Different effects of cimetidine and ranitidine on gastric emptying in rats and man

Cimetidine and ranitidine were tested for their effect on gastric emptying in the rat. At low doses, cimetidine was inactive, whereas it significantly delayed emptying rate when administered at higher doses. Ranitidine always accelerated gastric emptying. At variance with rats, ranitidine delayed human gastric emptying whereas cimetidine was completely inactive. All these data are consistent with the idea that these effects of H2-antagonists are independent of H2-receptor blockade.