A comparison between the in vivo and in vitro activity of five potent and competitive NMDA antagonists

D. Lodge, S. N. Davies, M. G. Jones, J. Millar, D. T. Manallack, P. L. Ornstein, A. J.M. Verberne, N. Young, P. M. Beart

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Phosphonate analogues of glutamate have been tested and compared as N‐methyl‐d‐aspartate (NMDA) antagonists in electrophysiological and binding experiments. The compounds tested were three established NMDA antagonists: d‐2‐amino‐5‐phosphonopentanoate (d‐AP5), dl‐2‐amino‐7‐phosphonoheptanoate (dl‐AP7), 3‐(2‐carboxypiperazin‐4‐yl)propyl‐l‐phospnonate (CPP), and two novel putative NMDA antagonists: 3‐(2‐carboxypiperidin‐4‐yl)propyl‐l‐phosphonate (CPPP) and 3‐(2‐carboxy‐piperidin‐4‐yl)methyl‐1‐phosphonate (CPMP). When administered electrophoretically to rat spinal neurones in vivo, these compounds were found to be selective NMDA antagonists with little effect on excitations evoked by quisqualate and kainate. CPMP and CPPP were approximately equipotent with CPP and about 5 times more potent than d‐AP5. Following systemic administration, 2–5 mg kg−1 i.v. of CPP, CPMP and CPPP reduced NMDA‐evoked excitations by 70–100% whereas 50–100 mg kg−1 of d‐AP5 and dl‐AP7 produced a similar effect. The onset of the effects required 20–30 min and lasted more than six hours. On bath application to cortical wedges, the IC50 values (μm) for antagonism of 40 μm NMDA were: CPP, 0.64 ± 0.06 (mean ± s.e.mean; n > 4); CPMP, 1.65 ± 0.13; CPPP 0.89 ± 0.09; d‐AP5, 3.7 ± 0.32; dl‐AP7, 11.1 ± 2.1; and dl‐AP4 and dl‐AP6 were inactive at 100 μm. In binding studies with [3H]‐CPP, the Ki values (nm) were: CPP, 446 ± 150 (mean ± s.e.mean; n ≥ 3); CPMP, 183 ± 74 and CPPP, 179 ± 13 whereas against NMDA (10 μm)‐stimulated [3H]‐TCP (thienylcyclohexylpiperidine) binding the IC50 values (μm) for CPMP and CPPP respectively were 5.6 ± 2.7 and 4.5 ± 2.2. Systemic administration of CPPP and CPMP, at doses sufficient to antagonize NMDA, also reduced cardiovascular responses to 5‐hydroxytryptamine (Bezold‐Jarisch reflex). This illustrates a role for NMDA receptors in central cardiovascular control. The results indicate the systemic doses of piperidine and piperazine analogues of d‐AP5 which may be used for assessing the role of NMDA receptors in central synaptic function. 1988 British Pharmacological Society

Original languageEnglish
Pages (from-to)957-965
Number of pages9
JournalBritish Journal of Pharmacology
Issue number3
Publication statusPublished - 1 Jan 1988
Externally publishedYes

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