Functional Effects of Hyperthyroidism on Cardiac Papillary Muscle in Rats

Abstract

BackgroundHyperthyroidism is currently recognized to affect the cardiovascular system, leading to a series of molecular and functional changes. However, little is known about the functional influence of hyperthyroidism in the regulation of cytoplasmic calcium and on the sodium/calcium exchanger (NCX) in the cardiac muscle.ObjectivesTo evaluate the functional changes in papillary muscles isolated from animals with induced hyperthyroidism.MethodsWe divided 36 Wistar rats into a group of controls and another of animals with hyperthyroidism induced by intraperitoneal T3 injection. We measured in the animals' papillary muscles the maximum contraction force, speed of contraction (+df/dt) and relaxation (-df/dt), contraction and relaxation time, contraction force at different concentrations of extracellular sodium, post-rest potentiation (PRP), and contraction force induced by caffeine.ResultsIn hyperthyroid animals, we observed decreased PRP at all rest times (p < 0.05), increased +df/dt and -df/dt (p < 0.001), low positive inotropic response to decreased concentration of extracellular sodium (p < 0.001), reduction of the maximum force in caffeine-induced contraction (p < 0.003), and decreased total contraction time (p < 0.001). The maximal contraction force did not differ significantly between groups (p = 0.973).ConclusionWe hypothesize that the changes observed are likely due to a decrease in calcium content in the sarcoplasmic reticulum, caused by calcium leakage, decreased expression of NCX, and increased expression of a-MHC and SERCA2.

Effects of Hyperthyroidism on Contractility and Na+/Ca2+ Exchanger Activity in the Isolated Papillary Muscle of Rats

“…11 Fmax in response to caffeine (Table 3) also showed no differences, which demonstrated that the SR Ca 2+ content has not changed, which is in agreement with previous data published by Alba-Aguayo et al 1 Regarding contractility, represented by +dF/dt and -dF/dt, the available information is conflicting, and there is paucity of data. Our data revealed no changes in +dF/dt and a significant increase in diastolic function in HG when compared to the CG (Table 2); similar results were observed by Szkudlarek et al 14 and Palmieri et al 19 Vieira et al 11 reported an increment in + and -dF/dt and a decrease in time to peak contraction. On the contrary, Wolska et al 8 reported an increase in time to peak contraction, while…”

“…The CG received daily injections of saline solution during the same period. 11 The sample size was calculated based on the following statistical criteria: r=2tα 2 s 2 /d 2 , where r is the sample size, s 2 is an estimate of the experimental variance from previously performed experiments; tα is the t value with the s 2 degrees of freedom for the α level of probability; d is the desired difference between treatments. The sample size for each group was calculated as follows: r=s 2 q 2 F/ d 2 , where s and d were defined in the equation above, and F is the F value for the α level of probability with γ1 and γ2 degrees of freedom from performed experiments, and q is the studentized range for the experiment to be performed.…”

Contractility detection of isolated mouse papillary muscle using myotronic Myostation‐Intact device

“…[2][3][4][5] Because of the anatomical structure of the heart, papillary muscle is usually used as a representative part of the heart for the measurement of myocardial contractility. [6][7][8] Ex vivo muscle contractility has been detected in many studies for a long time. An organ bath is a traditional ex vivo testing system used for contractility detections; however, the solution in the detection chamber must be replaced at certain periods to ensure sufficient oxygen in the solution.…”

“…Presently, myocardial contractility detection has been widely used in scientific research 2–5 . Because of the anatomical structure of the heart, papillary muscle is usually used as a representative part of the heart for the measurement of myocardial contractility 6–8 …”