Regulation of lipid metabolism by dipyridamole and adenosine antagonists in rat adipocytes

1. Acute effects of dipyridamole, an inhibitor of adenosine transport, direct activators of adenylate cyclase and thirteen adenosine antagonist analogs on fatty acid synthesis have been examined in terms of the control of [1-14C]acetate incorporation into labeled fatty acids in the presence of glucose. 2. This monosaccharide acts as a stimulator of lipogenesis by generating NADPH for the lipid synthesis. 3. The relationship between lipogenesis and lipolysis was compared with a variety of adenylate cyclase stimulators. 4. The data obtained reveals that dipyridamole potentiated the inhibitory or stimulatory effects of isoproterenol and forskolin on lipogenesis and on lipolysis, respectively. 5. In these cases the data show that it exists an inverse relationship between lipogenesis and lipolysis. 6. Dipyridamole and methylxanthine analogs only moderately affect the rate of lipolysis whereas its effects are more potent on lipogenesis and lend further support to the hypothesis that dipyridamole antagonize adenosine actions as well as methyl xanthines. 7. These results suggest that dipyridamole and adenosine antagonists alter lipogenesis independently of the lipolytic process and that it exists an inverse relationship between lipogenesis and lipolysis under some conditions whereas there are not under others.     

Changes in lipid and carbohydrate metabolism during starvation in adult Manduca sexta

Summary Adult Manduca sexta feed very irregularly in the laboratory, and many adult males never feed. Feeding adults live longer and feeding females lay many more eggs; however, in both feeding (sugar water) and starving adults a decrease of metabolic reserves is observed. Carbohydrates disappear from hemolymph and from fat body. Fat body lipid also decreases, while hemolymph lipid concentration increases strongly in starving adults. The activity of fat body glycogen phosphorylase increases strongly in starving adult M. sexta. The activity of glycogen phosphorylase is correlated inversely with hemolymph sugar concentration. Injected trehalose inactivates glycogen phosphorylase within 2 h, and lowers the hemolymph lipid level within 6 h. In starving adult M. sexta, neither the activation of glycogen phosphorylase nor the increase of hemolymph lipid concentration depends on adipokinetic hormone, since cardiacectomy does not prevent the activation of glycogen phosphorylase nor the increase of hemolymph lipid level.Abbreviations AKH adipokinetic hormone - EDTA ethylenediamine tetraacetate Present address: Department of Biochemistry and Center for Insect Science, The University of Arizona, Tucson, AZ 85721, USA     

Some aspects of buoyancy adaptations of chaetognaths

Chaetognaths mainly keep to a preferred depth range by movement and resistance achieved by body shape. Some species, for exampleSagitta lyra andS. hexaptera, developed conspicuous, voluminous, gelatinous inner parts in the lateral fins. These are considered an aid toward buoyancy, as they compensate the increasing density caused by maturing gonads. Probably, the small size of the sexual organs ofS. enflata can also be regarded as a buoyancy adaptation. Member of the Taxonomy Group at the Biologische Anstalt Helgoland     

Some aspects of amino acid metabolism in the rat fetus

• 1.1. In spite of an eventual catabolic phase during the last third of pregnancy, nitrogen retention seems to increase in pregnant rats. Furthermore, the high uterine blood flow and the high placental transfer of amino acids maintains an adequate nutrient supply to the fetuses.
• 2.2. The terminal rat fetus has a high circulating plasma amino acid level, as well as an increased free amino acid tissue pool when compared to its mother's.
• 3.3. In the rat fetus the development of enzymatic capabilities shows a sudden emergence (also denomined clustering) in late fetal life. In a general trend, the activities of enzymes related with amino acid metabolism are not well developed during rat fetal life.
• 4.4. The rate of amino nitrogen excertion in rat fetus is low, mainly due to the low development of urea cycle enzyme activities.
• 5.5. The rates of protein synthesis in many tissues are high in the rat fetus and they show a progressive decrease until delivery. On the other hand, the rates of protein breakdown are also higher during fetal life than in the adult.

     

Upregulation of lipid synthesis in small rat adipocytes by microvesicle-associated CD73 from large adipocytes

Filling-up lipid stores is critical for size increase of mammalian adipocytes. The glycosylphosphatidylinositol (GPI)-anchored protein, CD73, is released from adipocytes into microvesicles in response to the lipogenic stimuli, palmitate, the antidiabetic sulfonylurea drug glimepiride, phosphoinositolglycans (PIG), and H(2)O(2). Upon incubation of microvesicles with adipocytes, CD73 is translocated to cytoplasmic lipid droplets (LD) and esterification is upregulated. The role of CD73-harboring microvesicles in coordinating esterification between differently sized adipocytes was studied here. Populations consisting of either small or large or of both small and large isolated rat adipocytes as well as native adipose tissue pieces from young and old rats were incubated with or depleted of endogenous microvesicles and analyzed for translocation of CD73 and esterification in response to the lipogenic stimuli. Large adipocytes exhibited higher and lower efficacy in releasing CD73 into microvesicles and in translocating CD73 to LD, respectively, compared to small adipocytes. Populations consisting of both small and large adipocytes were more active in esterification in response to the lipogenic stimuli than either small or large adipocytes. With both adipocytes and adipose tissue pieces from young rats esterification stimulation by the lipogenic stimuli was abrogated by depletion of CD73-harboring microvesicles from the incubation medium and interstitial spaces, respectively. In conclusion, stimulus-induced lipid synthesis between differently sized adipocytes is controlled by the release of microvesicle-associated CD73 from large cells and its subsequent translocation to LD of small cells. This information transfer via microvesicles harboring GPI-anchored proteins may shift the burden of triacylglycerol storage from large to small adipocytes.     

Lipid metabolism of rat adipocytes in culture

Isolated differentiated rat adipocytes embedded in a collagen matrix were maintained in culture for 0, 4 and 14 days. Assessment of viability by either anabolic glucose metabolism or catabolic lipolytic metabolism can be misleading; both types of metabolism should be measured to establish the status of cells. Cells maintained morphological integrity even when not viable as judged by anabolic glucose metabolism.     

Role of growth hormone in the adaptations of lipolysis in rat adipocytes during recovery from lactation.

Removal of the litter from lactating rats results in a fall in the rate of noradrenaline-stimulated lipolysis of adipocytes. This adaptation can be prevented by administration of growth hormone (somatotropin) to such rats and mimicked by injecting lactating rats with an antiserum to growth hormone, whereas lowering serum prolactin by injecting bromocriptine had no effect. The anti-lipolytic effect of adenosine is increased during lactation and is still increased by 2 days after litter removal. Injection of growth hormone into lactating rats decreased slightly the response to adenosine, whereas injection of growth hormone into rats after removal of their litters resulted in a much greater decrease in the response to adenosine, to that found in virgin and pregnant rats.     

Some new aspects of the metabolism of phenacetin in the rat

1. Four new metabolites of phenacetin in the urine of the rat are described; these are (i) N-acetyl-S-ethylcysteine, (ii) quinol, (iii) acetamide and (iv) probably N-acetyl-S-2-(4-ethoxyacetanilido)cysteine S-oxide. 2. Metabolites (i), (iii) and (iv) were characterized and estimated by g.l.c., by t.l.c., by paper chromatography, by chemical reactions or by radioactive techniques after administration to rats of [ethyl-¹⁴C]phenacetin and [acetyl-³H]phenacetin; metabolite (ii), which was excreted mainly as conjugates of sulphuric acid and glucosiduronic acid, was measured by paper chromatography and characteristic colour reactions after enzymic and chemical hydrolysis of the conjugates. 3. Small amounts of azoxy-4-[ethyl-¹⁴C]ethoxybenzene and an unknown metabolite were also found in the urine of rats after administration of [ethyl-¹⁴C]phenacetin. 4. The likely mechanisms and some biological implications of these metabolic reactions are discussed.     

Some aspects of glycosylation in rat liver during pregnancy

The aim of the present report was to analyze the pattern of glycoprotein synthesis in rat liver on 19th and 22nd day of pregnancy by following the incorporation of¹⁴C-glucosamine and³H-galactose into isolated rat hepatocytes, the N-acetylglucosaminyl-1-P and galactosyl transferase activities, and the liver content of dolichol and dolichyl-phosphate.The data obtained show a decrease of precursor incorporation into glycoproteins during the last period of pregnancy; this decrease is independent of enzyme activities. The dolichol content increases and the dolichyl-phosphate content, usually considered as rate limiting for glycosylation, decreases.These results, present in other conditions of proliferation and differentiation of rat liver, could explain the differences in membrane organization, the increase of hepatic proteolysis and the alteration in secretory activity during the last phase of gestation.     

Some metabolic aspects of ecology

Summary

Due to the similarity of the major metabolic pathways in all living organisms it might be thought unlikely that the study of metabolic variation would add to an understanding of ecological differences. However, a quantitative study of the regulation of metabolism and its end-products indicates a link between cell biochemistry and the capability of certain species to succeed in particular environments. A study of anaerobic metabolism in animals and plants shows a number of similarities in those species able to survive in oxygen-poor environments. These include the production of nontoxic end-products and the avoidance of a large oxygen debt. As a large variety of organisms is examined, these comparisons suggest that the metabolic solutions to a given environmental stress, whether in plants or animals, can be strikingly similar. Therefore, although the main metabolic pathways in most living organism are the same, the regulation of metabolism varies with the ecology of the species. Examples are discussed in which a knowledge of metabolism in relation to ecology could have practical applications in forestry and agriculture.     

Cadmium stimulates glucose metabolism in rat adipocytes

Cd²⁺ caused an increase in CO₂ formation from glucose in rat adipocytes. The apparent K_m value for glucose was 2.02 mM for control condition, with Cd²⁺, and with insulin. Cd²⁺ stimulates glucose metabolism even though specific diffusion of glucose is blocked. A possible site effected by Cd²⁺ is discussed.