Angiotensin II-induced increase in myocardial distensibility and its modulation by the endocardial endothelium in the rabbit heart.
As recently demonstrated, angiotensin II (Ang II) induces an increase in myocardial distensibility. Although endothelin-1 and the endocardial endothelium (EE) also modulate myocardial diastolic properties, their interaction with Ang II at this level has not yet been investigated. Increasing concentrations of Ang II (from 10(-8) to 10(-5) M) were studied in rabbit right papillary muscles in the following conditions: (1) baseline; (2) after selective removal of EE with Triton X-100; and (3) with intact EE in presence of a non-selective endothelin receptor antagonist (PD-145065), a selective endothelin type A receptor antagonist (BQ-123), an inhibitor of nitric oxide synthesis (N(G)-nitro-L-arginine (L-NA) or an inhibitor of the NAD(P)H oxidase (apocynin). At baseline, Ang II induced a concentration-dependent positive inotropic effect and an increase in passive muscle length (L) up to 1.020 +/- 0.004 L/L(max). After restoring muscle length to maximal physiological length (L(max)), passive tension decreased by 46.1 +/- 4.0%. When the EE was removed, the effect on myocardial distensibility was abolished. With intact EE in presence of PD-145065, BQ-123 or L-NA, the effects of Ang II on myocardial distensibility were attenuated, with a maximal increase in passive muscle length of 1.0087 +/- 0.0012, 1.0068 +/- 0.0022 and 1.0066 +/- 0.0020 L/L(max) and a decrease in resting tension of 22.6 +/- 3.6, 16.1 +/- 6.0 and 20.4 +/- 5.6%, respectively. In the presence of apocynin, the effect on myocardial distensibility was abolished. In conclusion, the Ang II-dependent acute increase in myocardial distensibility is abolished by the selective removal of the EE and attenuated in the presence of endothelin-1 receptor antagonists, an inhibitor of nitric oxide synthesis or an inhibitor of NAD(P)H oxidase.
Department of Physiology, Faculty of Medicine, University of Porto, Porto, Portugal.
Paulo
P
Castro-Chaves
Ricardo
R
Fontes-Carvalho
Mariana
M
Pintalhao
Pedro
P
Pimentel-Nunes
Adelino F
AF
Leite-Moreira
D000098:Acetophenones / Q000494:pharmacology; D000804:Angiotensin II / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D000818:Animals; D003971:Diastole / Q000187:drug effects* / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004699:Endocardium / Q000187:drug effects* / Q000502:physiology*; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000037:antagonists & inhibitors / Q000502:physiology; D004727:Endothelium / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology; D010456:Peptides, Cyclic / Q000494:pharmacology; D011817:Rabbits; D017466:Receptors, Endothelin / Q000502:physiology
D000098:Acetophenones; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D010456:Peptides, Cyclic; D017466:Receptors, Endothelin; D000804:Angiotensin II; C082887:PD 145065; D019335:Nitroarginine; D009569:Nitric Oxide; C056165:acetovanillone; D019001:Nitric Oxide Synthase; D019255:NADPH Oxidases; C072247:cyclo(Trp-Asp-Pro-Val-Leu)