THE INFLUENCE OF OPIOIDS ON LOCAL CEREBRAL GLUCOSE-UTILIZATION IN THE NEWBORN PIG

Topical methionine enkephalin, leucine enkephalin, and dynorphin (10(-6) M) previously have been observed to produce prominent pial arteriolar dilation. Dilation to these opioids could be caused directly by opioids acting on vascular receptors, or indirectly, as a consequence of increased metabolism. Therefore, we examined this possibility by determining the influence of opioids on cerebral glucose utilization in piglets with closed cranial windows using the [C-14]deoxyglucose method. Qualitatively, the autoradiographic images expressed as a change in relative optical density from vehicle were unchanged by these opioids. Quantitatively, the opioids similarly had no effect on cerebral glucose utilization (53 +/- 5, 70 +/- 8, 63 +/- 5, and 52 +/- 3, mu-mol . 100 g-1 . min-1 for vehicle, methionine enkephalin, leucine enkephalin, and dynorphin, respectively). In contrast, topical glutamate (10(-3) M) produced similar dilation but increased cerebral glucose utilization (41 +/- 3 vs 89 +/- 8-mu-mol. 100 g-1 . min-1 for vehicle and glutamate, respectively). Therefore, these opioids do not appear to produce vascular effects through a change in cerebral metabolic utilization of glucose.