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Endothelium‐dependent relaxations mediated by inducible B 1 and constitutive B 2 kinin receptors in the bovine isolated coronary artery

1995; Wiley; Volume: 116; Issue: 5 Linguagem: Inglês

10.1111/j.1476-5381.1995.tb15098.x

1476-5381

Grant R. Drummond, Thomas M. Cocks,

Nitric Oxide and Endothelin Effects

Rings of bovine left anterior descending coronary artery (LAD) were contracted with the thromboxane A 2 ‐mimetic, U46619 (1–30 nM), to approximately 40% of their maximum contraction to 125 mM KCl Krebs solution (KPSS max ) for comparison of responses to the B 1 and B 2 kinin receptor agonists, des‐Arg 9 ‐bradykinin (des‐Arg 9 ‐BK) and bradykinin (BK), respectively. Relaxation responses were normalized as percentages of the initial U46619‐induced contraction level, while contractile responses were expressed as percentages of KPSS max . After 6 h of in vitro incubation in Krebs solution at 37°C, des‐Arg 9 ‐BK (pEC 50 , 8.00 ±0.08; maximum response (R max ), 93.9 ±1.9%) and BK (pEC 50 , 9.75 ±0.07; R max , 100.1 ±0.7%) caused endothelium‐dependent relaxations in precontracted rings of bovine LAD which were competitively and selectively antagonized by the B . receptor antagonist, des‐Arg 9 ‐[Leu 8 ]‐BK (pA 2 , 6.27 ±0.11) and the B 2 receptor antagonist Hoe‐140 (pA 2 , 9.63 +0.14), respectively. At 3 h of in vitro incubation, the sensitivity (pEC 50 , 7.45 ±0.10) and R max (84.6 ±3.3%) to des‐Arg 9 ‐BK were significantly less than those obtained in the same tissues at 6 h (pEC 50 , 7.94 ± 0.06; R max , 91.4±2.5%), whereas endothelium‐dependent relaxations to BK and ACh were unaffected by incubation time. Relaxation responses to des‐Arg 9 ‐BK, but not BK, at both 3 h and 6 h were significantly attenuated by the protein synthesis inhibitors, cycloheximide (30 and 100 μ m ) and actinomycin D (2 μ m ). At 6 h, the nitric oxide (NO) synthase inhibitor, N G ‐nitro‐L‐arginine (L‐NOARG, 100 μ m ), caused a significant 2 fold decrease in pEC 50 (9.58 ±0.03) but had no effect on R max for BK. For des‐Arg 9 ‐BK, L‐NOARG (100 μ m ) caused a marked and significant decrease in both the pEC 50 and R max and revealed contractions to low concentrations of des‐Arg 9 ‐BK. In both cases, L‐NOARG inhibition was reversed in the presence of L‐arginine (10 mM). At 6 h, removal of the endothelium abolished relaxation responses to des‐Arg 9 ‐BK and BK, and for des‐Arg 9 ‐BK, but not BK, unmasked concentration‐dependent contractions (pEC 50 , 7.57 ±0.09; R max , 83.4±9.1%). The sensitivity of contractions to des‐Arg 9 ‐BK increased slightly from 3h (pEC 50 , 7.37 ±0.08) to 6 h (pEC 50 , 7.62 ±0.12) of in vitro incubation; however, there was a small but significant depression in the maximum response over this time (R max , 126.8 ±8.5% and 103.3 ±8.6% for 3 h and 6 h of incubation respectively). In conclusion, the bovine LAD contains inducible B 1 and constitutive B 2 endothelial cell kinin receptors, both of which mediate endothelium‐dependent relaxation partly via the release of NO. B 1 receptors were also present on the smooth muscle layer of the bovine LAD .