On the mechanism of histamine H2 receptor activation

The H2 receptor activation mechanism model proposed by Weinstein et al. [Mol. Pharmacol. 12:738-745 (1976)] has been considered for the set of H2 agonists. The energetics of the model proton transfer processes from a proton-donor site to the heterocycle ring of the agonist molecule and from this one to a proton acceptor site have been studied by using the semiempirical AM1 and MNDO quantum mechanical methods. The STO-3G ab initio molecular electrostatic potential for each compound in its active form has also been computed. Results show the mechanistic model to be satisfactory and lead to a qualitative and quantitative explanation of the H2 activity data.