Theophylline-induced endothelium-dependent vasodilation is mediated by increased nitric oxide release and phosphodiesterase inhibition in rat aorta

by Selleckchem | Dec 06 2023

This study aimed to examine the endothelial dependence of vasodilation induced by the phosphodiesterase inhibitor theophylline in isolated rat thoracic aortas and elucidate the underlying mechanism, with emphasis on endothelial nitric oxide (NO). The effects of various inhibitors and endothelial denudation on theophylline-induced vasodilation, and the effect of theophylline on vasodilation induced by NO donor sodium nitroprusside, cyclic guanosine monophosphate (cGMP) analog bromo-cGMP, and β-agonist isoproterenol in endothelium-denuded aorta were examined. The effects of theophylline and sodium nitroprusside on cGMP formation were also examined. We examined the effect of theophylline on endothelial nitric oxide synthase (eNOS) phosphorylation and intracellular calcium levels. Theophylline-induced vasodilation was greater in endothelium-intact aortas than that in endothelium-denuded aortas. The NOS inhibitor, NW-nitro-L-arginine methyl ester; non-specific guanylate cyclase (GC) inhibitor, methylene blue; and NO-sensitive GC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one inhibited theophylline-induced vasodilation in endothelium-intact aortas. Theophylline increased the vasodilation induced by sodium nitroprusside, bromo-cGMP, and isoproterenol. Theophylline increased cGMP formation in endothelium-intact aortas, and sodium nitroprusside-induced cGMP formation in endothelium-denuded aortas. Moreover, theophylline increased stimulatory eNOS (Ser1177) phosphorylation and endothelial calcium levels, but decreased the phosphorylation of inhibitory eNOS (Thr495). These results suggested that theophylline-induced endothelium-dependent vasodilation was mediated by increased endothelial NO release and phosphodiesterase inhibition.

Comments:

The study you described investigated the mechanisms underlying vasodilation induced by theophylline in isolated rat thoracic aortas, with a focus on endothelial nitric oxide (NO). Here's a breakdown of the key findings and conclusions from the study:

### Methodology:
1. **Objective:** The study aimed to understand the endothelial dependence of theophylline-induced vasodilation and explore the underlying mechanisms, particularly involving endothelial nitric oxide (NO) pathways.

2. **Experimental Setup:** The researchers used isolated rat thoracic aortas for their experiments. They examined the effects of theophylline and various inhibitors on vasodilation. Additionally, they explored the impact of theophylline on vasodilation induced by NO donor sodium nitroprusside, cyclic guanosine monophosphate (cGMP) analog bromo-cGMP, and β-agonist isoproterenol.

### Key Findings:
1. **Endothelial Dependence:** Vasodilation induced by theophylline was more significant in endothelium-intact aortas compared to endothelium-denuded (without endothelial layer) aortas. This suggests that endothelial cells play a crucial role in theophylline-induced vasodilation.

2. **Inhibitor Effects:** Inhibitors like NW-nitro-L-arginine methyl ester (NOS inhibitor), methylene blue (non-specific guanylate cyclase inhibitor), and 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (NO-sensitive GC inhibitor) inhibited theophylline-induced vasodilation in endothelium-intact aortas. This indicates the involvement of NO pathways and guanylate cyclase activation in theophylline-induced vasodilation.

3. **Enhanced Vasodilation:** Theophylline enhanced vasodilation induced by sodium nitroprusside, bromo-cGMP, and isoproterenol, suggesting that theophylline potentiated the effects of NO, cGMP, and β-agonists in vasodilation.

4. **cGMP Formation:** Theophylline increased cGMP formation in endothelium-intact aortas and enhanced sodium nitroprusside-induced cGMP formation in endothelium-denuded aortas. This finding further supports the involvement of the NO-cGMP pathway in theophylline-induced vasodilation.

5. **eNOS Phosphorylation and Calcium Levels:** Theophylline increased stimulatory eNOS (Ser1177) phosphorylation and endothelial calcium levels. Additionally, it decreased the phosphorylation of inhibitory eNOS (Thr495). These changes suggest that theophylline influenced eNOS activity, leading to increased NO production and vasodilation.

### Conclusion:
The study concludes that theophylline-induced vasodilation in isolated rat thoracic aortas is endothelium-dependent. The mechanism involves increased endothelial NO release, activation of guanylate cyclase, and elevated cGMP levels. Theophylline achieves this by enhancing eNOS phosphorylation and influencing intracellular calcium levels, ultimately leading to vasodilation.

This research provides valuable insights into the specific pathways through which theophylline acts to induce vasodilation, shedding light on its potential applications in cardiovascular health.