Mechanical Properties of Cardiac Muscle from Spontaneously Hypertensive Rats: Accentuated Aftercontractions

Abstract

Isometric properties of the isolated cardiac muscle of spontaneously hypertensive rats (SHR) were compared to those from age-matched normotensive Wistar-Kyoto (WKY) preparations to assess the contribution of alterations in intrinsic contractile properties of cardiac muscle to the well-documented increase in cardiac output seen during the early phases of hypertension. At Lmax, there were no detectible differences in resting tension, active tension, rate of tension development or rate of relaxation between SHR and WKY preparations, indicating that neither the hypertension nor the accompanying cardiac hypertrophy influences these particular contractile characteristics. Interactions between individual contractions of cardiac muscle were different. With paired pulse stimulation, SHR preparations had longer mechanical refractory periods and larger and more frequent aftercontractions. During the SHR high cardiac output phase, certain, but not all, of the intrinsic mechanical properties of heart muscle are different from age-matched WKY.