Autoradiographic assessment of pineal gland glucose utilization and capillary permeability in the unanesthetized rat

Pineal gland glucose utilization (GU) and capillary permeability (CP) were measured in unanesthetized rats, using complementary quantitative autoradiographic techniques. GU values within the pineal tissue were homogeneously distributed around 70 μmol of glucose/100 g each min, i.e., they were approximately 30% lower than in the cortical gray structures. The blood-to-brain transfer constant of [14C]-α-aminoisobutyric acid, as an index of CP, was up to ten orders of magnitude higher than that for the rest of the brain. These measurements were carried out at that point in the circadian rhythm that corresponds to the minimum level of neurosecretory activity of the pineal gland.