IN SKELETAL-MUSCLE OF HYPERTHYROID AND HYPOTHYROID RATS

Hyper- and hypothyroid states occasionally induce skeletal muscle dysf unction i.e. periodic paralysis and thyroid myopathy. The etiology of these diseases remains unclear, but several findings suggest that the catecholamine-beta-receptor-cAMP system or other messenger systems are disturbed in these diseases. In this context, we evaluated changes in the cyclic 3',5'-nucleotide metabolic enzyme, cyclic 3',5'-nucleotide phosphodiesterase (PDE) and calmodulin concentrations in skeletal mus cles of hyper- and hypothyroid rats. Activities of cyclic AMP-PDE were low in skeletal muscle both from hyper- and hypothyroid rats, and cal modulin concentration was high in hyperthyroid and low in hypothyroid rats, as compared with normal rats. DE-52 column chromatographic analy sis showed that the cGMP hydrolytic activity in peak I and the cAMP hy drolytic activity in peak II were decreased in hypothyroid rats, where as cAMP hydrolytic activity in peak III was unchanged. The cAMP hydrol ytic activity in peak III was decreased in hyperthyroid rats, but the activities in peaks I and II were unchanged. These findings indicate t hat cAMP and calmodulin may have some role in skeletal muscle function in the hyperthyroid state, and that cAMP and calmodulin-dependent met abolism may be suppressed in the hypothyroid state.