Elastin and Mechanics of Pig Pericardial Resistance Arteries (pPRA)

Resistance arteries are remodeled in hypertension and diabetes. Elastin was reported to play a role herein. The parietal pericardium is opened during cardio-thoracic surgeries and might be a valuable biopsy for research in cardio-vascular diseases. We tested the hypothesis that resistance arteries can be isolated from the pericardium to study the micro-architecture of elastin and vascular wall mechanics. The pericardium of pigs served to test the hypothesis. pPRAs were microdissected. Their structure was examined using multiphoton excitation fluorescence microscopy. Diameter-tension and pressure-diameter-length relationships were recorded in myographs. Findings are compared to rodent mesenteric resistance arteries and –basilar arteries (rMRA, rBA) with comparable lumen diameter (±300µm at 100mmHg). pPRA have no clear external elastic lamina (present in rMRA, but not rBA), scant elastin fibrils between their medial smooth muscle cells and a net-stocking-like internal elastic lamina underneath the endothelium (perforated sheet with fenestrae in rMRA and rBA). Isolated pPRA lengthen ~30% when pressurized to 100mmHg, like rMRA but not rBA (<10%). At 100mmHg, pPRA wall/lumen is ~15% (<10% in rMRA and rBA) and maximal active wall tension >7N/m (<5N/m in rMRA and rBA). In pPRA, transmural pressure corresponding to the diameter and wall tension at which the largest isometric contractions can be obtained (optimal preload) is >180mmHg compared to <50mmHg in rMRA and rBA. We confirm that resistance arteries with different micro-architecture of elastin display different bi-axial mechanical properties. This will have to be taken into account in future analyses of human pericardial resistance arteries.