Beta3-adrenoceptors modulate left ventricular relaxation in the rat heart via the NO-cGMP-PKG pathway.
OBJECTIVE
Using a model of isolated and Langendorff-perfused rat heart we analysed whether activation of beta3-adrenergic receptors (beta3-ARs) influences ventricular lusitropic performance. We also focused on the NOS/NO/cGMP/PKG cascade as the signal transduction mechanism.


METHODS
Hearts were treated with increasing concentrations (from 10(-12) to 10(-6) m) of BRL(37344), a selective beta3-AR agonist, and cardiac performance was evaluated by analysing both lusitropic parameters and coronary motility. Cardiac preparations were also perfused with BRL(37344) in the presence of either isoproterenol (ISO) or nadolol, or pertussis toxin (PTx), or selective inhibitors of the NOS/NO/cGMP/PKG pathway.


RESULTS
BRL(37344) caused a significant concentration-dependent reduction in (LVdP/dt)(min), a decrease in half time relaxation significant starting from 10(-12) m, and an increase in (LVdP/dt)(max)/(LVdP/dt)(min) ratio (T/-t). BRL(37344) abolished the ISO-mediated positive lusitropism. beta3-AR-dependent effects on relaxation were insensitive to beta(1)/beta2-AR inhibition by nadolol (100 nm), and were abolished by G(i/o) protein inhibition by PTx (0.01 nm). NO scavenging by haemoglobin (10 microm), and nitric oxide synthase (NOS) inhibition by NG-monomethyl-l-arginine (10 microm) revealed the involvement of NO signalling in BRL(37344) response. Pre-treatment with inhibitors of either soluble guanylate cyclase (ODQ; 10 microm) or PKG (KT(5823); 100 nm) abolished beta3-AR-dependent negative lusitropism. In contrast, anantin (10 nm), an inhibitor of particulate guanylate cyclase, did not modify the effect of BRL(37344) on relaxation.


CONCLUSIONS
Taken together, our findings provide functional evidence for beta3-AR modulation of ventricular relaxation in the rat heart which involves PTx-sensitive inhibitory Gi protein and occurs via an NO-cGMP-PKG cascade. Whether the effects of beta3-AR stimulation on lusitropism are beneficial or detrimental remains to be established.
Angelone
T
T
Department of Pharmaco-Biology, University of Calabria, Arcavacata di Rende (CS), Italy.
Filice
E
E
Quintieri
A M
AM
Imbrogno
S
S
Recchia
A
A
Pulerà
E
E
Mannarino
C
C
Pellegrino
D
D
Cerra
M C
MC
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D017869:Cyclic GMP-Dependent Protein Kinases / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004983:Ethanolamines / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology; D007545:Isoproterenol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D009924:Organ Culture Techniques; D051381:Rats; D017208:Rats, Wistar; D022702:Receptors, Adrenergic, beta-3 / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D016277:Ventricular Function, Left / Q000187:drug effects / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004983:Ethanolamines; D022702:Receptors, Adrenergic, beta-3; D009569:Nitric Oxide; C057368:BRL 37344; D017869:Cyclic GMP-Dependent Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D007545:Isoproterenol