ABSTRACT
The mechanisms underlying the neuroprotective effects of the group II metabotropic glutamate receptor (mGluR) agonist LY379268 were investigated in a gerbil model of global ischemia. LY379268 (10 mg/kg i.p.) 30 or 60 min after 5-min bilateral carotid artery occlusion (BCAO) attenuated the ischemia-induced hyperactivity and provided protection in the CA1 hippocampal cells. This neuroprotective effect was maintained (P <.001) when histological analysis was performed 14 and 28 days after BCAO. Furthermore, 24- or 48-h pretreatment with LY379268, 10 mg/kg i.p., before 5-min BCAO markedly reduced (P <.001 and P <.05, respectively) the damage to CA1 hippocampal neurons. This result is consistent with the induction of neuroprotective factors or a very long brain half-life. To study the possible induction of neuroprotective factors as contributing to this action of LY379268, brains were examined for expression of neurotrophic factors. Results indicated that LY379268 (10 mg/kg i.p.) failed to alter the expression of transforming growth factor-beta, brain-derived neurotrophic factor, nerve growth factor, and basic fibroblast growth factor in the hippocampal regions of brains taken from gerbils sacrificed at 6, 24, 72, and 120 h postinjection. The new group II mGlu antagonist, LY341495, administered 1 h before 5-min BCAO, attenuated the neuroprotective effect of LY379268 administered 24 h before 5-min BCAO. Complementary pharmacokinetic studies showed that a significant receptor-active concentration persisted in the brain 24 h after LY379268 10 mg/kg i.p. We conclude that group II mGluR occupancy, rather than induction of neuroprotective factors, explains the long-lasting neuroprotective effect of LY379268 in the gerbil model of global ischemia.
Subject(s)
Amino Acids/pharmacology , Brain Ischemia/drug therapy , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , Excitatory Amino Acid Agonists/pharmacology , Neuroprotective Agents/pharmacology , Receptors, Metabotropic Glutamate/agonists , Animals , Arterial Occlusive Diseases/complications , Brain Ischemia/etiology , Brain Ischemia/metabolism , Brain Ischemia/physiopathology , Brain-Derived Neurotrophic Factor/metabolism , Carotid Artery Diseases/complications , Gerbillinae , Hippocampus/drug effects , Hippocampus/pathology , Immunohistochemistry , Male , Motor Activity/drug effects , Nerve Growth Factor/metabolism , Neurons/pathology , Transforming Growth Factor beta/metabolismABSTRACT
1. The urinary excretion of meptazinol and its metabolites has been studied in five healthy human volunteers following oral administration of 200 mg of the 3H-labelled drug. 2. Meptazinol was well absorbed, with 90% of the radioactivity excreted in the urine; elimination of drug-related material took place rapidly. 3. Metabolism was extensive, no unchanged material being detected in the urine. Following selective enzymic hydrolysis the major metabolites were identified as glucuronide and sulphate conjugates of the parent drug present in an approximate ratio of 4:1. 4. A number of minor metabolites, also present in conjugated form, were tentatively identified.
