Differences in load dependence of relaxation between the left and right ventricular myocardium as a function of age in rats.

Abstract

To determine whether the variation in the magnitude of work load sustained by the left and right ventricles during adulthood and senescence affects the load-dependent aspect of relaxation, posterior papillary muscles from the left and right ventricles of rats at 4, 10, and 20 months of age were studied under variably loaded conditions in vitro. Because of differences between the life spans of Fischer and Sprague-Dawley rats, the functional characteristics of relaxation were investigated to evaluate the possibility of a differential age-associated response in these two strains of animals. The kinetic performance of the diastolic phase of myocardial contraction was measured by assessing the relative time during which load bearing occurred in a series of afterloaded isotonic twitches. This measurement was expressed as the ratio of the duration of afterloaded isotonic shortening and relengthening to the time required for isometric force to decline to the same level during isometric relaxation. A ratio of less than unity identified a load-dependent state whereas a value greater than one reflected a load-independent condition. Results showed that the right myocardium was completely load independent whereas the left myocardium was fully load dependent at all physiological afterloads. Aging reduced the load independence of the right ventricle and the load dependence of the left ventricle in Fischer rats. In contrast, no aging effect on the properties of afterloaded isotonic relaxation was seen in Sprague-Dawley rats. In conclusion, distinct differences exist in the mechanical dynamics of inactivation between the left and right ventricular myocardium. Aging reduced these variations in Fischer rats but had no apparent influence in Sprague-Dawley animals up to 20 months after birth.

Thaliporphine Preserves Cardiac Function of Endotoxemic Rabbits by Both Directly and Indirectly Attenuating NFκB Signaling Pathway

“…Therefore, the pressure-volume (P-V) relationship obtained by varying the cardiac loading is widely used, which is relatively specific index for preload-independent contractility [25]. In endotoxemic volunteers or animals, this relationship is decreased, even without hypotension [26], [27].…”

Fischer and Lewis rat strains differ in basal levels of neurofilament proteins and their regulation by chronic morphine in the mesolimbic dopamine system

“…LEW vs. F344 rats also differ in other ways, including immune (and in particular autoimmune) responses to a number of antigens (Hansen and Pender, 1989;Mannie et al, 1989;Sternberg et al, 1989a). Moreover, F344 rats are known to exhibit exaggerated stress responses (Rosecrans et al, 19861, and to age at different rates (Capasso et al, 1989), compared to some other strains, although direct comparisons to LEW rats were not made in these investigations.…”

Inhibition of Rat Cardiac Muscle Contraction and Mitochondrial Respiration by Endogenous Peroxynitrite Formation During Posthypoxic Reoxygenation

“…18,19 The posterior papillary muscle (0.5 to 1 mm in diameter, 5 to 7 mm in length, and Ϸ30 mg in weight) was carefully and rapidly removed. The nontendinous end of the papillary muscle was tied to a fixed steel segment with Ethicon 6-0 braided silk, and the tendinous end of the papillary muscle was tied to a steel wire hook that was connected to a force transducer for measurement of changes in isometric contraction with a Grass polygraph recorder (model 79).…”