The Effect of Thromboxane on Contraction of Canine Mesenteric and Lingual Arteries

Abstract

Thromboxane A2 (TXA2), a potent vasoconstrictor agent, is released from platelets and smooth muscle during inflammation and trauma. TXA2 may cause lingual artery (LA) contraction, leading to lingual paresthesia. The effects of U-46619, a TxA2 mimetic, on isolated rings of canine LA and mesenteric artery (MA) were examined. U-46619 (1 nmol/L to 1 μmol/ L) caused a triphasic contraction of LA and MA; a rapid, phasic contraction; a slow, sustained contraction; and, upon washout of U-46619, a maintained contraction. The MA relaxed slowly, but the LA remained contracted for at least three h after washout. Decreasing extracellular calcium ion (Ca²⁺ ₀) to <0.1 μmol/L with 2 mmol/L EGTA relaxed MA, but not LA. EGTA (4 mmol/L) partially relaxed the maintained contraction of LA. Inhibition of protein kinase C with amphotericin B or staurosporine inhibited the phasic and sustained contractions of LA, but did not affect the maintained contraction in the presence or absence of EGTA. Thus, CA ²⁺ ₀ was required for the initial contraction of the LA by U-46619, but did not appear to be required for the maintained contraction following washout of U-46619. The data support the conclusion that following a brief exposure to U-46619, maintained contraction of LA persists by a unique mechanism that may be independent of Ca2+ and protein kinase C. Sustained LA contraction after exposure to endogenous TXA₂ during inflammation and trauma may contribute to impaired lingual blood flow and orofacial tissue injury.