The glucose effect and cortisone action upon rat liver and muscle protein metabolism

Alterations in serum protein levels in patients with Cushing's syndrome before and after successful treatment

Alteration in serum protein concentration is used commonly in clinical practice as a nonspecific indicator of underlying disease or to monitor disease activity. Although hypercortisolemia may affect protein metabolism directly or indirectly, data regarding alterations of levels of serum protein in a large series of patients with Cushing's syndrome (CS) have been lacking. We have now evaluated, retrospectively, the levels of circulating serum albumin, globulins, total proteins, and the albumin to globulin ratio in 99 patients with endogenous CS before, immediately after, and 3, 6, and 12 months following successful treatment. Subjects with concomitant infections or other chronic diseases were excluded from the analysis. Although mean serum albumin and total protein levels were within the normal reference ranges, in general, they gradually increased after treatment with maximal values being reached at 12 months after normalization of hypercortisolemia (P < 0.0001 for both); there were no significant changes in serum globulin levels or in the albumin to globulin ratio. Patients with CS as a whole showed a weak but significant negative correlation between serum albumin and 0900 h cortisol level (r = -0.303; P = 0.0035). In conclusion, our data suggest that CS is associated with a small but significant reduction in circulating serum protein levels, which are restored following treatment of hypercortisolemia, although these changes occur within the reference range. Thus, extreme alterations in serum total protein or albumin levels in patients with CS should alert physicians to the presence of concomitant pathology, and additional specific investigation should be undertaken to elucidate the cause.

Effects of triamcinolone acetonide on plasma amino acids and urinary urea output in rabbits

1. The effect of administering triamcinolone acetonide (10 mg/kg/day), 6 consecutive s.c. injections given daily, on plasma free amino acids and urinary urea output was studied in rabbits. 2. The total free amino acids in plasma decreased significantly from day 2 while ammonia increased significantly only on day 2, glutamine, lysine and branched amino acids increased significantly from day 3 or 5. 3. The output of urinary urea increased significantly from day 3. 4. These findings suggest the inhibition of protein synthesis observed in steroid myopathy may result from a decrease in the amino acid pool in skeletal muscle.

Decreased cell proliferation and PGE2 production by fibroblasts treated with a modified hexose sugar, amiprilose hydrochloride

Amiprilose hydrochloride, a modified hexose sugar effectively decreases proliferation of human skin and synovial fibroblasts and of rabbit synovial fibroblasts. It also decreases production of the inflammatory mediator prostaglandin E2 (PGE2) by these cells. Cell proliferation, measured by incorporation of 3H-thymidine and by cell number, is decreased by concentrations of amiprilose hydrochloride of 1 mg/ml, while PGE2 synthesis is decreased by concentrations as low as 10 micrograms/ml. Concentrations of 1 mg/ml are not cytotoxic, as measured by protein synthesis. The anti-proliferate and anti-inflammatory effects of amiprilose hydrochloride, combined with its lack of cytotoxicity, suggest that this compound may be useful in the treatment of rheumatoid arthritis, a chronic autoimmune proliferate and inflammatory disease of connective tissue.

Effect of exogenous cortisone on amino acid metabolism in rats

1. The effect of exogenous cortisone on concentration of free amino acids in serum, skeletal muscle, kidney, small intestine and liver was studied. 2. The amino acid pool in serum, skeletal muscle and small intestine decreased significantly. 3. Glutamine synthesis increased significantly in skeletal muscle. 4. Levels of branched amino acids increased in serum and small intestine. 5. Levels of alanine increased in kidney and liver.

Myofibrillar protein catabolism in rat steroid myopathy measured by 3-methylhistidine excretion in the urine

The fractional rate of breakdown of myofibrillar protein in rat skeletal muscle was measured during subcutaneous cortisone acetate treatment (10 mg/100 g body weight per day). The daily urinary excretion of 3-methylhistidine divided by the 3-methylhistidine pool of the skeletal muscle was used to determine the fractional breakdown rate of myofibrillar protein. The mean fractional breakdown rate remained within the normal range throughout the first 5 days, but decreased significantly from the 16th day of treatment. When the daily 3-methylhistidine excretion was divided by the creatinine excretion, the rate showed the same trend of change. These results strongly suggest that the loss of myofibrillar protein induced by cortisone administration is not caused by increased breakdown but by decreased synthesis.

Influence of hydrocortisone acetate of the longissimus dorsi muscle during gestation of rats

The evolution in detail of the N retention during gestation was studied, dividing it in short periods of time, and how that retention affects Longissimus dorsi muscle. Simultaneously, the same study in pregnant rats treated with hydrocortisone acetate was done. During gestation N balance maintains high values that tend to increase at days 18 to 21. The greatest metabolic utilization of the N dietary corresponds to this period in which the percentage of the N retained in relation to the N absorbed is markedly higher than in previous days of gestation. In spite of the excellent quality and adequate concentration of protein in the diet, the administration of 4 mg/100 g weight and day of hydrocortisone acetate maintains the pregnant rat in a negative balance until day 18, as a consequence of the decrease in food intake and faecal and urinary N losses. From day 18 to day 21 of gestation the balance of N increases and the metabolic utilization of the dietary N is similar between pregnant rats injected with NaCl 0.9% and pregnant rats injected with hydrocortisone acetate. The Longissimus dorsi normal growth pattern (in relation to weight and N content) in young adult rats is not modified by gestation. The catabolic effects of hydrocortisone acetate on Longissimus dorsi muscle in pregnant rats can be observed from day 9 of treatment. The longer the treatment the higher the effect is.

The AIDS virus as an opportunistic organism inducing a state of chronic relative cortisol excess: therapeutic implications

The AIDS virus is an opportunistic organism which requires a previously immunocompromised host for successful replication. We propose that the primary and as yet unlocalized lesion caused by the AIDS virus involves disruption of physiologically balanced responses to stressors, effectively creating a state of chronic relative cortisol excess. Such a state inhibits successful anti-pathogen strategies including those directed against the AIDS virus itself and leads to a self-sustaining downhill clinical course. Therapies based on this model are discussed.

[Course of minimal oxygen consumption in the young rat during protein energy malnutrition followed by return to a balanced diet]

Growth and resting oxygen consumption (VO2 minimal) were studied on two strains of six post-weaning male rats during 60 days. The first strain was fed with a balanced diet (15% casein) for 60 days, the second received a 2% casein diet for 30 days, and then the balanced diet for the remaining 30 days. The 2% casein diet completely stopped the body weight and VO2 minimal increases. When return to a balanced diet, these parameters show an evolution similar to that of controls of the same body weight. The VO2 minimal had the same kind of evolution as body weight and was well correlated with growth speed. The protein restriction involves a strong and temporary reduction of the VO2 minimal, which will correspond to a nutritional stress.

The catabolic effect of glucocorticoids on different types of skeletal muscle fibres and its dependence upon muscle activity and interaction with anabolic steroids

Myofibrillar protease activity was found to be elevated, and content of RNA and DNA reduced in m. quadriceps femoris, especially in the fast-twitch white fibers, after dexamethasone treatment. Moderate physical activity prevents, to some extent, the effect of synthetic glucocorticoids. Exhaustive exercise augments the myofibrillar protease activity in both types of muscle fibers. The fast-twitch white type of muscle fibers in exhausted rats are found to have an elevated anticatabolic activity after the treatment of rats with anabolic steroid. It appears that there exists a close correlation between myofibrillar protease activity and muscle weight in the fast-twitch white fibers in dexamethasone treated and exhausted rats.

Effects of dexamethasone on fibre subtypes in rat muscle

The extent to which dexamethasone treatment produced atrophy of fast-twitch (EDL) and slow-twitch (SOL) muscles in rat was investigated. The mean weight of steroid-treated EDL muscles was decreased as compared to normal, whereas SOL muscles from normal and dexamethasone-treated animals showed no significant difference. Muscle fibre diameters also showed comparatively minor changes in SOL, which consists of Type 1 (slow oxidative) and Type 2A (fast oxidative/glycolytic) fibres. Rat EDL contains, in addition to Type 1 and Type 2A fibres, two sub-populations of fast glycolytic fibres (Types 2B and 2B'). These fibre types showed the most severe degree of atrophy both after dexamethasone treatment and after denervation. The mean ratio of the weights of denervated to innervated EDL muscles was lower in steroid-treated rats than in normal animals suggesting that the atrophy produced by steroid treatment in conjunction with denervation was more than simply additive. Analysis of the proportions of histochemical fibre types in SOL and EDL showed that dexamethasone treatment produced no major alterations in the fibre type constitution of these muscles. However, further histochemical studies showed that there was relatively severe impairment of myophosphorylase activity in Type 2B' (fast glycolytic) fibres as compared to other fibre types; conversely Type 1 fibres frequently contained increased myophosphorylase. Levels of beta-hydroxybutyrate dehydrogenase were low in both normal and steroid-treated EDL but high in SOL which also showed higher general oxidative activity. It is suggested that the particular susceptibility of fast glycolytic fibres to atrophy as a result of steroid treatment may be linked to: 1 the relatively severe reduction of myophosphorylase activity in these fibres and 2 their comparative inability to utilize alternative energy sources, especially substrates derived from free fatty acids.

Stimulation by glucocorticoids of protein degradation in hepatocyte monolayers

1. Protein degradation in rat hepatocytes in stationary monolayer culture was measured as release of radioactive trichloroacetic acid-soluble material from intracellular proteins labelled with [3H]leucine. 2. Glucocorticoids, but not other steroids, stimulated protein breakdown in the hepatocyte monolayers. The effects observed were greater when the cells were preincubated with the hormones, indicating that the stimulation was not immediate. In addition, the stimulation by glucocorticoids persisted for up to 4 h after hormone removal. 3. Cycloheximide and the lysosomotropic agents leupeptin and ammonia effectively blocked glucocorticoid stimulation of protein degradation. 4. Insulin blocked dexamethasone stimulation when added at the same time as the steroid, but not when added 3 h later. 5. Stimulation of protein breakdown by dexamethasone was additive with that by glucagon or dibutyryl cyclic AMP, suggesting that its mechanism of action is different from that of the latter two agents. 6. Total activities of several lysosomal enzymes were unaffected under conditions where protein breakdown was stimulated by either glucagon or dexamethasone. 7. It is suggested that, whereas glucagon, dibutyryl cyclic AMP and insulin modulate protein breakdown in these cells via changes in autophagocytosis, the stimulation by glucocorticoids is exerted independently, perhaps by stimulating the synthesis of membrane proteins essential to the autophagic process.

Experimental corticosteroid myopathy: effect on myofibrillar ATPase activity and protein degradation

Corticosteroid myopathy was studied in young, mature New Zealand white rabbits given daily injections of betamethasone (0.3 mg/kg body weight/day) for two weeks. Control rabbits were pair-fed and received saline injections. Bethamethasone treatment caused significant wasting of type 2 gluteus medius and psoas muscles but did not cause any atrophy of type 1 soleus and gluteus minimus muscles. The Mg2+- and Ca2+-activated myofibrillar ATPase activities of the corticosteroid-treated rabbits did not differ from controls despite a 30% reduction in muscle wet weight and pronounced reduction in cross-sectional area of fibers. SDS-polyacrylamide gel electrophoresis profiles of myofibrillar proteins did not differ quantitatively or qualitatively between experimental and control rabbits. Studies of net muscle protein degradation (using 3H-leucine) in betamethasone-treated and control rabbits indicate that both type 1 and type 2 muscle fiber proteins are degraded several times faster in the corticosteroid-treated group. This suggests that a compensatory mechanism exists for those type 1 and mixed fiber type muscles which have increased degradation but do not undergo wasting.

Regulation of cardiac protein balance by hydrocortisone: interaction with insulin

In fetal mouse hearts in organ culture the rate of protein synthesis was substantially reduced and the rate of protein degradation slightly increased by hydrocortisone in the absence of insulin, but in the presence of insulin the steroid caused a small increase in protein synthesis and a significant reduction in protein degradation. Hydrocortisone promoted the net uptake (or reduced the net release) of branched-chain amino acids independent of insulin and independent of simultaneous changes in protein balance. The specific activities of the lysosomal enzymes cathepsin D and glucosaminidase were reduced by hydrocortisone in all media, whereas the specific activity of creatine kinase increased when the medium contained insulin but decreased in the absence of insulin. It is concluded that hydrocortisone regulates cardiac protein balance via alterations both in synthesis and in degradation. Some of the hormone's myocardial effects are influenced by insulin so that hydrocortisone is anabolic in its presence but catabolic in its absence.

The effect of cortisone on protein breakdown and synthesis in rat skeletal muscle

The effect of cortisone administration on the rates of muscle protein breakdown and synthesis has been studied in the rat extensor digitorum longus muscle. Cortisone acetate (100 mg/kg body weight/day) was administered intraperitoneally for 1--3 days. Muscle wieght and protein content were significantly reduced by cortisone administration. Rates of protein breakdown were measured by tyrosine release from the isolated muscle into the intracellular pool and medium during a 2-h incubation with cycloheximide to block protein synthesis. Rates of protein synthesis were assayed by [14C]tyrosine incorporation into protein of the isolated muscle during a 2-h incubation. Cortisone administration inhibited significantly the rate of protein synthesis after 1--3 days treatment and also reduced significantly the rate of protein breakdown per muscle after 3 days treatment. The synthesis of myofibrillar and soluble proteins was affected to the same extent. These results strongly suggest that the effect of cortisone administration on muscle protein is mainly through its inhibition of protein synthesis rather than through an acceleration of protein breakdown.

The effects of glucose and cyclic GMP on RNA synthesis and nuclear morphology in starved rats

Feeding rats in diet high in glucose has been demonstrated to inhibit the induction of many enzymes, block the action of glucocorticoids, and, in general, appears to result in decreased cyclic AMP activity. We found that glucose feeding depresses both messenger RNA (mRNA) and non-mRNA synthesis. Electron microscopic examination of the nucleus revealed that glucose feeding decreases the granular component of liver cell nucleoli. It only slightly decreases liver cyclic AMP levels, but produces a sixfold elevation in levels of the cyclic AMP antagonist, cyclic GMP. Administration of bromocyclic GMP, like glucose feeding, depresses mRNA synthesis, but does not simulate the effect of the carbohydrate on nuclear morphology. In addition, glucose feeding halves liver inorganic phosphate and triples ATP levels. Phosphorylation of nuclear proteins, however, remains unaltered. Despite the antagonism between glucose feeding and glucocorticoid activity, the former compound did not change the binding of dexamethasone to liver nuclei.