Gastric erosions induced by intracisternal thyrotropin-releasing hormone (TRH) in rats

Intracisternal injection of TRH (1 microgram) under light ether anesthesia induced within 4 hr gastric lesions in 24-hr fasted rats maintained unrestrained at room temperature. Saline, ovine corticotropin-releasing factor (oCRF, 10 micrograms), or human pancreatic growth hormone-releasing factor [hpGRF(1-40), 10 micrograms] tested under the same conditions did not modify the integrity of the gastric mucosa. TRH injected intravenously (100 micrograms/kg) proved to be ineffective. The production of gastric erosions elicited by intracisternal TRH (0.1-1 microgram) or by a stabilized TRH analog, RX 77368 [pGlu-His-(3,3'-dimethyl)-ProNH2, (0.01-0.1 microgram)] was dose-dependent. RX 77368 shows an enhanced potency over TRH. TRH action on gastric mucosa was reversed by atropine, omeprazole and cimetidine. These results demonstrate that TRH, unlike the other hypothalamic releasing factors CRF or GRF, is able to act within the brain to cause the formation of gastric erosions probably through mechanisms involving changes in gastric acid secretion. Intracisternal injection of TRH or its potent analog RX 77368 appears also as a new, simple method to produce centrally mediated experimental gastric erosions in 24 hr-fasted rats.     

Effect of thyrotropin-releasing hormone (TRH) on EEG topography

EEG topography by a microcomputer system (ATAC-3700 Nihon-Kohden) was performed in the rabbit in order to investigate the mechanism of TRH action on the brain wave. Power spectral analysis was carried out using a fast Fourier transform algorithm. The square root of the power spectra was defined as the equivalent potential over each frequency band by Ueno & Matsuoka's method. Potential fields of EEG frequency band were printed out on the topographic maps. The potentials of the electrocortical delta and theta waves were high, while the potentials of the alpha, beta 1 and beta 2 waves were low. Stimulation of the nucleus ventralis anterior (VA) by 3 Hz and 8 Hz resulted in a decrease in these potentials, especially, those of the alpha, beta 1 and beta 2 waves. The potentials of the alpha and fast waves were increased following unilateral destruction of VA. In the rabbit, in which TRH 0.5 mg/kg had been administered beforehand, there was no decrease in the potential of each wave induced by stimulation of VA with frequencies of 3 Hz and 8 Hz. The findings suggest involvement of the diffuse thalamocortical projection system in the activation of EEG by TRH.     

Comparative utilization in vivo of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose and [1-C14] palmitate in the rat

Female rats were injected i.v. with comparable trace amounts of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose, or [1-14C] palmitate, and killed 30 min afterwards. The radioactivity remaining in plasma at that time was maximal in animals receiving [U-14C] glucose while the appearance of radioactive lipids was higher in the [U-14C] glycerol animals than in other groups receiving hydrosoluble substrates. The carcass, more than the liver, was the tissue where the greatest proportion of radioactivity was recovered, while the greatest percentage of radioactivity appeared in the liver in the form of lipids. The values of total radioactivity found in different tissues were very similar when using either labelled glucose or glycerol but the amount recovered as lipids was much greater in the latter. The maximal proportion of radioactive lipids appeared in the fatty-acid form in the liver, carcass, and lumbar fat pads when using [U-14C] glycerol as a hydrosoluble substrate, and the highest lipidic fraction appeared in adipose tissue as labelled, esterified fatty acids. In the spleen, heart, and kidney, most of the lipidic radioactivity from any of the hydrosoluble substrates appeared as glyceride glycerol. The highest proportion of radioactivity from [1-14C] palmitate appeared in the esterified fatty acid in adipose tissue, being followed in decreasing proportion by the heart, carcass, liver, kidney, and spleen. Thus at least in part, both labelled glucose and glycerol are used throughout different routes for their conversion in vivo to lipids. A certain proportion of glycerol is directly utilized by adipose tissue. The fatty acids esterification ability differs among the tissues and does not correspond directly with the reported activities of glycerokinase, suggesting that the alpha-glycerophosphate for esterification comes mainly from glucose and not from glycerol.     

Increase of thyrotropin response to thyrotropin-releasing hormone (TRH) and TRH release in rats during pregnancy

Regulation of thyrotropin (TSH) release by thyrotropin releasing hormone (TRH) in the anterior pituitary gland (AP) of pregnant rats was studied. The pregnant (day 7, 14, and 21) and diestrous rats were decapitated. AP was divided into 2 halves, and then incubated with Locke's solution at 37 degrees C for 30 min following a preincubation. After replacing with media, APs were incubated with Locke's solution containing 0, or 10 nM TRH for 30 min. Both basal and TRH-stimulated media were collected at the end of incubation. Medial basal hypothalamus (MBH) was incubated with Locke's medium at 37 degrees C for 30 min. Concentrations of TSH in medium and plasma samples as well as the cyclic 3':5' adenosine monophosphate (cAMP) content in APs and the levels of TRH in MBH medium were measured by radioimmunoassay. The levels of plasma TSH were higher in pregnant rats of day 21 than in diestrous rats. The spontaneous release of TSH in vitro was unaltered by pregnancy. TRH increased the release of TSH by AP, which was higher in pregnant than in diestrous rats. Maternal serum concentration of total T3 was decreased during the pregnancy. The basal release of hypothalamic TRH in vitro was greater in late pregnant rats than in diestrous rats. After TRH stimulation, the increase of the content of pituitary cAMP was greater in late pregnant rats than in diestrus animals. These results suggest that the greater secretion of TSH in pregnant rats is in part due to an increase of spontaneous release of TRH by MBH and a decrease of plasma thyroid hormones. Moreover, the higher level of plasma TSH in rats during late pregnancy is associated with the greater response of pituitary cAMP and TSH to TRH.     

Oxidation of D-[U-(14)C] glucose and [1,12-(14)C] dodecanedioic acid by pancreatic islets from Goto-Kakizaki rats.

In pancreatic islets from hereditarily diabetic GK rats, [1,12 -(14)C] dodecanedioic acid (5.0 mM) was oxidized at a rate representing about 5 % of that of D-[U - (14)C] glucose (8.3 mM). Dioic acid and hexose failed to exert any significant reciprocal effects on their respective oxidation. The production of (14)CO(2) from [1,12 -(14)C] dodecanedioic acid was proportional to its concentration in the 0.2 - 5.0 mM range. These results were essentially comparable to those obtained in islets from control rats. They extend, therefore, to GK rats the knowledge that dodecanedioic acid acts as a nutrient in pancreatic islet cells.     

The effect of tumour-bearing on 2-deoxy[U-14C]glucose uptake in normal and neoplastic tissues in the rat.

The extent to which normal and neoplastic tissues of the rate take up glucose was assessed by the 2-deoxy[U-14C]glucose tracer technique. Measurements of glucose uptake were made over 40 min in anaesthetized rats under conditions where the blood glucose concentration was constant. In fed tumour-bearing rats, the relative rates of glucose uptake per g wet wt. of tissue were tumour (100), small intestine (72), brain (61), heart (61), spleen (50), lung (42), adipose tissue (11) and muscle (8). Normal tissues of the fed tumour-bearing rats had decreased rates of glucose uptake as compared with the same tissues in fed non-tumour-bearing control rats. Blood glucose concentrations were similar in both groups, but insulin concentrations were decreased in tumour-bearing rats. Starvation decreased the rates of glucose uptake by normal tissues in both control and tumour-bearing rats, but the difference between the fed and starved states was greater in the control rats. Starvation did not decrease glucose uptake by the tumour. On an organ basis, the tumour (12-14% of body wt.) took up 4 times more glucose than did muscle (40% of body wt.).     

Local cerebral tissue glucose utilization in graded arterial hemorrhagic hypotension, studied by the 14C-2-deoxyglucose method in rats.

The effect of hemorrhagic arterial hypotension on local cerebral glucose metabolism was studied on 33 rats. The mean arterial pressure was set with the aid of a reservoir at 80, 60, 50 and 40 mmHg pressures. Local cerebral glucose utilization was measured with the 14C-2-D-deoxyglucose accumulation autoradiographic technique. Local glucose consumption decreased somewhat in cortical structures when mean arterial pressure was reduced to 60-50 mmHg. Further decrease in mean arterial pressure to 50-40 mmHg caused inhomogeneity of tissue metabolism. Columns and patches of high glucose consumption interchanged with areas of very low glucose consumption in most telencephalic and cerebellar gray matter structures. Brain stem and white matter structures seem to be less sensitive to decreased mean arterial pressure in the range studied. We found a decrease in glucose utilization rather than an increase with decreasing mean arterial pressure down to 60-50 mmHg (in the range of the autoregulation of cerebral circulation). This finding makes it improbable that autoregulation would be connected with elevated anaerobic metabolism of the tissue. Patchy areas and columns of high glucose consumption found at 50-40 mmHg in all probability reflect areas of increased anaerobic metabolism of glucose. Here, circulation was not enough to transport adequate quantity of oxygen to the tissue, but still it transported relative large amount of glucose. Columns and patches of very low glucose consumption should reflect areas, where circulation was inadequate to transport both enough glucose and oxygen.     

In vitro oxidation of [U-14C] palmitate, [1-14C] and [6-14C] glucose in newborn and adult rats and pigs

Studies have been made on the intensity of oxidation of [U-14C]-palmitate, [1-14C]- and [6-14C]-glucose by slices of the liver and skeletal muscles of new-born, 1-day, 5-day and adult Wistar rats and domestic pigs. It was found that the level of 14CO2 production from these substrates is higher in tissues of rats than in those of pigs. At early stages of ontogenesis, in tissues of both species intensive oxidation of glucose is observed together with oxidation of fatty acids. In the course of ontogenetic development, the intensity of glucose utilization significantly decreases, whereas the level of fatty acid catabolism remains relatively unaffected.     

The determination of the local cerebral glucose utilization with the 2-deoxyglucose method

Summary In the adult mammalian brain, the energy metabolism is almost entirely dependent on glucose. Furthermore, a close relationship between the energy metabolism and the functional activity could be shown. Thus, the functional activity of the brain or parts thereof can be quantified by measuring the cerebral metabolic rate for glucose. Studying in vivo the fate of a radioactive labeled analogue of glucose, the 2-deoxy-d-[1-¹⁴C]glucose, and using quantitative autoradiographic techniques, it is possible to estimate the cerebral glucose utilization of every discrete brain region. The advantage of the 2-deoxyglucose method is, that the local cerebral glucose utilization represents a metabolic encephalography (Sokoloff 1982).     

Labelling of lipids by D-[1-14C]glucose, D-[6-14C]glucose and D-[3-3H]glucose in pancreatic islets from normal and GK rats

In pancreatic islets prepared from either normal or GK rats and incubated at either low (2.8 mM) or high (16.7 mM) D-glucose concentration, the labelling of both lipids and their glycerol moiety is higher in the presence of D-[1-¹⁴C]glucose than D-[6-¹⁴C]glucose. The rise in D-glucose concentration augments the labelling of lipids, the paired ¹⁴C/³H ratio found in islets exposed to both D-[1-¹⁴C]glucose or D-[6-¹⁴C]glucose and D-[3-³H]glucose being even slightly higher at 16.7 mM D-glucose than that found, under otherwise identical conditions, at 2.8 mM D-glucose. Such a paired ratio exceeds unity in islets exposed to D-[1-¹⁴C]glucose. The labelling of islet lipids by D-[6-¹⁴C]glucose is about 30 times lower than the generation of acidic metabolites from the same tracer. These findings indicate (i) that the labelling of islet lipids accounts for only a minor fraction of D-glucose catabolism in pancreatic islets, (ii) a greater escape to L-glycerol-3-phosphate of glycerone-3-phosphate generated from the C₁-C₂-C₃ moiety of D-glucose than D-glyceraldehyde-3-phosphate produced from the C₄-C₅-C₆ moiety of the hexose, (iii) that only a limited amount of [3-³H]glycerone 3-phosphate generated from D-[3-³H]glucose is detritiated at the triose phosphate isomerase level before being converted to L-glycerol-3-phosphate, and (iv) that a rise in D-glucose concentration results in an increased labelling of islet lipids, this phenomenon being somewhat more pronounced in the case of D-[1-¹⁴C]glucose or D-[6-¹⁴C]glucose rather than D-[3-³H]glucose.     

Pineal regulation of circadian rhythms of 2-deoxy[14C]glucose uptake and 2[125I]iodomelatonin binding in the visual system of the house sparrow,Passer domesticus

The pineal gland and its hormone melatonin are crucial for the generation of circadian rhythms in several species of passerine birds. The sites and mechanisms by which they influence avian behavior are therefore of particular interest. Recent research employing several brain imaging techniques has indicated that the sites of melatonin action within the avian brain are wide-spread within the 4 major visual pathways. In this study, we have investigated whether the avian homologue of the mammalian suprachiasmatic nucleus, the visual suprachiasmatic nucleus (vSCN), and other visually sensitive structures express circadian rhythms of 2-deoxy[¹⁴C]glucose (2DG) uptake and 2[¹²⁵I]iodomelatonin (IMEL) binding in house sparrows,Passer domesticus, under constant environmental conditions in the presence or absence of the pineal gland. The results indicate that 2DG uptake in the vSCN is oscillatory in sham-operated sparrows but damps to arrhythmicity in pinealectomized birds, suggesting this structure contains a damped circadian oscillator independent of pineal input. We have also asked whether IMEL binding is rhythmic under these conditions in the same brains. These results indicate IMEL binding is rhythmic in several structures in the circadian, tectofugal, thalamofugal visual pathways and that pinealectomy increases the level of IMEL binding 2–4 fold suggesting that IMEL binding is down regulated by endogenous melatonin. However, the circadian rhythm of this binding is only gradually abolished, suggesting it too is regulated by a non-pineal circadian clock. These data are discussed in the context of the behavioral neurobiology of avian circadian systems and the neuroendocrine loop model.     

Regulation of myocardial [(13)C]glucose metabolism in conscious rats

Administration of supplemental glucose and/or insulin is postulated to improve the outcome from myocardial ischemia by increasing the heart's relative utilization of glucose as an energy substrate. To examine the degree to which circulating glucose and insulin levels actually influence myocardial substrate preference in vivo, we infused conscious, chronically catheterized rats with D-[1-(13)C]glucose and compared steady-state (13)C enrichment of plasma glucose with that of myocardial glycolytic ([3-(13)C]alanine) and oxidative ([4-(13)C]glutamate) intermediary metabolites. In fasting rats, [3-(13)C]alanine-to-[1-(13)C]glucose and [4-(13)C]glutamate-to-[3-(13)C]alanine ratios averaged 0.16 +/- 0.12 and 0.14 +/- 0.03, respectively, indicating that circulating glucose contributed 32% of myocardial glycolytic flux, whereas subsequent flux through pyruvate dehydrogenase contributed 14% of total tricarboxylic acid (TCA) cycle activity. Raising plasma glucose to 11 mmol/l, or insulin to 500 pmol/l, increased these contributions equivalently. At supraphysiological (>6,500 pmol/l) insulin levels, the plasma glucose contribution to glycolysis increased further, and addition of hyperglycemia made it the sole glycolytic substrate, yet [4-(13)C]glutamate-to-[3-(13)C]alanine ratios remained /=40% of myocardial TCA cycle flux.     

Principles of the 2-deoxyglucose method for the determination of the local cerebral glucose utilization

Sokoloff and co-workers developed the 2-deoxy-D-[1-14C]glucose (2DG) method in order to study the local cerebral glucose utilization (LCGU) of discrete brain regions in vivo. Energy metabolism of the adult mammalian brain is almost entirely dependent on glucose. The majority of the glucose taken up by the brain is needed for the maintenance of the membrane potentials and the electrical activity. The functional activity could thus be shown to be closely linked to energy metabolism. Consequently, examination of the energy metabolism by measuring the cerebral metabolic rate for glucose can provide information concerning functional activity in all of the neuroanatomically defined regions of the brain. Studying the fate of experimentally injected 2-deoxy-D-[1-14C]glucose, a radioactive labeled analogue of glucose, and, subsequently, employing quantitative autoradiographic techniques, it is possible to estimate the levels of the local cerebral glucose utilization in specific regions of the brain. According to Sokoloff (1982) the LCGU represents a "metabolic encephalography".