Renato H. Migliorini

Effect of acute cold exposure on norpinephrine turnover rates in rat white adipose tissue

The present studies were carried out to assess directly sympathetic activity in white adipose tissue in response to cold exposure. Norepinephrine (NE) content and NE turnover rates were determined in epididymal and retroperitoneal adipose tissue from rats exposed to cold (4 degrees C) and controls kept at ambient temperature. Parallel measurements were made in interscapular brown adipose tissue (IBAT), in which activation of catecholaminergic innervation by cold exposure is well known. Exposure to 4 degrees C for 4 h reduced the endogenous NE content by 50% in IBAT and by 30% in both epididymal and retroperitoneal adipose tissues. Compared to warm controls, average values of fractional rates of turnover and cf turnover rates, estimated with alpha-methyl-tyrosine, increased 5-fold in IBAT and 2.5-3-fold in epididymal and retroperitoneal tissues from rats exposed to cold. The present data provide the first direct evidence that white adipose tissue sympathetic activity is increased during acute cold exposure.

Effects of starvation, refeeding, and insulin on energy-linked metabolic processes in catfish (Rhamdia hilarii) adapted to a carbohydrate-rich diet.

The effects of starvation and of a short period of refeeding on energy-linked metabolic processes, as well as the effects of insulin administration, were investigated in an omnivorous fish (catfish, Rhamdia hilarii) previously adapted to a carbohydrate-rich diet. Following food deprivation blood sugar levels declined progressively to about 50% of fed values after 30 days. During the same period plasma free fatty acid (FFA) concentration increased twofold. Starvation resulted in reduced concentrations of lipid and glycogen in the liver and of glycogen, lipid, and protein in white muscle. However, taking into account the initial and final concentrations of tissue constituents, the liver weight, and the large fractions of body weight represented by muscle, it could be estimated that most of the energy utilized during starvation derived from the catabolism of muscle lipid and protein. Refeeding starved fishes for 48 hr induced several-fold increases in the rates of in vivo and in vitro incorporation of [14C]glucose into liver and muscle lipid and of [14C]glycine into liver and muscle protein. Incorporation of [14C]glucose into liver glycogen was also increased. However; refeeding did not affect the incorporation of labeled glucose into muscle glycogen, neither in vivo nor in vitro. Administration of pharmacological doses of insulin to normally fed catfishes resulted in marked increases in the in vivo incorporation of 14C from glucose into lipid and protein in both liver and muscle. In contrast, labeled glucose incorporation into muscle glycogen was not affected by insulin and label incorporation into liver glycogen was actually lower than that in noninjected controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic control of protein metabolism in skeletal muscle.

This review summarizes evidence indicating that the sympathetic nervous system, through hormonal and neurotransmitter actions, produces anabolic, protein-sparing effects on skeletal muscle protein metabolism. Studies are reviewed which indicate that catecholamines secreted by the adrenal medulla have an inhibitory effect on muscle Ca2+-dependent protein degradation independently of other hormones. In addition, norepinephrine released from adrenergic terminals may increase the rate of protein synthesis in oxidative muscles, leading to increased protein accretion. Evidence is also presented that these effects seem to be mediated by β2-adrenoceptors and cyclic adenosine monophosphate-dependent pathways. The understanding of the precise mechanisms by which endogenous catecholamines promote muscle anabolic effects may bring new perspectives for efficient treatment of muscle-wasting conditions and enhancement of growth efficacy in farm species.

Glucose contribution to in vivo synthesis of glyceride-glycerol and fatty acids in rats adapted to a high-protein, carbohydrate-free diet

Triacylglycerol (TAG) synthesis from all carbon sources and from glucose carbon was evaluated in rats fed a high-protein, carbohydrate-free (HP) diet or control diet by determining simultaneously in the same animal the rate of incorporation of 3H2O and of 14C-glucose into the two TAG moieties in the carcass, liver, and retroperitoneal and epididymal adipose tissue. Incorporation rates of 3H2O into TAG-fatty acids (FAs) in the two adipose tissues and in liver were reduced in HP rats to about 20% and 50%, respectively, of the rates in control rats. In the two experimental groups, glucose was a poor precursor for FA synthesis, contributing only 22.8% of whole-body (carcass plus liver) total FA synthesis in control rats and even less (14%) in HP rats. In contrast to the reduction in FA synthesis, incorporation of 3H2O into TAG-glycerol in HP rats did not differ significantly or was even higher (in epididymal tissue) versus the control level. In all tissues of both HP and control rats, the rate of 14C-glucose incorporation into TAG-glycerol was much higher than the rate of incorporation into FA. Glyceroneogenesis, estimated by subtracting TAG-glycerol synthesis from glucose from the rate obtained with 3H2O, was significantly increased in adipose tissue from HP rats, with almost all of the glycerol formed by this route being used to esterify preformed FAs. It is suggested that the increased adipose tissue glyceroneogenesis is important for esterification of diet-derived FA and preservation of body fat stores in rats adapted to the HP diet.

Brown adipose tissue triacylglycerol synthesis in rats adapted to a high-protein, carbohydrate-free diet

Adaptation of rats to a high-protein, carbohydrate-free (HP) diet induced a marked reduction of brown adipose tissue (BAT) fatty acid (FA) synthesis from both3H2O and [14C]glucose in vivo, with pronounced decreases in the activities of four enzymes associated with lipogenesis: glucose-6-phosphate dehydrogenase, malic enzyme, citrate lyase, and acetyl-CoA carboxylase. In both HP-adapted and control rats, in vivo incorporation of3H2O and [14C]glucose into BAT glyceride-glycerol was much higher than into FA. It could be estimated that most of the glycerol synthetized was used to esterify preformed FA. Glycerol synthesis from nonglucose sources (glyceroneogenesis) was increased in BAT from HP rats, as evidenced by an increased capacity of tissue fragments to incorporate [1-14C]pyruvate into glycerol and by a fourfold increase in the activity of phospho enolpyruvate carboxykinase activity, a key glyceroneogenic enzyme. The data suggest that high rates of glyceroneogenesis and of esterification of preformed FA in BAT from HP-adapted rats are essential for preservation of tissue lipid stores, necessary for heat generation when BAT is recruited in nonshivering thermogenesis.Adaptation of rats to a high-protein, carbohydrate-free (HP) diet induced a marked reduction of brown adipose tissue (BAT) fatty acid (FA) synthesis from both 3H2O and [14C]glucose in vivo, with pronounced decreases in the activities of four enzymes associated with lipogenesis: glucose-6-phosphate dehydrogenase, malic enzyme, citrate lyase, and acetyl-CoA carboxylase. In both HP-adapted and control rats, in vivo incorporation of 3H2O and [14C]glucose into BAT glyceride-glycerol was much higher than into FA. It could be estimated that most of the glycerol synthetized was used to esterify preformed FA. Glycerol synthesis from nonglucose sources (glyceroneogenesis) was increased in BAT from HP rats, as evidenced by an increased capacity of tissue fragments to incorporate [1-14C]pyruvate into glycerol and by a fourfold increase in the activity of phosphoenolpyruvate carboxykinase activity, a key glyceroneogenic enzyme. The data suggest that high rates of glyceroneogenesis and of esterification of preformed FA in BAT from HP-adapted rats are essential for preservation of tissue lipid stores, necessary for heat generation when BAT is recruited in nonshivering thermogenesis.

Effect of guanethidine-induced adrenergic blockade on the different proteolytic systems in rat skeletal muscle

Overall proteolysis and the activity of skeletal muscle proteolytic systems were investigated in rats submitted to guanethidine-induced adrenergic blockade for 4 days. In soleus, overall proteolysis increased by 15-20% during the first 2 days of guanethidine treatment but decreased to levels below control values after 4 days. Extensor digitorum longus (EDL) did not show the initial increase in total proteolysis, which was already reduced after 2 days of guanethidine treatment. The initial rise in the rate of protein degradation in soleus was accompanied by an increased activity of the Ca(2+)-dependent proteolytic pathway. In both soleus and EDL, the reduction in overall proteolysis was paralleled by decreased activities of the Ca(2+)-dependent and ATP-dependent proteolytic processes. No change was observed in the activity of the lysosomal proteolytic system. Overall proteolysis in soleus and EDL from nontreated rats was partially inhibited by isoproterenol, in vitro. The data suggest an acute inhibitory control of skeletal muscle proteolysis by the adrenergic system, well evident in the oxidative muscle, with an important participation of the Ca(2+)-dependent pathway.

Adenylyl cyclase deficient cr-1 (Crisp) mutant of Neurospora crassa: cyclic AMP-dependent nutritional deficiencies.

The inability to synthesize cyclic AMP drastically affects the nutritional metabolism of Neurospora crassa. The adenylyl cyclase-less mutant cr-1 (crisp) did not utilize several carbon sources, including glycerol, mannitol, arabinose, and casaminoacids. However, in glucose or acetate it grew as well as the wild type. The following evidence suggested that these nutritional deficiencies were a direct result of the cr-1 mutation: (i), in crosses to wild type they segregated together with the crisp morphological marker; (ii), cyclic AMP added to the cr-1 mutant growth medium overcame the nutritional deficiencies; (iii), the cyclic AMP effect was specific for the crisp mutant, for it was not observed with the wild type, nor with a spontaneous glycerolutilizing cr-1 strain.

Reduced lipogenesis in rats fed a high-protein carbohydrate-free diet

Rates of fatty acid synthesis were assessed in carcass, liver, and adipose tissue from rats fed for 30 to 40 days a balanced diet (66% wt/wt carbohydrate, 17% casein, 8% fat) or a high-protein carbohydrate-free diet (70% casein, 8% fat). Despite similar body weight increases, carcass fatty acid content of rats on the high-protein (HP) diet was 13% less, and the weight of their epididymal fat pads was reduced by 29% in relation to the controls. In vivo incorporation of 3H2O into carcass fatty acids (FA) and into liver triacylglycerol (TAG) was significantly reduced in HP-fed rats. FA synthesis from 14C-acetate, glucose, or leucine and from 3H2O was also markedly decreased in liver slices from HP rats. The amount of 3H-TAG that accumulated in plasma of rats injected with triton WR 1339 to block peripheral utilization of lipoprotein corresponded in HP and control rats to only 4.1% and 5.0%, respectively, of 3H-FA recovered in carcasses from animals not treated with triton, indicating that almost all of the carcass 3H-TAG was synthesized in situ. However, on a long term basis, the reduced hepatic lipogenesis and the resulting decreased transport of TAG might affect lipid accumulation in HP rats. In vivo lipogenesis from 3H2O and in vitro FA synthesis from 3H2O and from 14C-precursors did not differ significantly in retroperitoneal and epididymal adipose tissue from HP and control rats. In both groups of animals, in vivo rates of lipogenesis were higher in retroperitoneal than in epididymal adipose tissue but still did not account for rates of FA synthesis by carcasses, suggesting the existence of other sites with higher lipogenic activity.

Cyclic adenosine monophosphate-phosphodiesterase inhibitors reduce skeletal muscle protein catabolism in septic rats

ABSTRACT We have previously shown that catecholamines exert an inhibitory effect on muscle protein degradation through a pathway involving the cyclic adenosine monophosphate (cAMP) cascade in normal rats. In the present work, we investigated in vivo and in vitro effects of cAMP-phosphodiesterase inhibitors on protein metabolism in skeletal muscle from rats submitted to a model of acute sepsis. The in vivo muscle protein metabolism was evaluated indirectly by measurements of the tyrosine interstitial concentration using microdialysis. Muscle blood flow (MBF) was monitored by ethanol perfusion technique. Sepsis was induced by cecal ligation and puncture and resulted in lactate acidosis, hypotension, and reduction in MBF (−30%; P < 0.05). Three-hour septic rats showed an increase in muscle interstitial tyrosine concentration (˜150%), in arterial plasma tyrosine levels (˜50%), and in interstitial-arterial tyrosine concentration difference (˜200%; P < 0.05). Pentoxifylline (50 mg/kg of body weight, i.v.) infusion during 1 h after cecal ligation and puncture prevented the tumor necrosis factor &agr; increase and significantly reduced by 50% (P < 0.05) the interstitial-arterial tyrosine difference concentration. In situ perfusion with isobutylmethylxanthine (IBMX; 10−3 M) reduced by 40% (P< 0.05) the muscle interstitial tyrosine in both sham-operated and septic rats. Neither pentoxifylline nor IBMX altered MBF. The addition of IBMX (10−3 M) to the incubation medium increased (P < 0.05) muscle cAMP levels and reduced proteolysis in both groups. The in vitro addition of H89, a protein kinase A inhibitor, completely blocked the antiproteolytic effect of IBMX. The data show that activation of cAMP-dependent pathways and protein kinase A reduces muscle protein catabolism during basal and septic state.

Intra-ventromedial hypothalamic injection of cholinergic agents induces rapid hyperglycemia, hyperlactatemia and gluconeogenesis activation in fed, conscious rats

Microinjections of carbachol (50 nmol) or neostigmine (25 nmol) in 0.5 ml saline into the ventromedial nucleus of the hypothalamus (VMH) (but not into the lateral hypothalamic area) of fed, conscious rats produced marked increases in plasma glucose and lactate, which were suppressed or markedly reduced by previous adrenodemedullation. The rate of incorporation of 14C from infused bicarbonate (0.60 microliter, 0.20 microCi/min), an index of gluconeogenic activity, increased significantly after VMH administration of neostigmine. The data suggest that cholinergic synapses in the VMH participate of a central glucoregulatory system that increases hepatic glucose production mainly through a stimulation of adrenal medulla epinephrine secretion.