The effects of derivatives of adenosine 3',5'-monophosphate on fluid secretion by the salivary glands of Calliphora.

Fluid secretion by the salivary glands of the blowfly Calliphora is regulated by 5-hydroxytryptamine (5-HT) (Berridge, 1970, 1972; Berridge & Prince, 1972). The action of 5-HT is apparently mediated by adenosine 3',5'-monophosphate (cyclic AMP) which thus functions as an intracellular 'second messenger' as has been postulated in many other systems (Robison, Butcher & Sutherland, 1968). Exogenous cyclic AMP can reproduce the action of 5-HT on fluid secretion (Berridge & Patel, 1968; Berridge, 1970). The phosphodiesterase inhibitor theophylline is capable of stimulating secretion and can also sensitize salivary glands to both 5-HT and cyclic AMP (Berridge, 1970). Finally, the intracellular concentration of cyclic AMP is elevated during the action of 5-HT (Prince, Berridge & Rasmussen, 1972). An analysis of the electrical events associated with the actions of both 5-HT and cyclic AMP suggest that the latter functions by stimulating potassium transport (Berridge & Prince, 1972; Prince & Berridge, 1972). The specificity of this cyclic AMP-sensitive transport site has been analysed by testing the effects of a wide range of analogues closely related to cyclic AMP.