CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 3, May/June 2010
134
AFRICA
suppressed (
p
<
0.05) or attenuated the initial stimulant effects of
quercetin, suggesting that quercetin might be activating L-type
voltage-dependent calcium channels (Fig. 2).
Fig. 3 summarises the time effect of quercetin (10
-4
M) in
the absence and presence of nifedipine (10
-7
M). On their own,
neither L-NAME (100
µ
M) nor indomethacin (10
µ
M) modified
the contractile amplitudes of the spontaneously contracting prep-
arations [425
±
13 vs 420
±
11 mg (L-NAME) and 427
±
15 mg
(indomethacin), respectively]. However, the vasorelaxant effects
of quercetin were only slightly inhibited but not significantly (
p
>
0.05) by either nitric oxide synthase inhibitor, L-NAME (100
µ
M) or prostanoid synthase inhibitor, indomethacin (10
µ
M),
suggesting that the vasorelaxant effect of quercetin was probably
neither mediated via endothelium-dependent relaxing factor
(EDRF), nor through prostacyclin (PGI
2
) pathways (Fig. 4).
TPCK alone did not modify the contractile amplitudes of the
spontaneously contracting preparations (425
±
13 vs 419
±
10
mg). However, TPCK significantly antagonised (
p
<
0.01) but
did not completely abolish quercetin-induced vasorelaxation,
causing a shift of quercetin IC
50
value from 12.9
±
0.7
µ
M (quer-
cetin alone) to 16.6
±
0.8
µ
M (quercetin
+
TPCK) (Fig. 5).
Discussion
Previous studies have shown that quercetin exhibited vasodilator
effects in rat isolated aorta.
23,24
The results of the present study
indicate that the inhibitory effect of quercetin on portal vein
preparations was usually preceded by initial brief but significant
(
p
<
0.05) rises in the basal tone and, in 75% of the venous
preparations set up, increases in contractile frequencies, followed
by more pronounced and longer-lasting secondary relaxations of
Fig. 1. Effect of quercetin (10
-4
M) on a rat isolated portal
vein. Quercetin (QCT, 10
-4
M) was added to the bath fluid
at the left-hand-side solid arrow and washed out four to
five times at the adjacent right-hand-side open arrow.
0.5
g
0
QCT
WASH
0 min 2
Fig. 2. Effect of quercetin (10
-4
M) on a rat isolated portal
vein pre-incubated with nifedipine (10
-7
M). Quercetin (10
-4
M) was added to the bath fluid at the left-hand-side solid
arrow and washed out four to five times at the adjacent,
right-hand-side open arrow.
0.5
g
0
Quercetin
WASH
0 min 3
Log [Quercetin] (M)
0
20
40
60
80
100
–4
% Relaxation
–5
–6
*
Control
Fig. 4. Concentration–effect curves of quercetin (10
-7
–10
-4
M) on contractile amplitudes of spontaneously contract-
ing rat isolated portal veins in the absence and presence
of L-NAME (100
µ
M) or indomethacin (10
µ
M). Each point
represents the mean (
±
SEM) of six to eight observations,
while vertical bars denote standard errors of the means
(SEM). *
p
<
0.05; **
p
<
0.01; ***
p
<
0.001 for quercetin
alone versus control.
*
*
***
***
Quercetin + L-NAME (100
µ
M)
Quercetin alone
Quercetin + Indomethacin (10
µ
M)
50
0
–50
% Change in contractile amplitude
Fig. 3. Time–effect curve of quercetin (10
-4
M) on contrac-
tile amplitudes of spontaneously contracting rat isolated
portal veins in the absence and presence of nifedipine
(10
-7
M). Each point represents the mean (
±
SEM) of six to
eight observations, while vertical bars denote standard
errors of the means (SEM). *
p
<
0.05; **
p
<
0.01; ***
p
<
0.001 for quercetin alone versus control;
δδ
p
<
0.01;
δδδ
p
<
0.001 for quercetin alone versus quercetin
+
nifedipine
(10
-7
M).
Quercetin (10
–4
M) + Nifedipine (10
–7
M)
Quercetin (10
–4
M)
***
***
***
**
**
*
*
δδδ
δδδ
δδδ
δδδ δδ
δδ
