NORMAL LEFT-VENTRICULAR DIASTOLIC COMPLIANCE AFTER REGRESSION OF HYPERTROPHY

We wished to determine whether (a) left ventricular (LV) diastolic chamber compliance and tissue elastic modulus were decreased with hypertrophy and improved after reversal of hypertension and regression of hypertrophy and whether collagen concentration was a major determinant of LV chamber compliance during hypertrophy or aging. Spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY), aged 8 months at time of study, were used for the hypertension-regression experiments. The aging study was based on 14- and 24-month-old Fischer-344 rats. LV chamber compliance was measured in isolated perfused hearts arrested in diastole. Length-tension curves (tissue elastic modulus) were obtained from ventricular strips, and hydroxyproline assays were used to estimate LV collagen content. Captopril and hydrochlorothizide were given for an 8-week period to both normotensive and hypertensive rats. Treatment normalized arterial pressure and caused regression of LV hypertrophy in SHR. LV diastolic compliance was less (pressure-volume curve steeper) in SHR than in WKY, but stiffness was similar in the two groups, as indicated by similar slopes when volume was adjusted for heart mass. Treatment significantly decreased ventricular stiffness in both SHR and WKY. Length-tension curves were almost identical in SHR and WKY, but treated SHR demonstrated less tension per given length. These changes occurred although collagen did not decrease in parallel to the decrease in LV mass. Aging was associated with 66 and 60% increases in collagen content and concentration, respectively, but did not alter LV chamber compliance significantly. We conclude that normalization of arterial pressure and regression of LV hypertrophy in SHR increase chamber compliance and decrease tissue elastic modulus and that increased collagen concentration does not necessarily affect LV chamber compliance during LV hypertrophy or during aging.