| pA2
online © Copyright 2003 The British Pharmacological Society |
033P
University of Surrey Summer Meeting June 2003 |
Characterisation
of  1-adrenoceptors
in mouse femoral resistance arteries
|
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The aim of the present study
was to characterise 
1-adrenoceptor
subtype(s) involved in responses to exogenous noradrenaline and electrical
field stimulation (EFS) in mouse femoral resistance arteries using the
antagonists prazosin (1-selective),
5-methyl-urapidil (5MU, 1A-selective),
BMY 7378 (1D-selective)
and the preferential 1B-alkylating
agent, chloroethylclonidine (CEC).
Second order branches of femoral artery (normalised diameter L0.9
= 184±3µM, n = 43) were dissected out from male DBA/2 mice
(25-30 g, 20-30 weeks) and mounted on a small vessel wire myograph in
physiological salt solution at 37oC continuously
bubbled with carbogen for isometric recording. The vessels were activated
by 123 mM KCl twice followed by 10 µM noradrenaline. For studies
with exogenous noradrenaline the vessels were incubated with the 2-adrenoceptor
antagonist RS 79948 (0.1 µM), the ß-adrenoceptor antagonist
propranolol (1 µM), the uptake-1 inhibitor cocaine (3 µM)
and the uptake-2 inhibitor corticosterone (3 µM). For EFS, vessels
were incubated with RS 79948 (0.1 µM) and were stimulated at 20
V and 0.05 ms pulse width applied for 10 sec at frequencies of 2-20 Hz
using platinium electrodes. For CEC treatment, arterial segments were
incubated with CEC (1-10 µM) for 30 min followed by washing for
60 min (each wash every 15 min).
Prazosin inhibited noradrenaline-induced (n=6) and neurogenic responses
(n=6) at all frequencies with a pKB value
of 9.3 (from a Schild plot) and a pIC50
value of 9.3±0.04 (10 Hz) respectively. 5MU inhibited noradrenaline-induced
(n = 5) and neurogenic responses (n = 6) at all frequencies with a pKB
value of 9.0 (from a Schild plot) and pIC50
value of 8.00±0.03 (10 Hz) respectively. BMY 7378 (10 nM - 100nM,
n = 3) and CEC (1 µM, n = 4) had no significant effect on the responses
to exogenous noradrenaline. BMY 7378 (1 µM) inhibited noradrenaline-induced
responses with a pKB value of 6.8 (from
the Schild equation). CEC (10 µM) reduced maximum responses (89±4%
of control). Nerve-mediated responses were more sensitive to BMY 7378
at lower frequencies (e.g. pIC50 at 5
Hz was 8.14±0.07, n = 7, significantly smaller than the pIC50
at 10 Hz, 6.67±0.04, n=7, P<0.001). CEC (1-10 µM, n =
4) inhibited responses at 2-5 Hz (e.g. 1 µM at 5 Hz, 76±3%
of control, P<0.001) but had no significant effect at higher frequencies
(e.g. 1 µM at 5 Hz, 97±3% of control, P>0.05).
In conclusion, exogenous noradrenaline-induced and nerve-mediated vasoconstriction
in mouse femoral resistance arteries were predominantly mediated by 1A-adrenoceptors.
Responses to EFS were more sensitive to BMY 7378 at low frequencies raising
the possibility of a contribution from
1D-adrenoceptors
at these frequencies. CEC also inhibited responses at low frequencies
but its actions may be attributed to the alkylation of 1D-adrenoceptor
(Schwinn et al., 1991).
Schwinn et al., 1991. Journal of Biochemistry, 40,
619 - 626.