Dual effect of antihistamines on rat peritoneal mast cells: induction and inhibition of histamine release.

A variety of H1- and H2-receptor agonists and antagonists are shown to have a dual effect on isolated rat peritoneal mast cells. At high concentrations the drugs induce histamine release while at low concentrations they inhibit the secretion of the amine evoked by antigen. These effects do not appear to be directly related. The ability of the H1-antagonists to inhibit histamine release does not appear to correlate in simple fashion with their recorded pA2 values as measured on the guinea pig ileum, suggesting that the effect is not mediated through H1-receptors. These results are discussed in terms of the clinical utility of antihistaminic drugs.