Heterogeneity in the response to histamine of isolated dog arteries.

Arterial rings were used to evaluate the differences in the effect of histamine (HIS) on canine dorsal pedal (DPA) and coronary arteries. Moreover, the responses of intact coronary arteries (IA) to HIS were compared with those of arteries isolated from sham operated dogs (SA) and from dogs in the late postinfarction period (PA). DPA responded to HIS added cumulatively with contraction which was potentiated by cimetidine (CIM) and reversed by mepyramine (MEP). IA responded with relaxation potentiated by MEP and reversed by CIM. Under resting conditions, coronary arteries responded to a single concentration of HIS with contraction or relaxation (in IA, SA). In PA, only contractions were seen. Responses of PA were significantly higher than those of IA and SA. It appears that in PA the ratio of H1- and H2-receptors is changed.