| pA2 online © Copyright 2004 The British Pharmacological Society |
062P
University of Bath Summer Meeting July 2004 |
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Investigation of the role of J. Zacharia1, C. Hillier1, C.J. Daly2, J.C. McGrath2 & A. MacDonald1. 1Department of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow. 2IBLS, University of Glasgow, Glasgow |
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1B-adrenoceptors in contraction of mouse femoral small arteries using 
Print abstract Previously we have shown that 
1A-adrenoceptors (ARs) mediate vasoconstriction in mouse femoral small arteries with a contribution from 1D-adrenoceptors at low frequencies of stimulation (Zacharia et al., 2003). However, investigation of the role of 1B-ARs is hampered by the lack of highly subtype selective antagonists. The present study investigated the role of 1B-ARs in responses of mouse femoral small arteries to exogenous and endogenous (using electrical field stimulation) noradrenaline using 1A-AR knockout (KO) mice. Antagonists prazosin ( 1A-selective), 5-methyl-urapidil (5MU, 1D-selective), BMY 7378 ( 1D-selective) and the preferential 1B-alkylating agent, chloroethylclonidine (CEC) were used.
Small femoral arteries (c. 175 µm) were isolated from male C57BL (wild type, WT) and 1B-KO mice (32-38 g, 16 weeks old) and mounted on a small vessel wire myograph in physiological salt solution at 37oC for isometric recording. For electrical field stimulation (EFS), vessels were incubated with 0.1µM RS 79948 ( 2-AR antagonist) and were stimulated at 20 V and 0.09 ms pulse width applied for 10 sec at frequencies of 2-20 Hz.
1B-KO mice showed a 1.6-fold decrease in sensitivity to exogenous noradrenaline (NA) (pEC50s: WT, 6.8±0.1; 1B-KO, 6.6±0.1, P<0.05, n=14. Max responses: WT, 1.7±0.1; 1B-KO, 1.8±0.1 mN/mm, P>0.05, n=14). Prazosin and 5MU inhibited responses to exogenous NA and to nerve stimulation with high affinity, with no significant differences between WT and 1B-KO. BMY 7378 (1 µM) produced significant shifts of the NA CRC with no significant difference in the pKBs (WT, 7.1± 0.2; 1B-KO, 7.1±0.3, n=4). In WT and 1B-KOs, nerve-mediated responses were more sensitive to BMY 7378 at lower frequencies (2 & 5 Hz) than at higher frequencies (10 & 20 Hz) indicating a greater contribution of 1D-ARs at low frequencies of stimulation. CEC (10 µM) produced greater inhibition of responses to exogenous NA in 1B-KO compared to WT (e.g. % of inhibition of maximum responses; WT, 79±2, n=4; 1B-KO, 67±4, n=4, P<0.05). Inhibition of neurogenic responses by CEC (10 µM) was similar in WT and 1B-KOs (e.g. % of control at 5 Hz; WT, n=4; 50±4; 1B-KO, n=6, 47±2, P>0.05).
In conclusion, responses to exogenous noradrenaline and nerve stimulation in mouse femoral small arteries are predominantly mediated by 1A-ARs. The decrease in sensitivity to exogenous noradrenaline in 1AB-KOs, indicates that there may be a minor contribution from 1A-AR. CEC inhibited responses to exogenous and endogenous NA in both WTs and 1B-KOs and thus its inhibitory effects are not mediated by blockade of 1B-ARs.
Zacharia J. et al., 2003. pA 2, 1(3), 26P