Hypertension Reduces Aortic Strain in Both Sexes, but only Aorta from Female Rats Showed Increase in Stress: The Role of Appropriate Normalization Method to Evaluate Strain-Stress Parameters

Abstract

The gold standard of arterial stiffness measurements in isolated aorta is the stress-strain (SS) relationship. Wall thickness (WT) and artery inner diameter (ID) are variables that plot the SS curve and should be normalized to the dimensions of the individual subject. Previously, we used measurements from the current literature, but the data collected were not accurate. Therefore, we hypothesized that the measurements of the vascular structure using echocardiogram (ECHO) should be applied to evaluate tissue puller to obtain SS data. With that, we also hypothesized that aorta from spontaneously hypertensive rats (SHR) has greater stress and lower strain levels than normotensive Wistar rats. To test this hypothesis, thoracic aorta parameters from 3-month-old male Wistar (WM) (body weight: 449±6.87g, n=4), SHR male (SM) (body weight: 295±3.34g, n=4), Wistar Female (WF) (body weight: 250±8.50g, n=4), and SHR Female (SF 169.4±2.69g, n=4) rats were measured from an ECHO. After, animals were killed and aortas were cut in 2 mm segments and mounted on Tissue Puller to measure SS. The inner diameter (ID) and wall thickness (WT) were measured by the ECHO for all animals: [WM (WT: 0.519±0.014mm, ID: 2.042±0.11mm), SM (WT: 0.485±0.026mm, ID: 2.023±0.055mm), WF (WT: 0.504±0.01mm, ID: 1.628±0.092mm), SF (WT: 0.521±0.011mm, ID: 1.64±0.099mm)] and there were no significant difference between these values. We then normalized the SS curves to each of the arteries’ parameters for ECHO and we found there were significant decreases in the strain values in aorta from hypertensive rats, regardless of sex (WM: 1.775±0.108 vs SM: 1.370±0.058; p=0.0146), and (WF: 2.056±0.218 vs. SF: 1.713±0.224; p=0.0517). We found a trend in the stress from female rats (WF: 1367±61 mN/mm2 vs SF 2361±391 mN/mm2; p=0.0597). There were no differences between male rats (WM:1.269±153 mN/mm2 vs SM: 1319±80 mN/mm2; p=0.671).Overall, these data show that ECHO should be used to accurately measure rat aorta structural parameters under the tissue puller. They also show SHR and Wistar were different in both sexes in strain, but only female SHR vs Wistar showed differences in stress. National Institutes of Health - R00GM118885, R01HL149762, and R00HL151889. and McNair Junior Fellows (MJF) Program This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.