Regulation of muscle differentiation: stimulation of myoblast fusion in vitro by catecholamines.

Epinephrine and isoproterenol provoke primary chick myoblasts to initiate precocious cell fusion. Both the rise in intracellular adenosine 3' ,5-monophosphate (cyclic AMP) and cell fusion generated by these effectors are prevented by propranolol, which is a specific blocker of the beta-adrenergic receptor. Propranolol has no effect either on the precocious cell fusion provoked by prostaglandin E or on cell fusion in control cultures. The results support the idea that a rise in cyclic AMP is the critical intracellular change responsible for initiating events that culminate in myoblast differentiation 4 to 5 hours later. They also indicate that the culminate in myoblast differentiation 4 to 5 hours later. They also indicate that the hormone responsible for the positive regulation of myoblast differentiation in vitro is not acting through the beta-adrenergic receptor.