Contractile Behavior of Right Atrial Myocardium of Healthy Rats and Rats with the Experimental Model of Pulmonary Hypertension

Abstract

There is a lack of data about the contractile behavior of the right atrial myocardium in chronic pulmonary heart disease. We thoroughly characterized the contractility and Ca transient of isolated right atrial strips of healthy rats (CONT) and rats with the experimental model of monocrotaline-induced pulmonary hypertension (MCT) in steady state at different preloads (isometric force-length), during slow force response to stretch (SFR), and during post-rest potentiation after a period of absence of electrical stimulation (PRP). The preload-dependent changes in the isometric twitch and Ca transient did not differ between CONT and MCT rats while the kinetics of the twitch and Ca transient were noticeably slowed down in the MCT rats. The magnitude of SFR was significantly elevated in the MCT right atrial strips and this was accompanied by the significantly higher elevation of the Ca transient relative amplitude at the end of SFR. The slow changes in the contractility and Ca transient in the PRP protocol did not differ between CONT and MCT. In conclusion, the alterations in the contractility and Ca transient of the right atrial myocardium of monocrotaline-treated rats with pulmonary hypertension mostly concern the elevation in SFR. We hypothesize that this positive inotropic effect in the atrial myocardium may (partly) compensate the systolic deficiency of the right ventricular failing myocardium.

Evaluation of right atrium structure and function in a rat model of monocrotaline‐induced pulmonary hypertension: Exploring the possible antiarrhythmic properties of amiodarone

“…To better describe RA function and evaluate the susceptibility of the tissue to develop arrhythmias, we studied RA mechanical function from CTRL and MCT animals. A previous study reported that RA strips, from CTRL and MCT rats 24 to 28 days after the beginning of the experiments, once electrical stimulated at 2 Hz at 30°C did not present any changes in the mechanical properties of the tissue 7 . Interestingly, in a previous report using RA under sinus node beating frequency 14 days after MCT administration in rats, we found a faster contraction and relaxation time in the RA of MCT rats compared to the CTRL 20 .…”

“…A previous study reported that RA strips, from CTRL and MCT rats 24 to 28 days after the beginning of the experiments, once electrical stimulated at 2 Hz at 30 C did not present any changes in the mechanical properties of the tissue. 7 Interestingly, in a previous report using RA under sinus node beating frequency 14 days after MCT administration in rats, we found a faster contraction and relaxation time in the RA of MCT rats compared to the CTRL. 20 This is in line with the recent observation that spontaneous activity of sinoatrial-node preparations from rabbits treated with MCT show faster beat rates.…”

“…Among them, the well-defined rat model of monocrotaline (MCT)-induced PH (MCT-PH) with RV and RA involvement is one of the most studied. [6][7][8] Impaired RA electrical function and susceptibility to develop AA was previously demonstrated in the MCT-PH rat model. 6,9 However, it is not known if RA mechanical function is impaired in the MCT-PH model later in the disease progression and if the RA is susceptible to develop arrhythmias.…”

“…There are several animal models available to study RA function and arrhythmias during PH. Among them, the well‐defined rat model of monocrotaline (MCT)‐induced PH (MCT‐PH) with RV and RA involvement is one of the most studied 6–8 . Impaired RA electrical function and susceptibility to develop AA was previously demonstrated in the MCT‐PH rat model 6,9 .…”

Ranolazine exerts atrial antiarrhythmic effects in a rat model of monocrotaline‐induced pulmonary hypertension

“…Some groups have reported that RA mechanical function is not compromised in MCT rats. In one study, the authors treated rats with MCT and between 24 and 28 days later evaluated RA strips under electrical stimulation at 2 Hz at 30°C 31 and reported no significant change in the mechanical properties of the tissue. However, in our study, we found that RA function was compromised in the MCT rats.…”