THE INFLUENCE OF ANGIOTENSIN-II-INDUCED INCREASE IN AORTIC-WALL MASS ON COMPLIANCE IN RATS IN-VIVO

Objective: This study was undertaken to examine the effects of angiote nsin II-induced structural changes in the aortic wall on the dynamic m echanical properties of the vessel in the rat. Methods: Wistar rats we re infused s.c. with 250 ng/kg/min angiotensin II(Ang II) for 14 days (ANG). Both ANG and control rats (CON) were equipped with an arterial catheter for measurement of arterial blood pressure. Thoracic aorta di ameter, compliance coefficient (CC), and distensibility coefficient (D C) were determined non-invasively in pentobarbital-anesthetized animal s using a B-mode imager attached to a vessel wall tracking system. Aft er sacrifice, medial cross-sectional area (CSA), and elastin and colla gen densities were determined by morphometry on cross-sections. Media thickness (Mt) and wall-to-lumen ratio (W/L) were subsequently calcula ted. Results: Ang II infusion significantly increased mean arterial bl ood pressure in conscious rats (122 +/- 3 mmHg CON vs. 157 +/- 4 mmHg ANG). This was normalized when the rats were anesthetized, thus making it possible to determine CC and DC under isobaric conditions where th e diastolic diameters were also similar. Two-week infusion of Ang II i nduced a significant increase in CSA from 0.48 +/- 0.02 mm(2) in CON t o 0.61 +/- 0.03 mm(3). Mt and W/L were likewise increased, but collage n and elastin densities remained unchanged. CC and DC were not effecte d by this increase in aortic wall mass (CC: 0.143 +/- 0.009 CON, 0.147 +/- 0.014 mm(2)/kPa ANG, DC: 0.052 +/- 0.005 CON, 0.051 +/- 0.004 kPa (-1) ANG). Conclusions: An increase in aortic wall mass resulting from chronic infusion of angiotensin II does dot alter the dynamic complia nce of the vessel under isobaric conditions.