Local cerebral glucose utilization in Long-Evans and Brattleboro rats during acute dehydration

The quantitative autoradiographic deoxyglucose method was used to study the effects of acute dehydration on local cerebral glucose utilization in Long-Evans and homozygous Brattleboro rats. Water-sated Brattleboro rats had high rates of glucose utilization in the subfornical organ, habenular complex, septal triangular nucleus and pituitary neural lobe. Deprivation of water for 16-18 h enhanced glucose utilization in these structures, more intensely in the Brattleboro rats, and activated others, particularly those connected to the subfornical organ. In Long-Evans rats, water deprivation increased metabolic activity in the subfornical organ, in several structures with which it is connected, and in other brain regions putatively involved in maintaining fluid balance.     

Local glucose utilization and local blood flow in hearts of awake rats

Summary Local cardiac glucose utilization and local cardiac blood flow in rat heart were measured in vivo by quantitative autoradiographic techniques with 2-[¹⁴C] deoxyglucose and [¹⁴C] iodoantipyrine, respectively. [¹⁴C]methylmethacrylate standards were calibrated for quantitative autoradiography of dried sections of heart tissue; the calibration values for heart tissue differed from those for brain by 8%, probably because of differences in self-absorption within the tissues. The lumped constant required by the deoxyglucose method was determined in isolated, perfused, working rat hearts and found to be 1.11±0.36 (mean±SD, n=21). The heart: blood partition coefficient for iodoantipyrine required by the [¹⁴C]iodoantipyrine method was measured and found to be 1.25. The results obtained in awake rats showed: 1) overall cardiac glucose utilization varied considerably among animals with a mean of 53 (left ventricle) and 30 (right ventricle) mol/100 g/min; 2) cardiac blood flow was less variable among animals with a mean of 592 (left ventricle) and 420 (right ventricle) ml/100 g/min; 3) glucose utilization was found to be particularly high in the papillary muscle; 4) systematic gradients of glucose utilization or blood flow in the ventricular wall were not observed; 5) glucose utilization and blood flow were not closely correlated on a local level. It is concluded that autoradiographic methods are suitable for the quantification of local glucose utilization and local blood flow in the rat heart in vivo. These methods could not demonstrate transmural gradients for glucose utilization and blood flow between epi- and endocardium in awake rats.Abbreviations IAP 4-iodo-N-methyl-antipyrine - 2-DG 2-deoxy-D-glucose     

Brain distribution of idebenone and its effect on local cerebral glucose utilization in rats

To investigate the possible action sites of a cerebral metabolism activator, idebenone, (6-(10-hydroxydecyl)-2,3-dimethoxy-5-methyl-1,4-benzoquinone), its distribution in the brain and effect on local cerebral glucose utilization (LCGU) were studied in normal (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) with cerebrovascular lesions. 14C-Idebenone distributed rapidly into the brain after intravenous administration (10 mg/kg), and the total 14C contents in the brain at peak time corresponded to 0.45-0.56% of the dosages. An autoradiographic study showed that the 14C levels were higher in the white than in the gray matter. When 14C-idebenone was administered orally (100 mg/kg) and intraperitoneally (30 mg/kg), the total 14C levels were not markedly different among the brain regions of the rats. The concentration of unchanged idebenone was higher in the cerebral cortex, thalamus, and cerebellum than that in the other brain regions. Studies on LCGU demonstrated that idebenone (30 mg/kg/day, i.p., for 3 days) improved the reduction of LCGU in SHRSP with stroke, especially in the temporal cortex, thalamus dorsomedial nucleus, subthalamic nucleus, mamillary body, hippocampus dentate gyrus, caudate-putamen, inferior colliculus, and cerebellar nucleus. Based on these results, possible action sites of idebenone for its main pharmacologic effects are discussed.     

Troglitazone improves insulin-stimulated glucose utilization associated with an increased muscle glycogen content in obese Zucker rats

Recent studies have demonstrated that troglitazone has the capacity to improve insulin resistance. The present study was undertaken to determine the effect of troglitazone on in vivo insulin action, the activities of the pyruvate dehydrogenase (PDH) complex and 3-hydroxyacyl-CoA dehydrogenase (3-HADH) in muscle, and muscle GLUT-4 and glycogen content in obese and lean Zucker rats. Rats were fed a normal chow diet with and without troglitazone as a food admixture (0.2%) for 3 weeks. In vivo insulin action was measured by the sequential euglycemic clamp technique at two different insulin infusion rates (6 and 30 mU/kg BW/min). At the basal (fasting) state and after the clamp studies, the activities of PDH complex and 3-HADH, and the amounts of GLUT-4 and glycogen contained in the red gastrocnemius muscles were determined. Troglitazone treatment produced a significant rise in the metabolic clearance rate of glucose (MCR) during the 6-mU/kg BW/min insulin clamp study (19.5+/-3.9 vs 9.9+/-1.5 ml/kg BW/min, mean+/-SE, P<0.05) in obese rats, but not in lean rats. Troglitazone significantly increased the muscle glycogen content after the clamp study, compared to non-treated rats, in obese rats (9.9+/-0.5 vs 6.5+/-0.4 mg/g tissue, P<0.05) and has the tendency to increase the activity state of PDH complex in obese and lean rats at the fasting state. However, no effect of the drug on muscle GLUT-4 content was found. These results indicate that troglitazone may improve insulin sensitivity associated with increased muscle glycogen content.     

Measurement of local cerebral glucose utilization before and after V-P shunt in congenital hydrocephalus in rats

Local cerebral glucose utilization (LCGU) was measured by the [¹⁴C]deoxyglucose autoradiographic method in rats with congenital hydrocephalus before and after a V-P shunt. LCGU was decreased throughout the brain in hydrocephalus. The most severely affected regions were found in the cortex, with which a marked degree of subcortical cerebrospinal fluid (CSF) edema was associated; regions in the brain-stem structures were less affected. These metabolic disturbances were improved in many regions after a V-P shunt. However, no improvement was found in the cortex; therefore, damage was considered irreversible. CSF edema was also found in the periaqueductal gray matter in which impaired LCGU was observed; however, this metabolic disturbance was normalized after a V-P shunt. This study suggests that regional differences in the brain seen in hydrocephalus and CSF edema may have varying ill effects on cerebral metabolism. Without prompt treatment, metabolic damage progresses and becomes irreversible. It is suggested that metabolic impairment in the brain stem which is reversible is due mainly to increased intracranial pressure (ICP).     

The effect of early postnatal hypoxia on the regional cerebral utilization of glucose in adult rats

The purpose of this study was to establish if there are any later changes in the local cerebral energy metabolism after exposing 1-day-old rats for 5 days (10 hr daily) to hypobaric hypoxia (pO ₂=10.5 kPa). For this study the 2-[¹⁴C]deoxyglucose method for the determination of the regional utilization of glucose in the rat brain was employed. The results, obtained in 41 cerebral structures, show that rats subjected to an early postnatal hypoxia exhibit a significant decrease (–41%) 3 months later in the utilization of glucose in the CA₃ area of the hippocampus. This finding is a new one in the chain of several biochemical and behavioral changes observed in this experimental model. It is suggested that this finding could be useful in the search for a new therapeutic agent eventually able to alleviate the consequences of perinatal hypoxia.     

Insulin-stimulated glucose disposal is not increased in anorexia nervosa

Insulin-stimulated glucose disposal was investigated using the euglycemic hyperinsulinemic glucose clamp technique in six women with anorexia nervosa (27.3 +/- 4.9 yr old; weight, 38.8 +/- 6.6 kg) and compared to results obtained in six normal women (22.6 +/- 1.2 yr old; weight, 58 +/- 2.5 kg) and seven obese women (26.8 +/- 7.7 yr old; weight, 92.5 +/- 13.8 kg). The glucose clamp was performed for 2 h using the Biostator and a continuous insulin infusion of 100 mU kg-1 h-1. Plasma levels of insulin were determined at 30-min intervals. Plasma levels of glucagon, FFA, glycerol, 3-hydroxy-butyrate, and alanine were measured basally. Blood glucose levels were similar in normal subjects and anorectic patients; they were slightly but significantly higher in the obese patients. The indices of insulin sensitivity measured were the MCR of glucose and the ratio of glucose infused to insulin infused (G/I). They were very similar in anorectic subjects [MCR, 13.5 +/- 2.4 (+/- SEM) ml kg-1 min-1; G/I, 5.2 +/- 0.9 mg/mU) and normal subjects (MCR, 13.5 +/- 1.7 ml kg-1 min-1; G/I, 5.2 +/- 0.4 mg/mU), but were significantly reduced in obese patients (MCR, 5.1 +/- 0.8 ml kg-1 min-1; G/I, 2.6 +/- 0.3 mg/mU; P less than 0.0025). Differences in plasma insulin among the three groups were not statistically significant. Plasma alanine levels were higher in anorectic than in normal or obese subjects, suggesting defective gluconeogenesis. Thus, insulin-stimulated glucose disposal is normal in patients with anorexia nervosa, a finding that contrasts with the previously reported increase in erythrocyte insulin receptors in this disease.     

Colonic proliferation is increased in senescent rats

Our previous studies suggested that crypt size enlarged and that proliferation rate might be greater in the small intestine of rats during senescence. Crypt cell numbers and crypt cell proliferation rates, using the vincristine-induced metaphase arrest technique, now have been measured in the colon of aging and young Fischer 344 rats. The proximal colon of 26-28-mo-old unfasted rats had 10% more crypt cells and a higher proliferative rate than 3-4-mo-old young controls. In the distal colon, the crypt cell proliferation rate in aging rats was 56% greater than in the young. A 3-day fast reduced crypt cell proliferation about fourfold in young rats but only by 20% in aging rats. One-day refeeding abruptly increased the crypt cell population and proliferation rate in rats of both age groups. The crypt zone of proliferating cells from aging rats was broader than that seen in young rats. In addition, starvation lowered colonic crypt cell cycling rate much less in aging than in young animals. We conclude that the colons of aging rats demonstrate a hyperproliferative state and a failure to adapt appropriately to changes in food intake. These observations may be relevant to states of altered proliferation that occur in the premalignant colon.     

Changes in local cerebral glucose utilization during rewarding brain stimulation.

The quantitative 2-deoxy[14C]glucose method was used to determine local cerebral glucose utilization in unrestrained rats responding (lever-press) for rewarding electrical stimulation to area A10 (ventral tegmental area) and in similarly implanted inactive controls. Self-stimulation was associated with significant increases in metabolic activity, highly circumscribed in the ventral tegmental area, that continued rostrally within a rather compact zone of activity through the medial forebrain bundle, extending via the diagonal band of Broca to the level of the preoptic area. In the forebrain terminal areas bilateral increases in local cerebral glucose utilization were noted in the nucleus accumbens, lateral septum, hippocampus, and the mediodorsal nucleus of the thalamus. Ipsilateral (i.e., side of stimulation) increases in glucose utilization were noted in the bed nucleus of the stria terminalis, the basolateral and central amygdaloid nuclei, and the medial prefrontal cortex. Caudal to the stimulation site, increases in glucose utilization were found in the midline dorsal raphe, the ipsilateral pontine gray, medial parabrachial nucleus, and the locus coeruleus. Significant bilateral increases were noted in various sensory and motor areas. These results indicate that rather than a diffuse pattern of activity, rewarding brain stimulation is associated with discrete activation of specific neuronal projection fibers and selective terminal sites.     

Regional cerebral glucose utilization during morphine withdrawal in the rat.

Regional cerebral glucose utilization was studied by 2-deoxy[14C]glucose autoradiography in morphine-dependent rats and during naloxone-induced morphine withdrawal. In morphine-dependent rats, glucose utilization was increased compared with naive controls uniformly (23-54%) in hippocampus, dentate gyrus, and subiculum and reduced in frontal cortex, striatum, anterior ventral thalamus, and medial habenular nucleus. On precipitation of morphine withdrawal by subcutaneous administration of naloxone at 0.5 mg/kg to morphine-dependent rats, glucose utilization was increased in the central nucleus of amygdala (51%), lateral mammillary nucleus (40%), lateral habenular nucleus (39%), medial mammillary nucleus (35%), and medial septal nucleus (35%) (all, P less than 0.01). Significant increases also occurred in several other limbic structures including interpeduncular nucleus, anterior medial and ventral thalamic nuclei, and lateral septal nucleus. Knowledge of the functional cerebral anatomy of the morphine-withdrawal syndrome should facilitate studies directed toward understanding the molecular mechanisms of opiate withdrawal.     

Growth hormone acutely increases glucose output by hepatocytes isolated from hypophysectomized rats

A series of experiments using isolated rat hepatocytes was carried out to establish rat liver cells in suspension as a physiological model for examining GH responses, and to determine whether acute recombinant bovine GH (rbGH) treatment of rat liver cells increased glucose output and/or suppressed fatty acid synthesis from lactate. Rat liver cells were isolated by collagenase perfusion and incubated in short-term (less than 60 min) suspension. The amount of insulin, glucagon or vasopressin required to elicit a half-maximal response was within the physiological range of the circulating hormone. When hepatocytes from normal rats were acutely (less than 60 min) treated with 0, 0.1, 10, 100 or 1000 nmol rbGH/l, rates of hepatocyte glucose output and fatty acid synthesis were unaltered. In addition, acute rbGH treatment (1000 nmol/l) did not alter hepatocyte responsiveness to insulin or vasopressin. However, acute rbGH treatment of hepatocytes isolated from hypophysectomized rats significantly (P less than 0.05) increased the rate of glucose output twofold and moderately (P less than 0.10) enhanced fatty acid synthesis. The accelerated rate of glucose production was not accompanied by an increase in the amount of glycogen phosphorylase-a. The observations with liver cells from hypophysectomized rats are not consistent with a GH receptor-transducing mechanism which is like that for glucagon (adenylate cyclase-linked) or insulin (tyrosine kinase-linked).     

Ascorbic acid metabolism in adrenalectomized rats

Male albino rats were adrenalectomized and their ascorbic acid, dehydroascorbic acid, and diketogulonic acid were determined in liver and urine, while only the total ascorbic acid was determined in blood, at the intervals of 4, 8, and 12 days after adrenalectomy. Activities of ascorbic acid synthesizing enzyme d-glucurono-δ-lactone hydrolase, l-gulono-γ-lactone hydrolase, and l-gulono-γ-lactone oxidase were estimated in liver. The activities of ascorbic acid degrading enzymes dehydroascorbatase and 2,3 diketoaldonate decarbozylase were studied in liver and kidney. In adrenalectomized rats there was a slight decrease in the ascorbic acid level and an appreciable decrease in dehydroascorbic acid content of the liver. On the other hand, there was about two-fold increase in the diketogulonic acid content of liver. The content of ascorbic acid and dehydroascorbic acid in the urine of adrenalectomized rats decreased significantly, while there was slight increase in the diketogulonic acid content. There was also a slight decrease in total ascorbic acid content of blood. Decreases of about 20% and 30% were observed in the activities of d-glucurono-δ-lactone hydrolase and l-gulono-γ-lactone oxidase respectively, while the activity of l-gulono-γ-lactone hydrolase remained practically unchanged. An appreciable increase in the activity of dehydroascorbatase and a moderate increase in the activity of diketoaldonate decarboxylase were observed in liver and kidney of adrenalectomized rats. All corresponding alterations were more conspicuous in rats 12 days after adrenalectomy.     

Hypoglycemic effects of a beta-agonist, Ro 16-8714, in streptozotocin-diabetic rats: decreased hepatic glucose production and increased glucose utilization in oxidative muscles.

Streptozotocin (STZ)-induced diabetic rats are glycosuric, hyperglycemic, hyperketonemic, overproduce glucose, and have a decreased glucose utilization in oxidative muscles. Treatment with a beta-agonist, Ro 16-8714, decreases the glycosuria, hyperglycemia, hyperketonemia, and hepatic glucose production. Tissue glucose utilization was unchanged, except in oxidative muscles, where it was increased.     

Corticosterone, but not glucose, treatment enables fasted adrenalectomized rats to survive moderate hemorrhage

Fed adrenalectomized rats survive the stress of hemorrhage and hypovolemia, whereas fasted adrenalectomized rats become hypotensive and hypoglycemic after the first 90 min and die within 4 h. We have studied the effects of glucose and corticosterone (B) infusions after hemorrhage as well as treatment with B at the time of adrenalectomy on the capacity of chronically prepared, conscious, fasted, adrenalectomized rats to survive hemorrhage. We have also measured the magnitudes of vasoactive hormone responses to hemorrhage. Maintenance of plasma glucose concentrations did not sustain life; however, treatment of rats at the time of adrenalectomy with B allowed 100% survival, and acute treatment of adrenalectomized rats at the time of hemorrhage allowed about 50% survival during the 5-h posthemorrhage observation period. Rats in the acute B infusion group that died exhibited significantly increased plasma B and significantly decreased plasma glucose concentrations by 2 h compared to the rats that lived. Plasma vasopressin, renin, and norepinephrine responses to hemorrhage were markedly augmented in the adrenalectomized rats not treated with B, and plasma vasopressin concentrations were significantly elevated at 1 and 2 h in all of the rats that subsequently died compared to values in those that lived. We conclude that: 1) death after hemorrhage in fasted adrenalectomized rats is not a result of lack of glucose; 2) chronic and, to an extent, acute treatment of fasted adrenalectomized rats with B enables survival; 3) fasted adrenalectomized rats exhibit strong evidence of hepatic insufficiency which is not apparent in either fed adrenalectomized rats or B-treated fasted adrenalectomized rats; 4) death after hemorrhage in fasted adrenalectomized rats may result from hepatic failure as a consequence of marked splanchnic vasoconstriction mediated by the actions of extraordinarily high levels of vasoactive hormones after hemorrhage; and 5) B appears to act to decrease the magnitude of response of vasoactive hormones after hemorrhage in fasted adrenalectomized rats.