Effects of prostaglandin E1 on lipolysis and plasma free fatty acids in the fasted rat

Contrary to published reports, prostaglandin E(1) (PGE(1)) in vitro and in vivo inhibited fasting lipolysis in rats. Adipose tissue lipolysis was inhibited when the tissue was incubated in the presence of PGE(1) and when the compound was administered intravenously. A biphasic plasma free fatty acid (FFA) response was obtained in fasted rats after intravenous injection of 80 micrograms of PGE(1) per kg body weight; plasma FFA concentrations were lowered at 7 min, elevated at 15 min, and at normal concentrations at 30 min. The FFA depression at 7 min was independent of the animal's nutritional state, but the rebound at 15 min did not occur in fed rats. The plasma FFA rebound in fasted rats at 15 min may be a consequence of rapid inactivation of PGE(1), followed by unopposed activity of factors which enhance fasting lipolysis.     

A1 adenosine receptor partial agonist lowers plasma FFA and improves insulin resistance induced by high-fat diet in rodents

There is substantial evidence in the literature that elevated plasma free fatty acids (FFA) play a role in the pathogenesis of type 2 diabetes. CVT-3619 is a selective partial A(1) adenosine receptor agonist that inhibits lipolysis and lowers circulating FFA. The present study was undertaken to determine the effect of CVT-3619 on insulin resistance induced by high-fat (HF) diet in rodents. HF diet feeding to rats for 2 wk caused a significant increase in insulin, FFA, and triglyceride (TG) concentrations compared with rats fed chow. CVT-3619 (1 mg/kg) caused a time-dependent decrease in fasting insulin, FFA, and TG concentrations. Acute administration of CVT-3619 significantly lowered the insulin response, whereas glucose response was not different with an oral glucose tolerance test. Treatment with CVT-3619 for 2 wk resulted in significant lowering of FFA, TG, and insulin concentrations in rats on HF diet. To determine the effect of CVT-3619 on insulin sensitivity, hyperinsulinemic euglycemic clamp studies were performed in C57BL/J6 mice fed HF diet for 12 wk. Glucose infusion rate was decreased significantly in HF mice compared with chow-fed mice. CVT-3619 treatment 15 min prior to the clamp study significantly (P < 0.01) increased glucose infusion rate to values similar to that for chow-fed mice. In conclusion, CVT-3619 treatment lowers FFA and TG concentrations and improves insulin sensitivity in rodent models of insulin resistance.     

Applications and limitations of measurement of 15-keto,13,14-dihydro prostaglandin E2 in human blood by radioimmunoassay

It has been anticipated that the inherent limitations of radioimmunoassays for prostaglandin E (PGE) would be obviated by assays for its major circulating metabolite, 15-keto, 13,14-dihydro PGE2) which has a longer half-life in blood. We examined the effects of PGE2 infusion and alterations in lipolysis in vivo, and of clotting, prolonged storage and hemolysis in vitro, on KH2-PGE2 immunoreactivity in unextracted human plasma and serum samples. Indeed KH2-PGE2 levels rose several hundred fold during infusions of PGE2 at doses which cause little or no increment in peripheral PGE levels. During stimulation of lipolysis by infusions of epinephrine, apparent KH2-PGE2 levels rose five-fold. However, the dilution curve of plasma obtained during stimulation of lipolysis was not parallel to the standard curve; furthermore, apparent KH2-PGE2 levels were correlated strongly with free fatty acid (FFA) levels, suggesting that FFA's cross-reacted in the RIA weakly but significantly due to their very high molar concentration in blood. Clotting and prolonged storage of samples, but not hemolysis, also caused marked apparent increments in KH2-PGE2 levels. Competition curves using dilutions of such samples were again not parallel to the standard curves in plasma or buffer, but resembled dilution curves of samples containing high levels of FFA. These results suggest that handling of human blood samples for KH2-PGE2 measurement must be carefully standardized to avoid significant artifacts which presumably are due in part to fatty acids released from triglyceride stores in vivo or from disrupted membrane phospholipids in vitro. Unextracted plasma appears to be unsatisfactory for use in this RIA.     

Effect of beta1- and beta2-adrenergic stimulation on energy expenditure,substrate oxidation,and UCP3 expression in humans

In humans, beta-adrenergic stimulation increases energy and fat metabolism. In the case of beta1-adrenergic stimulation, it is fueled by an increased lipolysis. We examined the effect of beta2-adrenergic stimulation, with and without a blocker of lipolysis, on thermogenesis and substrate oxidation. Furthermore, the effect of beta1-and beta2-adrenergic stimulation on uncoupling protein 3 (UCP3) mRNA expression was studied. Nine lean males received a 3-h infusion of dobutamine (DOB, beta1) or salbutamol (SAL, beta2). Also, we combined SAL with acipimox to block lipolysis (SAL+ACI). Energy and substrate metabolism were measured continuously, blood was sampled every 30 min, and muscle biopsies were taken before and after infusion. Energy expenditure significantly increased approximately 13% in all conditions. Fat oxidation increased 47 +/- 7% in the DOB group and 19 +/- 7% in the SAL group but remained unchanged in the SAL+ACI condition. Glucose oxidation decreased 40 +/- 9% upon DOB, remained unchanged during SAL, and increased 27 +/- 11% upon SAL+ACI. Plasma free fatty acid (FFA) levels were increased by SAL (57 +/- 11%) and DOB (47 +/- 16%), whereas SAL+ACI caused about fourfold lower FFA levels compared with basal levels. No change in UCP3 was found after DOB or SAL, whereas SAL+ACI downregulated skeletal muscle UCP3 mRNA levels 38 +/- 13%. In conclusion, beta2-adrenergic stimulation directly increased energy expenditure independently of plasma FFA levels. Furthermore, this is the first study to demonstrate a downregulation of skeletal muscle UCP3 mRNA expression after the lowering of plasma FFA concentrations in humans, despite an increase in energy expenditure upon beta2-adrenergic stimulation.     

Extreme decrease of linoleic acid in renal medulla from rats after a diet supplemented with cod liver oil

Spontaneously hypertensive (SHR) and normotensive rats were fed a diet supplemented with linseed oil or cod liver oil for 22 weeks. The most remarkable finding was an extreme fall of linoleic acid in lipids from renal medulla after cod liver oil supplementation. In free fatty acids (FFA) eicosatrienoic acid (C2): 3n-9) appeared increased as a sign of essential fatty acid (EFA) deficiency.     

Effects of low-zinc status and essential fatty acid deficiency on bone development and mineralization

1. The effects of essential fatty acids (EFAs) and zinc on the development and mineralization of bones were studied in young growing rats. 2. Female weaning rats were maintained on the diets deficient in EFAs, low in zinc (6 ppm) or both deficient in EFAs and low in zinc. 3. The low-zinc status accentuated signs of EFA deficiency including reduction of the growth rate and weights of bones and resulted in greater incidences of dental caries. 4. There were qualitative and quantitative differences in the fatty acid components of lipids extracted from the femur of the rats. 5. The overall effect was that eicosatrienoic (C20:3) and arachidonic (C20:4) acids were accumulated in EFA deficiency and low-zinc state respectively. 6. Bones of rats fed a low-zinc diet containing no EFAs were totally hypomineralized while those maintained on a diet that was either low in zinc or deficient in EFAs was partially hypomineralized. 7. Dietary zinc may have some roles to play in the biosynthesis of prostaglandins from EFAs and the process of bone mineralization.     

Effects of noradrenaline and nicotinic acid on plasma free fatty acids and oxygen consumption in cold-adapted rats.

A 3-h noradrenaline (NA) infusion (1.5 microgram kg-1 min-1) produced a sustained enhanced oxygen consumption (O2 cons.) in cold-adapted rats. Plasma free fatty acid (FFA) levels were elevated by NA in control and in cold-adapted rats, but to lesser extent in cold-adapted rats; the increase was maintained at a plateau in both groups during the entire period of NA infusion. A 1-h nicotinic acid (Nic A) infusion (1.5 mg kg-1 min-1) added to the NA infusion inhibited the calorigenic response to NA in cold-adapted rats and reduced the elevated plasma FFA concentration in control and in cold-adapted rats to values below basal levels. However, when the Nic A infusion was stopped, the O2 cons. was increased again in cold-adapted rats by the uninterrupted NA infusion, without the simultaneous increase of the plasma FFA concentration; the plasma FFA concentration was maintained in cold-adapted rats below basal values and merely brought back to basal levels in control rats. From these results, it is suggested that plasma FFA are not an essential substrate to the calorigenic response to NA observed in cold-adapted rats, as 85% of the response can occur when the plasma FFA concentration is very low.     

Fatty acid cycling in the fasting rat

Adipose tissue lipolysis and fatty acid reesterification by liver and adipose tissue were investigated in rats fasted for 15 h under basal and calorigenic conditions. The fatty acid flux initiated by adipose fat lipolysis in the fasted rat is mostly futile and is characterized by reesterification of 57% of lipolyzed free fatty acid (FFA) back into adipose triglycerides (TG). About two-thirds of FFA reesterification are carried out before FFA release into plasma, whereas the rest consists of plasma FFA extracted by adipose tissue. Thirty-six percent of the fasting lipolytic flux is accounted for by oxidation of plasma FFA, whereas only a minor fraction is channeled into hepatic very low density lipoprotein-triglycerides (VLDL-TG). Total body calorigenesis induced by thyroid hormone treatment and liver-specific calorigenesis induced by treatment with beta, beta'-tetramethylhexadecanedioic acid (Medica 16) are characterized by a 1.7- and 1.3-fold increase in FFA oxidation, respectively, maintained by a 1.5-fold increase in adipose fat lipolysis. Hepatic reesterification of plasma FFA into VLDL-TG is negligible under both calorigenic conditions. Hence, total body fatty acid metabolism is regulated by adipose tissue as both source and sink. The futile nature of fatty acid cycling allows for its fine tuning in response to metabolic demands.     

Continuous 24-h nicotinic acid infusion in rats causes FFA rebound and insulin resistance by altering gene expression and basal lipolysis in adipose tissue

Nicotinic acid (NA) has been used as a lipid drug for five decades. The lipid-lowering effects of NA are attributed to its ability to suppress lipolysis in adipocytes and lower plasma FFA levels. However, plasma FFA levels often rebound during NA treatment, offsetting some of the lipid-lowering effects of NA and/or causing insulin resistance, but the underlying mechanisms are unclear. The present study was designed to determine whether a prolonged, continuous NA infusion in rats produces a FFA rebound and/or insulin resistance. NA infusion rapidly lowered plasma FFA levels (>60%, P < 0.01), and this effect was maintained for ≥5 h. However, when this infusion was extended to 24 h, plasma FFA levels rebounded to the levels of saline-infused control rats. This was not due to a downregulation of NA action, because when the NA infusion was stopped, plasma FFA levels rapidly increased more than twofold (P < 0.01), indicating that basal lipolysis was increased. Microarray analysis revealed many changes in gene expression in adipose tissue, which would contribute to the increase in basal lipolysis. In particular, phosphodiesterase-3B gene expression decreased significantly, which would increase cAMP levels and thus lipolysis. Hyperinsulinemic glucose clamps showed that insulin's action on glucose metabolism was improved during 24-h NA infusion but became impaired with increased plasma FFA levels after cessation of NA infusion. In conclusion, a 24-h continuous NA infusion in rats resulted in an FFA rebound, which appeared to be due to altered gene expression and increased basal lipolysis in adipose tissue. In addition, our data support a previous suggestion that insulin resistance develops as a result of FFA rebound during NA treatment. Thus, the present study provides an animal model and potential molecular mechanisms of FFA rebound and insulin resistance, observed in clinical studies with chronic NA treatment.     

Treatment of EFA deficiency with dietary triglycerides or phospholipids in a murine model of extrahepatic cholestasis

Essential fatty acid (EFA) deficiency during cholestasis is mainly due to malabsorption of dietary EFA (23). Theoretically, dietary phospholipids (PL) may have a higher bioavailability than dietary triglycerides (TG) during cholestasis. We developed murine models for EFA deficiency (EFAD) with and without extrahepatic cholestasis and compared the efficacy of oral supplementation of EFA as PL or as TG. EFAD was induced in mice by feeding a high-fat EFAD diet. After 3 wk on this diet, bile duct ligation was performed in a subgroup of mice to establish extrahepatic cholestasis. Cholestatic and noncholestatic EFAD mice continued on the EFAD diet (controls) or were supplemented for 3 wk with EFA-rich TG or EFA-rich PL. Fatty acid composition was determined in plasma, erythrocytes, liver, and brain. After 4 wk of EFAD diet, induction of EFAD was confirmed by a sixfold increased triene-to-tetraene ratio (T/T ratio) in erythrocytes of noncholestatic and cholestatic mice (P < 0.001). EFA-rich TG and EFA-rich PL were equally effective in preventing further increase of the erythrocyte T/T ratio, which was observed in cholestatic and noncholestatic nonsupplemented mice (12- and 16-fold the initial value, respectively). In cholestatic mice, EFA-rich PL was superior to EFA-rich TG in decreasing T/T ratios of liver TG and PL (each P < 0.05) and in increasing brain PL concentrations of the long-chain polyunsaturated fatty acids (LCPUFA) docosahexaenoic acid and arachidonic acid (each P < 0.05). We conclude that oral EFA supplementation in the form of PL is more effective than in the form of TG in increasing LCPUFA concentrations in liver and brain of cholestatic EFAD mice.     

Inhibition of adipose tissue lipolysis increases intramuscular lipid and glycogen use in vivo in humans

This study investigates the consequences of inhibition of adipose tissue lipolysis on skeletal muscle substrate use. Ten subjects were studied at rest and during exercise and subsequent recovery under normal, fasting conditions (control trial, CON) and following administration of a nicotinic acid analog (low plasma free fatty acid trial, LFA). Continuous [U-13C]palmitate and [6,6-2H2]glucose infusions were applied to quantify plasma free fatty acid (FFA) and glucose oxidation rates and to estimate intramuscular triacylglycerol (IMTG) and glycogen use. Muscle biopsies were collected to measure 1) fiber type-specific IMTG content; 2) allosteric regulators of hormone-sensitive lipase (HSL), glycogen phosphorylase, and pyruvate dehydrogenase; and 3) the phosphorylation status of HSL at Ser563 and Ser565. Administration of a nicotinic acid analog (acipimox) substantially reduced plasma FFA rate of appearance and subsequent plasma FFA concentrations (P < 0.0001). At rest, this substantially reduced plasma FFA oxidation rates, which was compensated by an increase in the estimated IMTG use (P < 0.05). During exercise, the progressive increase in FFA rate of appearance, uptake, and oxidation was prevented in the LFA trial and matched by greater IMTG and glycogen use. Differential phosphorylation of HSL or relief of its allosteric inhibition by long-chain fatty acyl-CoA could not explain the increase in muscle TG use, but there was evidence to support the contention that regulation may reside at the level of the glucose-fatty acid cycle. This study confirms the hypothesis that plasma FFA availability regulates both intramuscular lipid and glycogen use in vivo in humans.     

Lipolytic and metabolic response to glucagon in fasting king penguins: phase II vs. phase III

This study aims to determine how glucagon intervenes in the regulation of fuel metabolism, especially lipolysis, at two stages of a spontaneous long-term fast characterized by marked differences in lipid and protein availability and/or utilization (phases II and III). Changes in the plasma concentration of various metabolites and hormones, and in lipolytic fluxes as determined by continuous infusion of [2-3H]glycerol and [1-14C]palmitate, were examined in vivo in a subantarctic bird (king penguin) before, during, and after a 2-h glucagon infusion. In the two fasting phases, glucagon infusion at a rate of 0.025 microg. kg(-1). min(-1) induced a three- to fourfold increase in the plasma concentration and in the rate of appearance (Ra) of glycerol and nonesterified fatty acids, the percentage of primary reesterification remaining unchanged. Infusion of glucagon also resulted in a progressive elevation of the plasma concentration of glucose and beta-hydroxybutyrate and in a twofold higher insulinemia. These changes were not significantly different between the two phases. The plasma concentrations of triacylglycerols and uric acid were unaffected by glucagon infusion, except for a 40% increase in plasma uric acid in phase II birds. Altogether, these results indicate that glucagon in a long-term fasting bird is highly lipolytic, hyperglycemic, ketogenic, and insulinogenic, these effects, however, being similar in phases II and III. The maintenance of the sensitivity of adipose tissue lipolysis to glucagon could suggest that the major role of the increase in basal glucagonemia observed in phase III is to stimulate gluconeogenesis rather than fatty acid delivery.     

Fat oxidation, lipolysis, and free fatty acid cycling in obesity-prone and obesity-resistant rats

Defects in fat metabolism may contribute to the development of obesity, but what these defects are and where they occur in the feeding/fasting cycle are unknown. In the present study, basal fat metabolism was characterized using a high-fat diet (HFD)-induced model of obesity development. Male rats consumed a HFD (45% fat, 35% carbohydrate) ad libitum for either 1 or 5 wk (HFD1 or HFD5). After 1 wk on the HFD, rats were separated on the basis of body weight gain into obesity-prone (OP, > or =48 g) or obesity-resistant (OR, 相似文献   

Physiological circulating levels of secretin-like immunoreactivity in the human do not stimulate free fatty acid production

An in vivo study was carried out to establish whether infused secretin, which achieves physiological levels of secretin-like immunoreactivity (SLI), promotes lipolysis. Six healthy volunteers received two infusions after separate 8 h overnight fasts. The paired infusions of either 500 ml of normal saline or 150 C.U. of porcine secretin in 500 ml of normal saline were infused at a constant rate of 1.38 ml/min. Venous blood was sampled at 0, 1, 2, 3, 4, 5 and 6 h after the infusion started. Mean plasma concentrations of SLI were significantly higher after infusion of saline with secretin in comparison to infusion of saline alone but remained within the physiological range. Mean serum free fatty acid (FFA) and 3-hydroxybutyrate concentrations rose significantly with time during both infusions but the mean FFA and 3-hydroxybutyrate concentrations did not differ significantly between infusions at each time of assessment. We conclude that a lipolytic role for secretin has not been shown to be of importance in relation to the in vivo rise in FFA concentrations observed in the fasting normal subject.     

Adipose tissue sensitization to insulin induced by troglitazone and MEDICA 16 in obese Zucker rats in vivo

The putative role played by insulin sensitizers in modulating adipose tissue lipolysis in the fasting state was evaluated in obese conscious Zucker rats treated with troglitazone or beta,beta'-tetramethylhexadecanedioic acid (MEDICA 16) and compared with nontreated lean and obese animals. The rates of appearance (R(a)) of glycerol and free fatty acid (FFA), primary intra-adipose reesterification, and secondary reuptake of plasma FFA in adipose fat were measured using constant infusion of stable isotope-labeled [(2)H(5)]glycerol, [2,2-(2)H(2)]palmitate, and radioactive [(3)H]palmitate. The overall lipolytic flux (R(a) glycerol) was increased 1.7- and 1.4-fold in obese animals treated with troglitazone or MEDICA 16, respectively, resulting in increased FFA export (R(a) FFA) in the troglitazone-treated rats. Primary intra-adipose reesterification of lipolysis-derived fatty acids was enhanced twofold by insulin sensitizers, whereas reesterification of plasma fatty acids was unaffected by either treatment. Despite the unchanged R(a) FFA in MEDICA 16 or the increased R(a) FFA induced by troglitazone, very low density lipoprotein production rates were robustly curtailed. Total adipose tissue reesterification, used as an estimate of glucose conversion to glyceride-glycerol, was increased 1.9-fold by treatment with the insulin sensitizers. Our results indicate that, in the fasting state, insulin sensitizers induce, in vivo, a significant activation rather than suppression of adipose tissue lipolysis together with stimulation of glucose conversion to glyceride-glycerol.     

The influence of dietary essential fatty acids on uterine C20 and C22 fatty acid composition.

The effect of dietary fatty acids on uterine fatty acid composition was studied in rats fed control diet or semi-synthetic diet supplemented with 1.5 microliter/g/day evening primrose oil (EPO) or fish oil (FO). Diet-related changes in uterine lipid were detected within 21 days. Changes of 2- to 20-fold were detected in the uterine n-6 and n-3 essential fatty acids (EFA) and in certain saturated and monounsaturated fatty acids. The FO diet was associated with higher uterine C20 and C22 n-3, and the EPO diet, with higher uterine n-6 fatty acid. High uterine C18:2 n-6 was detected in neutral lipid (NL) of rats fed high concentrations of this fatty acid, but there was little evidence of selective incorporation or retention of C18:2 n-6 by uterine NL. The incorporation of EFA into uterine phospholipids (PL) was greater than NL EFA incorporation, and uterine PL n-3/n-6 ratios showed greater diet dependence. Tissue/diet fatty acid ratios in NL and PL also indicated preferential incorporation/synthesis of C16:1 n-9, and C16:0, and there was greater incorporation of C12:0 and C14:0 into uteri of rats fed EPO and FO. Replacement of 50-60% of arachidonate with n-3 EFA in uterine PL may inhibit n-6 EFA metabolism necessary for uterine function at parturition.     

α-Linolenate reduces the dietary requirement for linoleate in the growing rat

Background: We hypothesized that due to the absence of a dietary source of omega-3 fatty acids, the essential fatty acid (EFA) deficiency model leads to an overestimate of linoleic acid (LA) requirements. Methods: over 7 wk, young rats consumed an EFA diet containing either 0 en% linoleate (0LA) and 0 en% α-linolenate (0LNA) or a diet containing 0.5 en% LNA plus one of seven levels of added LA (0.12–4.0 en%; n=6/group).Results: Rats consuming the 0LA–0LNA diet had the lowest final body weight, 34–68% lower LA and arachidonate in plasma and liver, 87% lower LA in epididymal fat, and an 8–20 fold higher eicosatrienoate in plasma, liver and muscle lipids. 0.5LNA completely prevented the lower growth and partly prevented the rise in eicosatrienoate seen in the 0LA–0LNA group.Conclusion: Providing dietary LNA at 0.5 en% reduces the rat's physiological requirement for LA by an estimated factor of at least four (0.5 en% instead of 2 en%). Since LA requirements in humans are also based on the same flawed model of EFA deficiency, it is plausible that they too have been overestimated and should therefore be reinvestigated.     

Colonic fermentation from lactulose inhibits lipolysis in overweight subjects

One of the strategies to prevent insulin resistance is to reduce circulating free fatty acids (FFA). The aim of this study is to assess the effect of an oral lactulose load on fatty acid metabolism in overweight subjects. Eight overweight subjects received a primed constant intravenous infusion of [1-(13)C]acetate and of [1,1,2,3,3-(2)H(5)]glycerol for 9 h. After 3 h of tracer infusion, patients ingested 30 g lactulose, or saline solution. Arterialized blood samples were collected every 20 min. Basal plasma concentrations of acetate were similar before and between oral treatments as well as glycerol and FFA concentrations. Plasma acetate turnover was 11.4 +/- 2.4 vs. 10.7 +/- 1.4 micromol.kg(-1).min(-1) [not significant (NS)], and plasma glycerol turnover was 3.8 +/- 0.4 vs. 4.8 +/- 1.9 micromol.kg(-1).min(-1) (NS). After lactulose ingestion, acetate concentration increased twofold and then decreased to baseline. Acetate turnover rate increased to 15.5 +/- 2.2 micromol.kg(-1).min(-1) after lactulose treatment, whereas it was unchanged after saline treatment (10.3 +/- 2.2 micromol.kg(-1).min(-1), P < or = 0.0001). In contrast, FFA concentrations decreased significantly after lactulose ingestion and then increased slowly. Glycerol turnover decreased after lactulose ingestion compared with saline, 2.8 +/- 0.4 vs. 3.5 +/- 0.3 micromol.kg(-1).min(-1) (P < or = 0.05). A significant negative correlation was found between glycerol and acetate turnover after lactulose treatments (r = -0.78, P < or = 0.02). These results showed in overweight subjects a short-term decrease in FFA level and glycerol turnover after lactulose ingestion related to a decrease of lipolysis in close relationship with an increase of acetate production.     

The inhibition of human leukocyte elastase by basic pancreatic trypsin inhibitor

The effects of 30-min intravenous infusions of ethanol (about 50 mm blood concentration), acetaldehyde (about 100 μm blood concentration), and acetate (equimolar dose to acetaldehyde) were studied in normal and adrenalectomized rats. Blood glucose, plasma free fatty acids (FFA), plasma immunoreactive insulin, and glucagon and hepatic glycogen concentrations were measured. Ethanol itself in the presence of 4-methylpyrazole (4-MP) produced no marked changes in the parameters measured. Its infusion without 4-MP reduced plasma insulin by 35% in the normal rats, but not in the adrenalectomized rats, with no simultaneous changes in blood glucose. Acetaldehyde infusion produced hyperglycemia and relatively slight hyperinsulinemia in the normal rats, but not in the adrenalectomized rats. Equimolar acetate was not as potent a stimulator of glycogenolysis as acetaldehyde. Plasma FFA concentrations were markedly reduced by ethanol (without 4-MP), acetaldehyde and acetate both in the normal and adrenalectomized rats, but in the presence of 4-MP ethanol was without effect. The results indicate that metabolites of ethanol (mostly acetaldehyde) produced during ethanol oxidation in vivo are responsible for the stimulation of glycogenolysis through the release of catecholamines from the adrenal glands. The ethanol-induced decrease in plasma FFA is also attributable to the metabolites of ethanol, acetaldehyde having a more potent depressing action than acetate. The mode of inhibition of lipolysis is not related to hormonal factors.     

Applications and limitations of measurement of 15-keto,13,14-dihydro prostaglandin E2 in human blood by radioimmunoassay

It has been anticipated that the inherent limitations of radioimmunoassays for prostaglandin E (PGE) would be obviated by assays for its major circulating metabolite, 15-keto, 13,14-dihydro PGE₂ (KH₂-PGE₂) which has a longer half-life in blood. We examined the effects of PGE₂ infusion and alterations in lipolysis , and of clotting, prolonged storage and hemolysis , on KH₂-PGE₂ immunoreactivity in unextracted human plasma and serum samples. Indeed KH₂-PGE₂ levels rose several hundred fold during infusions of PGE₂ at doses which cause little or no increment in peripheral PGE levels. During stimulation of lipolysis by infusions of epinephrine, apparent KH₂-PGE₂ levels rose five-fold. However, the dilution curve of plasma obtained during stimulation of lipolysis was not parallel to the standard curve; furthermore, apparent KH₂-PGE₂ levels were correlated strongly with free fatty acid (FFA) levels, suggesting that FFA's cross-reacted in the RIA weakly but significantly due to their very high molar concentration in blood. Clotting and prolonged storage of samples, but not hemolysis, also caused marked apparent increments in KH₂-PGE₂ levels. Competition curves using dilutions of such samples were again not parallel to the standard curves in plasma or buffer, but resembled dilution curves of samples containing high levels of FFA. These results suggest that handling of human blood samples for KH₂-PGE₂ measurement must be carefully standardized to avoid significant artifacts which presumably are due in part to fatty acids released from triglyceride stores or from disrupted membrane phospholipids . Unextracted plasma appears to be unsatisfactory for use in this RIA.