Stress fiber strain is zero in normal aortic smooth muscle, elevated in hypertensive stretch, and minimal in wall thickening rats

Figures

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  Fig. 1. Experimental devices. (a) Experimental setup of the pressure-diameter test. (b) Image of the aorta during intraluminal pressurization. (c) Binarized image of (b). Diameter was measured at three positions (yellow lines). (d) Experimental setup for the tensile tester. The sample was fixed on a PET film with adhesive, and a fluorescent image was captured using a microscope. (e) Representative image of the specimen under a tensile test.

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  Fig. 2. Schematic of image analysis. (a) Image of EL autofluorescence captured in the radial-circumferential (r-θ) plane. (b) An analysis line segment was drawn near the marker along the r-axis, toward the center of the image from the marker, to obtain the marker coordinate in the r-axis. (c) A Gaussian function was fitted to the intensity curve along the analysis line in (b). (d) Inverted image of (a). (e) An analysis line segment was drawn on the marker along the θ axis, aligned with the centerline of the EL, to obtain the marker coordinate in the θ axis. (f) A Gaussian function was fitted to the intensity curve along the analysis lines in (e). (g and h) The four makers (i, j, k, l) in (g) real coordinates (r, θ) were converted to (± 1, ± 1) in (h) the imaginary coordinates (ξ, η) before deformation. The same converting function was then applied to the markers after deformation. Strain was first calculated in the imaginary coordinates and then converted to the real coordinates. For details, see Sugita et al.23.

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  Fig. 3. Blood pressure and wall thickness of individuals and their mean ± SD. (a) Systolic and diastolic blood pressures of SHR and WKY. Those pressures were significantly higher in SHR than in WKY (U value = 0). (b) SHR and WKY wall thickness. The SHR wall thickness tended to be higher, but the difference was not significant (U value = 3). (c) Wall thickness normalized by rat weight. The normalized SHR wall thickness was significantly higher than that of WKY (U value = 0). These results confirmed that SHRs are hypertensive and have thickened aortic walls. WKY, Wistar Kyoto rat; SHR, spontaneously hypertensive rat; Dia, diastolic blood pressure; Sys, systolic blood pressure; N, number of rats. Analyzed using the Mann–Whitney U test.

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  Fig. 4. Elastic laminas (ELs, red) and stress fibers (SFs, green) in the aorta in the radial-circumferential (r- θ) plane. Images were captured at (a) diastolic pressure from WKY, (b) systolic pressure from WKY, (c) 179 mmHg from WKY, (d) diastolic pressure from SHR, and (e) systolic pressure from SHR. Yellow arrowheads indicate the photobleached marker positions in ELs used to calculate strains. Insets at the bottom right of each panel indicate enlarged areas of the white-boxed regions. WKY, Wistar Kyoto rat; SHR, spontaneously hypertensive rat. Image intensity was adjusted to enhance visibility. Scale bars = 50 μm.

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  Fig. 5. Normal circumferential strain εθθ, normal radial strain εrr, and absolute shear strain |εrθ| in the radial-circumferential (r-θ) plane. (a) Schematic illustration of strains εθθ, εrr, and εrθ. Aortic tissue before deformation (dashed line) changes into the tissue after deformation (solid line). (b–d) Strains of (b) εθθ, (c) εrr, and (d) |εrθ| of WKYphys, WKYhigh, and SHRphys. A significant difference was found for εθθ and εrr only in WKYhigh. WKYphys, state from diastolic to systolic blood pressure in WKY rats; WKYhigh, state from diastolic to hypertensive blood pressure (179 mmHg) in WKY rats; SHRphys, state from diastolic to systolic blood pressure in spontaneously hypertensive rats. Analyzed using the Steel–Dwass test.

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  Fig. 6. The magnitude and direction of the first principal strain ε1 and the strain in the SF direction εSF for WKYphys, WKYhigh, and SHRphys. In this graph, the direction and distance from the origin to the plots indicate the strain direction and magnitude, respectively. Numbers on gray circles indicate strain magnitude. WKYphys, state from diastolic to systolic blood pressure changes in WKY rats; WKYhigh, state from diastolic to hypertensive blood pressure (179 mmHg) changes in WKY rats; SHRphys, state from diastolic to systolic blood pressure changes in spontaneously hypertensive rats; r, radial direction; θ, circumferential direction.

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  Fig. 7. SF direction αSF and strain in the SF direction εSF in WKYphys, WKYhigh, and SHRphys. (a) The absolute value of SF direction αSF relative to the circumferential direction. (b) Strain in the SF direction εSF. Significant differences in αSF and εSF were found only in WKYhigh. WKYphys, state from diastolic to systolic blood pressure in WKY rats; WKYhigh, state from diastolic to hypertensive blood pressure (179 mmHg) in WKY rats; SHRphys, state from diastolic to systolic blood pressure in spontaneously hypertensive rats. Analyzed using the Steel–Dwass test.

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  Fig. 8. Summary of strain in the circumferential direction εθθ, SF direction αSF, strain in the SF direction εSF, and zero strain direction αmin during normal blood pressure, initial phase of hypertension, and after wall thickening.