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 [ 14C]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, μ 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 ± 3vs89 ± 8 μmol·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.