Proceedings of The Physiological Society
Trinity College Dublin (2003) J Physiol 551P, C57
Vasomotor properties of rat coronary and accessory arteries
Stuart J. Bund and James F.X. Jones
Department of Human Anatomy and Physiology, University College Dublin, Earlsfort Terrace, Dublin 2, Ireland
The determination of the direct effects of autonomic control of coronary resistance arteries is complicated by concomitant changes in myocardial metabolism and extravascular compression. In the rat, cardiac muscle extends into the cranial venae cavae and receives its blood supply from an accessory circulation provided by branches of the subclavian arteries. This circulation is a potential experimental surrogate for the coronary circulation because the vessels are not subject to myocardial compression and are more accessible. We studied the responses of coronary and accessory arteries to autonomic vasomotor stimuli by the application of agonists to isolated arterial segments in vitro.
Male Wistar rats (331 ± 33 g, n = 13) were killed humanely by stunning followed by cervical dislocation in accordance with institutional guidelines. The heart and superior vena cava were rapidly excised and placed in ice-cold physiological salt solution (PSS). A branch from the septal coronary artery or a segment of the accessory artery was dissected free and mounted onto two glass microcannulae in an arteriograph. The segment was pressurized to 80 mmHg and bathed in PSS at 37°C, pH 7.4 and permitted to generate spontaneous myogenic tone. Internal diameter was continuously recorded using a video imaging system. Concentration-response curves (1 nM to 10 mM) to noradrenaline (NA), acetylcholine (ACh) and phenylephrine (PE) were determined in random order. Responses were taken as peak changes in internal diameter (mm) from the myogenic baseline. Fully relaxed internal diameters in calcium-free PSS were then determined. All values are expressed as means ± S.D. (n = number of animals).
Relaxed internal diameters of the coronary and accessory arteries were 229 ± 73 (5) and 150 ± 23 mm (8), respectively. After generation of myogenic tone, arteries achieved baseline diameters approximately 50 % of the fully relaxed diameter. ACh effected a dilator response in all coronary arteries (93 ± 48 mm (5)) and all accessory arteries (70 ± 23 mm (6)) and PE effected a constrictor response in all coronary arteries (20 ± 10 mm (4)) and all accessory arteries (49 ± 18 mm (6)). All coronary arteries dilated in response to NA (65 ± 55 (5)). On average, accessory arteries responded to NA with a small vasoconstrictor response (3 ± 50 mm (8)) but two distinct subgroups were apparent: one responded with dilatation (39 ± 13 mm (4)) and the other with constriction (46 ± 28 mm (4)).
These data show that coronary and accessory arteries respond similarly to ACh and PE. However, accessory arteries could be classified differently according to the nature of their response to NA. The neglected accessory circulation of the rat heart shows promise as an experimental surrogate for the coronary circulation.
This work was funded in part by the Health Research Board.
Where applicable, experiments conform with Society ethical requirements