Cyclic amp : the ubiquitous hormone

Abstract

It is now being claimed that many hormones act by way of a two-messenger system. The hormones may be regarded as first messengers which travel from their cells of origin to their target tissues to stimulate the formation therein of a second, intracellular messenger. Although one cannot exclude that other second messengers will eventually be discovered, the only one identified so far is cyclic adenosine 3', 5' monophosphate, or cyclic AMP. The function of this cyclic nucleotide as second messenger mediating the effects of a variety of hormones and other biologically active agents has now been definitely proved. Since the recognition of its physiological role, from the discovery that it mediated the hyperglycaemic effect of adrenaline and glucagon by stimulating the conversion of inactive to active glycogen phosphorylase, work in many lalboratories has established both the ubiquity of cAMP in living organisms and the large number of its regulatory mechanisms.