Increased Contraction of Myocytes Isolated From the Young Spontaneously Hypertensive Rat Relationship Between Systolic and Diastolic Function

Abstract

This study was designed to assess heart performance in young (10-week-old) spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats, in terms of whole heart function in vivo and mechanics of isolated ventricular myocytes in vitro. The data suggest that left ventricular pressure (LVP) generation is greater, and the maximal velocities of LVP generation and decline are faster in SHR than in WKY. Two-dimensional morphologic measurements show that SHR myocytes are hypertrophied and that augmented contractile function is also present in isolated cells as determined by the extent of shortening and velocity of shortening. Relaxation is also faster at the myocyte level as determined by velocity of relengthening. However, the slope of the relationship between myocyte peak shortening and velocity of relaxation was similar in both groups. These results suggest that hyperdynamic myocyte relengthening may reflect changes in elastic recoil from increased shortening rather than intrinsic changes in cellular mechanisms, which are independent of shortening.

Noninvasive Evaluation of the Time Course of Change in Cardiac Function in Spontaneously Hypertensive Rats by Echocardiography

“…In the same way, Cingolani et al (23) showed an increase in τ in adult SHR (10 to 11 months old) using a catheter pressure transducer. It is unclear when diastolic dysfunction develops in the SHR heart, but at 10 weeks of age the length and diameter of cardiomyocytes are larger than normal (22) and there is increased collagen content in the LV wall (32). These data are in line with our finding that diastolic dysfunction of SHR was present early in life.…”

“…They also reported that this increase disappeared with pharmacological inhibition of extrinsic autonomic input to the heart. Other investigators found increased contractility in myocytes isolated from the SHR heart (21,22). Hemodynamic measurements using a catheter pressure transducer in vivo have shown increased systolic performance of SHR hearts (22,23).…”

“…Other investigators found increased contractility in myocytes isolated from the SHR heart (21,22). Hemodynamic measurements using a catheter pressure transducer in vivo have shown increased systolic performance of SHR hearts (22,23). However, there have also been reports that contractility was not changed in these animals (24,25).…”

“…Diastolic dysfunction is to be expected in the SHR because of the increased wall thickness and fibrosis (29−31). Okayama et al (22) reported that relaxation was not altered in isolated myocytes of SHR at 10 weeks of age, but Nishimura et al (29) analyzed LV diastolic function using τ and demonstrated prolongation at 28 and 50 weeks of age compared with agematched WKY. In the same way, Cingolani et al (23) showed an increase in τ in adult SHR (10 to 11 months old) using a catheter pressure transducer.…”

Effects of Angiotensin II Type 1 Receptor Antagonist on Smooth Muscle Cell Phenotype in Intramyocardial Arteries from Spontaneously Hypertensive Rats

“…It has been reported that young SHR show hyperdynamic circulation associated with elevated afterload and normal LV relaxation, and LV hypertrophy was accompanied by structural remodeling of the myocardium that included myocyte hypertrophy and cardiac fibrosis (28); inhibition of the renin-Ang system reduced the LV hypertrophy (8,29). Thus, compared with the aged SHR, LV hypertrophy in 20-week-old SHR is thought to be a physiological adaptation of the heart to increase its performance and thereby maintain cardiac output despite the increased afterload for the heart in SHR (28,30). By reducing blood pressure within 6 weeks of treatment by either enalapril or FK-739, LV hypertrophy and fibrosis were significantly reduced, and little differences in LV hypertrophy or cardiac fibrosis were seen between the vehicle WKY and drug-treated SHR, whereas vascular remodeling of the intramyocardial arteries was not inhibited in the two drugtreated SHR groups.…”