Variations of cyclic AMP and cyclic GMP contents of the liver and of brown and white adipose tissues of the rat during the first week of cold exposure.

The variation in the amounts of cyclic AMP and cyclic GMP were studied in white and brown adipose tissues and in the liver of rats during the first week of cold exposure (5 degrees C). In white fat, only a small increase in cAMP was observed on the first day. In brown fat, parallel decreases in cAMP and cGMP contents were induced which might be related to a large mobilization of tissue fatty acids. In the liver, cold exposure barely affected the cAMP content but the level of cGMP was markedly increased. These results are discussed with regard to the respective role of these different tissues in cold-induced energetic substrate mobilization.     

Effect of ambient temperature on perinatal variations of cyclic AMP and cyclic GMP in rat brown adipose tissue

The level of cyclic AMP in the brown adipose tissue of perinatal rats was found to increase by the end of pregnancy and decrease during the first two days of life. It then increased in newborn rats maintained at either 28° or 16°. However, in the 16° group, the cAMP level remained high until the 21st day whereas, in the 28° group decreases were noted after the tenth day. These variations are discussed in regard to norepinephrine content and lipid metabolism in the tissue. Inverse variation of cAMP and cGMP levels were not observed during the period studied.     

Effects of cold exposure on cyclic AMP concentration in plasma,liver, and brown and white adipose tissues in cold-acclimated rats

Effects of acute cold exposure on plasma energy substrates and tissue 3,5-adenosine monophosphate (cAMP) were analyzed in intact rats, to define an involvement of the nucleotide in nonshivering thermogenesis (NST) and resultant cold acclimation. After an acute cold exposure to –5°C, the plasma glucose level increased gradually in warm-kept control rats (C) while it decreased significantly in cold-acclimated rats (CA). However, it was increased considerably by an extreme cold exposure to –15°C in both C and CA. By contrast, plasma levels of free fatty acids (FFA) increased immediately after cold exposure and the release lasted during the period of exposure especially in C. The cold exposure also increased plasma cAMP concentration but no concomitant increase was found in the liver. In both brown (IBAT) and white (WAT) adipose tissues the nucleotide concentration showed a stepwise decrease. The observed correlation between lipolysis and plasma cAMP response after cold exposure suggests an involvement of the adenylate cyclase-cAMP system in NST via lipid metabolism, at least, in the early stages of cold acclimation.Abbreviations cAMP cyclic 3,5-adenosine monophosphate - NST nonshivering thermogenesis - FFA free fatty acids - IBAT brown adipose tissue - WAT white adipose tissue     

Evidence for a role of somatostatin in lipid metabolism of liver and adipose tissue

We have studied the effects of somatostatin on lipid metabolism in liver and adipose tissue of fasted mice. The animals were injected subcutaneously with 8 micrograms somatostatin and killed 5 min after injection. In vivo incorporation of [14C]acetate into triglycerides in both tissues and into hepatic cholesterol was significantly enhanced by somatostatin. Concomitantly, a decrease of triglyceride lipase activity was observed, which corresponds well with the variation undergone by cyclic AMP-protein kinase system. In addition, a marked increase of serum cholesterol levels was observed. Additionally, in vitro experiments were also performed by employing 2.4 X 10(-6) M somatostatin. The results showed that the direct effect of somatostatin on liver seems to be a decrease in acetate uptake. The results obtained with the adipose tissue were similar to those obtained in in vivo conditions. On the other hand, when somatostatin was administered in vivo, the ability to incorporate ortho[32P]phosphate into phospholipids was enhanced in both tissues. Likewise in the in vitro experiments with [14C]acetate, the somatostatin seems to act by decreasing the ortho[32 P]phosphate uptake in liver. While in adipose tissue the somatostatin only caused a strong increase in the specific activity of phosphatidylcholine. These data demonstrate in fasted mice that somatostatin is able to counteract the lipolytic manifestations of the fasted state.     

Behaviour of cyclic nucleotides and Ca2+ levels in liver tissue of rats poisoned by white phosphorus and trichlorobromomethane

The content of hepatic cyclic AMP was increased soon after intoxication by white phosphorus. Its level reached a maximum 4 h after poisoning, but in subsequent phases tended to return to normal. In contrast, the cyclic GMP concentration was altered only 24 and 36 h after treatment with the same hepatotoxin. Similar modifications of cAMP and cGMP content were also detected after poisoning by trichlorobromomethane (CBrCl3). As a consequence, an altered cGMP/cAMP ratio was found in both experimental conditions. Further, the modification of cAMP content after white phosphorus was detected prior to liver damage (steatosis and necrosis), while the highest concentration of the cyclic nucleotide in CBrCl3-poisoned rats was found when fatty liver was already evident. In addition, in phosphorus-poisoned rats, the hepatic content of Ca2+ was found to be unmodified during all phases of the intoxication, while after CBrCl3 a phasic increase of the Ca2+ level was observed at 4, 24 and 36 h.     

Ligand binding and activation in a prokaryotic cyclic nucleotide-modulated channel

We designed a technique that directly determines binding of cyclic nucleotides to the prokaryotic cyclic nucleotide modulated ion channel MloK1. The ability to purify large quantities of MloK1 facilitated equilibrium binding assays, which avoided the inherent problem of relatively low affinity binding which hindered the use of eukaryotic channels. We found that MloK1 specifically binds cAMP and cGMP with affinity values in the range of those observed for activity assays for eukaryotic channels. Notably, the concentration of ligand that elicited 50% of maximum response in (86)Rb flux assays (K1/2), also referred to as ligand sensitivity, was smaller than the corresponding value obtained from binding assays (Kd) potentially indicating significant channel activity in partially liganded states. To gain further insight into the mechanism of binding and activation of these channels, we mutated several amino acids in the ligand-binding pocket of MloK1, known from electrophysiological studies of homologous eukaryotic channels to affect ligand selectivity and binding efficacy. The S308V MloK1 mutant (a mutation which decreases cGMP selectivity in eukaryotic channels) decreased both the observed cGMP binding affinity and the sensitivity to cGMP relative to the wild-type (WT) channel, leaving those for cAMP unchanged. Conversely, the A352D MloK1 mutant (a mutation which increases cGMP selectivity in eukaryotic channels) increased both the affinity and the sensitivity for cGMP relative to the WT channel, again leaving those for cAMP unchanged. Mutations at R307 in MloK1, the most conserved residue in the binding pocket of cyclic nucleotide-binding proteins, were not tolerated as these mutants do not form functional channels. Furthermore, for each mutation, changes in binding affinities were mirrored by equivalent changes in ligand sensitivity. These data, together with the evidence that partially liganded channels open significantly, suggested strong coupling between cyclic nucleotide binding and MloK1 channel opening.     

A comparison of the effects of duodenal glucose infusion on carbohydrate and lipid metabolism in liver, adipose tissue and small intestinal mucosa in sheep

The effects of duodenal glucose infusion on the specific activities of some enzymes of carbohydrate and lipid metabolism in the liver, perinephric adipose tissue and small intestinal mucosa of sheep were examined. Lipogenic enzyme activity was generally greatest in adipose tissue and lowest in liver and the response of these enzymes to glucose infusion was similarly greatest in adipose tissue. Glycolytic enzyme activity was significantly increased in all three tissues following duodenal glucose infusion. The effects of increasing carbohydrate availability in the small intestine in relation to tissue metabolism in sheep are discussed.     

Effect of andrenalectomy on cyclic 3',5'-guanosine monophosphate metabolism of rat liver and other tissues

Adrenalectomy increased guanyl cyclase and cyclic GMP phosphodiesterase activities in liver and other rat tissues. Liver guanyl cyclase activities from adrenalectomized rats were increased above those of normal controls according to kinetic analysis, gel filtration, ion-exchange chromatography, discontinuous sucrose gradient fractionation, sulfhydryl inhibition, and secretin activation. The effects of adrenal insufficiency on hepatic guanyl cyclase and cyclic GMP phosphodiesterase were prevented by cortisone acetate administration. Immunoassay of liver and skeletal muscle cyclic GMP after adrenalectomy showed markedly decreased levels in liver, but increased levels in skeletal muscle. In liver and other tissues, basal adenyl cyclase and cyclic AMP phosphodiesterase activities were unaffected by adrenalectomy. Hepatic levels of cyclic AMP were also unchanged by adrenalectomy. Hypophysectomy raised guanyl cyclase activity in liver but had no effect on liver cyclic GMP phosphodiesterase activity. These alterations are discussed in relation to possible glucocorticoid regulation of cyclic GMP metabolism.     

Effect of insulin and prednisolone on cyclic nucleotides and phosphoenolpyruvate carboxykinase activity in brown fat and liver of developing rats

The concentrations of cyclic AMP and cyclic GMP in brown fat and liver of both suckling and adult rats at fixed times after injection of insulin (2.5 U/100 g body weight) or prednisolone (2.5 mg/100 g body weight) were compared with the activity of phosphoenolpyruvate carboxykinase assayed 24 h after the injections. A stimulus that produced an increase in cyclic AMP content also produced an increase in the enzyme activity. If the content of cyclic GMP was also increased there was no rise in phosphenolpyruvate carboxykinase activity. A rise in the content of cyclic GMP alone was associated with a reduction in the activity of the enzyme. These preliminary results indicate that cyclic AMP could be involved in the induction of phosphenolpyruvate carboxykinase and that cyclic GMP may somehow be related to its repression. The known differences in the response of phosphenolpyruvate carboxykinase activity to insulin and prednisolone in different tissues and at different stages of ontogenic development may thus be linked to differences in the responsiveness of enzymes concerned with the metabolism of cyclic nucleotides.     

HIV protease inhibitor induces fatty acid and sterol biosynthesis in liver and adipose tissues due to the accumulation of activated sterol regulatory element-binding proteins in the nucleus

The mechanism by which human immunodeficiency virus (HIV) protease inhibitor therapy adversely induces lipodystrophy and hyperlipidemia has not been defined. This study explored the mechanism associated with the adverse effects of the prototype protease inhibitor ritonavir in mice. Ritonavir treatment increased plasma triglyceride and cholesterol levels through increased fatty acid and cholesterol biosynthesis in adipose and liver. Ritonavir treatment also resulted in hepatic steatosis and hepatomegaly. These abnormalities, which were especially pronounced after feeding a Western type high fat diet, were due to ritonavir-induced accumulation of the activated forms of sterol regulatory binding protein (SREBP)-1 and -2 in the nucleus of liver and adipose, resulting in elevated expression of lipid metabolism genes. Interestingly, protease inhibitor treatment did not alter SREBP mRNA levels in these tissues. Thus, the adverse lipid abnormalities associated with protease inhibitor therapy are caused by the constitutive induction of lipid biosynthesis in liver and adipose tissues due to the accumulation of activated SREBP in the nucleus.     

Extracellular metabolism of cyclic AMP

Intravenously administered cyclic [8-³H]AMP to rats was quickly eliminated from the circulation. After 2 min 93% of the administered radioactivity disappeared from the plasma, and most of it was recovered in the kidney, liver and muscles. The label in the tissues was recovered mainly in the form of nucleotides, ATP, ADP, AMP and IMP.In vitro contact of cyclic AMP with perfused liver, isolated liver cells and adipose tissue resulted in a rapid breakdown of the nucleotide, presumably on the outer surface of the cells. The degradation products have been identified mainly as adenosine and inosine.Incubation of adipose tissue and isolated liver cells with [³H]AMP also resulted in the breakdown of the nucleotide in the medium. The rate of AMP degradation by these tissues was faster than that for cyclic AMP degradation.The data suggest that cyclic AMP is readily metabolized on the outer surface of cells to products which may be converted within the cells to nucleotides. These findings seem of importance for the quantitative assessments of cellular cyclic AMP outflow during hormonal stimulation.     

Extracellular metabolism of cyclic AMP.

Intravenously administered cyclic [8-3H]AMP to rats was quickly eliminated from the circulation. After 2 min 93% of the administered radioactivity disappeared from the plasues was recovered mainly in the form of nucleotides, ATP, ADP, AMP and IMP. In vitro contact of cyclic AMP with perfused liver, isolated liver cells and adipose tissue resulted in a rapid breakdown of the nucleotide, presumably on the outer surface of the cells. The degradation products have been identified mainly as adenosine and inosine. Incubation of adipose tissue and isolated liver cells with [3H] AMP also resulted in the breakdown of the nucleotide in themedium. The rate of AMP degradation by these tissues was faster than that for cyclic AMP degradation. The data suggest that cyclic AMP is readily metabolized on the outer surface of cells to products which may be converted within the cells to nucleotides. These findings seem of importance for the quantitative assessments of cellular cyclic AMP outflow during hormonal stimulation.     

Neuropeptide-stimulated cyclic guanosine monophosphate immunoreactivity in the neurosecretory terminals of a neurohemal organ

The neuropeptide eclosion hormone acts on the nervous system of the tobacco hornworm, Manduca sexta, to increase cyclic guanosine monophosphate (cGMP) levels. In this study I describe the localization of some of the sites where these increases occur. Prior to pupal ecdysis, eclosion hormone stimulates an increase in cGMP in a network of fibers in the transverse nerve of each abdominal ganglion. Double-label experiments with propidium iodide suggest that the cGMP immunoreactivity is primarily localized in neurosecretory nerve endings. The time course of the increase in cGMP immunoreactivity and its requirement for lipid metabolism is similar to that of the cGMP increase measured by radioimmunoassay. The cGMP response in the transverse nerve is stage-specific, occurring prior to pupal ecdysis and not prior to larval or adult ecdysis. © 1996 John Wiley & Sons, Inc.     

Postirradiation changes in the cGMP system of the mouse thymus and liver

Changes have been revealed in the function of cyclic GMP system of thymus and liver of irradiated (8 Gy) mice. In the thymus the cGMP level increased during the first 60 min following irradiation. In the liver the concentration of cGMP exhibited two peaks: 30 min and 24 hr after irradiation. The changes observed in the cGMP level are connected with the increased guanylate cyclase activity of thymocytes and liver of irradiated mice and, less likely, with changes in the activity of cGMP phosphodiesterase of these tissues.     

Effects of somatostatin-25 on lipid mobilization from rainbow trout,Oncorhynchus mykiss,liver and adipose tissue incubated in vitro. Comparison with somatostatin-14

Summary The physiological effects of the pancreatic peptides somatostatin-14 and somatostatin-25 on lipid metabolism in rainbow trout were evaluated by in vitro culture of liver and adipose tissue. The culture medium was subsequently analyzed for glycerol and fatty acid content and triacylglycerol lipase activity was measured within the tissues. Both somatostatin-14 and somatostatin-25 stimulated hepatic fatty acid and glycerol release within 3 h after treatment. Liver triacylglycerol lipase activity was elevated following treatment with somatostatin-14 (76% above control) or somatostatin-25 (94% above control). Somatostatin-14 and somatostatin-25 also significantly stimulated the release of fatty acid and glycerol from adipose tissue. Triacylglycerol lipase activity in adipose tissue also was enhanced by both somatostatins. These results indicate that somatostatin-14 and somatostatin-25 directly stimulate the mobilization of triacylglycerol from liver and adipose tissue, suggesting that these peptides are important systemic modulators of lipid metabolism in fish.Abbreviations bw body weight - cAMP cyclic adenosine monophosphate - FA ratty acids - fw fresh weight - GLU glucagon - INS insulin - MS-222 tricaine-methane sulphonate - SS-14 somatostatin-14 - SS-25 somatostatin-25 - TG triacylglycerol     

苯污染对大鼠脑组织环核苷酸与相关蛋白水平的影响

为了探索苯污染对人类健康损伤作用的因素, 选用SPF级Wistar大鼠为实验对象, 分为4组: 低剂量组灌胃苯 0.19 g·kg-1, 中剂量组灌胃苯 0.38 g·kg-1, 高剂量组灌胃苯 0.76 g·kg-1, 对照组灌胃菜籽油2 mL·kg-1;用酶联免疫吸附法(ELISA)检测脑组织中环核苷酸和相关蛋白的水平。结果发现, 连续给予大鼠不同剂量苯21 d, 低、中、高剂量大脑皮质cAMP、c-fos、Bax和caspase-9水平比对照组分别升高了22.41%-59.53%, 38.28%-81.34%, 29.08%-63.04%和44.53%-70.07%; cGMP、Bcl-2水平比对照组分别降低了15.20%-49.79% 和13.42%-46.98%。丘脑组织cAMP、c-fos、Bax和caspase-9水平比对照组分别升高了34.71%-63.34%, 28.32%-78.04%, 16.54%-49.46% 和9.10%-61.57%; cGMP、Bcl-2水平比对照组分别降低了20.00%-33.83% 和8.53%-39.53%。结果提示, 苯污染引起脑组织损伤和细胞凋亡主要与cAMP、c-fos、Bax、caspase-9水平升高及cGMP和Bcl-2水平降低有关。     

冷驯化条件下中缅树鼩脂肪组织代谢产物的变化

为探究冷驯化条件下中缅树鼩(Tupaia belangeri)白色脂肪组织(WAT)和褐色脂肪组织(BAT)的差异代谢物变化,本研究采集对照组和冷驯化28天组中缅树鼩的WAT和BAT,采用非靶向代谢组液相色谱—质谱联用检测技术分析其差异代谢物含量变化.结果 表明,冷驯化组较对照组WAT中有7种差异代谢物显著上调;BAT...     

Imaging mass spectrometry reveals characteristic changes in triglyceride and phospholipid species in regenerating mouse liver

After partial hepatectomy (PH), regenerating liver accumulates unknown lipid species. Here, we analyzed lipids in murine liver and adipose tissues following PH by thin-layer chromatography (TLC), imaging mass spectrometry (IMS), and real-time RT-PCR. In liver, IMS revealed that a single TLC band comprised major 19 TG species. Similarly, IMS showed a single phospholipid TLC band to be major 13 species. In adipose tissues, PH induced changes to expression of genes regulating lipid metabolism. Finally, IMS of phosphatidylcholine species demonstrated distribution gradients in lobules that resembled hepatic zonation. IMS is thus a novel and power tool for analyzing lipid species with high resolution.     

Phosphodiesterase type 2 and the homeostasis of cyclic GMP in living thalamic neurons

The ubiquitous second messenger cyclic GMP (cGMP) is synthesized by soluble guanylate cyclases in response to nitric oxide (NO) and degraded by phosphodiesterases (PDE). We studied the homeostasis of cGMP in living thalamic neurons by using the genetically encoded fluorescence resonance energy transfer sensor Cygnet, expressed in brain slices through viral gene transfer. Natriuretic peptides had no effect on cGMP. Basal cGMP levels decreased upon inhibition of NO synthases or soluble guanylate cyclases and increased when PDEs were inhibited. Single cell RT-PCR analysis showed that thalamic neurons express PDE1, PDE2, PDE9, and PDE10. Basal cGMP levels were increased by the PDE2 inhibitors erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) and BAY60-7550 but were unaffected by PDE1 or PDE10 inhibitors. We conclude that PDE2 regulates the basal cGMP concentration in thalamic neurons. In addition, in the presence of 3-isobutyl-1-methylxanthine (IBMX), cGMP still decreased after application of a NO donor. Probenecid, a blocker of cGMP transporters, had no effect on this decrease, leaving PDE9 as a possible candidate for decreasing cGMP concentration. Basal cGMP level is poised at an intermediate level from which it can be up or down-regulated according to the cyclase and PDE activities.