One session of exercise regulates cathepsin B activity in the livers of trained and untrained rats.

Physical exercise causes adaptive changes, mainly in muscles, but it also influences other organs, including liver. Most changes are beneficial; however, strenuous exercise is a strong stressor, and it can result in splanchnic hypoperfusion with subsequent disturbances in liver homeostasis and energy. Cathepsin B is a protease linked to protein turnover and extracellular matrix degradation. It is also involved in autophagy and the activation of proinflammatory and profibrotic pathways. This study investigated the influences of one session of exercise and endurance training on the mRNA, protein level, and activity of cathepsin B in rat liver. Healthy rats were randomly divided into two groups (n = 30, each); one group was untrained and the other received 6-weeks of endurance training with an increasing load. For each group, rats were sacrificed before (controls, n = 10), immediately after (n = 10), and 3 h after (n = 10) an acute bout of intense exercise. Liver gene expression was evaluated with quantitative real-time PCR. Liver protein content was measured with ELISA. Liver enzyme activity was measured fluorometrically. One session of exercise or training did not influence cathepsin B gene expression or protein concentration at any investigated time point. In untrained rats, cathepsin B activity decreased 3 hours after (P = 0.027) one session of exercise. In trained rats, cathepsin B activity increased immediately (P = 0.005) after one session of exercise. Training did not influence baseline cathepsin B activity. In conclusion, one session of exercise differentially influenced cathepsin B activity in the liver, depending on training status.

Oxidative Damage to the Salivary Glands of Rats with Streptozotocin-Induced Diabetes-Temporal Study: Oxidative Stress and Diabetic Salivary Glands.

Objective. This study evaluated oxidative damage caused to the salivary glands in streptozotocin-induced diabetes (DM). Materials and Methods. Rats were divided into 4 groups: groups 1 and 2, control rats, and groups 3 and 4, DM rats. 8-Hydroxy-2'-deoxyguanosine (8-OHdG), protein carbonyl (PC), 4-hydroxynonenal protein adduct (4-HNE), oxidized and/or MDA-modified LDL-cholesterol (oxy-LDL/MDA), 8-isoprostanes (8-isoP), and oxidative stress index (OSI) were measured at 7 (groups 1 and 3) and 14 (groups 2 and 4) days of experiment. Results. The unstimulated salivary flow in DM rats was reduced in the 2nd week, while the stimulated flow was decreased throughout the duration of the experiment versus control. OSI was elevated in both diabetic glands in the 1st and 2nd week, whereas 8-isoP and 8-OHdG were higher only in the parotid gland in the second week. PC and 4-HNE were increased in the 1st and 2nd week, whereas oxy-LDL/MDA was increased in the 2nd week in the diabetic parotid glands. Conclusions. Diabetes induces oxidative damage of the salivary glands, which seems to be caused by processes taking place in the salivary glands, independently of general oxidative stress. The parotid glands are more vulnerable to oxidative damage in these conditions.

One session of exercise or endurance training does not influence serum levels of irisin in rats.

Irisin induces the browning of adipose tissue. The goal of this study was to investigate the influence of acute exercise in untrained and trained rats and endurance training on FNDC5 mRNA and irisin levels in white and red skeletal muscle and serum. Rats (n=60) were randomly divided into two groups: untrained and trained (subjected to 6-week endurance training with increasing load). Subgroups of rats from each group were sacrificed before (controls), immediately after, or 3 hours following acute exercise with the same work load. Muscle samples (red and white) and serum were collected. FNDC5 mRNA was evaluated using RT-PCR. Irisin levels were measured using an immunoenzymatic method. Muscle FNDC5 mRNA decreased immediately after acute exercise compared with baseline levels, but not in red muscle in trained rats. Atrend toward a return to baseline appeared 3 hours after the exercise, but only in white muscle in untrained group. Irisin protein levels increased after acute exercise in red muscle 3 hours post-exercise compared with samples taken immediately after exercise, and decreased 3 hours post-exercise compared to pre-exercise level in white muscles. FNDC5 mRNA did not change following training, whereas irisin protein levels increased in red muscle and decreased in white muscle. Serum irisin levels remained unchanged following acute exercise and training. We concluded that changes in irisin mRNA and protein levels in rat muscle after acute exercise are limited and depend on training status and the muscle type. Irisin serum levels remained stable after acute exercise or endurance training.

Antioxidant profile of salivary glands in high fat diet-induced insulin resistance rats.

OBJECTIVE: There is no study analyzing the salivary antioxidant profile in the course of the insulin resistance. MATERIALS AND METHODS: Rats were divided into two groups. One group was fed with a normal diet, another one with a high fat diet for 5 weeks. The analysis included: catalase (CAT), superoxide dismutase, peroxidase activities, uric acid, and total antioxidant status concentrations. RESULTS: The activity of peroxidase in both kind of glands of insulin resistance rats was significantly reduced than in the control rats. The protein concentration, total amount of total antioxidant status in the parotid glands of insulin resistance rats were significantly lower than in the control glands The total amount of superoxide dismutase, CAT, and uric acid in the parotid glands of insulin resistance rats were significantly elevated in comparison with the control rats. The median values of the total amount of superoxide dismutase, CAT, peroxidase, total antioxidant status were significantly higher in the parotid than in the submandibular glands of the insulin resistance and control rats. CONCLUSION: Parotid and submandibular glands of rats react differently when exposed to insulin resistance condition; however, the parotid glands seem to be more affected. The main source of antioxidants is parotid glands of rats.

Sphingolipid profiles are altered in prefrontal cortex of rats under acute hyperglycemia.

Diabetes type 1 is a common autoimmune disease manifesting by insulin deficiency and hyperglycemia, which can lead to dementia-like brain dysfunctions. The factors triggering the pathological processes in hyperglycemic brain remain unknown. We reported in this study that brain areas with different susceptibility to diabetes (prefrontal cortex (PFC), hippocampus, striatum and cerebellum) revealed differential alterations in ceramide (Cer) and sphingomyelin (SM) profiles in rats with streptozotocin-induced hyperglycemia. Employing gas-liquid chromatography, we found that level of total Cer increased significantly only in the PFC of diabetic animals, which also exhibited a broad spectrum of sphingolipid (SLs) changes, such as elevations of Cer-C16:0, -C18:0, -C20:0, -C22:0, -C18:1, -C24:1 and SM-C16:0 and -C18:1. In opposite, only minor changes were noted in other examined structures. In addition, de novo synthesis pathway could play a role in generation of Cer containing monounsaturated fatty acids in PFC during hyperglycemia. In turn, simultaneous accumulation of Cers and their SM counterparts may suggest that overproduced Cers are converted to SMs to avoid excessive Cer-mediated cytotoxicity. We conclude that broad changes in SLs compositions in PFC induced by hyperglycemia may provoke membrane rearrangements in some cell populations, which can disturb cellular signaling and cause tissue damage.

Fiber specific changes in sphingolipid metabolism in skeletal muscles of hyperthyroid rats.

Thyroid hormones (T3, T4) are well known modulators of different cellular signals including the sphingomyelin pathway. However, studies regarding downstream effects of T3 on sphingolipid metabolism in skeletal muscle are scarce. In the present work we sought to investigate the effects of hyperthyroidism on the activity of the key enzymes of ceramide metabolism as well as the content of fundamental sphingolipids. Based on fiber/metabolic differences, we chose three different skeletal muscles, with diverse fiber compositions: soleus (slow-twitch oxidative), red (fast-twitch oxidative-glycolytic) and white (fast-twitch glycolytic) section of gastrocnemius. We demonstrated that T3 induced accumulation of sphinganine, ceramide, sphingosine, as well as sphingomyelin, mostly in soleus and in red, but not white section of gastrocnemius. Concomitantly, the activity of serine palmitoyltransferase and acid/neutral ceramidase was increased in more oxidative muscles. In conclusion, hyperthyroidism induced fiber specific changes in the content of sphingolipids that were relatively more related to de novo synthesis of ceramide rather than to its generation via hydrolysis of sphingomyelin.

Fatty acid transporters involved in the palmitate and oleate induced insulin resistance in primary rat hepatocytes.

AIMS: To determine the presence and possible involvement of FAT/CD36, FABPpm and FATP-2, transporters in (i) fatty acids movement across plasma membrane and (ii) an induction of insulin resistance by palmitic (PA) and oleic (OA) fatty acids in primary hepatocytes. METHODS: Primary hepatocytes were treated with either PA and OA or combination of activators (AICAR, Insulin) or inhibitors (SSO, phloretin) of FA transport. Expression of FA and glucose transporters as well as insulin signalling proteins was determined using Western blot analyses. Palmitate and glucose transport was measured using radioactive isotopes. Intracellular lipid content [ceramide, diacylglycerols (DG) and triacylglycerols] and FA composition were estimated by GLC. RESULTS: In primary hepatocytes, adding phloretin diminished insulin, and AICAR stimulated palmitate transport. Both PA and OA fatty acids induced the protein expression of FAT/CD36 and FATP-2 with concomitant: (i) reduction in GLUT-2 protein content, (ii) inhibition of insulin-stimulated glucose uptake, (iii) reduction in insulin-stimulated activation of AKT and GSK, (iv) accumulation of either DG (PA and OA) or ceramide (only PA). CONCLUSIONS: FA transport into hepatocytes is, at least in part, protein-mediated process, and both PA and OA induce the protein expression of FAT/CD36 and FATP-2. Both saturated (PA) and unsaturated (OA) fatty acids induce insulin resistance in primary hepatocytes, associated with the accumulation of DG and/or ceramide.

Change in blood gelsolin concentration in response to physical exercise.

Plasma gelsolin (pGSN) produced by muscle is an abundant protein of extracellular fluids capable of severing actin filaments and eliminating actin from the circulation. Additionally, pGSN modulates the cellular effects of some bioactive lipids. In this study we test the hypothesis that hormonal and metabolic adaptations to exercise are associated with changes in gelsolin concentration in blood. Plasma samples were collected from twenty healthy males recruited from untrained (UT, n=10) and endurance trained (ET, n=10) groups that performed 30-60 minutes of exercise on a cycloergometer at a workload corresponding to 70% of VO2max. Gelsolin concentration was determined by quantitative Western blot analysis with an anti-human gelsolin antibody. The gelsolin concentration in UT and ET subjects before starting exercise ranged from 104 to 330 and 163 to 337 µg · ml(-1) respectively. After 30 minutes of exercise we observed a significant decrease of plasma gelsolin in the UT group (p<0.05) while the gelsolin concentration in the ET group rose on average from 244 to 271 µg · ml(-1). However, this increase did not reach statistical significance. Endurance training might increase the ability of muscle tissue to express plasma gelsolin as part of an adaptive mechanism.

Effects of hyperthyroidism on lipid content and composition in oxidative and glycolytic muscles in rats.

Triiodothyronine (T(3)) can influence lipid metabolism via multiple mechanisms, which generally result in an increase of fatty acids (FAs) oxidation. Consequently, we hypothesize that hyperthyroidism may influence intramuscular lipids accumulation. This increased intramuscular lipid turn-over is possibly accompanied by an increase in fatty acid transporters expression (FAT/CD36, FABPpm, FATP-1,4). In the present study we examined the lipid content and fatty acid saturation status of free fatty acids (FFA), triacylglycerols (TAG), diacylglycerols (DAG) and phospholipids (PL) in skeletal muscle of hyperthyroid rats (n=8). We measured also fatty acid transporters as well as AMP-activated protein kinase (pAMPK/AMPK), peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), acetyl-CoA carboxylase (pACC/ACC), carnitine palmitoyltransferase I (CPT I) and citrate synthase (CS) protein expression in these muscles. In vivo T3 administration, decreased the content of FFA, particularly in the red gastrocnemius and the TAG fraction, in both the red and white portions of the gastrocnemius muscle. Concomitantly, saturated/unsaturated fatty acids (SFA/UFA) ratio was also decreased, but only in the FFA fraction, irrespectively of muscle's fiber composition. In contrast, T(3) treatment had no effect on the lipid content and saturation status in PL fraction. Triiodothyronine induced also modest activation of AMPK/ACC axis with subsequent increased expression of mitochondrial proteins: CPT I and CS. This was accompanied by increased content of FAT/CD36, but only in the red part of gastrocnemius muscle. These findings support the conclusion that hyperthyroidism increases lipid metabolism, especially in skeletal muscles with high capacity for fatty acid oxidation.

Not only accumulation, but also saturation status of intramuscular lipids is significantly affected by PPARγ activation.

AIM: Intramuscular lipid accumulation has been associated with insulin resistance, and after thiazolidinediones (TZD) treatment, it was shown to be reduced in some, but not all, studies. This work was undertaken to investigate the relationships between intramuscular lipids [free fatty acids (FFA), diacylglycerols (DAG), triacylglycerol (TAG) and phospholipids] and plasmalemmal expression of fatty acid (FA) transporter [FAT/CD36 and FABPpm] in the muscles of varying oxidative capacity, after peroxisome proliferator-activated receptors gamma (PPARγ) activation (rosiglitazone) in an animal model of high-fat-diet-induced insulin resistance. Endurance training was also included to further explore the differences in these relationships. METHODS: We have used gas liquid chromatography to estimate FA content and composition in each lipid fraction. For sarcolemmal expression of FA transporters, subfractionation of skeletal muscles with subsequent western blot technique was applied. RESULTS: High-fat diet induced intramuscular accumulation of FFA, DAG and TAG, irrespective of muscle's fibre composition. PPARγ activation (rosiglitazone) and, to a lesser extent, endurance training further increased TAG accumulation, while it reduced DAG in oxidative muscles (soleus and red gastrocnemius). Aforementioned interventions increased also sarcolemmal FAT/CD36 and FABPpm expressions in particular muscles. Irrespective of diet, rosiglitazone and exercise decreased significantly FA saturation status favouring proportionate enhancement in monounsaturated FA (rosiglitazone) or polyunsaturated FAs (endurance training). CONCLUSION: These findings support the conclusion that not only the change in total lipid content (DAG and TAG), but also FA composition is affected by rosiglitazone in an animal model of high-fat-diet-induced insulin resistance.

Chronic, in vivo, PPARalpha activation prevents lipid overload in rat liver induced by high fat feeding.

PURPOSE: Peroxisome proliferator-activated receptors (PPAR's) are lipid sensors and when activated they modify gene expression of proteins regulating fatty acid (FA) metabolism in liver cells. The aim of the present study was to examine the in vivo effects of PPAR alpha and gamma activation combined with high fat diet (HFD) feeding on the lipid content and FA profile in the liver. MATERIAL/METHODS: We assessed whether in vivo activation of PPARs (alpha or gamma) affects lipid accumulation in the liver induced by HFD feeding. Furthermore, as PPAR activity may be a key factor regulating long chain fatty acids (LCFA) flux and subsequent LCFA utilization in the liver, we prompted to investigate also the FA profile in different lipid fractions in this tissue. RESULTS: PPARalpha agonist (WY 14,643) treatment reduced the accumulation of liver lipids free fatty acids (FFA:-30%, diacylglycerols DAG: -27% and triacylglycerols TAG: -60%, p<0.05) evoked by HFD feeding. Interestingly, with PPARgamma stimulation liver lipid content was further elevated comparing to the effects of HFD (phospholipids PL: +48%, DAG: +231%, TAG: +346%, p<0.05). CONCLUSIONS: These findings suggest that in vivo PPARalpha and PPARgamma activation combined with HFD feeding exert different effects on lipid content in rat's liver and in vivo PPARalpha activation may prevent lipid overload in the liver cells provoked by HFD feeding.

Differential effects of in vivo PPAR alpha and gamma activation on fatty acid transport proteins expression and lipid content in rat liver.

Peroxisome proliferator-activated receptors (PPAR;s) serve as lipid sensors and when activated modify gene expression of proteins highly involved in the regulation of fatty acid metabolism. Recently, the accumulation of lipids in liver was shown to be depended on the excessive protein-mediated transmembrane transport of long chain fatty acids (LCFAs). The aim of the present study was to determine the in vivo effects of PPARalpha and gamma activation at two levels: 1) on the expression of fatty acid transporters, 2) on the content and fatty acids saturation status of lipids in rats liver. PPARalpha agonist (WY 14,643) treatment upregulated the liver expression of FAT/CD36 (+20%, p<0.05) and did not significantly affect the content of FABPpm and FATP-1. Accordingly there was a significant increase in the content of phospholipid (+12%, p<0.05), diacylglycerol (+65%, p<0.05) and triacylglycerol (+46%, p<0.05) fractions followed PPARalpha activation. In contrast, pioglitazone (PPARgamma agonist) had no effect on the content of fatty acid transporters (FAT/CD36, FABPpm and FATP-1) as well as the content of liver lipid fractions with the exception for triacylglycerols, which have been reduced significantly (-89%, p<0.05). These findings suggest that in vivo PPARalpha and PPARgamma activation exert different effects on both the expression of fatty acid transporters and lipid content in rat's liver.

The effect of acute and prolonged endurance exercise on transforming growth factor-beta1 generation in rat skeletal and heart muscle.

The serum level of the transforming growth factor-beta1 (TGF-beta1) is elevated after acute bouts of exercise and prolonged training, as well as after myocardial infarction. However, the source of this increase remains unclear. Contracting skeletal muscles are known to be the source of many cytokines. To determine whether skeletal or heart muscles produce TGF-beta1 during exercise, we investigated the effect of a single bout of acute exercise on TGF-beta1 generation in skeletal and heart muscles in untrained rats (UT, n=30) and in rats subjected to prolonged (6-week) endurance training (T, n=29). The UT and T (a day after final training) groups were subjected to an acute bout of exercise with the same work load. Rats from both groups were sacrificed and skeletal and heart muscle samples were collected before (pre), immediately after (0 h), or 3 hours (3 h) after acute exercise. TGF-beta1 mRNA was quantified by RT-PCR in these samples, and basal TGF-beta1 protein levels were determined in skeletal muscle in the UTpre and Tpre subgroups by ELISA. Acute exercise caused a non-significant increase in TGF-beta1 mRNA in skeletal muscle in UT0h rats, in compare to UTpre rats. There was a significant decrease of TGF-beta1 mRNA in the T0h group (p=0.0013) in compare to Tpre rats. Prolonged training caused a significant increase in TGF-beta1 mRNA (p=0.02); however, the TGF-beta1 protein level decreased (p=0.02). In heart muscle, there was a significant decrease of TGF-beta1 mRNA in UT0h (p=0.01) and UT3h (p=0.04) compared to UTpre rats. TGF-beta1 mRNA levels were unchanged in T0h and T3h compared to Tpre; basal TGF-beta1 mRNA expression after training was also unchanged (UTpre vs. Tpre). We conclude that physical exercise is a potent stimulus for inducing TGF-beta1 gene expression in skeletal muscle, but does not increase the protein level. Thus, skeletal and heart muscle do not contribute to increased serum levels of TGF-beta1 after physical exercise.

Effects of pioglitazone and high-fat diet on ceramide metabolism in rat skeletal muscles.

Ceramide is involved in the pathogenesis of insulin resistance in skeletal muscles of humans and rodents. However, there are conflicting reports in the literature on the effect of thiazolidinediones (a new class of insulin sensitizing drugs) on skeletal muscle ceramide content. Therefore, the aim of our study was to examine the effect of pioglitazone on the level of ceramide and its metabolites and on the activity of the key enzymes of ceramide metabolism in different skeletal muscle types of the rat. The experiments were carried out on rats fed either a standard chow or a high-fat diet for 21 days. Each group was divided into two subgroups: control and treated with pioglitazone for 14 days. High-fat diet increased the content of ceramide in the soleus and in the red section of the gastrocnemius, but not in the white section of the latter. The activity of neutral Mg(2+)-dependent sphingomyelinase and acid sphingomyelinase was simultaneously reduced in all examined muscles. Administration of pioglitazone decreased ceramide level in the soleus and in the red section of the gastrocnemius in rats fed either diet. This effect could not be attributed to decreased rate of ceramide formation from sphingomyelin or to its augmented deacylation to sphingosine. Pioglitazone treatment reduced the concentration of plasma free fatty acids in rats fed on either diet. Therefore, we conclude that the drug decreased the muscle content of ceramide by reducing its de novo synthesis. The results of our study indicate that reduction in ceramide level may be one of the mechanisms by which pioglitazone improves skeletal muscle insulin sensitivity.

Effect of endurance training on the sphingomyelin-signalling pathway activity in the skeletal muscles of the rat.

The sphingomyelin signalling pathway has been shown to function in different skeletal muscle types. The aim of the present study was to examine the effect of endurance training on the functioning of the pathway in the muscles. The experiments were carried out on two groups of male Wistar rats: sedentary and trained for six weeks. 24h after cessation of the training rats were anaesthetized and samples of the soleus, red and white section of the gastrocnemius were taken. The content and composition of sphingomyelin-fatty acids and ceramide - fatty acids was determined by means of gas-liquid chromatography. The content of sphingosine and sphinganine was determined by means of high-pressure liquid chromatography. The activity of neutral Mg(++)-dependent sphingomyelinase was determined spectophotometrically using trinitrophenylaminolauroyl-sphingomyelin as the substrate. It has been found that training reduces the total content of sphingomyelin- and ceramide-fatty acids, increases the content of sphinganine and does not affect the content of sphingosine in individual muscle types. The activity of the enzyme in the muscles is also elevated. It is concluded that training affects functioning of the sphingomyelin -signalling pathway in skeletal muscles. The reduction in the content of ceramide may contribute to elevation in glucose uptake in skeletal muscles observed after training.

Effect of streptozotocin-diabetes on the functioning of the sphingomyelin-signalling pathway in skeletal muscles of the rat.

AIMS/HYPOTHESIS: Ceramide is the main second messenger in the sphingomyelin-transmembrane signalling pathway. The compound is likely to play a role in the induction of insulin resistance. The aim of the present study was to examine the effect of streptozotocin diabetes on the content and composition of ceramides and sphingomyelins and the activity of neutral Mg (2+)-dependent sphingomyelinase and acid sphingomyelinase in different types of skeletal muscle of the rat. METHODS: The experiments were carried out on two groups of male Wistar rats weighing 250-280 g: controls and those treated with streptozotocin at a dose of 60 mg/kg. Determinations were performed on three types of skeletal muscle: the slow-twitch oxidative (soleus), fast-twitch oxidative-glycolytic (red section of the gastrocnemius) and fast-twitch glycolytic (white section of the same muscle). The content and composition of ceramide- and sphingomyelin-fatty acids were determined using gas-liquid chromatography. The activity of the enzymes was measured using N-[(14)CH (3)]-sphingomyelin as the substrate. RESULTS: Twelve different ceramides and sphingomyelins were identified and quantified in each muscle with regard to the fatty acid residue. The ratio of total content of ceramide-saturated fatty acids to the total content of ceramide-unsaturated fatty acids was more than two. In the case of sphingomyelin, the ratio was similar to ceramide in the soleus and much higher in both sections of the gastrocnemius. Treatment with streptozotocin increased the total content of ceramide-fatty acids by 78% (p < 0.001) in the soleus, 27.5% (p < 0.01) in the red and 36.9% (p < 0.001) in the white section of the gastrocnemius. Concomitantly, the total content of sphingomyelin-fatty acids decreased by 43.8%, 31.2%, 24.8% (p < 0.001 in each case) in the respective muscles. The activity of neutral Mg (2+)-dependent sphingomyelinase was elevated by 69.5%, 105.9% and 62.3% in the soleus and red and white gastrocnemius, respectively (p < 0.001 for each muscle). The activity of acid sphingomyelinase was stable in the soleus and white gastrocnemius and decreased by 15.7% (p < 0.01) in the red gastrocnemius. CONCLUSION/INTERPRETATION: The results obtained show that insulin deficiency results in elevation in the content of ceramide in skeletal muscles. This indicates that the hormone is involved in regulation of the activity of the sphingomyelin-signalling pathway in the muscles.

Diabetes affects phospholipid content in the nuclei of the rat liver.

The aim of the present study was to examine the effect of acute streptozotocin diabetes on the content of different phospholipids and the incorporation of blood-borne 14C-palmitic acid into the phospholipid moieties in the rat liver nuclei. Diabetes was produced by intravenous administration of streptozotocin, and determinations were carried out two and seven days thereafter. Phospholipids were extracted from isolated nuclei and separated into the following fractions: sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine and cardiolipin. Following that, they were quantified and radioactivity was measured. It was found that, in comparison to non-diabetic controls, two-day diabetes reduced the total content of phospholipids in the nuclei by 9.6%. The content of phospholipids in the nuclei by 9.6%. The content of phosphatidylcholine and phosphatidylserine was reduced and the content of the remaining phospholipids was stable. The specific activity of phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine and cardiolipin, based on radioactivity incorporated from 14C-palmitic acid, was elevated. Seven-day diabetes resulted in a reduction of the total phospholipid content in the nuclei by 39.4%. This was accounted for by a reduction in the content of each phospholipid fraction with the exception of cardiolipin. The specific activity of each phospholipid fraction, was elevated in this group. It is concluded that insulin is involved in the regulation of the nuclear phospholipid content.

Effect of triiodothyronine on the content of phospholipids in the rat liver nuclei.

The aim of the present study was to examine the effect of triiodothyronine (T3) on the content of phospholipids and on the incorporation of blood-borne palmitic acid into the phospholipid moieties in the nuclei of the rat liver. T3 was administered daily for 7 days, 10 microg x 100 g(-1). The control rats were treated with saline. Each rat received 14C-palmitic acid, intravenously suspended in serum. 30 min after administration of the label, samples of the liver were taken. The nuclei were isolated in sucrose gradient. Phospholipids were extracted from the nuclei fraction and from the liver homogenate. They were separated into the following fractions: sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine and cardiolipin. The content and radioactivity of each fraction was measured. It was found that treatment with T3 reduced the content of phosphatidylinositol and increased the content of cardiolipin in the nuclear fraction. In the liver homogenate, the content of phosphatidylinositol decreased and the content of phosphatidylethanolamine and cardiolipin increased after treatment with T3. The total content of phospholipids after treatment with T3 remained unchanged, both in the nuclear fraction and in the liver homogenate. T3 reduced the specific activity of phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine and cardiolipin and had no effect on the specific activity of sphingomyelin and phosphatidylinositol both in the fraction of the nuclei and the liver homogenate. It is concluded that excess of triiodothyronine affects the content of phospholipids in the nuclei. The changes in the content of phospholipids in the nuclei largely reflect changes in their content in the liver.

Effect of triiodothyronine on phospholipid metabolism in skeletal muscles of the rat.

The aim of the present study was to examine the effect of treatment with triiodothyronine (T3) on certain aspects of phospholipid metabolism in skeletal muscles. Rats were injected with triiodothyronine (T3) daily (10 microg x 100 g(-1) b.w., s.c.) for six days. Saline-treated rats served as controls. 24 h after the last dose of T3, 14C palmitic acid suspended in the serum of a donor rat, was administered intravenously. Thirty min later, samples of the soleus, white and red section of the gastrocnemius and blood from the abdominal aorta were taken. The muscle phospholipids were extracted and separated into different fractions by means of thin layer chromatography. The following fractions were obtained: shingomeylin, phosphatidylcholine phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and cardiolipin. The phospholipids were quantified and their radioactivity was measured. The plasma free fatty acid concentration and radioactivity was also determined. Treatment with T3 reduced the content of phosphatidylinositol and phosphatidylserine in each muscle type, whereas the concentration of other phospholipids remained stable. T3 increased markedly incorporation of the blood-borne fatty acids into each phospholipid fraction in the muscles. It is concluded that an excess of T3 influences the metabolism of phospholipids in skeletal muscles.