RESUMO
A positive inotropic responsiveness to serotonin, mediated by 5-HT(4) and 5-HT(2A) receptors, appears in the ventricle of rats with post-infarction congestive heart failure (HF) and pressure overload-induced hypertrophy. A hallmark of HF is a transition towards a foetal genotype which correlates with loss of cardiac functions. Thus, we wanted to investigate whether the foetal and neonatal cardiac ventricle displays serotonin responsiveness. Wistar rat hearts were collected day 3 and 1 before expected birth (days -3 and -1), as well as day 1, 3, 5 and 113 (age matched with Sham and HF) after birth. Hearts from post-infarction HF and sham-operated animals (Sham) were also collected. Heart tissue was examined for mRNA expression of 5-HT(4), 5-HT(2A) and 5-HT(2B) serotonin receptors, 5-HT transporter, atrial natriuretic peptide (ANP) and myosin heavy chain (MHC)-α and MHC-ß (real-time quantitative RT-PCR) as well as 5-HT-receptor-mediated increase in contractile function exvivo (electrical field stimulation of ventricular strips from foetal and neonatal rats and left ventricular papillary muscle from adult rats in organ bath). Both 5-HT(4) mRNA expression and functional responses were highest at day -3 and decreased gradually to day 5, with a further decrease to adult levels. In HF, receptor mRNA levels and functional responses reappeared, but to lower levels than in the foetal ventricle. The 5-HT(2A) and 5-HT(2B) receptor mRNA levels increased to a maximum immediately after birth, but of these, only the 5-HT(2A) receptor mediated a positive inotropic response. We suggest that the 5-HT(4) receptor is a representative of a foetal cardiac gene program, functional in late foetal development and reactivated in heart failure.
Assuntos
Desenvolvimento Fetal/genética , Regulação da Expressão Gênica no Desenvolvimento , Insuficiência Cardíaca/genética , Ventrículos do Coração/metabolismo , Receptores 5-HT4 de Serotonina/genética , Animais , Feminino , Perfilação da Expressão Gênica , Insuficiência Cardíaca/metabolismo , Masculino , Contração Miocárdica/genética , Fenótipo , Gravidez , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Receptores Adrenérgicos beta/genética , Receptores Adrenérgicos beta/metabolismo , Receptores 5-HT4 de Serotonina/metabolismo , Proteínas da Membrana Plasmática de Transporte de Serotonina/genética , Proteínas da Membrana Plasmática de Transporte de Serotonina/metabolismoRESUMO
AIMS: Whereas natriuretic peptides increase cGMP levels with beneficial cardiovascular effects through protein kinase G, we found an unexpected cardio-excitatory effect of C-type natriuretic peptide (CNP) through natriuretic peptide receptor B (NPR-B) stimulation in failing cardiac muscle and explored the mechanism. METHODS AND RESULTS: Heart failure was induced in male Wistar rats by coronary artery ligation. Contraction studies were performed in left ventricular muscle strips. Cyclic nucleotides were measured by radio- and enzyme immunoassay. Apoptosis was determined in isolated cardiomyocytes by Annexin-V/propidium iodide staining and phosphorylation of phospholamban (PLB) and troponin I was measured by western blotting. Stimulation of NPR-B enhanced beta1-adrenoceptor (beta1-AR)-evoked contractile responses through cGMP-mediated inhibition of phosphodiesterase 3 (PDE3). CNP enhanced beta1-AR-mediated increase of cAMP levels to the same extent as the selective PDE3 inhibitor cilostamide and increased beta1-AR-stimulated protein kinase A activity, as demonstrated by increased PLB and troponin I phosphorylation. CNP promoted cardiomyocyte apoptosis similar to inhibition of PDE3 by cilostamide, indicative of adverse effects of NPR-B signalling in failing hearts. CONCLUSION: An NPR-B-cGMP-PDE3 inhibitory pathway enhances beta(1)-AR-mediated responses and may in the long term be detrimental to the failing heart through mechanisms similar to those operating during treatment with PDE3 inhibitors or during chronic beta-adrenergic stimulation.
