Abstract
We have investigated factors modulating expression of inducible NO synthase (iNOS) in isolated adult rat cardiac fibroblasts. Treatment of cardiac fibroblasts with interleukin-1β (IL-1β) promotes induction of iNOS mRNA and protein and production of NO. Simultaneous incubation of cells with isoproterenol enhances the response to IL-1β, even though isoproterenol alone is without effect.N G-nitro-l-arginine methyl ester inhibits the effect of isoproterenol + IL-1β on NO production. β2-Adrenergic receptors appear to mediate this effect of isoproterenol. Reverse transcriptase-polymerase chain reaction analyses show that β2-receptor mRNA is the predominant β-receptor message; in pharmacologic studies, ICI-118,551 significantly antagonizes isoproterenol-stimulated cyclic AMP production whereas CGP20712A does not. Dibutyryl-cyclic AMP and forskolin mimic the synergistic effect of isoproterenol on IL-1β-induced NO production; H-89, a cyclic AMP-dependent protein kinase (PKA) inhibitor, antagonizes the enhancing effect of isoproterenol. Nuclear run-off experiments indicate that enhancement of iNOS by isoproterenol does not occur at the level of transcription. Message stability studies demonstrate that isoproterenol increases the half-life of iNOS mRNA from 1.0 to 1.9 h; this change is sufficient to account for the observed augmentation of iNOS mRNA and protein. Thus, cardiac fibroblasts produce significant amounts of NO in response to IL-1β via induction of iNOS; β-adrenergic stimulation enhances the IL-1β effect by stabilizing the iNOS message. These data suggest that cardiac fibroblasts could participate in a paracrine mechanism whereby the direct positive inotropic effect of β1-adrenergic stimulation of myocytes is opposed by β2-adrenergic enhancement of NO production, a negative inotropic event, in neighboring fibroblasts.
Footnotes
- Received January 31, 2000.
- Accepted September 19, 2000.
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Send reprint requests to: Åsa B. Gustafsson, Department of Pharmacology 0636, UCSD School of Medicine, 9500 Gilman Dr., La Jolla, CA 92093-0636. E-mail: agustafsson{at}ucsd.edu.
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This work was supported by National Institutes of Health Grants HL41307 and GM07752 and a predoctoral fellowship from the American Heart Association, Western States Affiliates (to Å.B.G).
- The American Society for Pharmacology and Experimental Therapeutics
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