Diastolic dysfunction in pulmonary artery hypertension: Creatine kinase and the potential therapeutic benefit of beta‐blockers

Figures

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  Figure 1. Beta‐Blocker treatment improves EDPVR and increases resting sarcomere length. (A), PV relationships from a CON (black), MCT+BB (blue) and MCT (red) animal. The EDPVR was recorded during progressive vena cava occlusion. The loops from the three groups are displaced along the x‐axis and averaged for clarity. (B), There was a significantly steeper EDPVR in MCT (N = 7 animals) than CON (N = 10 animals) (P < .05) indicating diastolic dysfunction in MCT. The relationship for MCT+BB (N = 5 animals) was intermediate indicating an improvement in diastolic function. One‐way ANOVA with Tukey post hoc test. (C), In isolated RV myocytes resting sarcomere length progressively shortened CON > MCT+BB > MCT (n = 30 cells from N = 6 rats per group). * P < .05, one‐way ANOVA with Holm‐Sidak post hoc test. CON, control; MCT, monocrotaline treated; MCT+BB, monocrotaline + beta‐blocker treated; EDPVR, end‐diastolic pressure‐volume relationship

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  Figure 2. Loss of creatine kinase was attenuated by BB treatment. (A), Creatine kinase (CK) isoenzyme distribution in cardiac muscle consists of 70% muscle (CK‐m), 20% mitochondrial (CK‐mt) and the remainder brain (CK‐b) isoforms. Expression of mRNA for the predominant CK isoforms were reduced in MCT+BB and MCT rats compared to CON. Mean values for MCT+BB were greater than MCT but not statistically so. N = 10 rats per group. One‐way ANOVA with Holm‐Sidak post hoc test. (B), Western blots for CK‐m and CK‐mt. C, CON; B, MCT+BB; M, MCT. Common CON samples were run on each gel as calibrator samples where N precluded use of a single gel. Blots were stripped and re‐probed for GAPDH hence changes in background density. Protein levels for (C), CK‐m (N = 6‐10 rats per group) were decreased in MCT compared to CON, levels for MCT+BB were intermediate. One‐way ANOVA with Dunn's post hoc test. (D) A similar trend was observed in CK‐mt expression, although differences were not statistically significant (N = 6‐7 rats per group). Protein levels were normalised to GAPDH and expressed relative to the mean value in CON. *P < 0.05 CON, control; MCT, monocrotaline treated; MCT+BB, monocrotaline + beta‐blocker…

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  Figure 3. Beta‐blocker treatment partially restored the profile of isolated RV myocyte contraction–frequency relationships. (A), Unloaded sarcomere fractional shortening was recorded in isolated cells electrically paced at 1 Hz. Shortening was greater in MCT than CON and MCT+BB (*P < .05, one‐way ANOVA with Tukey's post hoc test). (B), Shortening normalised to values at 1 Hz. When stimulation frequency was increased to 7 Hz CON myocytes showed a positive response whereas the response in MCT was negative. The response of MCT+BB was intermediate demonstrating an increased ability to maintain contraction amplitude in response to the increase in demand (n = 22‐30 myocytes from N = 6 rats per group). Only cells which contracted regularly at 7 Hz were included for analysis. *P < .05 vs CON, † P < .05 vs MCT+BB. Within‐group response to frequency was assessed using one‐way repeated measures ANOVA. Between‐group differences at each frequency were identified using one‐way ANOVA with Dunn's post hoc test while accounting for multiple comparisons using the Bonferroni method CON, control; MCT, monocrotaline treated; MCT+BB, monocrotaline + beta‐blocker treated