Dietary low linolenic acid compared with docosahexaenoic acid alter synaptic plasma membrane phospholipid fatty acid composition and sodium-potassium ATPase kinetics in developing rats

The objective of this study was to investigate if maternal dietary 20:4n-6 arachidonic acid (AA) and 22:6n-3 compared with adequate or low levels of 18:3n-3 linolenic acid (LNA) increases synaptic plasma membrane (SPM) cholesterol and phospholipid content, phospholipid 20:4n-6 and 22:6n-3 content, and Na,K-ATPase kinetics in rat pups at two and five weeks of age. At parturition, Sprague-Dawley rats were fed semi-purified diets containing either AA + docosahexaenoic acid (DHA), adequate LNA (control; 18:2n-6 : 18:3n-3 ratio of 7.1 : 1) or low LNA (18:2n-6 : 18:3n-39 ratio of 835 : 1). During the first two weeks of life, the rat pups received only their dams' milk. After weaning, pups received the same diet as their respective dams to five weeks of age. No significant difference was observed among rat pups fed the diet treatments for SPM cholesterol or total and individual phospholipid content at two and five weeks of age. Fatty acid analysis revealed that maternal dietary AA + DHA, compared with feeding the dams the control diet or the low LNA diet, increased 20:4n-6 in phosphatidylserine and 22:6n-3 content of SPM phospholipids. Rats fed dietary AA + DHA or the control diet exhibited a significantly increased Vmax for SPM Na,K-ATPase. Diet treatment did not alter the Km (affinity) of SPM Na,K-ATPase in rat pups at two and five weeks of age. It is concluded that dietary AA + DHA does not alter SPM cholesterol and phospholipid content but increases the 22:6n-3 content of SPM phospholipids modulating activity of Na,K-ATPase.     

β-adrenegic receptor-adenylate cyclase alterations during the postnatal development of skeletal muscle

The postnatal development of mammalian skeletal muscle is associated with an increased capacity for glycogenolysis. In the present study rabbit skeletal muscle underwent a 7-fold increase in glycogen synthase and glycogen phosphorylase activity over the postnatal period of 0–8 weeks. An enriched fraction of sarcolemma was prepared from neonatal and adult muscle to examine the development of the β-adrenergic receptor-adenylate cyclase system. Adult membranes possessed a 2-fold greater Na⁺K⁺(Mg²⁺)-ATPase activity and a 6–8-fold greater sodium fluoride- and epinephrine-stimulated adenylate cyclase activity. The activation ratio (effector activity/basal activity) increased 2–3-fold for epinephrine and sodium fluoride in adult sarcolemma. The activation by catecholamines conformed to the physiological β₂ type response with isoproterenol (1.8 · 10^?8 M) > epinephrine (1.1 · 10^?7 M) > norinephrine (3.2 · 10^?6 M). In contrast, binding studies employing (?)-[³H] dihydroalprenolol showed little difference between neonatal and adult membranes with respect to (1) number of binding sites, (2) equilibrium dissociation constant and (3) displacement of (?)-[³H]dihydroalprenolol by catecholamine agonists.Protein and lipid components of the sarcolemma were also modified during development. Neonatal membranes possessed two glycopeptides of M_r 80 000 and 86 000, whereas in the adult only a single M_r 133 000 species was evident. The total lipid phosphorus and phospholipid composition was unchanged during development. The content of linoleic acid increased approx. 3-fold during development in the phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine phospholipids. The cholesterol content of adult membranes was decreased by 29% compared to neonatal membranes.     

Postnatal development of intestinal bile salt transport. Relationship to membrane physico-chemical changes

The postnatal development of intestinal bile salt transport in the rat was examined using the villus technique. Jejunal uptake of taurocholate was linear with respect to incubation concentration at all study ages. Ileal uptake was linear with taurocholate concentration during the first 2 postnatal weeks; a curvilinear relationship indicating the presence of saturable transport appeared during the third week. With the appearance of ileal active transport at age 3 weeks, the Km (app) was constant at 0.49 mM, 0.59 mM, and 0.50 mM in 3-week, 4-week, and adult animals, respectively. The V(app) was 14.65 nmol X mg-1 (dry wt) X min-1 at 3 weeks and declined with age to 11.40 and 10.51 nmol X mg-1 (dry wt) X min-1 in 4-week and adult animals, respectively. The role of physico-chemical changes in the microvillus membrane in the development of ileal active transport was examined. With increasing postnatal age, microvillus membrane cholesterol content rose while the phospholipid content remained unchanged in both ileum and jejunum. Corresponding rises in the cholesterol/phospholipid ratio were observed in both sites. Simultaneously, the microvillus membrane fatty acid composition was changing from predominantly saturated to unsaturated species in both ileum and jejunum. The microvillus membrane fluorescence anisotropy (r) increased with postnatal age in jejunum when measured at 25 degrees C and 37 degrees C and ileum when measured at 25 degrees C; however, no change was noted in ileum when measured at 37 degrees C. Ileal active bile salt transport develops during the third postnatal week, and is associated with concurrent changes in membrane lipid composition and fluidity when measured at 25 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in metabolism and hepatic ultrastructure induced by estradiol and testosterone in immature female Epinephelus akaara (Teleostei,Serranidae)

Summary Estradiol injections increase serum level of calcium, amino acid, glucose, protein, ammonia and creatinine in immature Epinephelus akaara, and also increase levels of total lipid, cholesterol, phospholipid and esterified fatty acids. Hepatic protein, glycogen and lipid concentrations also rise after estradiol treatment, and some hepatic enzymes participating in the metabolism of nitrogen, lipid and carbohydrate, show increased activity. Serum vitellogenin levels are increased. Testosterone treatment increases serum protein, total lipid, cholesterol, amino acid and ammonia levels, and also hepatic glycogen content, but in contrast to estradiol treatment, testosterone does not change serum vitellogenin, glucose, calcium, phospholipid, esterified fatty acid and creatinine levels, nor the hepatic lipid and protein content. A small number of hepatic enzymes shows an increased activity. Vitellogenic fish show biochemical changes similar to that of estradiol-treated fish, but are different from those of immature fish. Estradiol treatment induces ultrastructural changes in the hepatocytes of immature fish that are similar to those found in vitellogenic fish. These include a proliferation of rough endoplasmic reticulum and Golgi apparatus, and an increase in glycogen and lipid, all indicative of enhanced metabolic activity.     

Effects of oxygen deficiency on survival and glycogen content of Chironomus anthracinus (Diptera,Chironomidae) under laboratory and field conditions

Growth and glycogen content of Chironomus anthracinus in Lake Esrom, Denmark was examined during summer stratification in 1992 and 1993. Simultaneously, effects of oxygen deficiency on glycogen utilization and survival were experimentally studied. The population consisted of almost fullgrown 4th instar larvae in 1992 and 2nd and 3rd instar larvae in 1993. Growth rate and glycogen content changed as hypolimnetic oxygen deficiency increased. During a 1st phase of stratification dry weight and glycogen content increased (2nd and 3rd instars) or was almost constant (4th instar) but decreased significantly during the following 2nd phase. This change from growth to degrowth and utilization of endogenous glycogen reserves correlated with a change in the thickness of the microxic layer (<0.2 mg O₂ 1^–1) above the sediment surface. The layer increased from 2–3 m in phase 1 to 4–5 m in phase 2, and we suggest that this deteriorated the oxygen conditions and resulted in a change in larval energy metabolism from fully aerobic during the 1st phase to partly anaerobic in the 2nd phase. During the 2nd phase larval metabolism was estimated at less than 20% of normoxic rate. Experimental exposure of the larvae to anoxia indicated highly different survival of young larvae (2nd and 3rd instars) and older larvae (large 4th instars). The morality of young larvae was 50% after three days in anoxia at 10 °C, whereas only 25% of the older larvae had died after 3–4 weeks under similar conditions. Extending the treatment, however, resulted in increased death rate of the 4th instar larvae with only 10% surviving after seven weeks. The anaerobic metabolism of 4th instar larvae as estimated from glycogen degradation at 10 °C was 5% of normoxia in the interval from 0–5 days but 1.5% in the interval from 20–25 days. It is concluded that survival of C. anthracinus in anoxia is very limited, but traces of oxygen in the environment allowing for faint aerobic metabolism prolong the survival time of the larvae from a few days (2nd and 3rd instars) or a few weeks (4th instar) to probably 3–4 months.     

Adaptive changes in lipid composition of rat liver plasma membrane during postnatal development following maternal ethanol ingestion

The fatty acid composition of constituent phospholipids and the cholesterol content of rat liver plasma membranes were determined subsequent to maternal alcohol ingestion during pregnancy and lactation. The alcoholic group was given a liquid Metrecal diet containing 37% ethanol-derived calories. The control group was pair-fed an isocaloric sucrose/Metrecal diet. Litters were killed for lipid analyses at days 5, 15 and 25 after birth. These studies revealed that the total phospholipid phosphorus was similar and increased significantly with age in both groups. Cholesterol also increased significantly with age in both groups but was greater in the alcoholic pups, resulting in a higher cholesterol/phospholipid molar ratio. While the phosphatidylethanolamine (PE) content increased with age in both groups, that of sphingomyelin decreased. Phosphatidylserine + phosphatidylinositol (PS + PI) was significantly higher in the control group at all ages studied. A consistent increase of C22:6 in phosphatidylcholine (PC), sphingomyelin, PS + PI and in the total phospholipid fraction from alcoholic pups was observed. Although other fatty acid changes were found in PC, PS + PI and sphingomyelin, PE was not affected. These results suggest that specific adaptive changes were induced in the liver plasma membrane lipids of the progeny from alcoholic rats.     

Effects of exercise on maternal glycogen storage patterns and fetal outcome in mature rats.

The purpose of the present study was to examine the effects of exercise on maternal glycogen storage patterns and fetal outcome in mature (approximately 12 months of age) Sprague-Dawley rats. The exercise consisted of treadmill running at 30 m.min-1, on a 10 degree incline, for 60 min, 5 days per week, for 4 weeks prior to pregnancy, which continued until day 19 of gestation. In mature animals, chronic exercise increased (p < 0.05) liver glycogen concentration in both pregnant and nonpregnant rats. In pregnant exercised animals, the glycogen concentration of the maternal liver increased almost twofold (p < 0.05) compared with the sedentary pregnant group. There was no difference in the amount of glycogen stored in the gastrocnemius or soleus muscles in response to training, pregnancy, or chronic maternal exercise in the mature rat. In the pregnant groups, there were fewer (p < 0.05) viable fetuses and more (p < 0.05) resorption sites than in young rats. In addition, exercise during pregnancy in the mature animal decreased (p < 0.05) fetal body weight. These results demonstrate that a conflict may exist between maternal exercise and fetal demands for energy in the mature rat. This conflict seems to favour the maternal system, as evidenced by the enhanced maternal liver glycogen storage and the negative effect on fetal growth.     

Prolonged melatonin administration in 6-month-old Sprague-Dawley rats: metabolic alterations

The aim of this work was to evaluate the effect of prolonged melatonin administration on chosen metabolic and hormonal variables in male and female Sprague-Dawley rats. Melatonin was administered in tap water (4 microg/ml) daily from the 6th month of age. Rats were fed a standard type of diet ad libitum and were kept in a light regimen L:D--12:12h. The experiment was terminated after 12 weeks of melatonin administration. Melatonin decreased body mass during the whole experiment in females and from the 42nd day of the experiment in males. Relative heart muscle weight in females and absolute/relative thymus weight in males were increased after melatonin administration. Melatonin decreased glycaemia, heart muscle glycogen concentration in females and liver glycogen concentration in both sexes. Serum insulin concentration in males was decreased; serum corticosterone concentration was increased in both males and females. Serum triacylglycerol and heart muscle cholesterol concentration in females were decreased, however in males serum and heart muscle cholesterol concentration was increased. Liver phospholipid concentration in females was decreased and heart muscle phospholipid concentration in males was increased. Melatonin increased malondialdehyde concentration in heart muscle in males and in liver in both sexes. Melatonin induced prominent sex-dependent changes in both carbohydrate and lipid metabolism.     

Uptake of HDL unesterified and esterified cholesterol by human endothelial cells. Modulation by HDL phospholipolysis and cell cholesterol content

Human HDL (1.070-1.210), doubly labelled with ³H/¹⁴C-labelled unesterified cholesterol and ³H-labelled esterified cholesterol were incubated for 1–5 h with monolayer cultures of human endothelial cells. HDL were preincubated for 60–120 min the presence of albumin and with/without purified phospholipase A₂ (control HDL, phospholipase A₂ HDL) before dilution in the cell culture medium. Average phosphatidyl-choline (PC) degradation was 62.10% ± 2.57% (range 45–80%). A purified lipase /phospholipase A₁ from guinea pig pancreas was used in some experiments (range of PC hydrolysis: 16–70%). (1) ³H/¹⁴C-labelled unesterified cholesterol and ³H-labelled esterified cholesterol appeared in cells during 0–5 h incubations. Trypsin treatment allowed a simple adsorption of HDL onto the cell surface to be avoided, and most of the ³H-labelled esterified cholesterol transferred to cells was hydrolysed. Cell uptake of radioactive cholesterol increased as a function of HDL concentration but no saturation was achieved at the highest lipoprotein concentration used (200 μg cholesterol/ml). Flux of ³H/¹⁴C-labelled unesterified cholesterol was related to the cell cholesterol content, suggesting that it might partly represent an exchange process. The cell cholesterol content was slightly increased after 5 h incubation with HDL (+16%). (2) Pretreatment of HDL with purified phospholipase A₂ doubled on average the amount of cell recovered ³H-labelled esterified cholesterol, while the flux of ³H/¹⁴C-labelled unesterified cholesterol was enhanced by 15–25%. Both transfer and cell hydrolysis of ³H-labelled esterified cholesterol were increased. A stimulation was also observed using purified lipase/phospholipase A₁, provided that a threshold phospholipid degradation was achieved (between 27 and 45%). (3) Endothelial cells were conditioned in different media so as to modulate their charge in cholesterol. The uptake of ³H-labelled esterified cholesterol was found to be significantly higher in cholesterol-enriched cells compared to the sterol-depleted state. Finally, movements of ³H-labelled esterified cholesterol from HDL to endothelial cells were essentially unaffected by cell density or by the presence of partially purified cholesterol ester transfer protein. The possible roles of the transfer of HDL esterified cholesterol to endothelial cells and its modulation by phospholipases are discussed.     

Carbohydrate metabolism in liver from foetal and neonatal sheep

1. During development of the sheep, the activities of UDP-glucose–α-glucan glucosyltransferase and UDP-glucose pyrophosphorylase and the glycogen content are highest in the liver of lambs 2 weeks old and considerably lower in liver from adult sheep. 2. The activity of hexokinase and the rate of incorporation of [¹⁴C]-glucose into glycogen are much lower in liver from postnatal sheep than in rat liver. 3. The activities of hexose diphosphatase and glucose 6-phosphatase and the rates of incorporation of [¹⁴C]pyruvate and [¹⁴C]propionate into glycogen increase from low levels in the liver of foetal sheep to maxima a few weeks after birth. The activities in the liver of adult sheep are slightly lower. 4. The incorporation rate of [¹⁴C]pyruvate into glucose has been measured in liver slices from rats, sheep and chick embryos at several ages of these animals. This pathway is active in liver from foetal sheep, embryonic chicks and postnatal rats or sheep, but is absent from the liver from foetal rats. 5. Fructose metabolism, as measured by the rates of incorporation of [¹⁴C]fructose into glycogen and glucose in liver slices and by assays of liver ketohexokinase, is barely detectable in the liver of foetal sheep and appears soon after birth. 6. During development of the sheep, the incorporation rate of [¹⁴C]galactose into glycogen in liver slices is highest in foetal sheep and decreases with increasing age of the animal. 7. These findings are discussed with reference to the changing pattern of carbohydrate metabolism during neonatal development of liver in the sheep.     

Preimplantation mouse embryos synthesize membrane sterols

The total cholesterol content of preimplantation mouse embryos increases approximately threefold (to 1 pmole) during the development of a blastocyst from a fertilized egg. From the two-cell stage onwards embryos are capable of converting [³H]mevalonate into the membrane sterols lanosterol and cholesterol. However, activity of the ratelimiting enzyme in sterol synthesis, hydroxymethylglutaryl coenzyme A reductase, was only measurable in late expanded blastocysts. These estimates of cholesterol content and the amounts of ³H-sterol formed suggest that the preimplantation mouse embryo can synthesize membrane sterols from early cleavage stages onwards. Late compaction and early fluid accumulation (approx. 84 hr post-hCG) are associated with a transition from lanosterol to cholesterol synthesis. The possible relationship between this transition and changes in the properties of embryo membranes which occur at this time is discussed. The results, taken together with previous evidence for phospholipid synthesis in early embryos, demonstrate that the preimplantation mouse embryo is capable of synthesizing major membrane lipids and hence has the potential for assembling cell membranes and modulating their lipid-mediated properties.     

Welfare status of cultured seabass (Dicentrarchus labrax L.) and seabream (Sparus aurata L.) assessed by blood parameters and tissue characteristics

Seabass (SBS) and seabream (SBM) juveniles were reared with the goal of obtaining three different final densities (SINT = 40 kg m^?3; INT = 20 kg m^?3; SEM = 0.2 kg m^?3) to ascertain the effects thereof on the welfare of the fish. Significant blood metabolites and hepatic glycogen were determined every 3 months and at harvest. Trials lasted 18 months in seabass and 17 months in seabream. At the end of experiment the main biometric productive parameters and quality of body composition were also recorded. Regarding intensively reared seabass (SINT‐SBS, INT‐SBS), the plasma triglycerids, total cholesterol and transaminases (AST, ALT) were always significantly higher than in semi‐intensively maintained fish (SEM‐SBS). At the final sampling in the SINT‐SBS batch, the total protein and glucose were also markedly increased. Conversely, at harvest the liver glycogen content decreased in SINT‐SBS (34 ± 8 mg g^?1 liver) with respect to INT‐SBS (57 ± 12 mg g^?1 liver) and SEM‐SBS (63 ± 11 mg g^?1 liver). No differences among groups were observed for creatine kinase (CK) and lactate dehydrogenase (LDH). With regard to seabream, SINT‐SBM and INT‐SBM constantly showed plasma triglycerids and total cholesterol as being significantly higher when compared to SEM‐SBM. In the final two blood samplings, SINT‐SBM exhibited the most elevated values for LDH. At harvest, AST, ALT, total protein and glucose markedly increased in SINT‐SBM, whereas liver glycogen content was reduced (22.5 ± 9 mg g^?1 liver), more than in INT‐SBM (70 ± 16 mg g^?1 liver) and SEM‐SBM (75 ± 20 mg g^?1 liver). In both seabass and seabream, body composition was very similar in the different stocking densities, except for total cholesterol. Total n‐3 polyunsaturated fatty acid (PUFA) in seabream was significantly different from fish of the semi‐intensive groups; however, nutritional values and fatty acid profiles were equally good. The intermediate final density of seabass and seabream at 20 kg m^?3 seemed to give the best results in terms of their well being when compared to fish reared at 40 kg m^?3. The absence of differences in blood metabolites and hepatic glycogen levels between the intensive batch and the semi‐intensive groups until harvest was a reference to the positive status of the fish. A density of 20 kg m^?3 can be considered acceptable for farm strategy planning for raising healthy on‐growing seabass and seabream juveniles.     

Postnatal maturation of rat intestinal membrane: lipid composition and fluidity.

1. We studied the lipid composition and the fluidity of small intestine brush border membrane (BBM) of rats of different age: 'very young' (5-7 weeks old), 'young' (9 weeks old), 'adult' (30 weeks old) and 'old' (85 weeks old). 2. Fluorescence anisotropy, as assessed by 1,6-diphenyl-1,3,5-hexatriene probe (DPH), was increased from very young to adult rats. 3. In agreement with these results the lipid composition in adult animals showed a lower lipid/protein ratio (derived mainly from a lower content of total polar lipids) and an increase of cholesterol esters and sphingomyelin (SM) saturation index. 4. A marked decrease of the order parameter was observed in the 'old' group, accompanied by a decreased cholesterol/phospholipid ratio. 5. The percentage distribution of membrane phospholipids significantly changed during development, but the modifications were not correlated with the anisotropy of DPH.     

Simultaneous occurrence of hypercholesterolemia and hemolytic anemia in rats fed cholesterol diet

Cholesterol diet-induced hemolytic anemia in rats was described. When rats were fed a cholesterol diet for 11 weeks, serum cholesterol rapidly increased within the first week, and was maintained in 5-10 times higher levels throughout the study as compared to those of control rats. Erythrocyte count, hematocrit and hemoglobin concentration decreased from about 2 weeks of feeding. The spleen showed an increase of hemosiderin deposition from 6 weeks of feeding. The half life of erythrocytes labelled with 51Cr was shortened significantly at 6 weeks of feeding. These findings indicate that cholesterol diet can induce hemolytic anemia. Serum cholesterol and phospholipid were markedly increased, but in erythrocyte membrane, free cholesterol content was not persistently increased and phospholipid content was decreased. In hemorrheological studies, erythrocyte deformability and mechanical hemolysis tended to reduce. In conclusion, it was considered that as a result of reduced phospholipid content the erythrocytes of cholesterol-fed rats were decreased in its deformability and were captured more easily by the spleen. The profile of hemolytic anemia in cholesterol-fed rats was quite different from those reported in cholesterol-fed guinea pigs, rabbits and dogs.     

Membrane fluidity and lipid composition of rat small intestinal brush-border membranes during postnatal maturation

Fluidity and lipid composition of rat small intestinal brush-border membranes (BBM) were studied during maturation in five age groups: newborns, sucklings (1-3 weeks), weaned (4-6 weeks), juveniles (8-10 weeks), and adults (12 weeks). Brush-border membrane fluidity was measured by steady-state fluorescence polarization. Fluorescent probes used were: 1,6-diphenyl-1,3,5-hexatriene, 1-(4-trimethylammonium)phenyl)-6-phenyl-1,3,5-hexatriene, and a set of n-(9-anthroyloxy) fatty acids. Fluorescence anisotropy measured with all fluorophores was increased in adult versus newborn rats (P less than 0.004). The weight ratio of saturated to cis-unsaturated fatty acids increased from birth to the suckling age (P less than 0.0004). The cholesterol to phospholipid molar ratio increased from birth to the weaned age (P less than 0.0001). Cholesterol to protein ratio and phospholipid to protein ratio decreased after the weaned age (P less than 0.004). The results not only describe maturational changes of brush-border membranes but also give a better understanding of the correlations between biophysical and biochemical data in biological membranes.     

Effects of Dietary Polychlorinated Biphenyls and Protein Level on Liver and Serum Lipid Metabolism of Rats

The effects of polychlorinated biphenyls (PCB) and dietary protein level on the liver and serum lipid metabolism of rats were studied. Rats were fed an experimental diet containing 7 or 30% casein with or without 0.1 % PCB for 24 days. Dietary PCB increased the level of triglyceride, phospholipid and cholesterol in the liver. The accumulation of triglyceride and cholesterol in liver was markedly increased with a low protein diet. The incorporation of injected ³H₂O into liver cholesterol was increased by PCB, but not affected by the dietary level of protein. The incorporation of the tracer into liver fatty acids was not increased by PCB intake. Dietary PCB also raised serum cholesterol and phospholipid, while PCB decreased triglyceride level, especially in rats on low protein diet. In addition, PCB intake clearly raised serum high density lipoprotein and diminished very low density lipoprotein. In the low protein group, PCB markedly repressed the incorporation of ³H₂O into serum lipids. The results suggest that the hepatic lipids accumulation by the addition of 0.1 % PCB to a low protein diet might be mainly ascribed to a repression in the transport of triglyceride from liver to blood. KEY WORDS: PCB, dietary protein, liver lipids, serum lipoprotein.     

Role of glucose and insulin in regulating glycogen synthase and phosphorylase activities in rainbow trout hepatocytes

This study, using ¹³C nuclear magnetic resonance spectroscopy showed enrichment of glycogen carbon (C1) from ¹³C-labelled (C1) glucose indicating a direct pathway for glycogen synthesis from glucose in rainbow trout (Oncorhynchus mykiss) hepatocytes. There was a direct relationship between hepatocyte glycogen content and total glycogen synthase, total glycogen phosphorylase and glycogen phosphorylase a activities, whereas the relationship was inverse between glycogen content and % glycogen synthase a and glycogen synthase a/glycogen phosphorylase a ratio. Incubation of hepatocytes with glucose (3 or 10 mmol·1^-1) did not modify either glycogen synthase or glycogen phosphorylase activities. Insulin (porcine, 10^-8 mol·1^-1) in the medium significantly decreased total glycogen phosphorylase and glycogen phosphorylase a activities, but had no significant effect on glycogen synthase activities when compared to the controls (absence of insulin). In the presence of 10 mmol·1^-1 glucose, insulin increased % glycogen synthase a and decreased % glycogen phosphorylase a activities in trout hepatocytes. Also, the effect of insulin on the activities of % glycogen synthase a and glycogen synthase a/glycogen phosphorylase a ratio were more pronounced at low than at high hepatocyte glycogen content. The results indicate that in trout hepatocytes both the glycogen synthetic and breakdown pathways are active concurrently in vitro and any subtle alterations in the phosphorylase to synthase ratio may determine the hepatic glycogen content. Insulin plays an important role in the regulation of glycogen metabolism in rainbow trout hepatocytes. The effect of insulin on hepatocyte glycogen content may be under the control of several factors, including plasma glucose concentration and hepatocyte glycogen content.     

Changes in lipid composition of cortical synaptosomes from different age groups of mice

Lipid composition of cortical synaptosomes differed with age in C57BL/6NNIA mice. Significant age differences were observed for cholesterol and the ratio of cholesterol to total phospholipid phosphorus content. The phospholipid to protein ratio of individual phospholipids also increased with age with diacyl-$\text{sn}$-glycero-3-phosphocholine (PC) increasing the most. Acyl group composition of individual phospholipids, however, showed little age difference. The double bond index for PC decreased significantly with age. Changes in membrane composition may help explain differences in the effects of ethanol on the physical and biochemical properties of membranes from different age groups that have been reported previously.     

Development of glycogen and phospholipid metabolism in fetal and newborn rat lung.

Glucose, a major metabolic substrate for the mammalian fetus, probably makes significant contributions to surface active phospholipid synthesis in adult lung. We examined the developmental patterns of glycogen content, glycogen synthase activity, glycogen phosphorylase activity and glucose oxidation in fetal and newborn rat lung. These patterns were correlated with the development of phosphatidylcholine synthesis, content and the activities of enzymes involved in phosphatidylcholine synthesis. Fetal lung glycogen concentration increased until day 20 of gestation (term is 22 days) after which it declined to low levels. Activity of both glycogen synthase I and total glycogen synthase (I + D) in fetal lung increased late in gestation. Increased lung glycogen concentration preceded changes in enzyme activity. Glycogen phosphorylase a and total glycogen phosphorylase (a + b) activity in fetal lung increased during the period of prenatal glycogen depletion. The activity of the pentose phosphate pathway, as measured by the ratio of CO2 derived from oxidation of C1 and C6 of glucose, declined after birth. Fetal lung total phospholipid, phosphatidycholine and disaturated phosphatidylcholine content increased by 60, 90 and 180%, respectively, between day 19 of gestation and the first postnatal day. Incorporation of choline into phosphatidylcholine and disaturated phosphatidylcholine increased 10-fold during this time. No changes in phosphatidylcholine enzyme activities were noted during gestation, but both choline phosphate cytidylyltransferase and phosphatidate phosphatase activity increased after birth. The possible contributions of carbohydrate derived from fetal lung glycogen to phospholipid synthesis are discussed.     

Carbohydrate metabolism in Manduca sexta during late larval development

The carbohydrate metabolism in Manduca sexta underwent significant changes during late larval development. Approximately 10% of fat body glycogen phosphorylase was active during the feeding period of the 5th instar, pharate-pupal development and after the pupal moult; it is concluded that glycogen synthesis prevailed. During the last larval and the pupal moult, as well as the wandering stage the percentage of active phosphorylase was significantly increased indicating that fat body glycogen stores were broken down to supply substrates to meet the demands of carbohydrate metabolism. In the course of the last larval moult and the wandering stage the fat body glycogen content decreased significantly from about 300 to about 200 μg mg⁻¹ dry mass substantiating that carbohydrates were released from the fat body. Prior to phosphorylase activation, the concentrations of total haemolymph sugars decreased significantly from about 12 to about 6 mg trehalose equivalents ml⁻¹ (last larval moult) and from about 18 to about 12 mg ml⁻¹ (wandering stage), and increased again slightly when phosphorylase was activated. The haemolymph glucose concentration decreased significantly from about 1.1 to 0.3 mg ml⁻¹ (last larval moult) and in the course of the 5th-instar feeding period from about 1.1 to 0.2 mg ml⁻¹, and remained at this level until the beginning of adult development. The amount of chitosan present in the cuticle increased steadily during the feeding period of the 5th instar from about 10 to 110 mg. It appears that fat body glycogen might be broken down during the last larval moult and the wandering period to provide substrates for chitin synthesis. A dramatic decrease in the amount of chitosan was observed prior to the pupal moult.