Nitroglycerin-induced tolerance affects multiple sites in the organic nitrate bioconversion cascade.

Area of Science:

• Pharmacology
• Cardiovascular Physiology

Background:

• Nitroglycerin (NTG) tolerance is a clinical issue affecting vasodilator efficacy.
• Understanding the mechanisms of NTG tolerance is crucial for optimizing cardiovascular treatments.

Purpose of the Study:

• To investigate the impact of NTG-induced tolerance on the spasmolytic effects of various vasodilators.
• To identify potential sites of tolerance within the vasodilation signaling cascade.

Main Methods:

• Bovine isolated coronary artery rings were used to assess vasodilator responses.
• Rings were pre-exposed to NTG to induce tolerance or used as controls.
• Concentration-effect curves were generated for NTG, isosorbide dinitrate, sodium nitroprusside (SNP), 3-morpholinosydonimine (SIN-1), and others.

Main Results:

• NTG-tolerant rings showed significantly reduced responsiveness to NTG, isosorbide dinitrate, SNP, and SIN-1.
• Responses to S-nitroso-N-acetylpenicillamine and nitric oxide were only marginally affected.
• No significant difference in relaxation was observed for endothelium-dependent (A23187) or guanylate cyclase-independent (theophylline) vasodilators.
• Cross-tolerance studies indicated distinct tolerance mechanisms for organic nitrates versus non-nitrate vasodilators.

Conclusions:

• NTG-induced tolerance in coronary arteries affects multiple sites in the signaling pathway leading to vasodilation.
• Tolerance mechanisms differ between organic nitrates and other vasodilators like SNP and SIN-1.