Inotropic effect of prostacyclin (PGI2) on isolated rat atria at different contraction frequencies

Abstract

The effects of a wide range of Prostacyclin (PGI2) concentrations on the Isometric Developed Tension (IDT) of isolated left auricles driven at different frequencies (0.8, 1.6 or 3.3 Hz) were explored. A comparison of the positive inotropism of PGI2, norepinephrine (NE), tyramine and phenylephrine (Phenyl) indicated that PGI2, NE and tyramine enhanced peak tension significantly less at slow (0.8 and 1.6 Hz) than at higher rates (3.3 Hz); whereas Phenyl augmented equally the IDT at all of these three driving frequencies. The positive inotropism evoked by PGI2 was inhibited by (-)-propranolol and also by a treatment with 6-OHDA. Cocaine, normetanephrine and U-0521, augmented the positive inotropic influence of PGI2 on atria paced at a slow rate (0.8 Hz) but not at a faster one (3.3 Hz). These results suggest that the action of PGI2 on atrial contractions is apparently indirect and mediated by the release of tissue catecholamines. In addition the effect of PGI2 and NE at slow and fast rates appears associated with a different relative relevance of the processes which terminate the action of added sympathomimetic agonists, namely, neuronal or extraneuronal uptake as well as metabolization via COMT. These mechanisms seen to be more prominent at slower driving frequencies and could explain the diminished effect of PGI2 and NE on slowly paced atria.

Cardiac Endothelial-Myocardial Signaling: Its Role in Cardiac Growth, Contractile Performance, and Rhythmicity

“…The possible inotropic actions of prostaglandins and their mainly cAMP-mediated underlying mechanisms are unresolved. Responses to PGI 2 and PGE 2 range from increased inotropy (1,98,150,255,260,376,389,397,477,553), to no effect (93, 255), to negative inotropy (510). In vitro studies on isolated papillary muscle have helped to explain some of these inconsistencies (392).…”

Pulmonary Hypertension-Associated Right Ventricular Cardiomyocyte Remodelling Reduces Treprostinil Function

“…Previously, some studies attributed the positive inotropic effect of PGI 2 to the release of tissue catecholamines, which is blocked by propranolol, a conventional β-AR blocker [51,52] and the synergistic effect of treprostinil and isoprenaline was reported on cell length shortening and to a lesser magnitude on isolated Langendorff hearts [28]. These studies did not report any changes in the speed of contraction or relaxation due to treprostinil on isolated cardiomyocytes, an effect that we were able to demonstrate.…”

“…The synergistic effect of a combination of treprostinil and isoprenaline was previously reported by many studies in cardiac tissues and cells [28,[49][50][51][52][53]. We wanted to investigate the effect in the setting of established PH-associated RV maladaptive remodelling.…”

Role of β2-adrenoceptors in the biological effect of autoimmune orchitis spleen cells

“…The ionic composition of KRB was reported previously (Sterin-Borcla et al 1974). After 1 h for equilibrium, initial control values for tension and spontaneous frequency of the isolated atria were recorded using a force transducer coupled to an ink writing oscillograph, as previously described (Stegin- Borda et al 1980). The preparations were paced with a bipolar electrode and an SK4 Grass stimulator.…”