Metabolic pathways involved in lipogenesis from lactate and acetate in bovine adipose tissue: Effects of metabolic inhibitors

Metabolic inhibitors were used in vitro in an attempt to elucidate the biochemical pathways by which lactate is converted to fatty acids by bovine adipose tissue. Subcutaneous adipose tissue samples were obtained by biopsy techniques from steers fed a high-energy ration. Kynurenate (α-2-diamino-γ-oxabenzenebutanoic acid) (5–10 mm), an inhibitor of acetyl-CoA carboxylase, and cerulenin (2,3-epoxy-4-oxo-7,10-dodecadienamide) (20–100 μg/ml), an inhibitor of the fatty acid synthetase enzyme complex, inhibited fatty acid synthesis from both acetate and lactate. The hydrogen acceptor, N-methylphenazonium methosulfate (10 μm) inhibited acetate but not lactate incorporation into fatty acids. α-Cyanohydroxycinnamate (5 mm) and phenylpyruvate (10 mm), which inhibit pyruvate entry into the mitochondria and pyruvate carboxylase, respectively, decreased lipogenesis from both acetate and lactate. The effects of phenylpyruvate on lipogenesis from acetate were greater in the presence of glucose plus insulin. Agaric acid (2-hydroxy-1,2,3-nonadecanetricarboxylic acid) (0.2 and 1.0 mm), which inhibits citrate efflux from the mitochondria also decreased lipogenesis from both acetate and lactate. Fluoroacetate (2.5 mm), an inhibitor of aconitate hydratase, had no effect on lipogenesis from acetate; but, in the presence of glucose or pyruvate, decreased lactate incorporation into fatty acids. n-Butylmalonate (5 mm), which blocks malate transport across the mitochondrial membrane, decreased lipogenesis from lactate but not acetate. Malate transport during lipogenesis is not associated with an operative malate:asparate shuttle in bovine adipose tissue, as indicated by the lack of effect of either 0.2 or 1.0 mm aminooxyacetate, a transaminase inhibitor, on lipogenesis from acetate or lactate. The results suggest a functional ATP-citrate lyase:NADP-malate dehydrogenase pathway in bovine subcutaneous adipose tissue and that this pathway may be involved in lipogenesis from acetate as well as lactate.     

Inhibition of lipogenesis by vasopressin and angiotensin II in glycogen-depleted hepatocytes

Vasopressin and angiotensin II inhibited lipogenesis (measured with 3H2O) in hepatocytes from fed rats. Inhibition was also observed with hepatocytes from fed rats which had been depleted of glycogen in vitro and incubated with lactate + pyruvate (5 mM + 0.5 mM) as substrates. The inhibitory actions of the hormones are therefore independent of hormone-mediated changes in glycogenolytic or glycolytic flux from glycogen, and thus the site(s) of hormone action must be subsequent to the formation of lactate. (-)Hydroxycitrate, a specific inhibitor of ATP-citrate lyase, decreased lipogenesis in hepatocytes from fed rats incubated with lactate + pyruvate by approx. 51% but had little effect on lipogenesis in glycogen-depleted hepatocytes similarly incubated. There was parallel inhibition of incorporation of 14C from [U-14C]lactate into fatty acid and lipogenesis as measured with 3H2O in each case. Thus depletion of glycogen, or conceivably the process of glycogen-depletion (incubation with dibutyryl cyclic AMP) causes a change in the rate-determining step(s) for lipogenesis from lactate. Vasopressin and angiotensin II also decreased lipogenesis and incorporation of 14C into fatty acids in glycogen-depleted hepatocytes provided with [U-14C]proline as opposed to [U-14C]-lactate. However, proline-stimulated lipogenesis was inhibited by (-)hydroxycitrate, and proline-stimulated lipogenesis and incorporation of 14C from [U-14C]-proline were not decreased in parallel by this inhibitor (inhibition of 52% and 85% respectively). It is inferred that lactate and proline stimulate lipogenesis by different mechanisms and incorporation of 14C from [U-14C]proline and [U-14C]lactate into fatty acid occurs via different routes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Proline and hepatic lipogenesis

The effects of proline on lipogenesis in isolated rat hepatocytes were determined and compared with those of lactate, an established lipogenic precursor. Proline or lactate plus pyruvate increased lipogenesis (measured with 3H2O) in hepatocytes from fed rats depleted of glycogen in vitro and in hepatocytes from starved rats. Lactate plus pyruvate but not proline increased lipogenesis in hepatocytes from starved rats. ( - )-Hydroxycitrate, an inhibitor of ATP-citrate lyase, partially inhibited incorporation into saponifiable fatty acid of 3H from 3H2O and 14C from [U-14C]lactate with hepatocytes from fed rats. Incorporation of 14C from [U-14C]proline was completely inhibited. Similar complete inhibition of incorporation of 14C from [U-14C]proline by ( - )-hydroxycitrate was observed with glycogen-depleted hepatocytes or hepatocytes from starved rats. Inhibition of phosphoenolpyruvate carboxykinase by 3-mercaptopicolinate did not inhibit the incorporation into saponifiable fatty acid of 3H from 3H2O or 14C from [U-14C]proline or [U-14C]lactate. Both 3-mercaptopicolinate and ( - )-hydroxycitrate increased lipogenesis (measured with 3H2O) in the absence or presence of lactate or proline with hepatocytes from starved rats. The results are discussed with reference to the roles of phosphoenolpyruvate carboxykinase, mitochondrial citrate efflux, ATP-citrate lyase and acetyl-CoA carboxylase in proline- or lactate-stimulated lipogenesis.     

No synergism between ionomycin and phorbol ester in fatty acid synthesis by isolated rat hepatocytes

With hepatocytes in suspension, freshly isolated from meal-fed rats, no significant effect of ionomycin on the rate of de novo fatty acid synthesis was observed, whereas phorbol myristate acetate (PMA) was strongly stimulatory. The combination of ionomycin and PMA produced the same stimulation as was seen with PMA alone. Stimulation of fatty acid synthesis by vasopressin was comparable and not additive to that observed with PMA, indicating that activation of protein kinase C is solely responsible for this metabolic effect of vasopressin. Both vasopressin and PMA increased acetyl-CoA carboxylase activity in isolated rat hepatocytes.     

Effect of insulin on ketogenesis and fatty acid synthesis in rat hepatocytes incubated with dichloroacetate

In parenchymal liver cells isolated from fed rats, insulin increased the formation of 14CO2 from [1-14C]pyruvate (and presumably the flux through pyruvate dehydrogenase) by 14%. Dichloroacetate, an activator of the pyruvate dehydrogenase complex, stimulated this process by 133%. As judged from the conversion of [2-14C]pyruvate to 14CO2, the tricarboxylic acid cycle activity was not affected by insulin, but it was depressed by dichloroacetate. In hepatocytes from fed rats, incubated with glucose as the only carbon source, dichloroacetate caused a stimulation (31%) of fatty acid synthesis, measured as 3H incorporation from 3H2O into fatty acid, and an increased (134%) accumulation of ketone bodies (acetoacetate + D-3-hydroxybutyrate). Dichloroacetate did not affect ketone body formation from [14C]palmitate, suggesting that the increased accumulation of ketone bodies resulted from acetyl-CoA derived from pyruvate. Insulin stimulated fatty acid synthesis in hepatocytes from fed rats. In the combined presence of insulin plus dichloroacetate, fatty acid synthesis was more rapid than in the presence of either insulin or dichloroacetate, whereas the accumulation of ketone bodies was smaller than in the presence of dichloroacetate alone. Although pyruvate dehydrogenase activity, which is rate-limiting for fatty acid synthesis in hepatocytes from fed rats, is stimulated both by insulin and by dichloroacetate, the reciprocal changes in fatty acid synthesis and ketone body accumulation brought about by insulin in the presence of dichloroacetate suggest that insulin is also involved in the regulation of fatty acid synthesis at a mitochondrial site after pyruvate dehydrogenase, possibly at the partitioning of acetyl-CoA between citrate and ketone body formation.     

De novo fatty acid synthesis by freshly isolated alveolar type II epithelial cells

Fatty acid synthesis was studied in freshly isolated type II pneumocytes from rabbits by 3H2O and (U-14C)-labeled glucose, lactate and pyruvate incorporation and the activity of acetyl-CoA carboxylase. The rate of lactate incorporation into fatty acids was 3-fold greater than glucose incorporation; lactate incorporation into the glycerol portion of lipids was very low but glucose incorporation into this fraction was approximately equal to incorporation into fatty acids. The highest rate of de novo fatty acid synthesis (3H2O incorporation) required both glucose and lactate. Under these circumstances lactate provided 81.5% of the acetyl units while glucose provided 5.6%. Incubations with glucose plus pyruvate had a significantly lower rate of fatty acid synthesis than glucose plus lactate. The availability of exogenous palmitate decreased de novo fatty acid synthesis by 80% in the isolated cells. In a cell-free supernatant, acetyl-CoA carboxylase activity was almost completely inhibited by palmitoyl-CoA; citrate blunted this inhibition. These data indicate that the type II pneumocyte is capable of a high rate of de novo fatty acid synthesis and that lactate is a preferred source of acetyl units. The type II pneumocyte can rapidly decrease the rate of fatty acid synthesis, probably by allosteric inhibition of acetyl-CoA carboxylase, if exogenous fatty acids are available.     

Development of insulin sensitivity in white adipose tissue during the suckling-weaning transition in the rat. Involvement of glucose transport and lipogenesis.

The changes of insulin responsiveness of white adipose tissue during the suckling-weaning transition in the rat were investigated in vitro on isolated adipocytes. Insulin binding, glucose transport and glucose metabolism in adipocytes from suckling rats and from rats weaned on to a high-carbohydrate (HC) or a high-fat (HF) diet were compared. Despite similar insulin binding, insulin-stimulated glucose transport rate is lower in adipocytes from suckling rats and HF-weaned rats than in adipocytes from HC-weaned rats. Moreover, whereas insulin markedly stimulates glucose metabolism in adipocytes from HC-weaned rats, glucose metabolism is totally unresponsive to insulin in adipocytes from suckling and HF-weaned rats. This insulin resistance is associated with a very low rate of lipogenesis and low activities of acetyl-CoA carboxylase, fatty acid synthase and pyruvate dehydrogenase.     

Effects of octanoate and acetate upon hepatic glycolysis and lipogenesis

Octanoate and N6,O2'-dibutyryl adenosine 3',5'-monophosphate (dibutyryl cyclic AMP) cause a marked inhibition of net glucose utilization and lactate and pyruvate accumulation by hepatocytes isolated from meal-fed rats. Acetate is much less effective as an inhibitor of glycolysis. Fatty acid synthesis, as measured by tritiated water incorporation, is inhibited by dibutyryl cyclic AMP, whereas it is stimulated by 10 mM acetate and 1 mM octanoate. Stimulation of fatty acid synthesis by 1 mM octanoate, however, is lost paradoxically at higher concentrations of octanoate. Rates of fatty acid synthesis estimated by [1-14C]octanoate incorporation were consistently higher than rates calculated on the basis of tritiated water incorporation, raising the question as to which is the better index of the rate of de novo fatty acid synthesis. The effects of octanoate were studied because it was reasoned that this fatty acid should not inhibit acetyl-CoA carboxylase but should inhibit glycolysis and supply acetyl-CoA for lipogenesis. This was found to be the case, proving that glycolytic activity is not necessary for rapid rates of de novo fatty acid synthesis by liver.     

Both insulin and epidermal growth factor stimulate lipogenesis and acetyl-CoA carboxylase activity in isolated adipocytes. Importance of homogenization procedure in avoiding artefacts in acetyl-CoA carboxylase assay.

Epidermal growth factor (EGF) stimulates lipogenesis by 3-4-fold in isolated adipocytes, with a half-maximal effect at 10 nM-EGF. In the same batches of cells insulin stimulated lipogenesis by 15-fold. Freezing and prolonged homogenization of adipocytes results in release of large quantities of pyruvate carboxylase from broken mitochondria, and sufficient pyruvate can be carried through into assays for this enzyme to cause significant interference with assays of acetyl-CoA carboxylase in crude adipocyte extracts. This may account for the high amount of citrate-independent acetyl-CoA carboxylase activity reported to be present in adipocyte extracts in some previous publications. This problem may be eliminated by homogenizing very briefly without freezing. By using the modified homogenization procedure, EGF treatment of adipocytes was shown to produce an effect on acetyl-CoA carboxylase activity almost identical with that of insulin. Both messengers increase Vmax. without significant effect on the Ka for the allosteric activator, citrate.     

The effects of lactate and acetate on fatty acid and cholesterol biosynthesis by isolated rat hepatocytes

1. The present study demonstrates that lactate and acetate stimulate fatty acid synthesis and inhibit cholesterogenesis by isolated rat hepatocytes. 2. Exposure of the intact cells to lactate increases the activity of acetyl-CoA carboxylase, as can be measured in homogenates of these cells. A similar effect by acetate was not observed. 3. Both acetate and lactate drastically increase the cellular level of citrate. 4. Possible mechanisms underlying the difference in response of fatty acid and cholesterol synthesis to an increase in substrate availability are discussed. Futhermore, a mechanism is proposed for the lactate effect on acetyl-CoA carboxylase.     

The regulation of triglyceride synthesis and fatty acid synthesis in rat epididymal adipose tissue. Effects of altered dietary and hormonal conditions

1. Epididymal adipose tissues obtained from rats that had been previously starved, starved and refed a high fat diet for 72h, starved and refed bread for 144h or fed a normal diet were incubated in the presence of insulin+glucose or insulin+glucose+acetate. 2. Measurements were made of the whole-tissue concentrations of hexose phosphates, triose phosphates, glycerol 1-phosphate, 3-phosphoglycerate, 6-phosphogluconate, adenine nucleotides, acid-soluble CoA, long-chain fatty acyl-CoA, malate and citrate after 1h of incubation. The release of lactate, pyruvate and glycerol into the incubation medium during this period was also determined. 3. The rates of metabolism of glucose in the hexose monophosphate pathway, the glycolytic pathway, the citric acid cycle and into glyceride glycerol, fatty acids and lactate+pyruvate were also determined over a 2h period in similarly treated tissues. The metabolism of acetate to CO(2) and fatty acids in the presence of glucose was also measured. 4. The activities of acetyl-CoA carboxylase, fatty acid synthetase and isocitrate dehydrogenase were determined in adipose tissues from starved, starved and fat-refed, and alloxan-diabetic animals and also in tissues from animals that had been starved and refed bread for up to 96h. Changes in these activities were compared with the ability of similar tissues to incorporate [(14)C]glucose into fatty acids in vitro. 5. The activities of acetyl-CoA carboxylase and fatty acid synthetase roughly paralleled the ability of tissues to incorporate glucose into fatty acids. 6. Rates of triglyceride synthesis and fatty acid synthesis could not be correlated with tissue concentrations of long-chain fatty acyl-CoA, citrate or glycerol 1-phosphate. In some cases changes in phosphofructokinase flux rates could be correlated with changes in citrate concentration. 7. The main lesion in fatty acid synthesis in tissues from starved, starved and fat-refed, and alloxan-diabetic rats appeared to reside at the level of pyruvate utilization and to be related to the rate of endogenous lipolysis. 8. It is suggested that pyruvate utilization by the tissue may be regulated by the metabolism of fatty acids within the tissue. The significance of this in directing glucose utilization away from fatty acid synthesis and into glyceride-glycerol synthesis is discussed.     

Cloning of yeast glycolysis genes by complementation

In hepatocytes isolated from fed rats, low concentrations of oxalate (50 to 100 μM) greatly enhance ketogenesis and decrease fatty acid synthesis. These metabolic changes are due to pyruvate carboxylase inhibition. Dichloroacetate, which can be catabolized into oxalate enhances ketogenesis only when cells are enriched with lactate and pyruvate and has no obvious effect on lipogenesis. The enhancement of ketogenesis, in both cases, is due to an imbalance between pyruvate dehydrogenase and pyruvate carboxylase but with oxalate, the primary event is oxaloacetate shortage and with dichloroacetate, mitochondrial acetyl CoA excess. This work demonstrates that the studied effects of dichloroacetate are not mediated by oxalate and that low concentrations of oxalate alter the lipid metabolism of hepatocytes.     

The effect of progesterone on prolactin stimulation of fatty acid synthesis, glycerolipid synthesis and lipogenic-enzyme activities in mammary glands of pseudopregnant rabbits, after explant culture or intraductal injection.

The activities of lipogenic enzymes, such as acetyl-CoA carboxylase, fatty acid synthetase and glucose-6-phosphate dehydrogenase, and glycerolipid synthesis increased significantly in mammary explants of 11-day-pseudopregnant rabbits in response to prolactin, in the presence of near-physiological concentrations of insulin and corticosterone in culture. Increasing the concentration of progesterone in culture resulted in suppression of glycerolipid synthesis and activities of acetyl-CoA carboxylase and fatty acid synthetase, but not the pentose phosphate dehydrogenases. However, at near-physiological concentration of progesterone, only acetyl-CoA carboxylase activity was decreased. Injection of prolactin intraductally into 11-day-pseudopregnant rabbits stimulated glycerolipid synthesis, fatty acid synthesis and enzymes involved in fatty acid synthesis, after 3 days. Intraductal injection of progesterone separately or together with prolactin had no significant effect on basal or stimulated lipogenesis in mammary glands. Intramuscular injection of progesterone at 10 mg/day did not suppress fatty acid synthesis stimulated when prolactin was injected intraductally, but a significant inhibition was observed at a higher dose (80 mg/day).     

Fatty acid inhibition of hormonal induction of acetyl-coenzyme A carboxylase in hepatocyte monolayers

Primary cultures of adult rat hepatocytes were utilized to ascertain the impact of free fatty acids on the insulin plus dexamethasone induction of acetyl-CoA carboxylase. Lipogenesis was induced threefold by the combination of insulin and dexamethasone. The rise in fatty acid synthesis was accompanied by a comparable increase in the rate-determining enzyme acetyl-CoA carboxylase. Dexamethasone was required for the insulin induction of acetyl-CoA carboxylase. Under the permissive action of glucocorticoid, 10(-7) M insulin maximally increased enzyme activity. Half-maximum stimulation occurred with 5 X 10(-9) M insulin. Media containing 0.2 mM palmitate, oleate, linoleate, arachidonate, or docosahexaenoate significantly suppressed the hormonal induction of acetyl-CoA carboxylase. The extent of suppression was only 30-35% and did not vary with chain length or degree of unsaturation. Carboxylase activity was not suppressed further by raising the concentration of linoleate to 0.5 mM; however, 0.5 mM palmitate depleted the cells of ATP and abolished acetyl-CoA carboxylase activity. Therefore, based upon the inhibitory characteristics of the various fatty acids and the lack of a concentration dependency of the fatty acid inhibition, it would appear that fatty acid inhibition of the induction of acetyl-CoA carboxylase activity may not be a direct, physiological regulatory mechanism.     

The control by vasopressin of carbohydrate and lipid metabolism in the perfused rat liver.

Vasopressin-induced glucose release from the perfused livers of fed rats is diminished in the presence of insulin or following adrenal ablation. The reduced rate of glucose release following vasopressin treatment in the perfused livers of adrenalectomized rats was restored towards the control value by cortisol treatment in vivo. Vasopressin did not influence the total rate of fatty acid synthesis in the livers of fed rats perfused with medium containing glucose and two concentrations of lactate. The contribution of these precursors to hepatic fatty acid synthesis and CO2 production was similarly uninfluenced by vasopressin. Vasopressin casued a transient increase in the release of K+ by the perfused liver which was observed within 2 min of hormone administration. These results are discussed in relation to the possible mode of action of vasopressin in the liver.     

Influences of intracellular pyridine nucleotide redox states on fatty acid synthesis in isolated rat hepatocytes.

The regulation of fatty acid synthesis, measured by ³H₂O incorporation into fatty acids, was studied in hepatocytes from rats meal-fed a high carbohydrate diet. Ca²⁺ increased fatty acid synthesis, which became maximal at physiological concentrations of Ca²⁺. Ethanol markedly inhibited fatty acid synthesis. Maximum inhibition was reached at 4 mm ethanol. However, ethanol did not decrease lipogenesis in the presence of pyruvate. dl-3-Hydroxybutyrate increased fatty acid synthesis. Acetoacetate decreased lipogenesis when used alone and reversed the effect of dl-3-hydroxybutyrate when both were added. dl-3-Hydroxybutyrate moderately decreased flux through the pyruvate dehydrogenase system and markedly inhibited citric acid cycle flux. By measurement of glycolytic intermediates, two ethanol-induced crossover points were observed: one between fructose 6-phosphate and fructose 1,6-diphosphate and the other between glyceraldehyde 3-phosphate and 1,3-diphosphoglycerate. The concentrations of pyruvate and citrate were decreased by ethanol and increased by dl-3-hydroxybutyrate. Aminooxyacetate and l-cycloserine inhibited fatty acid synthesis and these effects were overcome by dl-3-hydroxybutyrate. Results indicate that in hepatocytes in a metabolic state favoring a high rate of lipogenesis, production of reducing equivalents in the cytosol via ethanol metabolism inhibits fatty acid synthesis from glucose by inhibition of both phosphofructokinase and glyceraldehyde 3-phosphate dehydrogenase and by promoting reduction of pyruvate to lactate. Production of reducing equivalents in the mitochondria via dl-3-hydroxybutyrate enhances fatty acid synthesis in liver cells by altering the partition of citrate between oxidation in the citric acid cycle and conversion to fatty acids in favor of the latter pathway. These interactions indicate the importance of the intracellular pyridine nucleotide redox states in the rate control of hepatic fatty acid synthesis.     

Acute effects in vivo of anti-insulin serum on rates of fatty acid synthesis and activities of acetyl-coenzyme A carboxylase and pyruvate dehydrogenase in liver and epididymal adipose tissue of fed rats.

Plasma insulin concentrations in fed rats were altered acutely by administration of glucose or anti-insulin serum. Rates of fatty acid synthesis in adipose tissue and liver were estimated from the incorporation of 3H from 3H2O. In the adipose tissue dehydrogenase and acetyl-CoA carboxylase were evident. In liver, although changes in rates of fatty acid synthesis were found, the initial activity of pyruvate dehydrogenase did not alter, but small parallel changes in acetyl-CoA carboxylase activity were observed.     

The interaction between heme and protein in cytochrome c1

The hormonal regulation of two regulatory enzymes of fatty acid synthesis acetyl-CoA carboxylase (EC 6.4.1.2) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49), has been investigated in human diploid fibroblasts. There was a 35% increase in acetyl-CoA carboxylase activity, 72 h following addition of 10 microU/ml insulin to the culture medium. Addition of 1 microgram/ml of 3,3'5-triiodothyronine for 72 h resulted in an increase in acetyl-CoA carboxylase activity to 166% of the controls. The simultaneous addition of 1 microgram/ml triiodothyronine and 10 mU/ml insulin caused the enzyme activity to rise to 240% of the controls. A dose-dependent reduction in acetyl-CoA carboxylase activity was brought about by 1 X 10(-4) to 1 X 10(-3) M dibutyryl cyclic AMP. The earliest effect of dibutyryl cyclic AMP was observed within 24 h. Glucose-6-phosphate dehydrogenase followed qualitatively the same pattern of response, whereas the constitutive enzyme, lactate dehydrogenase (EC 1.1.1.27), did not show significant changes in these experiments. The data demonstrate common features of hormonal regulation of lipogenesis in human fibroblasts with liver and adipose tissue and substantiate the growing evidence that thyroid hormones are of major importance for the regulation of this process.     

Modulation of the activity of insulin-dependent enzymes of lipogenesis by glucocorticoids.

Administration of triamcinolone or dexamethasone to rats led to a prompt, marked and persistent rise in liver acetyl-CoA carboxylase activity. The activity of fatty acid synthetase increased to a lesser extent and after a more prolonged glucocorticoid treatment, whereas the changes in that of NADP-malate dehydrogenase and ATP-citrate lyase were not appreciable. The overall channeling of [1-14-C]acetyl-CoA to fatty acids was enhanced. The triamcinolone effect on acetyl-CoA carboxylase activity appeared to be dependent on the coincident hyperinsulinemia since it was not obtained in alloxan-diabetic rats, whereas the alanine-aminotransferase-inducing effect of this hormone was additive to that of insulin deficiency. In adipose tissue triamcinolone treatment caused a reduction in the activity of all lipogenesis enzymes and blunted their response to insulin administration. The antagonism of glucocorticoids toward insulin, selectively modulating the responses of the insulin-sensitive enzymes in liver and adipose tissue is discussed. The rise in hepatic lipogenic capacity, through the retention of the ability of insulin to induce acetyl-CoA carboxylase, may be physiologically important in restraining the ketogenesis from acetyl-CoA despite the increased fat utilization during glucocorticoid excess.