THE EFFECT OF MORPHINE ON THE TRANSPORT AND METABOLISM OF INTRACISTERNALLY-INJECTED LEUCINE IN THE RAT

—Intracisternally injected l or d-[¹⁴C]leucine was retained longer in the brains of morphine-treated rats than in saline-injected control animals. This resulted in higher levels of the labelled leucine and of labelled metabolites of the l-isomer in free pools of brain tissue. However, the absolute levels of brain amino acids and the relative distribution of radioactivity among l-leucine metabolites in brain were unaffected by treatment with morphine, indicating that no disturbance of leucine oxidation through the citric acid cycle was produced by the drug. The inhibition of protein synthesis caused by acute administration of morphine was calculated to be greater than previously reported since morphine treatment increased the specific radioactivity of the free pool of leucine in brain following the intracisternal injection of the labelled amino acid. Possible mechanisms responsible for these morphine effects are discussed.     

THE EFFECT OF INSULIN, ALLOXAN DIABETES, AND ANOXIA ON THE ULTRASTRUCTURE OF THE RAT HEART

Hearts from normal and alloxan diabetic rats were perfused in vitro with a bicarbonate-buffered medium containing glucose. Transport of glucose through the cell membrane was stimulated with insulin or by induction of anaerobiosis. The organs were rapidly fixed and examined by electron microscopy. Transport stimulation was not associated with any increase in the number of sarcolemmal invaginations or subsarcolemmal cytoplasmic vesicles. It was concluded that glucose transport and the effects of insulin or anoxia do not involve pinocytosis. The relationship of pinocytosis to glucose transport is discussed. The appearance of numerous lipid inclusions at the Z line level of the sarcomeres in the diabetic and anoxic myocardia is described.     

PATTERN OF RNA SYNTHESIS IN THE SCIATIC NERVE OF THE HEN DURING WALLERIAN DEGENERATION

The pattern of synthesis of rapidly-labelled RNA of hen sciatic nerve was studied during Wallerian degeneration. At 2,4,8, 16 and 30 days of degeneration the proximal and distal stumps of the severed nerve as well as the intact contralateral sciatic nerve (functional control) were excised and incubated with either [5-³H]uridine or [2-¹⁴C]uridine for 0.5 h. The electrophoretic pattern of RNA from the normal adult sciatic nerve showed that most of the radioactivity was incorporated into RNA species migrating between the 18 S and 4 S components of the bulk RNA. The synthesis of RNA was sensitive to actinomycin-D, an indication that it was directed by a DNA template. The electrophoretic patterns of the rapidly-labelled RNA in the proximal and distal nerve stumps demonstrated a change following nerve section. After 2–4 days of Wallerian degeneration the degenerating distal nerves incorporated more radioactivity in the 4 S region than the corresponding controls, but at 8 and 16-days after degeneration relatively more label appeared in higher molecular weight RNA species. In the intact sciatic nerve of the operated hens progressively more radioactivity was detected in the 4 S region with increasing time after the contralateral nerve section. At each stage of Wallerian degeneration the specific radioactivities of RNA in the control nerves from experimental hens were higher than those of the normal adult sciatic nerve. These results indicated a change of RNA metabolism in increased functional activity and during Wallerian degeneration.     

THE METABOLISM OF LEUCINE BY DEVELOPING RAT BRAIN: EFFECT OF LEUCINE AND 2-OXO-4-METHYLVALERATE ON LIPID SYNTHESIS FROM GLUCOSE AND KETONE BODIES

Abstract— The oxidation of l -[U-¹⁴C]leucine and l -[l-¹⁴C]leucine at varying concentrations from 0.1 to 5mM to CO₂ and the incorporation into cerebral lipids and proteins by brain slices from 1-week old rats were markedly stimulated by glucose. Although the addition of S mM-dl -3-hydroxybutyrate had no effect on the metabolism of [U-¹⁴C]leucine by brain slices from suckling rats, the stimulatory effects of glucose on the metabolism of l -[U-¹⁴C]leucine were markedly reduced in the presence of dl -3-hydroxybutyrate. The stimulatory effect of glucose on leucine oxidation was, however, not observed in adult rat brain. Furthermore, the incorporation of leucine-carbon into cerebral lipids and proteins was also very low in the adult brain. The incorporation of l -[U-¹⁴C]leucine into cerebral lipids by cortex slices was higher during the first 2 postnatal weeks, which then declined to the adult level. During this time span, the oxidation of l -[U-¹⁴C]leucine to CO₂ remained relatively unchanged. The incorporation in vivo of D-3-hydroxy[3-¹⁴C]butyrate into cerebral lipids was markedly decreased by acute hyperleucinemia induced by injecting leucine into 9-day old rats. In in vitro experiments, 5 mM-leucine had no effect on the oxidation of [U-¹⁴C]glucose to CO₂ or its incorporation into lipids by brain slices from 1-week old rats. However, 5 mM-leucine inhibited the oxidation of d -3-hydroxy-[3-¹⁴C]butyrate, [3-¹⁴C]acetoacetate and [1-¹⁴C]acetate to CO₂ by brain slices, but their incorporation into cerebral lipids was not affected by leucine. In contrast 2-oxo-4-methylvalerate, a deaminated metabolite of leucine, markedly inhibited both the oxidation to CO₂ and the incorporation into lipids of labelled glucose, ketone bodies and acetate by cortex slices from 1-week old rats. These findings suggest that the reduction in the incorporation in vivo of d -3-hydroxy[3-¹⁴C]butyrate into cerebral lipids in rats injected with leucine is most likely caused by 2-oxo-4-methylvalerate formed from leucine. Since the concentrations of leucine and 2-oxo-4-methylvalerate in plasma of untreated patients with maple-syrup urine disease are markedly elevated, our findings are compatible with the possibility that an alteration in the metabolism of glucose and ketone bodies in the brain may contribute to the pathophysiology of this disease.     

LIPID AND PROTEIN CHANGES IN SCIATIC NERVE DURING WALLERIAN DEGENERATION

Lipid and protein changes have been measured and correlated during early Wallerian degeneration in the same rat sciatic nerve. The major structural glycoprotein disappears at a steady rate and little remains after 8 days. There is a concomitant appearance of a protein with the same molecular size as basic protein B₂ and which is probably formed from the glycoprotein. Basic protein (B₁) is slowly lost, but Wolfgram protein tends to increase possibly because of glial cell proliferation. Cholesterol ester has appeared 3 days after sectioning, while cholesterol and probably cerebroside are reduced. Triglyceride levels show considerable variation, but biphasic increases tended to occur at 3-4 and 10-14 days. Loss of phospholipids is a later event. The changes in lipid and protein are discussed in relation to the stability of the peripheral nerve myelin membrane.     

ASPARAGINASE IN PERIPHERAL NERVES OF THE GUINEA PIG IN WALLERIAN DEGENERATION AND EXPERIMENTAL ALLERGIC NEURITIS

Abstract— Asparaginase ( 1 -asparagine amidohydrolase EC 3 , 5.1.1.) activity in peripheral nerves in Wallerian degeneration and in experimental allergic neuritis was studied in the guinea pig. After mechanical damage to the sciatic nerve, asparaginase enzymic activity increased markedly in the regenerating (central) stump at the end of the first week, followed by a decrease in activity almost to control values in the course of 4 weeks, whereas in the degenerating (peripheral) stump, after an increase in activity at the end of the first week the enzyme activity continued to increase reaching 250 per cent of the control values at the end of the fourth week. An increase in asparaginase activity was also observed in experimental allergic neuritis.     

THE INFLUENCE OF PORTOCAVAL ANASTOMOSIS ON THE METABOLISM OF LABELLED OCTANOATE, BUTYRATE AND LEUCINE IN RAT BRAIN

Rats were given a portocaval anastomosis and 3 weeks later, when the only ultrastructural change in the CNS is watery swelling of astrocytes, several aspects of brain metabolism were studied. The uptake of leucine by the brain, its incorporation into protein and its oxidation were followed after the simultaneous injection of a mixture of L-[1¹⁴C]leucine and L-[4,5-³H]leucine. The concentration of leucine in blood was lowered in the operated animals whereas in brain it was increased. The specific radioactivity of leucine in the brain was comparable to values in control animals and there was no evidence of a decrease in incorporation of [1-¹⁴C]leucine into brain proteins over the short experimental time period studied. The only difference from the controls in the oxidation of [4,5-³H]leucine was a greater accumulation in glutamine. The amount of glutamine in the brains of the operated animals had increased 4-fold at the time of the metabolic studies. From dual-labelled experiments in which a mixture containing [1-¹⁴C]butyrate and L-[4,5-³H]leucine was injected intravenously, it was shown that, in both control and operated animals, the pools of brain glutamate and glutamine labelled from butyrate were metabolically distinct from those labelled from leucine. The total radioactivity appearing in brain from [1-¹⁴C]butyrate was markedly reduced in operated animals, but the radioactivity from L-[4,5-³H]leucine was not. The metabolism of [1-¹⁴C]octanoate was compared with that of [1-¹⁴C]butyrate. In control animals the labelling of metabolites was almost identical with either precursor. In operated animals there was no reduction in the uptake of [1-¹⁴C]octanoate into the brain. There was evidence that the size of the glutamine pool labelled, relative to glutamate, was increased but that it had a slower fractional turnover coefficient. A link between astroglial changes and an impairment to the carrier mechanism for transport of short chain monocarboxylic acids across the blood-brain barrier is suggested.     

ON THE POSSIBILITY OF LYSOPHOSPHATIDE FORMATION DURING WALLERIAN DEGENERATION

—During an extensive decomposition of phospholipids, at the end of the second week of Wallerian degeneration, the decomposition of glycerophosphatides were studied in detail. In a degenerative process lasting for 2 weeks about one-third of the choline phosphatides, two-thirds of the ethanolamine phosphatides, one-third of the serine phosphatides and one-quarter of the inositol phosphatides, were destroyed. The amount of lysophosphatidylcholine decreased proportionally to the destruction of choline phosphatide. On the other hand, the amount of lysophosphatides formed from‘kephalin'-containing fatty aldehyde, during the marked destruction of these phospholipids, remained constant or increased to a small extent and its percentage distribution increased 2 or 3 times compared with other phospholipids. Ethanolamine phosphatides having a high fatty aldehyde content can be regarded as mainly responsible for the relative accumulation of lysophosphatides.     

THE EFFECT OF BROMOCRIPTINE ON RAT STRIATAL ADENYLATE CYCLASE AND RAT BRAIN MONOAMINE METABOLISM

In slices and homogenate from rat brain striatum bromocriptine in marked contrast to DA. NA and apomorphine. had no stimulatory effect on adenylate cyclase activity, but antagonised the stimulatory effects of both NA and DA. Bromocriptine (10 mg/kg s.c.) decreased the turnover of DA in striatum and limbic structures 3h after drug administration. However, an increase in the turnover of NA in the brain stem and that of 5-HT in the cortex was observed 4h following treatment with bromocriptine. Possible modes of action of bromocriptine are discussed.     

高淀粉膳食对血浆胰岛素、cAMP含量及组织cAMP代谢的影响

对高淀粉膳食(糖占总热量80％)对大鼠血脂、胰岛素及cAMP代谢的影响进行了研究。大鼠摄取高淀粉膳食3天,空腹血浆岛素及甘油三酯含量明显高于对照组(P<0.01;P<0.01)。6天后血浆甘油三酯含量增高近四倍(P<0.01),而血浆、肌肉和脂肪组织cAMP含量低于对照组,分别减低38％,45％和32％(P<0.05;P<0.05,0.1相似文献   

THE EFFECT OF HYPOXIA ON MONOAMINE SYNTHESIS, LEVELS AND METABOLISM IN RAT BRAIN

Abstract— Rats were exposed to 5.6% oxygen environments for up to 2 h. The accumulation of brain DOPA and 5-hydroxytryptophan at 30 min after decarboxylase inhibition was used to estimate cerebral tryosine and tryptophan hydroxylase activity, respectively, in vivo. There was a continuing decrease in tryosine hydroxylase activity during the 2 h in whole brain as well as five brain regions. Tryptophan hydroxylase activity declined during the 1st h, but then increased towards control levels during the 2nd h. There was an increase in brain tryptophan during the 2nd h as well. In whole brain and the five brain regions, there was no significant change in the levels of noradrenaline, dopamine or 5-hydroxytrypamine. During a 1 h exposure to 5.6% oxygen, there was decreased accumulation of noradrenaline, dopamine and 5-hydroxytryptamine after MAO inhibition and decreased accumulation of homovanillic acid and 5-hydroxyindoleacetic acid after probenecid administration. The dercreased synthesis and metabolism of the monoamines is most likely attributable to insufficient brain tissue oxygen as a substrate for the two hydroxylase enzymes.     

胰岛素对大鼠空肠和回肠锌吸收动力学作用的研究

用原位灌流的大鼠空肠和回肠研究了胰岛素对锌吸收动力学的作用。糖尿病大鼠血清胰岛素水平明显减低,空肠锌吸收速率常数K_(12)和K_(21)分别比对照组增大50％和31％,K_(20)减小59％;胰岛素治疗组血清胰岛素水平稍有恢复,空肠K值变化不大。糖尿病组回肠K_(12)和K_(21)分别比对照组减小29％和8％,K_(20)变化很小;胰岛素治疗组K_(12)和K_(21)分别比对照组增大36％和51％,K_(20)变化不大。糖尿病组空肠锌吸收慢速相半衰期比对照组增大29倍,胰岛素治疗组明显小于糖尿病组。糖尿病组K_(12)和K_(21)的空肠/回肠比值比对照组增大110％和41％,K_(20)的空肠/回肠比值减小57％;胰岛素治疗组K_(12)和K_(21)的空肠/回肠比值恢复到对照水平,K(20)的比值有所恢复。上述结果提示,胰岛素对锌从粘膜到血液的转运过程有促进作用,并对小肠锌吸收部位有一定影响。     

THE EFFECTS OF UNDERNUTRITION ON THE PROTEINS OF OPTIC AND SCIATIC NERVES DURING DEVELOPMENT

Abstract— Polyacrylamide gel electrophoresis has been used to assess the appearance of some optic and sciatic nerve proteins in normal developing rats and in undernourished rats. Of the myelin proteins, the'Wolfgram'proteolipid is already present about the time myelination begins. The basic myelin proteins appear later, first in sciatic and then in optic nerve. A non-myelin basic protein, assumed to be a histone, is present at high levels in both nerves before myelination begins. There is no apparent effect of undernutrition on the appearance and amount of myelin proteins at 12, 16 and 22 days of age. The'histone'protein is reduced in optic and sciatic nerves at times corresponding roughly to the transition periods from cellular proliferation to myelin formation. The possibilities are discussed that myelin basic proteins are synthesized as compact myelin formation occurs, and that there may be retarded cellular proliferation in nerves of undernourished rats.     

THE GEOMETRY OF PERIPHERAL MYELIN SHEATHS DURING THEIR FORMATION AND GROWTH IN RAT SCIATIC NERVES

In rat sciatic nerves, a small bundle of fibers was identified in which myelin sheaths were absent at birth, appeared within 3 days, and grew rapidly for 2 wk. During this interval, nerves were removed from littermates and were sectioned serially in the transverse plane. Alternating sets of thin and thick sections were used to prepare electron micrograph montages in which single myelinating axons could be identified and traced distally. During the formation of the first spiral turn, the mesaxon's length and configuration varied when it was studied at different levels in the same Schwann cell. The position of the mesaxon's termination shifted while its origin, at the Schwann cell surface, remained relatively constant. Along myelin internodes composed of two to six spiral turns, there were many variations in the number of lamellae and their contour. Near the mesaxon's origin, longitudinal strips of cytoplasm separated the myelin layers. Thicker sheaths were larger in circumference, more circular in transverse sections, and more uniform at different levels. Irregularities were confined to the paranodal region, and separation of lamellae by cytoplasm occurred at Schmidt-Lantermann clefts. Approximate dimensions of the bundle, its largest fibers, and their myelin sheaths were measured and calculated. The myelin membrane's transverse length and area increased exponentially with time; the growth rate increased rapidly during the formation of the first four to six spiral layers and remained relatively constant during the subsequent enlargement of the compact sheath.     

INTERACTION OF LEUCINE, GLUCOSE, AND KETONE METABOLISM IN RAT BRAIN IN VITRO

Brain cortex slices from fed, 48 h and 120 h fasted rats were incubated and ¹⁴CO₂ was measured from (a) [U-¹⁴C]glucose (5 mm ) either alone or in the presence of l -lcucine (0.1 or 1 mm ), and (b) [U-¹⁴C]leucine or [l-¹⁴C]leucine at 0.1 or 1 mm with or without glucose (5 mm ). In other experiments, sodium dl -3-hydroxybutyrate (3-OHB) or acetoacetate (AcAc) at 1 or 5 mm were added in the above incubation mixture. The rate of conversion of [U¹⁴C]glucose to CO₂ was decreased 20% by leucine at 1 mm and 30–50% by 3-OHB at 1 or 5 mm but not by leucine at 0.1 mm . The effects of 3-OHB and of leucine (1 mm ) were not additive. The effects of leucine were similar in the fed and fasted rats. The rate of conversion of [U-¹⁴C]leucine or [l-^,4C]leucine to ¹⁴CO₂ at 0.1 mm and 1.0 mm was increased by glucose (35%) in the fed or fasted rats. Ketone bodies in the absence of glucose had no effect on leucine oxidation. However, the stimulatory effect of glucose on the rate of conversion of leucine to CO₂ was inhibited by 3-OHB at 5 mm . These results suggest that (a) leucine in increased concentrations (1 mm ) may reduce glucose oxidation by brain cortex while itself becoming an oxidative fuel for brain, and (b) leucine oxidation by brain may be influenced by the prevailing glucose and ketone concentrations.     

前列腺素E_2对四氧嘧啶降低大鼠离体胰岛释放胰岛素的影响

本工作用新生大鼠体外分离的胰岛,观察了前列腺素E_2(PGE_2)对四氧嘧啶降低胰岛素释放的影响。实验结果如下:(1)离体胰岛与14mM四氧嘧啶共同孵育15min,使随后由16.7mM 葡萄糖诱导的胰岛素的释放明显减少。(2)16.7mM 葡萄糖和2.8μM PGE_2与离体胰岛预孵育15min,可以明显防止由四氧嘧啶引起的胰岛素释放的降低。PGE_2的这种预防作用在28nM—2.8μM 范围内存在剂量反应关系。(3)cAMP 磷酸二酯酶抑制剂—茶碱,也可防止由四氧嘧啶引起的胰岛素释放的减少,且茶碱与PGE_2 联合使用有相互加强效应。(4)Ca~(2 )整合剂EGTA对PGE_2 作用无明显影响,而细胞膜Ca~(2 )通道阻断剂异搏定则使PGE_2作用完全消失。上述结果表明,在离体条件下,PGE_2可以增强B细胞的抗损伤能力,PGE_2的保护作用可能与增加细胞内 cAMP水平及改变Ca~(2 )跨膜转运有关。     

EFFECT OF CYANIDE AND ELECTRICAL STIMULATION ON PHOSPHOINOSITIDE METABOLISM IN LOBSTER NERVES

The contents of phosphoinositides, ATP, glucose and lactate in leg and claw nerves of the lobster were determined. Nerves were also analysed after cyanide poisoning, after electrical stimulation, and 1 h after removing the leg from the lobster. Cyanide poisoning decreased the levels of ATP and glucose and increased the content of lactate but did not alter the levels of phosphoinositides. Nerves left in situ for 1 h after disconnection from the central nervous system exhibited a decrease in the content of tri-phosphoinositides (TPI) of 50 per cent, without changes in ATP, glucose or lactate. The TPI change was reversed after incubation for 1 h in oxygenated seawater. Nerves labelled in vivo with ³²P were removed and stimulated at 50 Hz for 5 min. The turnover of TPI phosphorus increased on stimulation in both normal and cyanide-poisoned nerves. In contrast, turnover of ATP increased after stimulation in normal nerves but not in cyanide-treated nerves. We sought to determine whether polyphosphoinositides play a greater role in resting metabolism of the nerve or in the conducting mechanisms. Our results make more likely the involvement of TPI in permeability changes of neural membranes during excitation.     

THE EFFECT OF BREATHING OXYGEN ON THE METABOLISM OF THE RAT BRAIN UNDER NORMAL AND ISCHAEMIC CONDITIONS

Abstract—

• 1 Breathing oxygen (1 atm.) for 2 hr increased the glycogen content of the rat brain from 3·38 to 4·35 μmoles glucosyl residues/g wet wt. At the same time the glucose and lactate concentrations were significantly decreased.
• 2 Both under normal conditions and when breathing oxygen, the sum (glycogen + glucose) × 2 + lactate, with which the balance of carbohydrate breakdown and lactate formation was assessed, was 13·5 μmoles/g wet wt.
• 2 Oxygen breathing effected a significant decrease in this sum after an ischaemic period of 1–15 min. In the control group breathing normal air, the sum, after all periods of ischaemia, ranged from 98 to 106 per cent of the starting value.
• 3 An increased partial pressure of oxygen did not change the breakdown rate of the high-energy phosphate compounds. This result was not consistent with an oxidation of the carbohydrates which were missing in the balance. It is probable that other metabolites, which were not tested for, accumulated.
• 5 0 We failed to find any indication of storage of oxygen which the ischaemic brain could use for oxidative energy production.