Insulin effects on monovalent cation transport and Na-K-ATPase activity

Cerebral blood flow and oxidative metabolism in conscious Fischer-344 rats of different ages

The cerebral metabolic rates for O2 and for glucose were measured in conscious, fasted male Fischer-344 rats at the ages of 3, 12, and 24 months, and cerebral blood flow was determined with 14C-iodoantipyrine. The metabolic rates for oxygen and glucose were obtained by multiplying blood flow by the O2 and glucose concentration differences, respectively, between blood in the femoral artery and in the superior sagittal sinus. Mean cerebral blood flow and the metabolic rates for oxygen and glucose did not differ significantly (p greater than 0.05) between 3 and 12 or between 12 and 24 months. Nor did the arteriovenous differences for O2 and for glucose change significantly with age. Because the superior sagittal sinus drains blood mainly from the cerebral cortex, the results indicate that average cerebral cortical oxidative metabolism, and the coupling ratios between the cerebral metabolic rate for oxygen and cerebral blood flow and between the cerebral metabolic rate for glucose and cerebral blood flow, do not change significantly with age in the Fischer-344 rat.

Barbiturate-enhanced detection of brain lesions by carbon-14-labeled 2-deoxyglucose autoradiography

Cerebral glucose metabolism in rats was examined 1 week after the production by ibotenic acid of unilateral striatal lesions. The incorporation of carbon-14-labeled deoxyglucose decreased within the lesion but much less than that of carbon-14-labeled glucose. Barbiturate anesthesia caused a reversal of the asymmetric striatal deoxyglucose labeling, such that the lesioned striatum retained more tracer than the contralateral side. The combined use of barbiturates and radiolabeled deoxyglucose may enhance the identification of recent brain infarction in experimental animals and in man.

The effects of dexamethasone administration and withdrawal on water permeability across the blood-brain barrier

We examined the effects of dexamethasone administration and withdrawal on regional cerebral blood flow (CBF) and the permeability surface area (PS) product for water in the central nervous system of conscious rats. There were no significant changes in CBF. Dexamethasone treatment produced a significant decrease in the PS product for water in the cerebral cortex, while withdrawal of dexamethasone resulted in a significant increase. Water content of the cerebral cortex was also increased in rats from which dexamethasone had been withdrawn. These findings may help in understanding the pathogenesis of brain swelling in some patients.

Neuronal injury following permanent middle cerebral artery occlusion in cats

The border of a chronic infarct is sharply demarcated. We found in our investigation, however, that this is merely a macroscopic diagnosis and does not say anything about the structure of the tissue and the content of morphologically preserved neurons in the marginal zones. In six cats the left cerebral artery was permanently occluded. Eight weeks later the animals were killed and autoradiographic investigations were conducted on cryostat sections to determine rCBF. Adjacent to every 20-microns section, a 10-microns HE section was prepared. Preserved nerve cells were counted in several areas of the cortex in a symmetric fashion in both the infarcted and the contralateral side in the identical regions where rCBF had been measured in the preceding section. Two additional non-ischemic cat brains served as controls, which were investigated in the same manner as described above. A marked loss of neurons was observed in the border zone of the infarct. Only occasionally preserved ganglion cells were seen in each cortical layer. Even in areas one gyrus distant to the margin of the infarct the number of neurons was still reduced by one third as compared to the contralateral side. Starting only with the lateral gyrus the number of ganglionic cells was found to be equal on both sides.

Effect of apomorphine on the relationship between local cerebral glucose utilization and local cerebral blood flow (with an appendix on its statistical analysis)

The alterations in local glucose utilization and local blood flow in 36 discrete regions of the central nervous system (CNS) that occur following the intravenous administration of the putative dopaminergic agonist, apomorphine (0.5 mg/kg), have been measured using the quantitative autoradiographic 14C-2-deoxyglucose and 14C-iodoantipyrine techniques. In eight of the regions examined (frontal and sensory-motor cortices, ventral thalamus, caudate nucleus, globus pallidus, substantia nigra, subthalamic nucleus, and posterior cerebellar hemisphere), significant elevations of local cerebral blood flow (CBF) were observed following apomorphine administration. In these eight regions, proportionately similar, significant elevations in local glucose utilization were observed following apomorphine. In two of the regions investigated (anterior cingulate cortex and lateral habenular nucleus), significant reductions in both local blood flow and glucose utilization were observed following apomorphine administration. In the majority of regions examined (26 of the total 36), apomorphine did not alter significantly either blood flow or glucose use. Using a statistical approach, described in detail in an appendix, the relationship between local rates of glucose utilization and local levels of tissue blood flow was analyzed. A relationship between local CBF and local glucose utilization was found following apomorphine, and the nature of this relationship was indistinguishable from that observed in control animals. In no region of the CNS was a significant deviation from the normal CBF–glucose use relationship demonstrated following apomorphine administration. These results point to the greater importance of the effects of apomorphine upon tissue metabolic activity, rather than its direct vascular action, as being the major mechanism underlying the observed alterations in local CBF. The statistical methods provide a rigorous analytical approach to the analysis of alterations in the relationship, both locally and globally, of blood supply to glucose utilization.

Influence of blood glucose concentration on brain lactate accumulation during severe hypoxia and subsequent recovery of brain energy metabolism

The effects of hypoxaemia on regional cerebral blood flow (CBF) and brain cortical metabolite concentrations were investigated at different blood glucose concentrations in rats under nitrous oxide anaesthesia. Tissue hypoxia of 15-min duration was induced by a combination of arterial hypoxaemia, hypotension, and clamping of the right carotid artery. Blood glucose concentrations were manipulated by varying the food intake in the 24 h before the experiment, and by glucose administration. Cortical CBF doubled during hypoxia on the intact side, but did not differ significantly from control values on the clamped side. In the clamped hemisphere there was a substantial decrease in adenylate energy charge. At brain tissue glucose concentration of 1 mumol g-1 and above, there was an inverse correlation between adenylate energy charge and brain lactate concentration. In starved animals with mean brain glucose of 0.32 +/- 0.00 mumol g-1, lactate concentration was significantly lower, in spite of equally severe disruption of energy state. Recovery of brain adenylate energy charge was worse in fed and glucose-infused groups than in the fasted group. These results demonstrate that limitation of substrate supply during severe hypoxia in the rat allows enhanced recovery of brain energy metabolism following the hypoxic episode.

Autoradiographic assessment of choroid plexus blood flow and glucose utilization in the unanesthetized rat

Choroid plexus blood flow (CPBF) and glucose utilization (CPGU) were measured in two groups, each of seven identically prepared, unanesthetized rats, using complementary quantitative autoradiographic techniques. Both CPBF and CPGU were lowest in the lateral ventricles (0.83 +/- 0.01 . g-1 . min-1 and 0.70 +/- 0.02 mumoles . g-1 . min-1, respectively) and highest in the fourth ventricle (1.56 +/- 0.05 ml l g-1 . min-1 and 1.39 +/- 0.05 mumoles . g-1 . min-1, respectively). Despite this heterogeneity, the proportionate relationship between CPBF and CPGU was relatively constant throughout the ventricular system. This suggests that blood flow and metabolism may normally be coupled in the choroid plexus, and that the choroid plexus of the fourth ventricle may account for a disproportionate share of the functional activity of this tissue.

Dexamethasone and local cerebral glucose utilization in freeze-traumatized rat brain

Local cerebral glucose utilization (LCGU) was studied using the 14C-deoxyglucose method in dexamethasone-treated rats with focal cortical freezing lesions. Widespread depression of LCGU, which developed with time after the lesion in untreated animals, was significantly diminished by dexamethasone(0.25 mg/kg/day) started either 6 to 18 hours before or 4 or 24 hours after the lesion. The effect of dexamethasone was most striking in cortical areas of the traumatized hemisphere, where the depression was most profound in untreated animals. Thus, three days after the lesion, average LCGU in these regions was 47% and 72% of normal in untreated and pretreated rats, respectively. Dexamethasone also affected LCGU bilaterally in subcortical structures and in white matter. The results suggest that dexamethasone modified the widespread depression in functional state of the rat brain that developed in response to injury. Since the spatial distribution and time course of the observed changes in LCGU did not parallel those of cerebral edema, these effects of dexamethasone do not appear to be mediated by effects on the edematous process.

Prostaglandin I2, indomethacin, and heparin promote postischemic neuronal recovery in dogs

Forty-five conditioned male mongrel dogs were exposed to multifocal ischemia sufficient to maintain suppression for 60 minutes of the P1-N1 amplitude of the cortical sensory evoked response (CSER), a quantifiable index of neuronal function. Ischemia was induced and regulated by successive embolization of 20 to 50 microliters increments of air via the right internal carotid artery. Subsequently, the P1-N1 amplitude recovery of the CSER was followed for an additional 15, 60, or 120 minutes while the dogs were treated or left untreated. The combination of prostaglandin I2 (PGI2), indomethacin, and heparin promoted a statistically significant augmentation of return of CSER amplitude relative to no treatment, PGI2 alone, indomethacin alone, PGI2 and heparin, indomethacin and heparin, or PGI2 and indomethacin. After 60 minutes of recovery, animals receiving combined PGI2, indomethacin, and heparin achieved a 57% recovery of P1-N1 amplitude relative to baseline, while the corresponding recoveries in all other groups clustered around 20%. By 120 minutes of postischemic follow-up, the CSER recovery induced by PGI2, indomethacin, and heparin was 80% compared to 17% in untreated animals. By 15 minutes into the recovery period, the combination of the three agents had eliminated very low flows in the "neuron-disabling" range (defined as 0 to 15 ml/100 gm/min for gray matter and 0 to 6 ml/100 gm/min for white matter) in contrast to the relative inefficacy of no treatment or treatment with other than the triple combination of drugs. The study lends some support to a planned clinical trial of PGI2, indomethacin, and heparin in acute occlusive stroke in humans.

Relationship between regional brain angiotensinogen and local blood flow and volume in the adrenalectomized rat: application of approach to quantification of brain corticosterone receptors

Prior studies from this laboratory have established that angiotensinogen, the prohormone of angiotensin, is unevenly distributed in the rat brain and that adrenalectomy selectively perturbs levels of the prohormone in regions associated with cardiovascular neural pathways. However, plasma angiotensinogen levels are 10(2)--10(3) times higher in plasma than in brain, so that the observation of a unique distribution of brain angiotensinogen may reflect variable plasma contamination. Studies were therefore undertaken to establish whether adrenalectomy selectively alters regional blood flow, blood volume, or plasma contamination of brain tissue, thereby artifactitiously altering apparent angiotensinogen levels. Radioactive 2-deoxyglucose, iodoantipyrine, and inulin were employed in these analyses. We conclude that variations in blood flow do not explain the selective effects of adrenalectomy, but that a variable extent of residual plasma contamination (remaining after transcardiac perfusion) is partially reflected in our earlier data. However, after correcting for plasma contamination, we still find significant changes in selected areas of the rat brain following adrenalectomy. Finally, our results demonstrate the necessity for direct quantitation of plasma contamination od brain tissue segments. This is shown to have relevance in other situations, such as corticosterone binding globulin contamination of brain corticosterone receptor binding.

Reduction of regional cerebral blood flow during brain retraction pressure in the rat

The use of brain retractors in intracranial operations may lead to focal cerebral ischemia and thereby cause brain infarction. To estimate the risk of ischemic damages, the authors investigated the regional cerebral blood flow (rCBF) in rats by means of autoradiography with 14C-iodoantipyrine at different brain retractor pressures (BRP). A reduction in rCBF to between 10 and 75 ml/100 gm/min with 20 mm Hg of BRP for 30 minutes was found in brain cortex lying under the retractor (normal 55 to 150 ml/100 gm/ min). With a BRP of 30 mm Hg for 30 minutes, rCBF was reduced to between 0 and 40 ml/100 gm/min, and with a BRP of 40 mm Hg for 15 minutes rCBF was 0 to 15 ml/100 gm/min. The rCBF in the basal ganglia remained unchanged. Even with a BRP of 20 mm Hg for 30 minutes, there seemed to be a risk of focal ischemic damage.

Studies on regional blood flow of the mouse using whole-body autoradiography of 14C-iodoantipyrine

In order to visualize regional blood flow in various tissues of the mouse at the same time, the distribution of radioactive carbon from 14C-iodoantipyrine was studied by whole-body autoradiography. The mice were frozen with Dry-Ice-hexane at 1, 10, 30 min, and 1 h and 3 h after intravenous injection of 14C-iodoantipyrine. Whole-sagittal sections of the frozen mouse, obtained by using a cryostat microtome, were dried in a cryostat and subjected to autoradiograhy. The resulting dry autoradiographs are called untreated autoradiographs in the present work. The sections were then fixed in cold 6% (w/v) HClO4, dried at room temperature and again subjected to autoradiography. Autoradiographs thus obtained are referred to as treated autoradiographs. It was found that the method could be suitable for the estimation of regional blood flow of the renal cortex, spleen, lung, skeletal muscle, bone marrow, thymus, testes, and brain.

A quantitative autoradiographic method for the measurement of local rates of brain protein synthesis

We have developed a new method for measuring local rates of brain protein synthesis in vivo. It combines the intraperitoneal injection of a large dose of low specific activity amino acid with quantitative autoradiography. This method has several advantages: 1) It is ideally suited for young or small animals or where immobilizing an animal is undesirable. 2 The amino acid injection "floods" amino acid pools so that errors in estimating precursor specific activity, which is especially important in pathological conditions, are minimized. 3) The method provides for the use of a radioautographic internal standard in which valine incorporation is measured directly. Internal standards from experimental animals correct for tissue protein content and self-absorption of radiation in tissue sections which could vary under experimental conditions.

Regulation of local cerebral blood flow in normal and hypoxic newborn dogs

Local cerebral blood flow (LCBF) was measured autoradiographically in newborn puppies by an indicator fractionation technique using 4-iodo-[14C]antipyrine as the diffusible indicator. Measurements were obtained in unanesthetized, normotensive animals, and the sensitivity of blood flow to hypercapnia and acute hypoxia was determined in 32 brain structures. LCBF in normal and hypoxic puppies was correlated with local cerebral glucose utilization (LCGU) obtained under the same experimental conditions (Duffy et al, 1982). In normocapnic (PaCO2 33 mm Hg) control animals, highest rates of blood flow were found in gray matter nuclei of the brainstem, in the medulla oblongata, and in the posterolateral nucleus of the thalamus (50 to 77 ml/100 gm/min); far lower flows were recorded among white matter structures (5 to 11 ml/100 gm/min). The vasodilatory response to both hypercapnia and hypoxia was greatest among brainstem gray matter structures, intermediate among cortical and diencephalic gray matter structures, and least in white matter. When LCBF was plotted as a function of LCGU for control animals, a positive linear correlation was obtained for all structures (p less than 0.001), implying that in newborns, as in adults, cerebral blood flow and metabolism are physiologically coupled. In hypoxic puppies, no consistent relationship between LCGU and LCBF could be demonstrated; however, there was suggestion that the two measurements correlated inversely, presumably reflecting enhanced anaerobic glycolysis in structures (e.g., hemispheric white matter) that were not adequately protected by compensatory hyperemia. White matter damage, a frequent complication of perinatal hypoxia-asphyxia, may be a consequence in part of the limited capacity of white matter to vasodilate in response to te chemical "signals" of hypercapnia and lactic acidosis.

A simplified in vivo autoradiographic strategy for the determination of regional cerebral blood flow by positron emission tomography: theoretical considerations and validation studies in the rat

A simplified mathematical model is described for the measurement of regional cerebral blood flow by positron emission tomography in man, based on a modification of the autoradiographic strategy originally developed for experimental animal studies. A modified ramp intravenous infusion of radiolabeled tracer is used; this results in a monotonically increasing curvilinear arterial activity curve that may be accurately described by a polynomial of low degree (= zeta). Integrated cranial activity CB is measured in regions of interest during the latter portion of the tracer infusion period (times T1 to T2). It is shown that (See formula: text) where each of the terms A chi is a readily evaluated function of the blood flow rate constant kappa, the brain:blood partition coefficient for the tracer, the cranial activity integration limits T1 and T2, the coefficients of the polynomial describing the arterial curve, and an iteration factor n that is chosen to yield the desired degree of precision. This relationship permits generation of a table of CB vs. kappa, thus facilitating on-line computer solution for blood flow. This in vivo autoradiographic paradigm was validated in a series of rats by comparing it to the classical autoradiographic strategy developed by Kety and associates. Excellent agreement was demonstrated between blood flow values obtained by the two methods: CBF in vivo = CBF classical X 0.99 - 0.02 (units in ml g-1 min-1; correlation coefficient r = 0.966).

Evaluation of [123I]isopropyliodoamphetamine as a tracer for local cerebral blood flow using direct autoradiographic comparison

We investigated [123I]isopropyliodoamphetamine (IMP) for potential use in the autoradiographic determination of local cerebral blood flow (LCBF) in animals. The technique of direct autoradiographic comparison, derived from double radionuclide autoradiography, was used to compare the simultaneous uptakes of IMP and [14C]iodoantipyrine (IAP), a reference tracer, in awake and anesthetized rats. This new technique offers several advantages over the previously developed methods of comparing tracers, brain uptake index and first pass extraction ratio. These include the avoidance of disrupting normal cerebral blood-brain tracer exchange and the ability to compare uptakes at substructural levels, whereas the other methods are limited to larger areas. Mean values of LCBF obtained with IMP agreed closely with those using IAP, from 20 to 300 ml/100 g/min. Because IMP was found to have an extremely high effective brain:blood partition coefficient, approximately 25:1, a linear uptake tracer model could be used for IMP yielding more precise values than could IAP for LCBF values above 150. IMP was found to measure choroid plexus flows much more accurately than IAP, values being greater than 500 for IMP compared to approximately 200 for IAP. Because the mechanism of the extremely high partition coefficient of IMP is not yet defined, however, care must be used in measuring LCBF with IMP where the trapping mechanisms of normal vessels may be disrupted.

Local cerebral blood flow and glucose consumption of rats with experimental gliomas

Experimental brain tumors were produced in rats by intracerebral implantation of a neoplastic glial cell clone. Within 2–6 weeks, spherical brain tumors developed at the implantation site with a mean diameter of 6 mm. Local blood flow and local glucose utilization were measured under light barbiturate anesthesia by quantitative autoradiography in the tumor and peritumoral brain tissue. In solid parts of the tumor, blood flow was 57.8 ± 2.0 ml/100 g/min (mean ± SE), and glucose utilization was 87.2 ± 5.8 μmol/100 g/min, respectively. In necrotic regions, flow and glucose utilization were zero. In peritumoral brain tissue of the ipsilateral hemisphere blood flow was reduced by 13–23%, as compared to homologous regions of the opposite side, the greatest decrease being recorded in the ipsilateral thalamus. Flow in the opposite hemisphere was of the same order of magnitude as in normal control rats. Glucose consumption, in contrast, was distinctly reduced in both hemispheres: in the cortex and putamen, it was 40–50% lower than in normal controls. The following conclusions are drawn: (1) during tumor development the high glucose consumption in the tumor tissue is not coupled to an equal increase in blood flow; (2) peritumoral cerebral blood flow decreases on the ipsilateral but not on the contralateral side, and (3) the metabolic rate of glucose is distinctly inhibited in both hemispheres of tumor-bearing animals. The dissociation between blood flow and metabolism suggests that metabolic inhibition is not the consequence of a diaschitic depression of functional activity.

Brain metabolism and blood flow during development and aging of the Fischer-344 rat

In cerebral cortical regions of the conscious Fischer-344 rat, regional cerebral blood flow (rCBF) as measured with 14C-indoantipyrine, and the cerebral metabolic rate for O2(CMRO2) do not decline after 3 months of age. On the other hand, the regional cerebral metabolic rate for glucose (rCMRglc) as measured with 14C-2-deoxy-D-glucose, falls significantly in some but not all cerebral cortical regions after 3 months. More generally, rCBF and rCMRglc do not follow identical courses during development and aging of the rat brain, although they remain stoichiometrically coupled among specific regions at any given age. Between 1 and 3 months, both increase in most brain regions, but after 3 months of age rCMRglc tends to fall throughout the brain, whereas rCBF tends to rise or remain unchanged in cerebral cortical regions, and falls after 12 months in posterior brain regions. The courses of rCBF, rCMRglc and CMRO2 during development and aging of the rat brain indicate that (a) stoichiometric coupling between flow and metabolism is maintained between 1 and 34 months of age, (b) the calculated coupling relation between rCBF and rCMRglc changes with age, possibly because rCBF increasingly sensitive to metabolism or because "constants" are employed to calculate rCMRglc or rCBF change with aging, and (c) cerebral cortical oxidative metabolism does not generally decline after 1 year of age. This constantly suggests that plasticity responses in the cerebral cortex of the rat compensate for senescence-associated morphological and neurochemical defects so as to preserve resting cortical functional activity.

Regional blood flow and capillary permeability in the ethylnitrosourea-induced rat glioma

Regional cerebral blood flow and capillary permeability of rat brains bearing ethylnitrosourea-induced gliomas of various size were investigated with 14C-antipyrine autoradiography and Evans blue staining. In the small tumors (less than 2 mm in diameter), blood flow was uniformly reduced when compared to the adjacent brain. Even in tiny tumors (0.3 to 0.4 mm in diameter), reduction in blood flow was evident. In the medium (2 to 4 mm in diameter) and large (greater than 4 mm in diameter) tumors, the blood flow increased or decreased depending on the part of the tumor examined. The necrotic center and peripheral edge had low blood flows, whereas the viable portion adjacent to the necrotic center had high blood flows. Blood flow in the brain tissue adjacent to medium and large tumors was lower than control brain tissue, probably due to local edema. Leakage of intravenous Evans blue in the tissue was only evident in the large tumors with central necrosis. The present findings suggest that neovascularization of the tumor may occur when the tumor reaches a certain size, and leaky new vessels may be the cause of brain edema associated with tumor.

Local cerebral glucose utilization in thermally traumatized rat brain

Local cerebral glucose utilization (LCGU) was studied using the 14C-deoxyglucose method in rats with focal thermally induced lesions in the left parietal cortex. A depression of LCGU developed with time after production of the lesion, being most prominent throughout the cortical areas of the lesioned hemisphere: 42 +/- 2% (SE) of normal 3 days after the lesion was induced. Corresponding results in other regions were: contralateral cortical areas, 86 +/- 2%; ipsilateral and contralateral subcortical structures, 74 +/- 2% and 84 +/- 1%, respectively. Brainstem structures were not affected. In white matter, bilateral depression of LCGU reached its peak 24 hours after production of the lesion--the reduction ipsilateral to the lesion was 61 +/- 4% of normal and the contralateral reduction was 64 +/- 4%. LCGU returned to normal within 5 days in all affected areas. No corresponding changes in local cerebral blood flow were observed. These results suggest a widespread depression in the functional state of traumatized brain.

Simultaneous measurement of cerebral blood flow and unidirectional movement of substances across the blood-brain barrier: theory, method, and application to leucine

The uptake of compounds by the brain depends upon cerebral blood flow. To determine the normal blood flow-cerebral extraction relationship, a method for rapid, simultaneous measurement of cerebral blood flow and brain extraction was developed and applied to blood-brain leucine transfer. Awake rats were injected intravenously with a mixture of n-[(14)C]butanol and [(3)H]leucine. The quantities of indicators accumulated over the following 5-12 s in brain and in a sample of arterial blood withdrawn at a know rate were used to determine the flux of butanol and leucine into brain. Butanol extraction was assessed independently by measuring arterial and cerebral venous concentrations of the indicator after a bolus injection. Cerebral blood flow was equal to the ratio of butanol flux into brain to butanol extraction by brain; leucine extraction was then calculated as the ratio of leucine influx to cerebral blood flow. Leucine extraction by brain and cerebral blood flow were shown to be related exponentially. The maximum velocity of active leucine transport was virtually the same at flows of 150 and 400 ml/100 g/min. The present method is theoretically applicable to the measurement of the extraction of any compound from blood by brain. By measuring the normal blood flow-extraction relationship, one can differentiate changes in extraction secondary to altered flow from changes intrinsic to pathologic conditions with inconstant cerebral blood flow.

Effect of hypoxia on nucleic acid and protein synthesis in different brain regions

The incorporation of [methyl-3H]thymidine into DNA, of [5-3H]uridine into RNA, and of [1-14C]leucine into proteins of cerebral hemispheres, cerebellum, and brainstem of guinea pigs after 80 hr of hypoxic treatment was measured. Both in vivo (intraventricular administration of labeled precursors) and in vitro (tissue slices incubation) experiments were performed. The labeling of macromolecules extracted from the various subcellular fractions of the above-mentioned brain regions was also determined. After hypoxic treatment the incorporation of the labeled precursors into DNA, RNA, and proteins was impaired to a different extent in the three brain regions and in the various subcellular fractions examined; DNA and RNA labeling in cerebellar mitochondria and protein labeling in microsomes of the three brain regions examined were particularly affected.

The effect of thiamine deficiency on local cerebral glucose utilization

Rats maintained on a thiamine-free diet for two to seven weeks and control animals were studied by the [14C]deoxyglucose technique prior to the development of histological lesions. This technique permits measurement of local cerebral glucose utilization (LCGU) in discrete nuclei and tracts. Levels of thiamine in brain and blood were also determined. In the 41 central nervous system (CNS) structures in which it was measured, cerebral glucose utilization decreased with diminishing concentration of cerebral thiamine. Thus, the primary metabolic consequence of thiamine deficiency is a widespread reduction in cerebral glucose utilization. Furthermore, with decreasing cerebral thiamine concentrations, glucose utilization declined more rapidly in many of the structures which in humans develop histological lesions with prolonged thiamine deficiency than in structures less susceptible to the development of lesions. One determinant of the specific distribution of histological lesions occurring in human thiamine deficiency may be the variable rate at which the CNS structures lose their metabolic activity with continuing thiamine deficiency.

Anticonvulsant doses of inosine result in brain levels sufficient to inhibit [3H] diazepam binding

Several purines have been shown to be competitive inhibitors of [3H] diazepam binding. Inosine has also been shown to have benzodiazepine-like neurophysiologic, pharmacologic and behavioral effects, and to partially inhibit caffeine-induced seizures in mice. Using presumptive therapeutic doses of inosine, levels were determined in mouse brain at various times following injection. Inosine and hypoxanthine concentrations in brain increased several fold following inosine administration, indicating that inosine permeated the blood-brain barrier. The levels of inosine and hypoxanthine attained in brain were sufficient to inhibit by more than 50% the GABA-stimulated [3H] diazepam binding. These data suggest that the anticonvulsant properties of inosine are related to its interaction with the benzodiazepine receptor.

Effect of propranolol on local cerebral blood flow under normocapnic and hypercapnic conditions

The effect of propranolol (2.5 mg kg-1, i.v.) on local cerebral blood flow (CBF) in normocapnia was studied in rats maintained artificially ventilated on 70% N2O and 30% O2. The method used was autoradiography with [14C]iodoantipyrine. Although a single dose of propranolol, given 30 min prior to CBF measurements, somewhat reduced mean CBF values in all of the 22 structures analysed, none of the changes were significant. The results confirm previous ones, in which overall CBF was measured, in showing that beta-adrenergic mechanisms have little effect on normal cerebrovascular tone. Following a single dose of propranolol, results obtained in hypercapnia were equally negative; neither did CBF fall significantly when propranolol was given by constant infusion during 15 min. Furthermore, local CBF did not differ between animals infused with dl-propranolol and d-propranolol. It is concluded that in the rat, propranolol has but small effects on the CBF response to hypercapnia, if any. The results reveal that local CO2 responsiveness, calculated as delta CBF/delta PCO2, varies with normocapnic flow rates.

Local cerebral blood flow values as estimated with diffusible tracers: validity of assumptions in normal and ischemic tissue

A theoretical assessment is made of the validity of assumptions underlying the theory for estimating local cerebral blood flow with diffusible tracer in the tissue under normal and ischemic conditions. First, Kety's derivation of equations that have commonly been used for calculating local cerebral blood flow values is examined in order to define the problems and assumptions. Second, the brain:blood partition coefficient of diffusible tracer, lambda, and the diffusion-limited factor, m, under normal and ischemic conditions are reviewed. An examination of the literature suggested that contrary to common belief, lambda appears to change very little in ischemia if the tissue constituents remain unchanged, whereas m does change with ischemia if the diffusible tracer used is greatly diffusion-limited in the exchange between brain and blood. Even when a gas with an m value close to unity is used as the diffusible tracer, the prolonged mean transit time of blood through the ischemic tissue would make it difficult to maintain the exponential assumptions. As part of the ischemic tissue became infarcted, which is the case with most stroke patients, so the assumptions of homogeneous perfusion would become invalid. This inevitably renders it difficult to estimate local cerebral blood flow with diffusible tracer in ischemic tissue containing an infarcted mass.

Effects of immobilization stress on regional cerebral blood flow in the conscious rat

Immobilization stress of conscious, normotensive, freely breathing 10-month-old Wistar-Kyoto rats produced an overall decline in regional cerebral blood flow (rCBF), as measured with [14C]iodoantipyrine, except at the frontal lobe. In 14 brain regions, rCBF fell by an average of 14.3% after 5 min of immobilization and by 11.9% after 15 min. Immobilization stress also stimulated hyperventilation and thereby reduced PaCO2. The slope relating rCBF to PaCO2 averaged 1.5 ml 100 g-1 min-1 mm Hg-1 in 9 significantly affected regions. The findings suggest that rCBF declines during immobilization stress because of cerebrovascular constriction caused by a reduction in PaCO2. Comparison of the average slope with published values in indicates furthermore that were PaCO2 to remain unchanged during immobilization, rCBF would increase by at most 20%.

Focal cerebral ischaemia in the rat: 2. Regional cerebral blood flow determined by [14C]iodoantipyrine autoradiography following middle cerebral artery occlusion

Local cerebral blood flow has been measured by quantitative autoradiography, employing [14C]iodoantipyrine as tracer, in rats killed half an hour after occlusion of the middle cerebral artery. The results were compared with pattern of local cerebral blood flow (CBF) in sham-operated rats and with neuropathological findings. In every animal there was a profound reduction (to 13% of control levels)in blood flow in the neocortex previously by the occluded artery. The level of blood flow in the areas in which ischaemic brain damage occurred was 0.24 +/- 0.03 ml g-1 min-1 (mean +/- SEM). this level of CBF is considerably greater than that reported following a similar surgical procedure in cats and primates. Moderate reductions in blood flow were also seen outside the territory of the occluded artery and in parts of the opposite hemisphere. Absolute increases in blood flow (hyperaemia) were seen only in the substantia nigra and globus pallidus ipsilateral to the occlusion. It is of the middle cerebral artery are reflections of alterations in neuronal function and metabolic activity secondary to the ischaemic lesion.

Brain lactic acidosis and ischemic cell damage: 1. Biochemistry and neurophysiology

This study explores the influence of severe lactic acidosis in the ischemic rat brain on postischemic recovery of the tissue energy state and neurophysiological parameters. Severe incomplete brain ischemia (cerebral blood flow below 5% of normal) was induced by bilateral carotid artery clamping combined with hypovolemic hypotension. We varied the production of lactate in the tissue by manipulating the blood glucose concentrations. A 30-min period of incomplete ischemia induced in food-deprived animals caused lactate to accumulate to 15-16 mumol g-1 in cortical tissue. Upon recirculation these animals showed: (1) a considerable recovery of the cortical energy state as evaluated from the tissue concentrations of phosphocreatine, ATP, ADP, and AMP; and (2) return of spontaneous electrocortical activity as well as of somatosensory evoked response (SER). In contrast, administration of glucose to food-deprived animals prior to ischemia caused an increase in tissue lactate concentration to about 35 mumol g-1. These animals did not recover energy balance in the tissue and neurophysiological functions did not return. In other experiments the production of lactate during 30 min of complete compression ischemia was increased from about 12 mumol g-1 (normoglycemic animals) to 20-30 mumol g-1 by preischemic hyperglycemia and, in separate animals, combined hypercapnia. The recovery of the cortical energy state upon recirculation was significantly poorer in hyperglycemic animals. It is concluded that a high degree of tissue lactic acidosis during brain ischemia impairs postischemic recovery and that different degrees of tissue lactic acidosis may explain why severe incomplete ischemia, in certain experimental models, is more deleterious than complete brain ischemia.

Cerebral circulation and histamine: 1. Participation of vascular H1- and H2-receptors in vasodilatory responses to carotid arterial infusion

We examined the cerebral circulatory effects of intra-carotid infusion of histamine or its receptor agonists in anesthetized rats. Cerebral blood flow was measured by two methods: an intracarotid 133Xe clearance technique and tissue sampling after systemic administration of the diffusible tracer, [14C]iodoantipyrine. Brain metabolic responses were estimated by the 2-deoxyglucose method and tissue sampling. Intracarotid infusion of histamine when the blood-brain barrier was intact did not increase cerebral blood flow. Following disruption of the blood-brain barrier by carotid injection of hypertonic urea, histamine evoked dose-dependent increases (133Xe clearance method) in cerebral blood flow to a maximum of 50% (20 μg min−1 kg−1); histamine produced increases in blood flow to areas supplied by the internal carotid artery, e.g., thalamus and parietal cortex ([14C]iodoantipyrine method). Both classes of histamine receptors (H1 and H2) participated in mediating increases in cerebral blood flow after blood-brain barrier opening. Mepyramine (H1-antagonist) and metiamide (H2-antagonist) attenuated blood flow responses to histamine infusion (133Xe clearance method); metiamide was the more effective blocking agent. Pyridylethylamine (H1-agonist) and dimaprit (H2-agonist) both caused increases in regional cerebral blood flow ([14C]iodoantipyrine method). Histamine infusion after blood-brain barrier opening did not increase cerebral glucose consumption. We suggest that increases in cerebral blood flow produced by histamine are the result of stimulation of vascular H1- and H2-receptors, rather than a secondary response to metabolic activation.

Extracellular potassium and blood flow in the post-ischemic rat brain

The concentration of extracellular potassium, [K+]e, was measured in parietal cortex and basal ganglia of rats during and after ten minutes of complete cerebral ischemia. The post-ischemic normalization of [K+]e was considerably delayed in parietal cortex compared to basal ganglia, but in both regions, [K+]e reached its normal concentration within 4 min of the end of the ischemia. Also, in both regions blood flow was elevated at the time of maximal [K+]e decrease. Our findings suggest that the normalization of [K+]e and cerebrovascular resistance after ischemia are related by positive feed-back, possibly via the stimulation of Na+-K+-ATPase.

Ouabain-resistant hyperpolarization induced by insulin in aggregates of embryonic heart cells

Spheroidal aggregates formed from trypsin-dissociated 14-day embryonic chicken hearts after 48 hr of rotation on a gyratory shaker. Intracellularly recorded resting membrane potentials of aggregates bathed in 1.3 mM K+ balanced salt solution had a mean (+/- SD) of 64 +/- 4 mV. After a stable potential was achieved, addition of 1-100 nM sodium bovine insulin caused a slow hyperpolarization of up to 19 mV after 4-5 min, followed, in some cases, by a further, more rapid, shift to a potential near EK. Equivalent hyperpolarizations were observed when insulin was added in the presence of 10 mM ouabain, indicating that enhanced Na+,K+ pump activity was not responsible for the change in membrane potential. The concentration of insulin that produced half-maximal hyperpolarization (2 nM) corresponded to the association constant of a high-affinity insulin receptor, suggesting that binding to this class of receptors led to the change in membrane potential. Steady-state current-voltage curves from current clamp experiments suggested that insulin produced an increase in slope conductance at potentials near rest by inducing an outward current with an apparent potential negative to -90 mV.

Dopaminergic control of serum potassium

Metoclopramide, a dopaminergic inhibitor, injected in 9 normal volunteers, was followed by a prompt decrease of serum potassium (10--20 min; p less than 0.01) and by an increase of plasma aldosterone (p less than 0.01). Renin slightly increased at 45 min (p less than 0.05); insulin and cortisol did not show any significant increase. The urinary excretion of potassium rose after metoclopramide (p less than 0.05). A bolus of aldosterone (250 micrograms i.v.) in 4 normal subjects was not followed by any modification of serum potassium, but increased urinary potassium excretion (p less than 0.05); the injection of metoclopramide in two patients with an aldosterone-secreting adenoma of the adrenal and in one patient with Addison's disease induced a decrease of serum potassium in absence of any modification of plasma aldosterone. The decrease of serum potassium after metoclopramide is not explained by changes of aldosterone or insulin, considered the most important hormonal controls of potassium. The rapidity of potassium decrease implies a change of distribution of potassium between extra- and intracellular compartments, which, in turn, may stimulate aldosterone secretion. It is conceivable that the dopaminergic system has a role in the control of serum potassium.

Measurement of regional brain glucose utilization in vivo using [2(-14)C] glucose

A new technique is described for the autoradiographic determination of regional brain glucose metabolism employing 14C labeled glucose as substrate and measurement principles previously described for whole brain. Regional glucose values correlate closely with those reported for the 14C-deoxyglucose technique. The method has the advantages of 1) a much shorter experimental period, 2) a relatively simple mathematical treatment, and 3) the utilization of the actual, fully metabolizable substance itself, glucose, as the label. In addition to normal rats, regional values are reported for 20 individual brain areas of rats in bicuculline induced status epilepticus, rats intoxicated with ammonium and rats anesthetized with pentobarbital sodium or ketamine.

The influence of insulin, cAMP and the calcium ionophore X 537 A on the growth of the cartilage analagen of limb buds in vitro

Limb buds of 11-day-old mouse embryos were cultured for 6 days with insulin, dibutyryl cAMP and X 537 A. The cartilage anlage was reduced by insulin and enlarged by dibutyryl cAMP and X 537 A. The effects are due to changes in the amount of intercellular substance.

Local cerebral glucose metabolism during controlled hypoxemia in rats

2-Deoxy-[14C]glucose metabolism was examined in brains of hypoxic, normotensive rats by autoradiography, which revealed alternating cortical columns of high and low metabolism. Activity in white matter was increased severalfold over that in adjacent gray matter. The columns were anatomically related to penetrating cortical arteries with areas between arteries demonstrating higher rates of metabolism. The results suggest the presence of interarterial tissue oxygen gradients that influence regional glucose metabolism. The relatively greater sensitivity of white matter metabolism to hypoxia may lead to an understanding of white matter damage in postanoxic leukoencephalopathy.

Monovalent cation transport in myotonic dystrophy. Na-K pump ratio in erythrocytes

Myotonic dystrophy is a dominantly-inherited disorder which affects skeletal muscle in combination with several other systems. Because of abnormalities in red blood cells, a universal membrane defect has been proposed as the primary disturbance. Erythrocyte cation pump ratios have also been reported to be abnormal. Hyperinsulinemia and glucose intolerance are present in a large number of patients. Since dramatic effects of insulin on membrane cation transport have been shown in several tissues, notably skeletal muscle, we wished first to confirm reports of altered pump ratio in these patients and then to evaluate the effects of insulin on cation fluxes. However, in our experiments myotonic dystrophy patients had normal pump ratios when compared with disease controls.