| pA2
online © Copyright 2003 The British Pharmacological Society |
029P
University of Surrey Summer Meeting June 2003 |
| Evidence
for cannabinoid-induced contractions in the rat isolated aorta
S.E.O'Sullivan, D.A. Kendall & M.D. Randall, School of Biomedical Sciences, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK. |
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Preliminary experiments showed
that the vasorelaxant effects of two endocannabinoids, anandamide and
N-arachidonoyl-dopamine (NADA), were potentiated by the CB1
antagonist SR141716 in the rat aorta. This could indicate the existence
of a cannabinoid-mediated vasoconstrictor response. To test this hypothesis,
the contractile responses to a number of cannabinoids were tested in the
rat thoracic aorta.
Male Wistar rats (250-350g) were stunned and killed by cervical dislocation.
The aorta was removed and all adherent tissue stripped from the vessel.
The aorta was mounted in oxygenated Krebs-Henseleit solution at 37oC
and connected, using hooks and thread to a force transducer for isometric
recording (Tep-areenan et al., 2003). Vessels were set at a baseline
tension of 9.8 mN and allowed to equilibrate for an hour. The contractile
integrity of each vessel was first tested by its ability to contract to
60 mM KCl. Following equilibration, cannabinoids were added to the bath
to obtain the appropriate concentrations from initial stock solutions
dissolved in ethanol. In some preparations, aortae came from animals pre-treated
with pertussis toxin (PTX, one 10 µg/kg i.p. injection, n=5) to
assess G-protein-coupled receptor involvement (Ninomiya et al.,
2002) or with WIN55,212-2 (WIN, 3 mg/kg/day i.p. for 14 days, n=3) to
desensitise cannabinoid receptors (Sim-Selley & Martin, 2002).
9-Tetrahydrocannabinol
(THC) caused contraction in the aorta (pEC50
4.42 ± 0.42, mean ± s.e.mean; maximal response at 100 µM
(Rmax) 1.76 ± 0.25 mN tension,
n=8), while neither anandamide nor NADA caused an increase in tension.
Pre-treated with PTX (Rmax 0.06 ±
0.26 mN, P<0.01, ANOVA) or WIN (0.26 ± 0.46 mN, P<0.05)
abolished the THC contractile response. Pre-incubation of aortic rings
with SR141716 (1 µM) reduced the THC response (Rmax
0.59 ± 0.38 mN, P<0.05, n=9). In the presence of indomethacin
(10 µM, Rmax 0.20 ± 0.14
mN, P<0.01, n=9) or flurbiprofen (10 µM, Rmax
0.61 ± 0.26 mN, P<0.05, n=8) aortae did not contract
to THC.
These results have demonstrated, for the first time, THC-mediated constriction
of the rat aorta. The mechanisms underlying this response appear to involve
a Gi/o-protein coupled receptor, which may be desensitised by WIN treatment
and is sensitive to SR141716 The contractile effect appears to be due
to release of a vasoconstrictor prostanoid.
This study was funded by the British Heart Foundation (PG2001/150).
Ninomiya, H., Otani, H., Lu, K., Uchiyama, T., Kido, M & Imamura,
H. (2002). Am. J. Physiol. 282, H1933-1943.
Sim-Selly, L.J. & Martin, B.R. (2002). J. Pharmacol. Exp Ther.
303, 36-44.
Tep-areenan, P., Kendall, D.A. & Randall, M.D. (2003). Eur. J.
Pharmacol. 465, 125-132.