Prostanoid-induced contractions are blocked by sulfonylureas

Area of Science:

• Pharmacology
• Vascular Physiology

Background:

• Sulfonylureas (glibenclamide, tolbutamide) are known blockers of ATP-regulated K+ channels.
• Prostanoids (prostaglandin F2 alpha, E2) and thromboxane A2 mimetic (U-46619) induce contractions in vascular smooth muscle.

Purpose of the Study:

• To investigate the effect of sulfonylureas on prostanoid-induced contractions in rat aorta.
• To determine the specificity of this blockade and its potential mechanism.

Main Methods:

• Vascular smooth muscle contraction assays on rat aorta and carotid artery.
• Testing blockade of contractions induced by various agonists including prostanoids, norepinephrine, phenylephrine, serotonin, endothelin-1, K+, and G-protein activators (AlF4-).
• Experiments conducted on both intact and endothelium-denuded aortic preparations.

Main Results:

• Sulfonylureas significantly blocked contractions induced by prostaglandin F2 alpha, prostaglandin E2, and U-46619 on rat aorta.
• This inhibitory effect was observed in endothelium-denuded preparations, indicating it is independent of the endothelium.
• The blockade was specific to prostanoids, as contractions induced by norepinephrine, phenylephrine, serotonin, endothelin-1, or high K+ were not significantly affected.
• Contractions induced by G-protein activation with AlF4- were significantly blocked by sulfonylureas.
• Glibenclamide also blocked prostaglandin F2 alpha-induced contractions on rat carotid artery.

Conclusions:

• Sulfonylureas (glibenclamide, tolbutamide) specifically inhibit prostanoid-induced vascular contractions.
• The mechanism of inhibition may involve interference with regulatory G-proteins, as evidenced by the blockade of AlF4--induced contractions.
• This contrasts with the lack of blockade on contractions mediated by other agonists that activate phospholipase C.