Search

The applicability of the [14C]deoxyglucose method for measuring local cerebral glucose utilization (lCMRglc) has been extended for use in hypoglycemia by determination of the values of the lumped constant to be used in rats with plasma glucose concentrations ranging from approximately 2 to 6 mM. Lumped constant values were higher in hypoglycemia and declined from a value of 1.2 at the lowest arterial plasma glucose level (1.9 mM) to about 0.48 in normoglycemia. The distribution of glucose, and therefore also of the lumped constant, was found to remain relatively uniform throughout the brain at the lowest plasma glucose levels studied. lCMRglc in moderate, insulin-induced hypoglycemia (mean arterial plasma glucose concentration +/- SD of 2.4 +/- 0.3 mM) was determined with the appropriate lumped constant corresponding to the animal's plasma glucose concentration and compared with the results obtained in six normoglycemic rats. The weighted average rate of glucose utilization for the brain as a whole was significantly depressed by 14% in the hypoglycemic animals, i.e., 61 mumols/100 g/min in hypoglycemia compared to 71 mumols/100 g/min in the normoglycemic controls (p less than 0.05). lCMRglc was lower in 47 of 49 structures examined but statistically significantly below the rate in normoglycemic rats in only six structures (p less than 0.05) by multiple comparison statistics. Regions within the brainstem were most prominently affected. The greatest reductions, statistically significant or not, occurred in structures in which glucose utilization is normally high, suggesting that glucose delivery and transport to the tissue became rate-limiting first in those structures with the greatest metabolic demands for glucose.

The [14C]deoxyglucose method for quantitative determination of local cerebral glucose utilization was employed in newborn macaque monkeys. Values ranged from a high of 180 mumol/100 gm/min in the inferior colliculus to a low of 14 mumol/100 gm/min in the centrum ovale, a wider range than had been found in this laboratory for pubescent monkeys. Relatively low values in white matter overlapped with the generally higher values in gray matter. Rates for structures in the lower neuraxis were equal to or exceeded those reported for the mature animal, while those above the midbrain were generally lower. The auditory system was unique in having rates equal to, or exceeding, its mature levels in all parts of the pathway including the cortex. In the visual system, subcortical structures were at their mature levels while rates in the cortical areas were variably low; nevertheless, the striate cortex had differential rates marking the various laminae. It was possible to demonstrate the metabolic counterpart of the ocular dominance columns in two newborn animals that had had one eye occluded during the experiment. Rates for white matter were above their mature levels, with the differences being greatest in the brainstem and cerebellum. A high correlation between glucose utilization and local blood flow measured with [14C]antipyrine (r = 0.92) was found.

Anesthetic is thought to depress the energy metabolism or oxygen consumption of the brain as a whole. It has been clear, however, that anesthetic agent may either decrease or increase local metabolic rate of the brain since [14C] 2-deoxyglucose method made one possible to measure local cerebral glucose utilization. In this paper, the authors report the effect of urethane anesthesia on the local cerebral glucose utilization. We measured local cerebral glucose utilization by means of [14C] 2-deoxyglucose method in 87 brain structures of albino rats (about 300 g) under urethane anesthesia, 1 g/kg (n = 5), and conscious state (n = 6). When the whole brain metabolism was computed as a weighted average with the acid of the computerized image-processing system, there was 33% reduction in glucose utilization of the brain as a whole in the rats under urethane anesthesia. Urethane decreased the local rate of glucose metabolism, but the metabolic effect was not homogeneous throughout the brain. The neural structures in which no metabolic depression was observed were entorhinal cortex, many nuclei in hypothalamus, medial habenula-interpeduncular nucleus, nucleus tractus solitarius, and some white matters. The selective metabolic sparing in the habenula-interpeduncular system was also reported to be observed during chloral hydrate and enflurane anesthesia. However, the mechanism involved in the phenomenon remains unclear. In the discussion, we discussed the differential effects of various anesthetics of the local cerebral glucose utilization. We reviewed the literatures on the effects of various anesthetics; barbiturate, chloralose, chloral hydrate, enflurane, ketamine, nitrous oxide and halothane on the local rate of metabolism of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)