Classification of antidotes based on mechanism of action. Part I.

The beta receptor is coupled to an adenylate cyclase. beta receptor stimula tion activates the production of AMPc, which activates protein kinases and promotes protein phosphorylation. The cell response varies with the cell ty pe; in myocytes, beta stimulation facilitates entry of calcium into the cel l. beta receptor antagonists inhibit this cascade, thus reducing inotropism , chronotropism, dromotropism, and bathmotropism. Glucagon stimulates an adenylate cyclase that is not coupled to the recepto r, thus restoring the cascade. Thus, glucagon acts as an antidote by bypass ing the link between the beta adrenoceptor antagonist and the receptor.