Influence of H1- and H2-receptor antagonists on the circulatory system and on the endogenous plasma histamine concentrations in dogs.

The effects of the H1-receptor antagonist dimethpyrindene and the H2-receptor antagonist burimamide on circulatory and respiratory parameters and on plasma histamine levels were tested in 21 mongrel dogs. Both drugs released histamine. The incidence for this effect was 10/11 in the case of dimethpyrindene and 5/10 in the case of burimamide. Following dimethpyrindene all animals showed arterial hypotension, pulmonal hypertension, decrease in peripheral resistance and hyperventilation. The portal venous pressure was increased in dogs reacting by a histamine release. Following burimamide both an initial arterial hypertension and a subsequent hypotension were observed the latter being more pronounced in the group with histamine release. In this group the portal venous pressure raised considerably. In the non-reacting animals cardiac output was elevated, probably due to a release of catecholamines. It seemed remarkable that the effect of exogenous histamine on portal venous pressure was completely blocked by dimethpyrindene, but not the action of histamine released by the drug itself. It is concluded that the effects of anti-histaminic drugs on possibly histamine-induced physiological and pathophysiological processes should be interpreted very carefully as far as their specificity is concerned.