Effects of the H2-receptor agonist dimaprit on lymphocyte responsiveness in vitro.

The histamine H2-agonist dimaprit was found to increase the response of rat spleen cells to the T-cell mitogen Concanavalin A, when present at concentrations of 10(-5) and 10(-4)M. Higher concentrations of dimaprit were cytotoxic. The enhanced response seemed to be associated with an inhibitory effect of dimaprit on T-suppressor cell activity rather than with a direct mitogen-like stimulation of lymphocyte proliferation or with an interference with monocyte/macrophage functions. The stimulatory effects of dimaprit were not reversed by the H2-receptor antagonist, cimetidine, nor by the beta-receptor antagonists metoprolol and H 35/25. Addition of the H1-receptor antagonist, mepyramine, further increased the stimulatory effect of dimaprit on lymphocyte responsiveness.