Effects of the beta3-adrenergic agonist BRL 37344 on endothelial nitric oxide synthase phosphorylation and force of contraction in human failing myocardium.
BACKGROUND
In nonfailing myocardium, beta(3)-adrenergic signaling causes a decrease in contractility via endothelial nitric oxide synthase (eNOS) activation and nitric oxide (NO) release. This study investigates the hypothesis that beta(3)-adrenergic signaling undergoes alterations in failing myocardium.


METHODS
We compared eNOS- and beta(3)-adrenoceptor expression using Western blot analysis in human nonfailing myocardium versus failing myocardium. With the use of immunohistochemistry, we investigated the distribution of the beta(3)-adrenoceptor protein and eNOS translocation and phosphorylation under basal conditions. beta(3)-adrenergic, eNOS activation, and inotropy were measured in failing myocardium using BRL37344 (BRL, a beta(3)-adrenoceptor agonist).


RESULTS
beta(3)-adrenoceptor expression was increased in failing myocardium. Under basal conditions, Akt- and eNOS(Ser1177) phosphorylation were reduced in failing myocardium. During stimulation with BRL in failing myocardium, a further dephosphorylation of eNOS(Ser1177) and Akt was observed, whereas eNOS(Ser114) phosphorylation was increased. These results suggest a deactivation of eNOS via beta(3)-adrenergic stimulation. Nevertheless, BRL decreased contractility in failing myocardium, but this effect was not observed in the presence of the NO blocker L-NMA. In failing myocardium, the beta(3)-adrenoceptor was predominantly expressed in endothelial cells. In the cardiomyocytes, the beta(3)-adrenoceptor was mainly located at the intercalated disks.


CONCLUSIONS
In failing cardiomyocytes, beta(3)-adrenergic stimulation seems to deactivate rather than activate eNOS. At the same time, beta(3)-adrenergic stimulation induced a NO-dependent negative inotropic effect. Because beta(3)-adrenoceptors are expressed mainly in the endothelium in failing myocardium, our observations suggest a paracrine-negative inotropic effect via NO liberation from the cardiac endothelial cells.
Napp
Andreas
A
Clinic I of Internal Medicine, Cardiology, Pneumology and Angiology, University of Aachen, Aachen, Germany.
Brixius
Klara
K
Pott
Christian
C
Ziskoven
Christoph
C
Boelck
Birgit
B
Mehlhorn
Uwe
U
Schwinger
Robert H G
RH
Bloch
Wilhelm
W
D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology / Q000627:therapeutic use*; D000328:Adult; D002311:Cardiomyopathy, Dilated / Q000188:drug therapy* / Q000503:physiopathology; D004983:Ethanolamines / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D010766:Phosphorylation; D013318:Stroke Volume; D016277:Ventricular Function, Left / Q000502:physiology
D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists; D004983:Ethanolamines; C057368:BRL 37344; D019001:Nitric Oxide Synthase