| pA2 online © Copyright 2004 The British Pharmacological Society |
018P
University of Newcastle Winter Meeting December 2004 |
Mice over-expressing the 5-HT transporter gene develop pulmonary hypertension and increased pulmonary reactivity MacLean, M.R., Dempsie, Y., *Sheward, J., *Harmar, A. & Morecroft, I.. Division of Neuroscience and Biomedical Systems, IBLS, University of Glasgow, *Division of Neuroscience, University of Edinburgh. |
|
Print abstractOver-expression of the 5-HT transporter (5HTT) may play a role in the development of familial pulmonary arterial hypertension (fPAH) (Eddahibi et al., 2001). We investigated whether mice which over-express the human 5-HTT gene (5-HTT+ mice) would be a suitable model for the study of PAH. We also investigated pulmonary vascular reactivity to 5-HT in these mice.
Development of PAH was investigated in mice (female, 5HTT+ and C57BL/6 x CBA wildtype (WT) controls) at both 2 months and 5 months of age under normoxic conditions and in 5 month old mice which were subjected to 2 weeks chronic hypoxia (10% O2). Right ventricular (RV): total ventricular (TV) ratio was used as an index of pulmonary hypertension and right ventricular pressure (RVP) was measured under anaesthesia as described previously (MacLean et al., 2004). Pulmonary arteries ( PAs) (~1000 µm i.d.) were mounted (Krebs, 37°C) on wire myographs and cumulative concentration responses to 5-HT (1nM-0.1mM) examined in the presence or absence of the 5HTT inhibitor citalopram (0.1 µM, pre-incubation time was 45 minutes). 5-HT2A receptor expression in whole lung was determined by TaqMan RT-PCR. Statistical analysis was by one-way ANOVA using the Newman-Keuls multiple comparison test. RVP was elevated in 2 month 5HTT+ mice (10.8 ±0.5mmHg, n=5, P<0.05) and further elevated by 5 months (30.0 ±6.0mmHg, n=7, P<0.01) when compared with age matched WT controls (7.8 ±0.8mmHg, n=6 and 9.5 ±0.9mmHg, n=9, respectively). Hypoxia induced an increase in RVP: 5HTT+ (40.5 ± 4.6mmHg, n=7, P<0.05) > WT (24.2 ± 3.4mmHg, n=11, P<0.05) 5 month old mice. There was no significant difference in right ventricular (RV): total ventricular (TV) ratio between 2 month old (0.183 ±0.020) and 5 month old (0.262 ±0.003) 5HTT+ mice when compared with age-matched WT controls (0.205 ±0.009 and 0.259 ±0.003 respectively). 5-HT induced constriction in both WT and 5-HTT+ mouse vessels. Whilst the potency was less in the 5HTT+ vessels (pEC50: 5.47 ± 0.05, 5-HTT+ (n=7) cf. 6.14 ± 0.07, WT (n=8), P<0.001), the maximum response (Emax, % of response to 50mM KCl) to 5-HT was markedly elevated in the 5-HTT+ vessels (86.1 ± 7.2, 5-HTT+ cf. 60.9 ± 5.0, WT, P<0.05). In the presence of citalopram responses to 5-HT were the same in both the WT and 5-HTT+ vessels in terms of Emax and potency (Emax: 87.3 ± 3.7, WT , n=7 cf. 88 ± 9.5, 5-HTT, n=6; pEC50: 5.86 ± 0.17, WT cf 6.01 ± 0.11, 5-HTT. 5-HT2A receptor were over-expressed in 5-HTT+ lung (relative expression: 11.75 ± 2.8 cf. 6.68 ± 0.66, n=5, P<0.05).
In conclusion, the 5HTT+ mouse develops spontaneous and progressive PAH. Hypoxic-induced PAH is also more severe in the 5-HTT+ mouse. The results suggest that over-expression of 5-HTT results initially in removing 5-HT from the 5-HT receptor site but when saturation of the 5-HTT occurs there is a subsequent accumulation of 5-HT at the receptor site resulting in increased 5-HT-induced constriction. Increased 5-HTT expression is also associated with an increase in 5-HT2A receptor expression.
Eddahibi et al., (2001). J. Clin. Invest. , 105, 1555-1562.
MacLean et al., (2004). Circulation, 109, 2150-2155.