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).