Comparative study on the effect of aspirin, TP receptor antagonist and TxA2 synthase inhibitor on the vascular tone of human saphenous vein and internal mammary artery

AIMS

Thromboxane (TxA₂) is synthesized from arachidonic acid (AA) via thromboxane synthase (TxS) enzyme and induces vasoconstriction via TP receptor. Our aim is to compare the effects of aspirin, TxS inhibitor and TP receptor antagonist on vascular reactivity of bypass grafts (saphenous vein and internal mammary artery).

MAIN METHODS

Using isolated organ bath, saphenous vein and internal mammary artery preparations were incubated with TP receptor antagonist, TxS inhibitor, aspirin, IP or EP4 receptor antagonist. Then prostaglandin (PG)E₂, PGF_2α, phenylephrine and AA were administered in concentration-dependent manner. The expression of prostanoid receptor and PGI₂ synthase (PGIS) enzyme was determined by Western Blot.

KEY FINDINGS

TP receptor antagonist inhibited the contraction induced by PGE₂, PGF_2α, and AA but not that induced by phenylephrine in both types of vessels. Aspirin increased phenylephrine-induced contraction only in internal mammary artery and decreased AA-induced contraction in saphenous vein. TxS inhibitor decreased both PGE₂ and AA-induced contraction in both types of vessels. This decrease was reversed by co-incubation of TxS inhibitor and IP/EP4 receptor antagonists. The expressions of EP3 receptor and PGIS enzyme were greater in internal mammary artery compared to saphenous vein while IP and TP receptors expressed at similar levels.

SIGNIFICANCE

TP receptor antagonist and TxS inhibitor are more effective to reduce contraction induced by different spasmogens in comparison to aspirin. Our results suggest that TP receptor antagonist and TxS inhibitor might have an advantage over aspirin due to their preventive effect on increased vascular reactivity observed in post-operative period of coronary artery bypass grafting.