Agents increasing cyclic GMP amplify 5-HT4-elicited positive inotropic response in failing rat cardiac ventricle

Activation of 5-HT4 receptors in failing ventricles elicits a cAMP-dependent positive inotropic response which is mainly limited by the cGMP-inhibitable phosphodiesterase (PDE) 3. However, PDE4 plays an additional role which is demasked by PDE3 inhibition. The objective of this study was to evaluate the effect of cGMP generated by particulate and soluble guanylyl cyclase (GC) on the 5-HT4-mediated inotropic response. Extensive myocardial infarctions were induced by coronary artery ligation in Wistar rats, exhibiting heart failure 6 weeks after surgery. Contractility was measured in left ventricular preparations. Cyclic GMP was measured by EIA. In ventricular preparations, ANP or BNP displayed no impact on 5-HT4-mediated inotropic response. However, CNP increased the 5-HT4-mediated inotropic response as well as the β1-adrenoceptor (β1-AR)-mediated response to a similar extent as PDE3 inhibition by cilostamide. Pretreatment with cilostamide eliminated the effect of CNP. Inhibition of nitric oxide (NO) synthase and soluble GC by l-NAME and ODQ, respectively, attenuated the 5-HT4-mediated inotropic response, whereas the NO donor Sin-1 increased this response. The effects were absent during PDE3 inhibition, suggesting cGMP-dependent inhibition of PDE3. However, in contrast to the effects on the 5-HT4 response, Sin-1 inhibited whereas l-NAME and ODQ enhanced the β1-AR-mediated inotropic response. cGMP generated both by particulate (NPR-B) and soluble GC increases the 5-HT4-mediated inotropic response in failing hearts, probably through inhibition of PDE3. β1-AR and 5-HT4 receptor signalling are subject to opposite regulatory control by cGMP generated by soluble GC in failing hearts. Thus, cGMP from different sources is functionally compartmented, giving differential regulation of different Gs-coupled receptors

Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

Expression of 5-HT_4(b), 5-HT_2A, 5-HT_2B and 5-HTT mRNA in left ventricular myocardium.

<p>Messenger RNA expression in cardiac ventricles from foetal (day 3 and 1 before expected birth; days -3 and -1), neonatal (day 1, 3 and 5 after birth; days 1, 3 and 5), adult (day 113), Sham and HF rats. (A) 5-HT_4(b) mRNA levels decreased with foetal and neonatal development and the level in adult myocardium was one tenth of that at day -3 but reappeared in HF; (B) 5-HT_2A mRNA expression increased at birth (day 1), decreased during neonatal development and was unaltered in HF; (C) 5-HT_2B mRNA expression was transiently increased at birth (day 1) compared to adult (day 113) and not changed in HF; (D) 5-HTT mRNA expression was lower in foetal hearts compared to neonatal, adult, Sham and HF which all showed a similar expression level. The results are normalised to the geometric mean of Arbp, Tbp, Rpl4 and Rpl32 and presented relative to day 113 (assigned value 1) for foetal and neonatal or to Sham (assigned value 1) for HF. *<i>vs</i>. day 113 p<0.05; **<i>vs</i>. day 113 p<0.01; ***<i>vs</i>. day 113 p<0.001; ##HF <i>vs</i>. Sham p<0.01.</p

Inotropic responses to serotonin and to isoproterenol in ventricles from foetal and neonatal hearts and left ventricular papillary muscles from 113-day-old, Sham and HF rats.

<p>Positive inotropic response to serotonin (10 µM) in ventricles from foetal and neonatal rats and papillary muscles from normal adult (day 113), Sham and HF rats driven at 1 Hz in the presence of prazosine (0.1 µM), timolol (1 µM) and atropine (1 µM); ketanserin (0.1 µM; A) or GR113808 (1 µM; B) and inotropic response to subsequent addition of isoproterenol (100 µM; C). The contractile response to serotonin or isoproterenol was measured after stabilisation at its maximum within 2–7 minutes as previously demonstrated <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045489#pone.0045489-Qvigstad1" target="_blank">[13]</a>. Panels show maximum inotropic response in % above basal. *<i>vs</i>. group indicated p<0.05; #HF <i>vs</i>. Sham p<0.05.</p

Expression profiles of mRNA markers of cardiac phenotypes.

<p>Messenger RNA expression in cardiac ventricles from foetal (day 3 and 1 before expected birth; days -3 and -1), neonatal (day 1, 3 and 5 after birth; days 1, 3 and 5), adult (day 113), Sham and HF rats. (A) Expression of ANP mRNA increases at birth and in HF; (B) MHC-α mRNA expression increases at birth and during transition from neonatal to adult and decreases in HF; (C) MHC-β mRNA expression demonstrates a transitional increase at birth and an increase in HF; (D) The ratio of MHC-β over MHC-α mRNA expression confirms transition in phenotype from foetal to adult and from Sham to HF. The results are normalised to the geometric mean of Arbp, Tbp, Rpl4 and Rpl32 and presented relative to day 113 (assigned value 1) for foetal and neonatal, and to Sham (assigned value 1) for HF. *<i>vs</i>. day 113 p<0.05; **<i>vs</i>. day 113 p<0.01; ***<i>vs</i>. day 113 p<0.001; ##HF <i>vs</i>. Sham p<0.01.</p

Animal characteristics of Sham and HF rats.

<p>Animal characteristics are given as mean values ± SEM. LVEDP, left ventricular end diastolic pressure; LVSP, left ventricular systolic pressure; LVDd, left ventricular diameter diastole; LVFS, left ventricular fractional shorting; LAD, left atrial diameter;</p>*<p>HF vs. Sham p<0.05;</p>***<p>HF vs. Sham p<0.001.</p

Correlation between the MHC-β/MHC-α mRNA expression ratio and the 5-HT₄ mRNA expression level in ventricles from foetal and neonatal hearts and left ventricular papillary muscles from 113-day-old, Sham and HF rats.

<p>The ratio of MHC-β to MHC-α mRNA levels and 5-HT₄ mRNA level showed a proportional relationship with a slope which significantly deviated from zero, p<0.0001 (linear regression analysis).</p