3.6 Endothelium-dependent relaxations
During contraction stimulated by 32 mM K+, the relaxing response to 1 μM BK was significantly reduced by L-NAME and by ODQ (Figure 7A and 7B). On average, the effect of both inhibitors was only partial and was more marked in the presence of indomethacin. Surprisingly, in both the absence and presence of indomethacin, c-PTIO did not alter relaxing responses to BK in depolarized arteries in which it abolished relaxing responses to SNP (Figure 7A and 7B, Figure 4A and 4B). Also, in contrast to exogenous NO, DETCA partly reduced relaxing responses to 0.01 nM – 1 μM BK but did not abolish them (Figure 7C). We therefore evaluated involvement of HNO which can be generated most notably by nNOS which in addition to eNOS is also expressed in the wall of the pericardial resistance arteries (Figure 3). However, neither the HNO-scavenger NAC nor the selective nNOS-inhibitors 7-NI and NPLA modified BK-induced relaxation in arteries in which L-NAME caused a partial inhibition (Figure 7C and Figure 8A). While amitrole moderately but significantly increased the potency and efficacy of the relaxing effect of BK during K+-induced contraction (Figure 7C), exogenous catalase did not modify them in the absence and presence of L-NAME (Figure 7D).
Effects of the various inhibitors were not only tested on BK-induced relaxation during contractions stimulated by 32 mM K+but also on BK-induced relaxation during contractions of similar amplitude stimulated by ET-1 in the same arterial segments (Figures 8 and 9). Indomethacin did not modify responses to BK during agonist-stimulated contraction (Figure 9B). In most experiments, also L-NAME failed to modify these responses to BK (Figure 8B, 9A, 9B), but in one experiment a small statistically significant reduction by L-NAME was observed (Figure 9D). In line with the on average failure of L-NAME to blunt BK-induced relaxation of ET-1-induced contraction, also 7-NI, NPLA, c-PTIO, NAC and ODQ were without effect (Figure 8B, 9A, 9B and 9C). While DETCA slightly but significantly reduced responses to BK, amitrole and exogenous catalase did not modify BK-induced relaxation during ET-1 stimulated contraction in both the absence and presence of L-NAME (Figure 9C and 9D). This contrasted with the effects of these inhibitors on the responses of the same arterial preparations to exogenous NO and H2O2 (Figure 4C and Figure 5B).
On average, he inhibitory effect of L-NAME on the maximal relaxing response of depolarized arteries to BK (from -63 ± 6 to -23 ± 4% and from -68 ± 5 to -30 ± 7%) and its effect on the relaxation of arteries precontracted with ET-1 (from -76 ± 8 to -61 ± 8% and from -76 ± 5 to -68 ± 9%) did not differ significantly between patients with coronary artery disease (N = 11) and patients that did not require bypass surgery (N = 9) (Figure 10). In both groups of patients, not only the BK-induced relaxation but also the extent to which it could be reduced by L-NAME differed considerably between individuals (Figure 10).