Functional and metabolic effects of terbutaline and propranolol in fast- and slow-contracting skeletal muscle in vitro.

The soleus, a slow-contracting, and the extensor digitorum longus (EDL), a fast-contracting skeletal muscle from guinea-pig were prepared for isometric recording of sub-tetanic contractions in vitro. The contents of adenosine-triphosphate (ATP) and creatinephosphate (CP) together with their metabolites and the contents of lactate, pyruvate and cyclic adenosine-monophosphate (c-AMP) in the muscles were determined. It was found that the energy and redox state of the isolated soleus and EDL muscles is very stable and does not significantly differ from the normal state in vivo. Moreover, there were no consistent changes in these variables after treatment with terbutaline (a beta 2-adrenoceptor agonist) or propranolol or both. Thus, effects on energy metabolism do not seem to cause the changes in muscle contraction, characteristic for beta-adrenoceptor stimulation. On the other hand, the functional effects were accompanied by elevation of the c-AMP level of the muscles.