Ifenprodil and SL 82.0715 as cerebral anti-ischemic agents. I. Evidence for efficacy in models of focal cerebral ischemia.

Recent studies have strongly implicated the excitatory neurotransmitter glutamate in the cascade of pathological mechanisms that cause neuronal loss after certain types of brain ischemia. The neurotoxic effects of glutamate are mediated, at least in global ischemia, via NMDA receptors. In the present study we have examined the effects of compounds that possess NMDA receptor antagonist properties (ifenprodil, SL 82.0715 [(+/-)-alpha-(4-chlorophenyl)-4-[(4-fluorophenyl)methyl]- 1-piperidineethanol] and 1-[1-(2-thienyl)cyclohexyl]piperidine) on the histological consequences of focal, as opposed to global, cerebral ischemia in both the rat and the cat. Ifenprodil (0.3-3 mg/kg i.v.) administered as a perfusion over 3 hr after occlusion of the feline middle cerebral artery reduced the volume of infarcted tissue (measured 4 days after occlusion) in a dose-related manner. At the highest dose a 42% reduction of infarcted volume was noted, essentially in cortical tissue. In an identical protocol, a derivative of ifenprodil, SL 82.0715, reduced the volume of infarction in a manner comparable to that described for ifenprodil. As SL 82.0715 possesses better p.o. bioavailability, this compound was also evaluated in the rat, again after middle cerebral artery occlusion. First administered 30 min after the induction of ischemia, SL 82.0715 (1 and 10 mg/kg p.o.) reduced infarction volume by 34 and 48%, respectively. The quantitative histology was performed 2 days after middle cerebral artery occlusion. The noncompetitive receptor antagonist, 1-[1-(2-thienyl)cyclohexyl]piperidine, administered (1 mg/kg i.p.) before the induction of focal ischemia, similarly and significantly decreased the final volume of infarction. As both ifenprodil and SL 82.0715 are noncompetitive antagonists of the NMDA receptor, two conclusions may be drawn from the present investigation. First, NMDA antagonism by ifenprodil and its derivative is an effective approach for tissue sparing in animal models of stroke and brain infarction. Second, these pharmacological observations provide evidence for the involvement of excitatory amino-acid induced-neurotoxicity in the evolution and consequences of focal cerebral ischemia.