Mitochondrial Α-glycerophosphate Dehydrogenase Research Articles

Thyroid hormone contributes to the hypolipidemic effect of polyunsaturated fatty acids from fish oil: in vivo evidence for cross talking mechanisms

n-3 polyunsaturated fatty acids (n-3 PUFA) from fish oil (FO) exert important lipid-lowering effects, an effect also ascribed to thyroid hormones (TH) and TH receptor β1 (TRβ1)-specific agonists. n-3 PUFA effects are mediated by nuclear receptors, such as peroxisome proliferator-activated receptors (PPAR) and others. In this study, we investigated a role for TH signaling in n-3 PUFA effects. Euthyroid and hypothyroid adult rats (methimazole-treated for 5 weeks) received FO or soybean oil (control) by oral administration for 3 weeks. In euthyroid rats, FO treatment reduced serum triglycerides and cholesterol, diminished body fat, and increased protein content of the animals. In addition, FO-treated rats exhibited higher liver expression of TRβ1 and mitochondrial α-glycerophosphate dehydrogenase (mGPD), at protein and mRNA levels, but no alteration of glutathione S-transferase or type 1 deiodinase. In hypothyroid condition, FO induced reduction in serum cholesterol and increase in body protein content, but lost the ability to reduce triglycerides and body fat, and to induce TRβ1 and mGDP expression. FO did not change PPARα liver abundance regardless of thyroid state; however, hypothyroidism led to a marked increase in PPARα liver content but did not alter TRβ1 or TRα expression. The data suggest that part of the effect of n-3 PUFA from FO on lipid metabolism is dependent on TH signaling in specific steps and together with the marked upregulation of PPARα in liver of hypothyroid rats suggest important in vivo consequences of the cross-talking between those fatty acids and TH pathways in liver metabolism.

Prolactin inhibition at the end of lactation programs for a central hypothyroidism in adult rat

Malnutrition during lactation is associated with hypoprolactinemia and failure in milk production. Adult rats whose mothers were malnourished presented higher body weight and serum tri-iodothyronine (T(3)). Maternal hypoprolactinemia at the end of lactation caused higher body weight in adult life, suggesting an association between maternal prolactin (PRL) level and programming of the offspring's adult body weight. Here, we studied the consequences of the maternal PRL inhibition at the end of lactation by bromocriptine (BRO) injection, a dopaminergic agonist, upon serum TSH and thyroid hormones, thyroid iodide uptake, liver mitochondrial alpha-glycerophosphate dehydrogenase (mGPD), liver and pituitary de-iodinase activities (D1 and/or D2), and in vitro post-TRH TSH release in the adult offspring. Wistar lactating rats were divided into BRO - injected with 1 mg/twice a day, daily for the last 3 days of lactation, and C - control, saline-injected with the same frequency. At 180 days of age, the offspring were injected with (125)I i.p. and after 2 h, they were killed. Adult animals whose mothers were treated with BRO at the end of lactation presented lower serum TSH (-51%), T(3) (-23%), and thyroxine (-21%), lower thyroid (125)I uptake (-41%), liver mGPD (-55%), and pituitary D2 (-51%) activities, without changes in the in vitro post-TRH TSH release. We show that maternal PRL suppression at the end of lactation programs a hypometabolic state in adulthood, in part due to a thyroid hypofunction, caused by a central hypothyroidism, probably due to decreased TRH secretion. We suggest that PRL during lactation can regulate the hypothalamus-pituitary-thyroid axis and programs its function.

Developmental Regulation of the α-Glycerophosphate Shuttle in Porcine Myocardium

The α-glycerophosphate (α-GP) shuttle has been shown to play a role in reducing equivalent transfer in neonatal cardiac mitochondria. In adult heart mitochondria, α-GP shuttle activity is not detectable. The goals of the current study were to define the time course of the age-dependent decline in α-GP shuttle capacity and to identify the enzymatic step(s) of the α-GP shuttle which are regulated during development. Intact mitochondria were isolated from porcine hearts of various ages and assayed for α-GP shuttle capacity. By 5 weeks of age, α-GP shuttle capacity had decreased by nearly 39%. The cytosolic step of the shuttle, catalysed by cytosolic α-glycerophosphate dehydrogenase (cα-GPDH), demonstrated a significant increase between 0–2-day-old animals and adults. Partial cDNA clones of porcine cα-GPDH and mitochondrial α-glycerophosphate dehydrogenase (mα-GPDH) were prepared and used to quantitate expression of these genes. Using mRNA isolated from neonatal and adult porcine myocardium, expression of the cα-GPDH was unchanged, while expression of the mα-GPDH gene was present in neonatal but absent in adult myocardium. These results demonstrate a rapid postnatal decline in myocardial α-GP shuttle capacity which appears to be regulated by a decline in mα-GPDH gene expression.

Response of triiodothyronine-dependent enzyme activities to insulin-like growth factor I and growth hormone in cultured rat hepatocytes.

Triiodothyronine (T3) is involved in the regulation of the growth hormone-insulin-like growth factor I (GH-IGF-I) axis. In this study we investigated the effect of GH and IGF-I on the metabolic response of T3 in target tissues by evaluating the activity of two T3-dependent liver enzymes: mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytosolic malic enzyme (ME) in rat hepatocytes in primary culture. Growth hormone (35 nmol/l) as well as IGF-I (0.5 mumol/l) reduced alpha-GPD and ME activities (p < 0.01) compared to the control group. Timecourse studies indicated that IGF-I (1.5 mumol/l) significantly decreased alpha-GPD and ME activities (P < 0.01) after 24 h, whereas the effect of GH (35 nmol/l) was recorded only after 36 h (p < 0.01). This delayed effect of GH compared to IGF-I suggested the possibility that the effect of GH could be mediated by IGF-I synthesis. To test this hypothesis, the effect of GH on the two enzyme activities was studied in the presence of anti-IGF-I antibodies. A gradual recovery of alpha-GPD and ME activities (p < 0.01) was observed in the presence of GH (35 nmol/l) plus increasing concentrations of anti-IGF-I antiserum. The maximal alpha-GPD and ME activities attained after the incubation of the liver cells with 1 mumol/l T3, a concentration high enough to fully saturate the nuclear T3 receptors for 24 h, were lowered significantly by 1.0 mumol/l IGF-I (p < 0.01). This finding suggests that the IGF-I effect might be independent of the saturation of the nuclear T3 receptors. In conclusion, in cultured rat hepatocytes, GH and IGF-I reduced the metabolic response of T3 evaluated by two liver T3-dependent enzyme activities. The effect of GH was mediated at least in part by IGF-I.

Effects of chronic ethanol feeding on rat liver mitochondrial energy metabolism

Chronic alcohol consumption is known to decrease hepatic mitochondrial respiration rate. It was shown here that the proton leak through the mitochondrial inner membrane was unaffected by chronic ethanol treatment. This indicates that changes in proton leak are not responsible for the alterations in respiration found in mitochondria isolated from ethanol-treated rats. Therefore, the lowered coupled respiration rate is solely due to a decrease in the activity of the electron transport chain. However, this alteration was oniy evident in coupled respiration (i.e. state 4) and was not apparent in uncoupied respiration. Thus, chronic ethanoi treatment decreases the activity of the mitochondrial electron transport chain components which bave control over coupled, but not uncoupled, respiration. Mitochondrial energy metabolism is regulated by thyroid hormone status. It was shown that the chronic alcohol treatment did not affect the circulating leveis of thyroxine. Furthermore, the activity of mitochondrial α-glycerophosphate dehydrogenase, which is strongly affected by thyroid hormones, was unaltered by alcohol treatment. Thus, the effects of ethanol treatment on mitochondria occur independently of changes in circulating thyroid hormone levels.

Ontogeny of flight in the little brown bat, Myotis lucifugus: behavior, morphology, and muscle histochemistry

Postnatal changes in wing morphology, flight ability, muscle morphology, and histochemistry were investigated in the little brown bat, Myotis lucifugus. The pectoralis major, acromiodeltoideus, and quadriceps femoris muscles were examined using stains for myofibrillar ATPase, succinate dehydrogenase (SDH), and mitochondrial α-glycerophosphate dehydrogenase (α-GPDH) enzyme reactions. Bats first exhibited spontaneous, drop-evoked flapping behavior at 10 days, short horizontal flight at 17 days, and sustained flight at 24 days of age. Wing loading decreased and aspect ratio increased during postnatal development, each reaching adult range before the onset of sustained flight. Histochemically, fibers from the three muscles were undifferentiated at birth and had lower oxidative and glycolytic capacities compared to other age groups. Cross-sectional areas of fibers from the pectoralis and acromiodeltoideus muscles increased significantly at an age when dropevoked flapping behavior was first observed, suggesting that the neuromuscular mechanism controlling flapping did not develop until this time. Throughout the postnatal growth period, pectoralis and acromiodeltoideus muscle mass and fiber cross-sectional area increased significantly. By day 17 the pectoralis muscle had become differentiated in glycolytic capacity, as indicated by the mosaic staining pattern for α-GPDH. By contrast, the quadriceps fibers were relatively large at birth and slowly increased in size during the postnatal period. Fiber differentiation was evident at the time young bats began to fly, as indicated by a mosaic pattern of staining for myosin ATPase. These results indicate that flight muscles (pectoralis and acromiodeltoideus) are less well developed at birth and undergo rapid development just before the onset of flight. By contrast the quadriceps femoris muscle, which is required for postural control, is more developed at birth than the flight muscles and grows more slowly during subsequent development.

Triiodothyronine and insulin effects on malic enzyme in hypothyroid and diabetic rats

We examined the effects of T3 and insulin on the activity of hepatic mitochondrial alpha-glycerophosphate dehydrogenase and cytosolic malic enzyme in control, thyroidectomized, thyroidectomized food-restricted, and thyroidectomized diabetic rats. In the three untreated thyroidectomized groups, the decrease in hepatic nuclear T3 content was accompanied by a marked reduction in the levels of alpha-glycerophosphate dehydrogenase and malic enzyme activity. Although the levels of both enzymes were increased by a receptor-saturating dose of T3, the alpha-glycerophosphate dehydrogenase response in the thyroidectomized groups was almost identical to that in controls, whereas that of malic enzyme was reduced to 45-62% of control values. Insulin failed to stimulate the alpha-glycerophosphate dehydrogenase levels in untreated and T3-treated thyroidectomized groups, but caused an increase in malic enzyme activity by 79-130% in untreated thyroidectomized groups, and enhanced the activity of this enzyme to about twice that seen with T3 alone. These effects were independent of changes in nuclear T3 binding parameters. The data suggest that insulin may act on malic enzyme synthesis through its general stimulatory effect on protein synthesis, or by antagonizing factors that inhibit the induction of this enzyme.

Effect of Triiodothyronine and Thyroxine on Mitochondrial α-Glycerophosphate Dehydrogenase Activity and Mitochondrial Protein Content of Liver, Muscle and Brain of Toad,Bufo melanostictus

The responsiveness of the adult toad to triiodothyronine (T3) and thyroxine (T4) was studied by measuring the mitochondrial alpha-glycerophosphate dehydrogenase activity and mitochondrial protein content of liver, muscle and brain of toad. Both T3 and T4 increased the alpha-GPD activity and mitochondrial protein content of liver and muscle of toad. The extent of increase in the alpha-GPD activity and mitochondrial protein content were more pronounced with T3 than with T4. Further that the muscle exhibited more alpha-GPD activity than liver, whenever liver showed greater mitochondrial protein content than that of muscle. Brain showed no significant change in the alpha-GPD activity and mitochondrial protein content. Injections of cycloheximide showed inhibition of T3 induced changes in liver and muscle. Injection of propylthiouracil also counteracted the T4 induced effects of liver and muscle.

Increase in Hepatic Mitochondrial α-Glycerophosphate Dehydrogenase Activity after Surgical Stress in Hyperthyroid Rats*

We have established a rat model to investigate the relationship among serum thyroid hormones, nuclear iodothyronine receptors, and biological responses in thyrotoxic and euthyroid rats after surgical stress. Euthyroid or hyperthyroid rats (1.0 microgram T3/ml drinking water for 14 days) were subjected to surgical stress (ether anesthesia, laparotomy plus 50 mg talc, ip). Groups of control or stressed rats were killed 1, 2, and 3 days after surgical stress for measurement of thyroid hormone-responsive hepatic enzymes, alpha-glycerophosphate dehydrogenase (alpha GPD) and cytosol malic enzyme, serum T3, T3 nuclear receptors, and GH mRNA. Thyrotoxic rats had a 3.8-fold increase in alpha GPD compared to euthyroid rats before surgical stress; alpha GPD increased further to 5.9-fold the euthyroid value 1 day after surgery (P less than 0.001) to 5.1-fold after 2 days (P less than 0.05) and was similar to control after 3 days. Malic enzyme activity increased 10.5-fold before surgical stress and decreased slightly after surgical stress perhaps due to multifactorial regulation of that enzyme. No increases in T3 nuclear receptor or GH mRNA occurred after surgery in hyperthyroid rats or in any of the above parameters after surgical stress in euthyroid rats. Our findings suggest that increased alpha GPD after surgical stress in thyrotoxic rats was not due to either increased serum total T3 or free T3 or to increased T3-nuclear receptor complexes. Increased alpha GPD, therefore, appeared to be a consequence of postreceptor amplification of this thyroidal response.

Effects of active immunization against L-triiodothyronine on serum thyrotropin levels and liver mitochondrial α-glycerophosphate dehydrogenase activity in rats: evidence for reduced hormone disposal to cells

Thyroid hormone binding autoantibodies have been observed in serum from patients affected by either thyroid disorders or autoimmune nonthyroid diseases. In most instances, no major involvement of thyroid status of these patients has been reported. However, some authors have attributed the occurrence of hypothyroidism to high capacity thyroid hormone binding autoantibodies. In order to verify such a hypothesis, the effect of these autoantibodies on serum TSH and liver mitochondrial alpha-glycerophosphate dehydrogenase has been investigated in rats, wherein circulating T3-binding antibodies (max cap 10(-12) 10(-8) to mol/l) were induced by active immunization. Starting from the 3rd week after antigen injection, the binding of 125I-T3 to serum immunoglobulins was progressively increased, with a peak at the 5th week. In immunized animals considered as a whole group, serum TSH levels were significantly higher and liver mitochondrial alpha-glycerophosphate dehydrogenase activity was significantly lower than in normal rats (m +/- SE: 145 +/- 15 vs 34 +/- 2 ng/dl and 0.0450 +/- 008 vs 0.0980 +/- 005 delta A. mg/prot/.min, respectively; p less than 0.001). The pattern of both TSH increase and alpha-glycerophosphate dehydrogenase decrease were similar to the evolution of 125-I-T3 binding to serum immunoglobulins, the maximal TSH values and lowest enzyme levels being observed at the 5th week after the beginning of the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of liver mitochondrial α-glycerophosphate dehydrogenase activity by L-thyroxine in thyroidectomized rats: comparison with the suppression of pituitary TSH secretion

The rate of liver mitochondrial alpha-glycerophosphate dehydrogenase (GPD) induction was compared to the suppression of pituitary thyrotropin (TSH) secretion in thyroidectomized rats submitted to prolonged administration of small amounts of L-thyroxine (T4). With both 350 and 530 ng T4/100 g bw/day, liver alpha-GPD activity remained at post-thyroidectomy level (mean +/- SE: 0.030 +/- 0.002 and 0.034 +/- 0.001 delta A/mg prot/min, respectively) throughout all experiment. A sharp increase in enzyme activity was observed after 3 weeks of treatment in rats receiving 715 ng T4 / 100 g bw / day (mean +/- SE: 0.086 +/- 0.003 delta A/mg prot/min). In contrast, serum TSH levels were lower than pretreatment values (199 +/- 8ng/dI) in rats receiving 350 ng T4/100 g bw/day (mean +/- SE: 104 +/- 15 ng/dI; t = 7.48, p less than 0.001), decreased progressively with increasing T4 doses (m +/- SE:530 ng T4/100 g/day = 36 +/- 7 ng/dI); after only 48 h of treatment and were not significantly modified thereafter. The data are in agreement with the hypothesis of a nonlinear relationship between the degree of thyroid hormone receptor occupancy and the rate of liver mitochondrial alpha-GPD induction.

Age-related changes in rat hepatic and renal thyroid hormone-sensitive enzymes — different responses to acute and chronic l-triiodothyronine stimulation

Using young (5–6 weeks) and adult (12–14 months) male Sprague—Dawley rats, the responses of hepatic and renal cytosolic malic enzymes (ME) and mitochondrial α-glycerophosphate dehydrogenase (α-GPDH), have been assessed following acute and chronic l-triiodothyronine (T3) administration. In control (untreated) animals a significant reduction of renal ME as well as hepatic and renal α-GPDH activity with increased age were observed but renal ME activity was not age-related. Following acute T3 stimulation (200 μg T3/100 g body wt single injection), the levels of hepatic ME and α-GPDH as well as renal α-GPDH but not renal ME remained lower in the adult than in the younger group. After chronic T3 stimulation (15 μg T3/100 g body wt for 7 days) or 200 μg T3/100 g body wt for 4 days), the enzyme levels remained significantly lower in older animals for hepatic ME but were no longer different for hepatic and renal α-GPDH, while renal ME, which was not altered with age, had values that were the same as in the younger group. These studies have demonstrated that age-related changes in hepatic and renal T3-sensitive enzymes could not be attributed solely to T3 occupancy of nuclear receptor binding sites, but may be influenced by other factors depending upon the specific tissues and subcellular T3-sensitive enzymes being assessed.

Histochemical demonstration of cytosolic α-glycerophosphate dehydrogenase (EC 1.1.1.8) and mitochondrial α-glycerophosphate dehydrogenase (EC 1.1.99.5)

Histochemical demonstration of cytosolic α-glycerophosphate dehydrogenase (EC 1.1.1.8) and mitochondrial α-glycerophosphate dehydrogenase (EC 1.1.99.5)

Hyperthyroidism selectively increases oxidative metabolism of slow-oxidative motor units

The effects of thyroid hormone on the NADH-tetrazolium reductase activity (oxidative metabolism marker) of soleus (slow-oxidative) and tensor fascia lata (fast-glycolytic) motoneurons were determined and compared with changes in a variety of enzyme activities in the corresponding muscle fibers. Histochemical assays have demonstrated a selective and qualitative conversion in muscle fiber ATPase and quantitative increases of NADH-tetrazolium reductase (oxidative) and mitochondrial α-glycerophosphate dehydrogenase (glycolytic) activities in the soleus muscle. Paralleling the selective action upon the soleus slow muscle fibers was a selective central nervous system effect of thyroid hormone on oxidative enzymes of soleus slow-oxidative motoneurons. This indicates that either thyroid hormones act directly and specifically on slow motoneurons or that conversion of the muscle fibers by thyroid hormones produces secondary changes in the motoneuron. These data strengthen the hypothesis that oxidative enzyme activities in motoneurons are tightly matched with oxidative enzyme activities in muscle fibers.

Studies on cytosol thyroid hormone binding proteins in the rat liver: Part II. Alterations of thyroid hormone binding proteins in various thyroid function states

Alterations of binding characteristics of cytosolic thyroid hormone binding proteins (CTHBPs) were examined in livers of rats with different thyroid function. Seven days after thyroidectomy, rats were divided into three groups. Group I received no treatment. Group II was treated with 230 ng triiodothyronine (T3)/100 g body weight per day for three days, and Group III with 40 micrograms T3/100 g body weight per day for three days. On the fourth day, each rat was given 0.7 microCi of 125I-T3/100 g body weight intraperitoneally and exsanguinated two hours later. During three days' treatment, body weight in Group II increased significantly compared with that in Group I (P less than 0.05), and body weight in Group III actually decreased. The ratio of liver weight to body weight in Group II was significantly higher than that in Group I or Group III (P less than 0.01). Percent distributions of 125I-T3 in cytosol fraction per liver or concentrations of cytosolic protein did not differ significantly among these three groups. Serum T3 concentrations (mean +/- SD ng/ml: Group I; not detectable, Group II; 0.50 +/- 0.27, Group III; 7.10 +/- 2.31), cytosolic T3 concentrations (mean +/- SD ng/ml: Group I; not detectable, Group II; 0.59 +/- 0.26, Group III; 10.38 +/- 3.08) and mitochondrial alpha-glycerophosphate dehydrogenase activities (mean +/- SD delta OD500 millimicrons/min/mg: Group I; 28.0 +/- 1.5, Group II; 46.7 +/- 7.3, Group III; 267.7 +/- 9.1) suggested that Group I was in hypothyroid state, Group II in euthyroid state and Group III in thyrotoxic state. Binding characteristics of cytosolic T3 binding protein (CT3BP) were different among the three groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Histochemical localization of glycolytic enzymes, alcohol and secondary-alcohol dehydrogenases in the testes of buffaloes, goats and rams

SUMMARYGlyceraldehyde-3-phosphate dehydrogenase (G-3-PDH), αglycerophosphate dehydrogenase (αGPDH), lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH) and secondary-alcohol dehydrogenase (SADH) were histochemically located in the testes of buffaloes, goats and rams. Two forms of αGPDH were observed: (i) NAD-dependent or cytoplasmic αglycero-phosphate dehydrogenase (αGPDHC) and (ii) NAD-independent or mitochondrial αglycerophosphate dehydrogenase (α GPDHM). The basic pattern of distribution of the various enzymes was similar in the three species; species-specific variations were observed but cell-specific variations were more pronounced. The main activities of G-3-PDH and αGPDHM were observed in the seminiferous tubules; interstitial tissue showed moderate (G-3-PDH) and trace to weak (αGPDHM) activity. In contrast, αGPDHC activity was more marked in the interstitial tissue and less in the seminiferous tubules, especially in the mature germinal elements. LDH and ADH respectively showed strong and moderate activities in the interstitial tissue and seminiferous tubules. SADH was noticeable only in the interstitial tissue of buffalo. The activities of all enzymes other than αGPDHC increased during spermiogenesis. The physiological significance of the results is discussed in relation to the carbohydrate metabolism of the testis.

Improved α-glycerophosphate dehydrogenase assay system suitable for continuous recording

Improvements have been made in the Lee and Lardy assay for mitochondrial α-glycerophosphate dehydrogenase. Sonication of mitochondria in 1% Triton X-100 assures uniform dispersion of the particles and prevents precipitation of formazan, thus allowing continuous recording of the progress of the reaction.

The role of calcium in the stimulation of gluconeogenesis by catecholamines

In hepatocytes isolated from fasted normal rats and incubated without albumin or gelatin, norepinephrine stimulated gluconeogenesis from fructose or dihydroxyacetone only in the absence of added calcium and from sorbitol or glycerol only in the presence of added calcium. The effects of calcium, norepinephrine, or calcium in combination with norepinephrine on the concentration of intermediary metabolites were therefore studied in hepatocytes metabolizing fructose or sorbitol as the representative oxidized or reduced substrate, respectively. With fructose as the substrate, addition of calcium increased the concentrations of lactate, pyruvate, glyceraldehyde 3-phosphate, and β-hydroxybutyrate, but decreased the concentrations of phosphoenolpyruvate, 2-phosphoglycerate, 3-phosphoglycerate, glucose 6-phosphate, malate, citrate, and α-oxoglutarate. With sorbitol as the substrate, calcium increased the concentrations of pyruvate, malate, β-hydroxybutyrate, and glucose. With either substrate, calcium caused a decrease in the lactate/ pyruvate ratio and an increase in the β-hydroxybutyrate/acetoacetate ratio, indicating the stimulation of transfer of reducing equivalents from cytosol to mitochondria. With sorbitol as the substrate, and with calcium present, norepinephrine promoted further electron transfer from cytosolic to mitochondrial NAD. Enhanced cytosolic calcium concentrations, when cells are exposed to catecholamines in the presence of medium calcium, stimulate the mitochondrial α-glycerophosphate dehydrogenase and thus the transfer of electrons between cell compartments.

Factors determining the level of activity of 3,5,3'-triiodothyronine-responsive hepatic enzymes in the starved rat.

Recent studies have indicated that starvation can cause profound alterations in components of the thyroid hormone system. A systematic study was therefore undertaken to assess the effect of these changes on the rate of appearance oftwo thyroid hormone-responsive hepatic enzymes, mitochondrial α-glycerophosphate dehydrogenase (α-GPD) and cytosolic malic enzyme (ME). The fractional rates of disappearance of enzyme activity, in both the fed and starved state, were determined after pretreatment with T3. An almost 2-fold increase in the fractional disappearance rate was noted for both enzymes during starvation (ME, 0.22 vs. 0.43 day-1; α-GPD, 0.18 vs. 0.32 day-1). Knowledge of these values together with measurements of the enzyme activity per mg DNA in uninjected rats allowed calculation of the simultaneous rates of appearance and disappearance of enzyme activity during the 5-day starvation period. During the first 3 days, the rate of appearance of α-GPD was preserved at near-normal values (89% of fed baseline...

Insulin and cortisol increase the response of rat hepatocytes in primary culture to 3,3′,5 triiodothyronine

Summary Primary cultures of adult rat hepatocytes respond to 3,3′,5 triiodothyronine added to the culture media. The specific activities of mitochondrial α-glycerophosphate dehydrogenase and cytosolic malic enzyme are increased. Although the addition of 3,3′,5 triiodothyronine causes a 30–70% increase in enzyme activity, the greatest response (150–200% increase) is obtained when both insulin and cortisol are present. Insulin and/or cortisol do not cause any marked increase in either enzyme in the absence of 3,3′,5 triiodothyronine.