The effects of cyclic N-2-O-dibutyryl- adenosine 3',5'-monophosphate, adrenaline and aminophylline on the isometric contractility of the isolated hemidiaphragm of the rat.

1 N-2-O-dibutyryl adenosine 3',5'-monophosphate (db cyclic AMP), adrenaline and aminophylline produce a potentiation of the tension developed (Td) and the maximum rate of rise of tension (dT/dt max) in the rat isolated diaphragm during indirect electrical stimulation. Aminophylline and db cyclic AMP also produce the same effect during direct stimulation. 2 Propranolol produced a depression of the action of adrenaline on Td and dT/dt max during indirect stimulation of the diaphragm. On the other hand, the potentiating actions of db cyclic AMP and of aminophylline on Td and dT/dt max during indirect stimulation were unaffected by propranolol. 3 The results support the idea that cyclic AMP may be involved not only in regulating the processes associated with synthesis, mobilization and storage of transmitter in the motor nerve terminal, but also in modifying some metabolic processes which regulate the function of the contractile elements.