Qualitative differences in reflex vagal control do exist controlling regional coronary flow resistance within and between mammalian species (1079.9)

Abstract

The literature extensively documents inconsistencies in the vagal and acetylcholine control of coronary blood vessels between species. The reasons may relate to variation in experimental models, but reflex vagal control of coronary flow in man must remain uncertain. In awake canine species with paced hearts baroreflexes activate the vagus to dilate flow resistance vessels in the circumflex (CX) and right (R) coronary beds but have no apparent effect in the anterior descending (AD) bed. The effects therefore vary within one species. Seeking a unifying hypothesis of neural coronary control in 2010 we challenged awake sheep with identical protocols to those used in the dog, where, as in dog R serves only RV. We reported1 that the pattern of regional change between sheep and dog are similar for CX and AD, but the effects for R are opposite. In sheep as aortic perfusion pressure rises 28 mmHg, R flow does not change and the bed constricts (conductance 82%; P<0.001, c.f. dog dilates 118%; P<0.01). The effects in both species are blocked by methscopolamine. These data suggest that evolution of vagal control of the coronary circulation does vary qualitatively within, and, between species. The data also imply that the myocardium known for poor oxygen reserve at rest when facing rapid changes in cardiac work normally calls on beat‐by‐beat, rapid time‐constant hypoxia defence mechanisms. Emerging data2 suggest that myocardial cells may be normally hypoxia‐adapted, using low‐threshold cellular interacting glycolytic and hypoxia‐inducible transcriptional factors. Finally, the data imply a differential pattern of reflex vagal coronary dilator/constrictor effects will apply regionally to the heart of man. 1. Quail A et al, FASEB J. A1034.6, 2010 2. Songyue Yin et al, PLoS ONE 8(9):e74011, 2013Grant Funding Source: Supported by project grants from NHMRC and HMRI Australia