Effects of GR-89696 and the novel peripherally selective OP2 agonists, EMD-61569 and EMD-61747, against focal cerebral ischemia in the rat
Barber, A.; Bender, H.M.; Gottschlich, R.; Greiner, H.E.; Harting, J.; Mauler, F.; Seyfried, C.A.
Methods and Findings in Experimental and Clinical Pharmacology 21(2): 105-113
1999
ISSN/ISBN: 0379-0355 PMID: 10327391 Document Number: 510291
We examined whether increases in blood-brain barrier (BBB) permeability occurring after stroke can be exploited to apply protective substances selectively to ischemic tissue. To do this, the actions of the peripherally selective OP2 agonists, EMD-61569 and EMD-61747, have been compared with those of the centrally acting OP2 agonist, GR-89696, in the rat permanent focal ischemia model. EMD-61569, EMD-61747 and GR-89696 all bound with high affinity to OP2 receptors and were potent agonists in the rabbit vas deferens functional assay. These substances also potently inhibited electrically-induced overflow of dopamine from slices of rat nucleus accumbens. EMD-61747 and EMD-61569 penetrate poorly into the CNS under normal conditions and reverse haloperidol-induced L-DOPA accumulation in the nucleus accumbens of the rat only at high doses, in contrast to GR-89696. Permanent unilateral occlusion of the middle cerebral artery (MCAO) was associated with a disruption of the BBB and an increase in the concentration of EMD-61747 in the area of the infarct. GR-89696 at a dose of 0.1 mg/kg s.c. produced a reduction in infarct volume by 38% after MCAO. EMD-61569 and EMD-61747 had no influence on swelling and ischemic damage. We conclude that EMD-61747 and EMD-61569 are potent OP2 agonists, which usually have a limited ability to penetrate the BBB. The change in the properties of the BBB in ischemic tissue was not sufficient to elicit neuroprotection, since both EMD-61747 and EMD-61569 were inactive in the focal ischemia model. Conversely, GR-89696 had a robust protective action, and probably powerful OP2-typical side effects as a consequence of its unrestricted central activity.