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Structural alterations in heart valves during left ventricular pressure overload in the rat
I E Willems1, M G Havenith, J F Smits
1Department of Pathology, Cardiovascular Research Institute, Maastricht, The Netherlands.
Background:
Heart valves are an important denominator of the function of the heart but detailed studies of structural alterations of heart valves after hemodynamic changes are lacking.
Experimental Design:
Structural alterations of heart valves, including DNA synthesis, collagen mRNA, and protein concentration were measured in heart valves of Wistar Kyoto (WKY) rats with acute left ventricular pressure overload, created by intrarenal aortic ligation (AL, N = 18) as well as in heart valves of age-matched spontaneously hypertensive rats, a model of chronic hypertension (N = 18). SHAM aortic ligation and normal WKYs (N = 17 and N = 17) served as controls. All animals received 5'bromo-2' deoxyuridine, during the last 7 days of the experiment, in a dose of 2.4 mg/kg.day.
Results:
The cumulative labeling fraction (LF) in the mitral valve of AL animals was 47.8 +/- 5.2% as compared with 9.4 +/- 2.6% in SHAM animals (mean +/- SEM, p < 0.01). The LF in the aortic valve of AL animals was 33.3 +/- 2.9% as compared with 7.7 +/- 0.7% in SHAM animals (p < 0.01). The LF in the tricuspid valve was also significantly increased: 11.3 +/- 1.4% in AL versus 5.8 +/- 0.7% in SHAM (p < 0.01). Labeling fractions of heart valves in SHR were not increased as compared with normal WKY. The total collagen concentration in the three heart valves, measured by the hydroxyproline assay, did not change. The mRNA amounts of both collagen type I and III, detected by in situ hybridization, were increased in the heart valves of AL and spontaneously hypertensive animals as compared with the two control groups (SHAM and WKY). In all 3 heart valves, interstitial cells were vimentin-positive, but desmin-negative. A fraction of interstitial cells showed alpha-smooth muscle actin positivity. This immunophenotype did not change during pressure overload.
Conclusions:
Heart valves have the capacity to adapt to acute pressure overload, by means of DNA synthesis and increased collagen turnover. The increase in LF in the normotensive tricuspid valve suggests a role for an additional circulating factor. A constant fraction of the interstitial heart valve cells consists of myofibroblasts.