H[2] receptor activity; effect in isolated rabbit heart

Histamine can stimulate the heart by directly interacting with cardiac histamine receptors. In the present study we have investigated the H[2] receptor activity in isolated rabbit heart. Cimetidine, a specific H[2] receptor antagonist was used. The isolated heart was mounted in langendroff apparatus. The heart was perfused at a constant pressure with oxygenated Ringer's Locke solution. H[2] receptor antagonist produces negative inotropic effect in the presence of histamine. This indicates that H[2] receptors are present in rabbit heart, and plays a role in mediation of positive inotropic effect produced through CAMP by histamine

Adrenaline; the effects in presence of beta blocker in isolated mammalian heart

There is no doubt that the effects of the catecholamines of the heart are mainly due to the stimulation of beta-adrenoceptors but in the mid 1960' s the first evidence was presented that a-adrenoceptors mediating positive inotrpoism exists also in the myocardium beside well established beta -adrenoceptors. In our observation adrenaline shows a positive inotropic response. The response of adrenaline in presence of metoprolol [beta1blocker] showed negative inotropic effect