Anin vivo study of dopamine metabolism in hyperglycemic rat striatum

The changes in the levels of the extracellular dopamine metabolites and the responses to various dopamine agents were studied by using microdialysis in hyperglycemic rat striatum. The hyperglycemia were induced by the administration of streptozotocin (40 mg/kg, i.p. for 3 days.). The basal levels of striatal dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were significantly decreased in hyperglycemic rat striatum. After the administration of D-1 and D-2 receptor antagonists, SCH-23390 and (?)sulpiride, to rats 14 days after the last administration of STZ, the increased rates in DOPAC levels were higher in hyper- than in normoglycemic rats. However after the administration of dopamine autoreceptor agonist, 3(?)PPP, the levels of the extracellular HVA were increased in normoglycemic rats, but those were not altered in hyperglycemic rats. The results indicate that the striatal dopamine activities were decreased in the hyperglycemic rats and suggest that the release of dopamine may be decreased in hyperglycemic rats. Furthermore it suggest that the increase in the levels of the extracellular dopamine metabolites by dopamine antagonists might be due to the increased sensitivities of the dopamine receptors in hyperglycemic state.