Reflex influence of selective coronary artery occlusion on the total capacitance vasculature in the dog.

Abstract

A bstract. While the reflex influence of selective coronary arterial occlusion on the resistance vasculature has been well delineated, the reflex influence of coronary occlusion on the total capacitance vasculature has not been examined. Thus, selective coronary occlusions were performed in 65 anesthetized dogs. Blood was drained from the vena cavae and returned to the right atrium at a constant rate so that changes in total intravascular volume could be recorded as reciprocal changes in extracorporeal reservoir volume. In 10 animals, 2.5 min of left anterior descending occlusion was associated with only an insignificant total volume increase of 6±4 ml (SEM), whereas 2.5 min of left circumflex occlusion was associated with a 27±4 ml (P < 0.001) increase in volume, which was significantly attenuated (P < 0.001) to only a 7±3 ml increase after cervical vagectomy. Epicardial lidocaine in four animals reduced the volume increment associated with circumflex occlusion from 30±3 to 11±4 ml (P < 0.025). The volume increase was attenuated from 45±6 to 24±5 ml with propranolol administration (P < 0.001) (seven animals) and from 26±5 to 17±6 ml with atropine (P < 0.025) (eight animals), but was not attenuated with phenoxybenzamine (28±7 ml before and 25±2 ml after phenoxybenzamine) (five animals). Double blockade with propranolol and atropine reduced the volume increase to 3±2 ml (NS) in four of these animals.In order to compare the influences of selective beta-1 adrenergic blockade and combined beta-1 and beta-2 blockade, volume responses were assessed before and after administration of metoprolol or propranolol in doses that produced the same amount of beta-1 blockade (15 animals). The volume increase associated with circumflex occlusion was not attenuated after beta-1 blockade (20±4 ml before and 18±5 ml after metoprolol) (eight animals) but was attenuated from 30±5 to 14±5 ml after propranolol (P < 0.05) (seven animals). To examine further the efferent limb of the observed reflex, circumflex occlusions were performed before and after either vagectomy at the level ofthe diaphragm or section ofthe sympathetic splanchnic nerves in 12 animals. The volume increment was significantly attenuated after either procedure. In four animals undergoing prior arterial baroreceptor denervation, volume still increased 30±6 ml (P < 0.001) with circumflex occlusion. Thus, inferior myocardial ischemia is associated with an autonomic reflex that acts to increase total intravascular volume. The afferent limb is mediated through the vagi, and the efferent limb, through changes in peripheral beta adrenergic and parasympathetic receptor stimulation.