MECHANICAL AND CONTRACTILE PROPERTIES OF IN-SITU LOCALIZED MESENTERIC-ARTERIES IN NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RATS

An in situ model was developed for studying mechanical properties of m esenteric arteries in rats, A branch of the mesenteric artery was expo sed and dissected in normotensive (WKY) and spontaneously hypertensive rats (SHR). A catheter was introduced into the larger branch of the m esenteric artery and connected to a pressure chamber. The artery was s ubmitted to transmural pressures ranging from 0 to 200 mmHg per steps of 25 mmHg and observed using a microscope-video-camera system. The di ameter-pressure relations were established under basal conditions, und er contraction (phenylephrine 10(-6)M), and after abolition of the smo oth muscle tone by potassium cyanide (KCN, 0.1 mg/mL). The arterial se gment was then fixed (glutaraldehyde 2.5%), and the wall cross-section al areas were measured in transverse sections. Compliances, distensibi lity, wall tensions, and wall stresses were calculated from diameter, pressure, and media thickness values under three conditions. Active te nsion and active stress were defined as differences in wall stresses a nd wall tensions calculated under passive and active conditions. Compa rision of WKY and SHR when arteries were studied at the respective ope rating pressure indicates (1) thicker and stiffer mesenteric arteries in SHRs than in WKY rats, (2) similar wall stresses in mesenteric arte ries from WKY and SHRs despite larger wall tensions in the hypertensiv e group, and (3) larger contractility to phenylephrine in SHRs than in WKY mesenteric arteries.