095P University of Oxford
BPS 75th Anniversary Meeting December 2006

 

Characterisation of the 5-HT2 receptors in the canine femoral artery

Doreen Davey, Mary Davison, Kerry af Forselles and Gordon McMurray. (Introduced by Wesley Miner). Discovery Biology, Pfizer Global Research and Development, Sandwich, Kent, CT13 9NJ.

 

5-HT induces contractions in various canine blood vessels (Sgard et al., 1995), mediating its action through different receptor subtypes, of which 5-HT2 receptors form a closely related group, subdivided into 5-HT2A, 5-HT2B and 5-HT2C receptors (Porter et al., 1999). The aim of this study was to identify the 5-HT2 receptor in the canine femoral artery.

All experiments were carried in compliance with UK legislation. Femoral arteries were taken from beagle dogs anaesthetised with pentobarbital sodique and the exsanguinated (male and female, 17-19kg), cut into 3mm rings, denuded and placed under 1g resting tension for 1h in modified Krebs’ solution (1µM cocaine,1µM corticosterone and 10μM naproxen) at 37oC, aerated with 95%O2/5% CO2. Tissues were sensitised with 80mM KCl followed by 10µM 5-HT. The potency and efficacy of the agonists 5-HT, αMe5-HT,BW-723C86, mCPP, RO-60-0175, norfenfluramine, MK212 and DOI R(-) were determined (1x10-9M - 3x10-4M). For antagonist studies single cumulative concentration response curves (CCRC) to 5-HT were carried out in the absence and presence of 5 concentrations of the antagonists MDL100907 (5HT2A ), RS127445 (5HT2B), SB 242084 (5HT2C) and GR125743 (5HT1B/ 1D) and pKB values were calculated using the Angus method of analysis (Lew et al., 1995) and quoted as mean pKB (95% confidence interval) n=3. Agonist data are reported as geometric mean (95% confidence interval) of the EC50 and arithmetic mean (standard deviation) of the % Emax values relative to 10μM 5-HT response.

 

Agonist

EC50 nM

% Emax

n

5-HT

301 (225-403)

108 (12.5)

11

αMe 5-HT

518 (161-1660)

108 (14.8)

8

BW-723C86

>30,000

19 at 30µM (11.9)

4

mCPP

1721 (783-3781)

4.8 (4.3)

4

RO-60-0175

4239 (3048-6017)

45 (19.1)

6

Norfenfluramine

>30,000

11.8 at 30µM (2.7)

3

MK212

>30,000

27 at 30µM (16.5)

4

DOI R(-)

119 (62-205)

36.9 (24.4)

4

 

The rank order of agonist potencies (DOI R(-)>RO-60-0175>>MK212=BW-723C86) indicate that the receptor responsible in the canine femoral artery is 5HT2A (see Table1). Additionally, MDL100907 caused rightward parallel shifts of the 5-HT CCRC with a pKB of 9.67 (9.0-10.39) whilst RS127445 and SB242084 had no effect. A pKB value of 7.18 (6.8-7.57) was determined for GR125743 reflecting its potency for the 5HT2A receptor (Razzaque et al., 1997).

This sensitive assay detected a range of agonist efficacy (Table 1) and estimates EC50 values with good precision. It is concluded that the 5HT-induced contraction in canine femoral artery is through the 5HT2A subtype .

 

Lew & Angus (1995).TiPS. 16 328-337.
Porter et al. (1999) Brit.J.Pharmacol. 128 13-20.
Razzaque et al. (1997) Brit.J.Pharmacol.Proc.Suppl. 211P.
Sgard et al. (1995) Pharmacol Res. 31 189.