Thiol agents separate nitric oxide formation from vasodilation induced by glyceryl trinitrate

Area of Science:

• Pharmacology
• Biochemistry
• Physiology

Background:

• Glyceryl trinitrate (GTN) is a vasodilator used clinically.
• The precise mechanism of GTN-induced vasodilation, particularly the role of nitric oxide (NO) and thiol-containing compounds, remains incompletely understood.
• Organic nitrates are generally considered prodrugs of NO, but their exact metabolic pathways are complex.

Purpose of the Study:

• To investigate the role of thiol-containing compounds in GTN-induced vasodilation.
• To elucidate the involvement of NO in the mechanism of GTN action.
• To determine if GTN acts solely as a direct prodrug of NO.

Main Methods:

• Bovine pulmonary artery (BPA) rings were used to assess vasodilation.
• The thiol-alkylating agent N-ethylmaleimide (NEM) was employed to modify thiol groups.
• Nitric oxide (NO) production was measured using the chemiluminescence-headspace gas method.
• Protection and reversal protocols using L-cysteine and D-cysteine were performed.

Main Results:

• N-ethylmaleimide (NEM) significantly decreased GTN-induced relaxation in BPA rings.
• L-cysteine pretreatment (protection protocol) prevented the NEM-induced decrease in relaxation, while D-cysteine did not.
• NEM completely abolished NO detection from GTN, whereas L-cysteine treatment restored NO production.
• NO production from GTN was significantly elevated with L-cysteine protection or reversal protocols.

Conclusions:

• Thiol compounds play a crucial role in the mechanism of glyceryl trinitrate (GTN)-induced vasodilation.
• The findings suggest that GTN's mechanism of action is more intricate than simply acting as an immediate prodrug of NO.
• Specific thiol interactions are likely involved in the bioactivation of GTN and subsequent NO release.