The effects of
hypoxia-reoxygenation on internal mammary (IMA) and radial (RA) arteries used for
coronary artery bypass grafting (CABG) were examined to identify mechanisms regulating contractile function and differences that could contribute to vasospasm. Isolated endothelium-intact IMA and RA rings precontracted with KCl (30 mM) rapidly dilated to
hypoxia (95% N(2)/5% CO(2)) with a greater relaxation in RA than IMA. Inhibitors of
cyclooxygenase (10 microM
indomethacin) and the
thromboxane A(2) (TxA)(2) receptor [1 microM [1S-[1alpha,2alpha(Z),3alpha,4alpha]]-7-[3-[2-(phenylamino)carbonyl]
hydrazine]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic
acid (
SQ-29548)] potentiated the relaxation to
hypoxia in IMA, but not RA, a response associated with increases in TxA(2). Relaxation of IMA and RA to
hypoxia appears to involve a
calcium-reuptake mechanism inhibited by
cyclopiazonic acid (0.2 mM), and it was not attenuated by a blocker of
potassium channels (10 mM
TEA). The recovery of force generation of IMA, but not RA, upon reoxygenation after 30 min of
hypoxia was significantly reduced in the initial phase of reoxygenation by
indomethacin and
SQ-29548 and by
endothelin receptor blocker
BQ-123 [cyclo(l-Leu-d-Trp-d-Asp-l-Pro-d-Val)]. Thus,
hypoxia relaxes IMA and RA by a
prostaglandin-independent mechanism potentially involving enhanced intracellular
calcium reuptake. The
prostaglandin-mediated alterations of responses to
hypoxia-reoxygenation seen in IMA, but not in RA, may predispose IMA to vasospasm-related complications of CABG.