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Characteristics of canine coronary resistance arteries: importance of endothelium
P R Myers1, P F Banitt, R Guerra
1Department of Internal Medicine, University of Iowa College of Medicine, Iowa City.
Insights
Canine coronary microvessels and large epicardial vessels show distinct endothelial responses to vasopressin and thrombin. The endothelium plays a key role in modulating vascular reactivity in both small and large coronary arteries.
Area of Science:
- Cardiovascular Physiology
- Endothelial Function
- Vascular Biology
Background:
- The endothelium critically regulates vascular tone and reactivity.
- Understanding differences in endothelial function between coronary microvessels and large epicardial arteries is crucial for cardiovascular health.
Purpose of the Study:
- To investigate the role of the endothelium in canine coronary resistance vessels.
- To compare endothelial modulation of vascular responses to acetylcholine, vasopressin, and thrombin in microvessels versus large epicardial vessels.
Main Methods:
- In vitro study of canine coronary resistance vessels and large epicardial arterial rings.
- Utilized acetylcholine, vasopressin, and thrombin to assess vascular responses.
- Employed hemoglobin to inactivate endothelium-derived relaxing factor (EDRF) and assess its role.
Main Results:
- Acetylcholine induced vasodilation in preconstricted microvessels and large arteries, dependent on EDRF.
- Vasopressin constricted microvessels (potentiated by hemoglobin) but dilated large arteries in an endothelium-dependent manner.
- Thrombin caused endothelium-dependent relaxation in large arteries but constriction in microvessels, unaffected by hemoglobin.
Conclusions:
- The endothelium of coronary microvessels modulates vascular reactivity to selected agents, similar to larger vessels.
- Significant differences exist in the responses of large coronary arteries and microvessels to vasopressin and thrombin.
- Endothelial mechanisms vary between different sizes of coronary vessels, impacting overall coronary blood flow regulation.
Abstract:
Canine coronary resistance vessels were studied in vitro to examine the role of the endothelium in modulating responses to acetylcholine, vasopressin, and thrombin and to compare these responses to those found in large epicardial vessels. Acetylcholine had no effect on passively distended microvessels; however, after preconstriction with the thromboxane analogue, U 46619 caused dose-dependent vasodilation [50% effective concentration (EC50), 0.05 microM; maximum response, 97.9 +/- 2.1% relaxation]. Large epicardial arterial rings studied in organ chambers similarly relaxed to acetylcholine (EC50, 0.07 microM; maximum response, 79 +/- 5% relaxation). Hemoglobin was utilized to inactivate endothelium-derived relaxing factor (EDRF), resulting in reversal of acetylcholine vasodilation in both the microvessels (92 +/- 3.2% reversal) and the large epicardial vessels (117 +/- 9%). Hemoglobin had no effect on passively distended or preconstricted microvessels. Vasopressin constricted resistance vessels by 22.3 +/- 5.9 microns at 500 microU/ml. Hemoglobin potentiated this response by 100%, suggesting that vasopressin elicited EDRF release. In large coronary arteries, however, vasopressin elicited endothelium-dependent dilation with maximal relaxation of 36 +/- 9% at 3,000 microU/ml. Thrombin produced endothelium-dependent relaxation of large epicardial arterial rings but only constricted coronary microvessels. The response to thrombin was not altered by hemoglobin. This study demonstrates that the endothelium of coronary microvessels, like that of larger vessels, importantly modulates vascular reactivity to selected agents. Furthermore, major differences exist between large and small coronary arteries in their response to vasopressin and thrombin.