Coronary Vasodilatation and Adrenergic Receptors in the Dog Heart and Coronary

Abstract

Abstract-The question of whether the coronary blood vessels contain an intrinsic adrenergic mechanism for vasodilatation of physiological significance has been ex amined in the canine heart-lung preparation with a donor by studying the response of the coronary vessels to epinephrine, norepinephrine, isoproterenol and salbutamol in combination with practolol. To differentiate the vasodilatation mediated through adrenoceptors in the coronary vessels from that resulting from an increase in the myo cardial 02 consumption, a special method of analysis was developed based on the linear relation between the coronary flow and the myocardial 02 consumption.It was found that all four compounds produced an increase in the coronary flow attri butable to an increased myocardial 02 consumption.Epinephrine and norepinephrine produced a decrease in the coronary flow after practolol which completely abolished the increase in the myocardial 02 consumption as well as the positive inotropic and chrono tropic effects produced by these compounds, while isoproterenol and salbutamol pro duced an increase. These results indicate that adrenergic-receptor exists in the coronary subserving a vasodilatation.However, the vasodilatation through this mechanism is of minor importance under physiological conditions and becomes com pletely masked in the presence of an overwhelmingly strong vasodilatation consequent to an increase in the myocardial 02 consumption. as manifested by relaxation in isolated coronary artery strips (1) and in the non-beating heart (2) do not necessarily mean that ;3-adrenergic receptor activity in the coronary vessels plays a paramount role in the coronary vasodilatation of the intact beating heart, since cate cholarnines produce in vivo a marked change in the mechanical and metabolic activities of the myocardium, which can, in its turn, affect the tone of the coronary vessels consider ably.

Competition between sympathetic vasoconstriction and metabolic vasodilation in the canine coronary circulation.

“…17 In the absence of /3-receptor blockade, electrical stimulation of the stellate ganglion has been reported to produce a lesser coronary vasodilation than that resulting when coronary sinus oxygen levels are reduced to similar levels by systemic hypoxia. 7 The present results with intracoronary norepinephrine infusion are very similar to those obtained by Imai et al 28 with catecholamine infusions in an isolated, supported heart-lung preparation. Oxygen extraction and coronary venous oxygen tension were not reported by Imai et al, but myocardial oxygen consumption was low (3 ml/100 g min~') in their preparation.…”

Cardiotonic and Coronary Vasodilatatory Effects of Amrinone in the Canine Heart-Lung Preparation with a Support Dog as Compared with Those of Dobutamine

“…6). For comparison, the regression line representing the effects of isoproterenol, taken from our previous paper (9), is also depicted in this figure. As is evident from this figure, amrinone produced disproportionately larger increases in the coronary blood flow, indicating that the agent exerted a direct dilatatory effect on the coronary vasculature.…”

“…The HLP c donor was prepared according to the method reported in our previous papers (9,10). Briefly, the coronary sinus outflow led out by a Morawitz cannula and measured by means of a can nulating type probe (2 mm, 1.d.)…”

Effects of drugs on the cerebral circulation of the dog in relation to the cerebral oxygen consumption

“…There was an excellent linear correlation (r =0.93, P<0.001) between these two parameters as shown in Figure 2. Thus, we felt justified in applying the same principle to analyse the effects of drugs on the cerebral circulation in relation to changes in the cerebral oxygen consumption as was used previously on the coronary circulation (Imai, Otorii, Takeda & Katano, 1975).…”