NORMAL LEFT-VENTRICULAR DIASTOLIC COMPLIANCE AFTER REGRESSION OF HYPERTROPHY

We wished to determine whether (a) left ventricular (LV) diastolic cha mber compliance and tissue elastic modulus were decreased with hypertr ophy and improved after reversal of hypertension and regression of hyp ertrophy and whether collagen concentration was a major determinant of LV chamber compliance during hypertrophy or aging. Spontaneously hype rtensive 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 cha mber compliance was measured in isolated perfused hearts arrested in d iastole. Length-tension curves (tissue elastic modulus) were obtained from ventricular strips, and hydroxyproline assays were used to estima te LV collagen content. Captopril and hydrochlorothizide were given fo r an 8-week period to both normotensive and hypertensive rats. Treatme nt normalized arterial pressure and caused regression of LV hypertroph y in SHR. LV diastolic compliance was less (pressure-volume curve stee per) 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, b ut treated SHR demonstrated less tension per given length. These chang es occurred although collagen did not decrease in parallel to the decr ease in LV mass. Aging was associated with 66 and 60% increases in col lagen content and concentration, respectively, but did not alter LV ch amber compliance significantly. We conclude that normalization of arte rial pressure and regression of LV hypertrophy in SHR increase chamber compliance and decrease tissue elastic modulus and that increased col lagen concentration does not necessarily affect LV chamber compliance during LV hypertrophy or during aging.