Melatonin protects Leydig cells from HT-2 toxin-induced ferroptosis and apoptosis via glucose-6-phosphate dehydrogenase/glutathione -dependent pathway.

HT-2 toxin is a mycotoxin commonly found in food and water that can have adverse effects on male reproductive systems, including testosterone secretion. Ferroptosis and apoptosis are two types of programmed cell death that have been implicated in the regulation of cellular functions. Melatonin, a powerful antioxidant with various physiological functions, has been shown to regulate testosterone secretion. However, the mechanisms underlying the protective effects of melatonin against HT-2 toxin-induced damage in testosterone secretion are not fully understood. In this study, we investigated the effects of HT-2 toxin on sheep Leydig cells and the potential protective role of melatonin. We found that HT-2 toxin inhibited cell proliferation and testosterone secretion of Leydig cells in a dose-dependent manner and induced ferroptosis and apoptosis through intracellular reactive oxygen species accumulation, leading to lipid peroxidation. Exposure of Leydig cells to melatonin in vitro reversed the defective phenotypes caused by HT-2 toxin via a glucose-6-phosphate dehydrogenase/glutathione-dependent mechanism. Interference of glucose-6-phosphate dehydrogenase disrupted the beneficial effect of melatonin on ferroptosis and apoptosis in HT-2 toxin-treated Leydig cells. Furthermore, similar results were observed in vivo in the testes of male mice injected with HT-2 toxin with or without melatonin treatment for 30 days. Our findings suggest that melatonin inhibits ferroptosis and apoptosis by elevating the expression of glucose-6-phosphate dehydrogenase to eliminate reactive oxygen species accumulation in HT-2 toxin-treated Leydig cells. These results provide fundamental evidence for eliminating the adverse effects of HT-2 toxin on male reproduction.

One-time ozone treatment improves the postharvest quality and antioxidant activity of Actinidia arguta fruit.

The major aim of this study was to check the effect of one-time ozonation on selected quality parameters and antioxidant status of Actinidia arguta fruit. For this purpose, A. arguta fruit was ozonated with gas at a concentration of 10 and 100 ppm, which was carried out successively for 5, 15 and 30 min. Next, the selected quality attributes, antioxidants level as well as NADPH and mitochondrial energy metabolism in mini-kiwi fruit after ozonation were analysed. Our research has shown that ozonation reduced the level of yeast and mould without affecting the content of soluble solids or acidity. In turn, ozonation clearly influenced the antioxidant activity and the redox status of the fruit. The ozonated fruit was characterised by a lower level of ROS due to the higher level of low molecular weight antioxidants, as well as the higher activity of superoxide dismutase and catalase. In addition, improved quality and antioxidant activity of the fruit were indirectly due to improved energy metabolism and NADPH level. The ozonated fruit showed a higher level of ATP, due to both higher activity of succinate dehydrogenase and higher availability of NADH. Moreover, the increased level of NAD+ and the activity of NAD+ kinase and glucose-6-phosphate dehydrogenase contributed to higher levels of NADPH in the fruit.

N-Acetylcysteine protects against cobalt chloride-induced endothelial dysfunction by enhancing glucose-6-phosphate dehydrogenase activity.

Hypoxia-induced endothelial dysfunction is known to be involved in the pathogenesis of several vascular diseases. However, it remains unclear whether the pentose phosphate pathway (PPP) is involved in regulating the response of endothelial cells to hypoxia. Here, we established an in vitro model by treating EA.hy926 (a hybrid human umbilical vein cell line) with cobalt chloride (CoCl2 ; a chemical mimic that stabilizes HIF-1α, thereby leading to the development of hypoxia), and used this to investigate the involvement of PPP by examining expression of its key enzyme, glucose-6-phosphate dehydrogenase (G6PD). We report that CoCl2 induces the accumulation of HIF-1α, leading to endothelial cell dysfunction characterized by reduced cell viability, proliferation, tube formation, and activation of cytokine production, accompanied with a significant decrease in G6PD expression and activity. The addition of 6-aminonicotinamide (6-AN) to inhibit PPP directly causes endothelial dysfunction. Additionally, N-Acetylcysteine (NAC), a precursor of glutathione, was further evaluated for its protective effects; NAC displayed a protective effect against CoCl2 -induced cell damage by enhancing G6PD activity, and this was abrogated by 6-AN. The effects of CoCl2 and the involvement of G6PD in endothelial dysfunction have been confirmed in primary human aortic endothelial cells. In summary, G6PD was identified as a novel target of CoCl2 -induced damage, which highlighted the involvement of PPP in regulating the response of endothelial cell CoCl2 . Treatment with NAC may be a potential strategy to treat hypoxia or ischemia, which are widely observed in vascular diseases.

Effects of cinnamaldehyde on glucose-6-phosphate dehydrogenase activity, some biochemical and hematological parameters in diabetic rats.

CONTEXT: Diabetes is a metabolic disorder related to blood insulin deficiency and high glucose level. Cinnamaldehyde is an important component of cinnamon and has an effect on blood glucose. OBJECTIVE: It was aimed to investigate the the effect of cinnamaldehyde on the liver glutathione (GSH), glucose-6-phosphate dehidrogenase (G6PD) activity, blood glucose, protein, lipid and erythrocyte parameters, live weight in diabetic rats. MATERIAL AND METHODS: Rat used for this research were divided 4 group as control, diabetic, cinnamaldehyde and diabetic + cinnamaldehyde group. The live weight and fasting blood glucose level, taken from tail vein were recorded every ten days. End of the trail the blood samples were taken from rats. Biochemical parameters with autoanalyzer and hematological parameters with blood cell counter were determined in blood. The activity of G6PD and GSH amounts were measured with ELISA in the liver tissues. RESULTS: Blood sugar, triglyceride, total cholesterol, VLDL, LDL, and urea levels increased in diabetic rats, and cinnemaldehyde significantly decreased these parameters. Cinnemaldehyde also showed a positive effect on body weight, blood total protein, and mean corpuscular volume in diabetes. A decrease in HbA1c and an increase in liver G6PD, GSH activity were found in treatment group, but these changes were not statistically significant. CONCLUSION: In conclusion, the antidiabetic, hypolipidemic and antioxidant effects of cinnamaldehyde were determined. It has also been shown to improve anaemia, ürea levels and weight loss.

Construction of Glucose-6-Phosphate Dehydrogenase Overexpression Strain of Schizochytrium sp. H016 to Improve Docosahexaenoic Acid Production.

Docosahexaenoic acid (DHA) is an important omega-3 polyunsaturated fatty acid (PUFA) that plays a critical physiological role in human health. Schizochytrium sp. is considered an excellent strain for DHA production, but the synthesis of DHA is limited by the availability of nicotinamide adenine dinucleotide phosphate (NADPH). In this study, the endogenous glucose-6-phosphate dehydrogenase (G6PD) gene was overexpressed in Schizochytrium sp. H016. Results demonstrated that G6PD overexpression increased the availability of NADPH, which ultimately altered the fatty acid profile, resulting in a 1.91-fold increase in DHA yield (8.81 g/L) and increased carbon flux by shifting it from carbohydrate and protein synthesis to lipid production. Thus, G6PD played a vital role in primary metabolism. In addition, G6PD significantly increased DHA content and lipid accumulation by 31.47% and 40.29%, respectively. The fed-batch fermentation experiment results showed that DHA production reached 17.01 g/L in the overexpressing G6PD strain. These results elucidated the beneficial effects of NADPH on the synthesis of PUFA in Schizochytrium sp. H016, which may be a potential target for metabolic engineering. Furthermore, this study provides a promising regulatory strategy for the large-scale production of DHA in Schizochytrium sp.

Mitochondrial glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase abrogate p53 induced apoptosis in a yeast model: Possible implications for apoptosis resistance in cancer cells.

BACKGROUND: Escape from apoptosis is an important hallmark of tumor progression and drug resistance in cancer cells. It is well demonstrated that over-expression of human wtp53 in Saccharomyces cerevisiae induces apoptosis by directly targeting the mitochondria. In this study, we showed that how S.cerevisiae escaped from p53 induced apoptosis in the presence of a fermentable carbon source (sucrose), but not on non-fermentable carbon source (glycerol). METHODS: Mitochondrial fractions from yeast cultures grown in the presence of sucrose or glycerol with and without p53 expression were fractionated and analyzed by LC-MS/MS. Differentially expressed proteins were studied and detailed biochemical analysis for selected proteins was performed.The effect of mitochondrial HXK-2 over-expression induced by p53 in sucrose grown cells on cell survival was evaluated using gene deletion/tagging, co-localisation and mitochondrial ROS detection. RESULTS: We observe that mitochondria isolated from p53 over-expressing cells accumulate Pentose phosphate Pathway (PPP) enzymes including glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) which led to enhanced mitochondrial NADPH production only when cells are cultured in sucrose but not glycerol. In contrast, mitochondria isolated from Δhxk2 p53 over-expressing cells grown in sucrose did not accumulate G6PDH and 6PGDH and resulted in defective growth. CONCLUSIONS: Enhanced association of HXK2 with the mitochondria with the concomitant accumulation of G6PDG and 6PGDH results in increased NADPH that scavenges ROS and provides resistance to apoptosis. GENERAL SIGNIFICANCE: Given the extensive similarity of aerobic glycolysis between humans and yeast, the phenomena described here could as well be responsible for the escape of apoptosis in cancer cells.

Protective effects of glucose-6-phosphate dehydrogenase on neurotoxicity of aluminium applied into the CA1 sector of rat hippocampus.

BACKGROUND & OBJECTIVES: Aluminum (Al) toxicity is closely linked to the pathogenesis of Alzheimer's disease (AD). This experimental study was aimed to investigate the active avoidance behaviour of rats after intrahippocampal injection of Al, and biochemical and immunohistochemical changes in three bilateral brain structures namely, forebrain cortex (FBCx), hippocampus and basal forebrain (BF). METHODS: Seven days after intra-hippocampal (CA1 sector) injection of AlCl3 into adult male Wistar rats they were subjected to two-way active avoidance (AA) tests over five consecutive days. Control rats were treated with 0.9% w/v saline. The animals were decapitated on the day 12 post-injection. The activities of acetylcholinesterase (AChE) and glucose-6-phosphate dehydrogenase (G6PDH) were measured in the FBCx, hippocampus and BF. Immunohistochemical staining was performed for transferrin receptors, amyloid ß and tau protein. RESULTS: The activities of both AChE and G6PDH were found to be decreased bilaterally in the FBCx, hippocampus and basal forebrain compared to those of control rats. The number of correct AA responses was reduced by AlCl3 treatment. G6PDH administered prior to AlCl 3 resulted in a reversal of the effects of AlCl3 on both biochemical and behavioural parameters. Strong immunohistochemical staining of transferrin receptors was found bilaterally in the FBCx and the hippocampus in all three study groups. In addition, very strong amyloid ß staining was detected bilaterally in all structures in AlCl3-treated rats but was moderate in G6PDH/AlCl3-treated rats. Strong tau staining was noted bilaterally in AlCl3-treated rats. In contrast, tau staining was only moderate in G6PDH/AlCl3-treated rats. INTERPRETATION & CONCLUSIONS: Our findings indicated that the G6PDH alleviated the signs of behavioural and biochemical effects of AlCl3-treatment suggesting its involvement in the pathogenesis of Al neurotoxicity and its potential therapeutic benefit. The present model could serve as a useful tool in AD investigations.

The effect of Zn2+ on glucose 6-phosphate dehydrogenase activity from Bufo arenarum toad ovary and alfalfa plants.

The effect of Zn2+ on glucose 6-phosphate dehydrogenase (G6PD) activity was monitored in samples from Bufo arenarum toad ovary and alfalfa plants, in the search for a possible new bioindicator able to detect levels of exposure through contaminated soils, and also to elucidate possible similarities between the enzyme from animal and plant tissues. The in vivo effect was evaluated after exposure of the toads to the metal in Ringer solution during 30 days and after 10 days of treatment in 6 weeks old plants, cultured under laboratory conditions. In vitro effects were measured in different extracts from control samples and partially purified enzyme from ovarian tissue as well as in different extracts from control alfalfa plants, by addition of the metal to the reaction mixture containing the enzyme. G6PD from toad ovary was noncompetitively inhibited by zinc both in vivo and in vitro, under all the experimental conditions studied. A kinetic analysis of the enzyme activity showed that the Michaelis-Menten constant (Km) was not modified, while maximal velocity (Vmax) decreased as the consequence of treatment. It was not possible to obtain a dose-response curve for the effects of Zn2+ on G6PD from alfalfa whole plants, measured in vivo or in vitro. Only leaf extracts evidenced a possible relationship between treatment with the metal and G6PD activity alteration. The results agree with a possible role for G6PD as a biomarker of effect and exposure to Zn2+ in B. arenarum ovarian tissue but not in alfalfa plants.

Effects of long-term exposure to Cu2+ and Cd2+ on the pentose phosphate pathway dehydrogenase activities in the ovary of adult Bufo arenarum: possible role as biomarker for Cu2+ toxicity.

The effects of copper and cadmium on metabolism through the pentose phosphate pathway were evaluated in Bufo arenarum toad ovary. The effects of the two metals on dehydrogenases from this pathway were evaluated by three experiments: (1) in samples obtained from control females with addition of the metals to the reaction mixture (in vitro), (2) in samples obtained from control females and after long-term exposure of females to 4 and 100 microg/L of Cu or Cd in the incubation media (in vitro after exposure to the metals in vivo), and (3) 14CO2 production through the pentose phosphate pathway was evaluated after [U-14C]glucose microinjection on ovulated oocytes (in vivo after microinjection of the metals). Results from (1) evidenced inhibition of both enzyme activities but only above 1.5 mM Cu and Cd added to the reaction mixture. In (2) both glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities decreased in samples from the ovaries of females exposed in vivo to Cu, in a concentration-dependent manner (up to 90% in females exposed to 100 microg/L Cu: 2.12 +/- 1.57 NADPH micromol/min microg protein x 10(-5) vs 19.97 +/- 8.54 in control females). Cd treatment of the toads only rendered an inhibitory effect on 6-phosphogluconate dehydrogenase activity after exposure to 4 microg/L of the bivalent cation. (3) In vivo 14CO2 evolution significantly decreased in oocytes coinjected with 6.3 x 10(-3) mM Cu (calculated intracellular final concentration of the metal injected) and radioactive glucose. Cu and Cd concentration in samples from exposed females were always under detection limit by particle-induced X-ray emission. The results presented here are in agreement with a role for both glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities determination as biomarkers of effect and exposure for Cu but not for Cd toxicity.

Effect of sulfur dioxide inhalation on the glutathione redox system in mice and protective role of sea buckthorn seed oil.

This study investigated the effects of sulfur dioxide (SO2) inhalation and protection by sea buckthorn seed oil from oxidative damage caused by SO2 in male Kunming-strain mice. One approach was set up to study the effects of SO2 inhalation on changes of the mice antioxidant defense system. SO2 at different concentrations (22 +/- 2, 64 +/- 3, and 148 +/- 23 mg/m3) was administered to animals in treatment groups for 7 days, 6 h per day, while control groups were exposed to filtered air under the same condition. The activities of glutathione-S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PD) and the contents of reduced glutathione (GSH) in brain, lung, heart, liver, and kidney of mice were measured. In the case of inhalation of a SO2 concentration of 148 +/- 23 mg/m3, the activities of GST and G6PD and contents of GSH in the brain, lung, heart, liver, and kidney were significantly decreased. Dose-dependent relations were found between various SO2-exposed concentrations and the activities of GST and G6PD and the content of GSH. Meanwhile another approach was taken to determine whether sea buckthorn seed oil could maintain the glutathione redox system and prevent the oxidative damage of lung induced by SO2. In groups given a high dosage (6 or 8 ml/kg) intraperitoneally, the level of TBARS (thiobarbituric acid-reactive substances) was decreased significantly (p < 0.05) by the injection of sea buckthorn seed oil, and the activity of GST was increased significantly (p < 0.05). Overall GST activity and TBARS level exhibited a significant negative correlation (r = 0.891, p < 0.05). The observations showed that SO2 inhalation resulted in a significant change in the glutathione redox system and indicated that sea buckthorn seed oil could contribute to the antioxidant effects in the case of SO2 exposure.

Effects of phenylhydrazine or recombinant human erythropoietin on deformability and activity of dehydrogenase glucose-6-phosphate and acetylcholinesterase in Wistar rats blood enriched in reticulocytes.

Deformability and activity of the enzymes: acetylcholinesterase (AChE) and dehydrogenase glucose-6-phosphate (G-6-PD), were assayed for RBC enriched in immature reticulocytes. Reticulocytosis was evoked by administration of two different drugs: recombinant human erythropoietin (rHuEPO) and phenylhydrazine (PHZ) to two groups of Wistar rats. After treatment with the former compound, a group of animals exhibited 17.33% reticulocytes in blood whereas a group of rats treated with the latter drug reached 57.66% of these cells in blood. A marked decrease in RBC deformability was found in both groups of animals. AChE did not significantly change activity neither in PHZ-treated nor in rHuEPO-treated rats, whereas G-6-PD activity was significantly decreased in the PHZ-treated group.

Effects of aluminum on physiological metabolism and antioxidant system of wheat (Triticum aestivum L.).

The Al-tolerant cultivar TAM202 and the Al-sensitive cultivar TAM 105 of winter wheat (Triticum aestivum L.) were exposed to 0, 50, 75, 100 or 150 microM of Al. The absorption of Al by wheat, the growth of root, several key enzymes concerned with C, N and P metabolism, as well as key constituents of antioxidant system, were investigated. The results showed that TAM105 absorbed more Al than TAM202 and its root growth (presented by the length) was inhibited more severely. The root growth was most closely related to mononuclear Al (Ala) activity. The metabolic enzymes (presented by glucose-6-phosphate dehydrogenase, nitrate reductase and acid phosphatase) in TAM202 were Al-tolerant. Presented by superoxide dimutase (SOD) and the content of reduced glutathione (GSH) and malondialdehyde (MDA), antioxidant system in TAM202 indicated lower oxidative stress and greater ability to protect the cultivar.

Sample pretreatment with nitrate reductase and glucose-6-phosphate dehydrogenase quantitatively reduces nitrate while avoiding interference by NADP+ when the Griess reaction is used to assay for nitrite.

An assay for the simultaneous measurement of nitrite and nitrate, products of nitric oxide metabolism, is described. Others have reported pretreating sample by using nitrate reductase (NR) and NADPH to reduce endogenous NO3- before assaying the resultant NO2- using the Griess reaction. However, we found that the NADP+ formed during pretreatment interfered with the Griess reaction when NADPH was used at concentrations necessary to drive the NR reaction. For instance, 500 microM NADP+ in 100 microM NaNO3- (without NR) causes a 90% interference with the formation of Griess reaction product. To limit interference, we modified the method by decreasing the NADPH concentration to 1 microM. NADPH was regenerated by coupling the NR reaction with that catalyzed by glucose-6-phosphate dehydrogenase (GD). Using this method, NaNO3- standard curves were linear up to 100 microM and coincided with control curves obtained using NaNO2- incubated in parallel. Addition of urine up to a strength of 20% did not interfere with the assay. Comparison with an alternative assay based on cadmium reduction resulted in the following linear regression: [Cd method] = 0.915*[NR-GD method] + 0.37, r2 = 0.997. Coupling GD to NR to recycle NADPH allows this cofactor to be used at a low concentration so that interference with the Griess reaction is negligible.

Biochemical mechanisms of hydrogen peroxide- and hypochlorous acid-mediated inhibition of human mononuclear leukocyte functions in vitro: protection and reversal by anti-oxidants.

Both H2O2 (IC50 = 70 microM) and HOCl (IC50 = 8.5 microM) inhibited mitogen-induced MNL proliferation in a dose-dependent manner. This was found to be due to a depletion of intracellular ATP by at least two distinct mechanisms. HOCl and high concentrations (greater than 100 microM) of H2O2 inhibit ATP generation via sulfhydryl group oxidation on the active site of the glyceraldehyde-3-phosphate dehydrogenase (G3PDH) enzyme of the glycolytic pathway. On the other hand, low H2O2 concentrations cause ATP depletion by an activation of the DNA repair enzyme, poly(ADP-ribose)polymerase (pADPRP), leading to consumption of NAD+, an essential cofactor for G3PDH. The anti-oxidants ascorbate and cysteine protected MNL against the anti-proliferative effects of HOCl. Similar results were achieved with the HOCl-mediated inhibition of ATP production and G3PDH activity. However, ascorbate was unable to protect against H2O2-mediated inhibition of MNL functions, while cysteine protected against the inhibitory effects on ATP production and G3PDH activity, induced by this oxidant.

Inhibition of N6-[3H]cyclohexyladenosine binding by carbamazepine.

The mechanism of action of carbamazepine (CBZ) (Tegretol), despite widespread use in the management of partial and tonic-clonic seizures in adults, is not completely understood. In animals, adenosine and adenosine analogues have anticonvulsant effects that may be due to interactions with central A1 adenosine receptors. CBZ (at therapeutically relevant concentrations) inhibits the binding of agonists and antagonists to brain A1 adenosine receptors, but whether as an agonist/antagonist is not clear. The adenosine agonist, N6-[3H]cyclohexyladenosine ([3H]CHA), binds to membranes from rat cortex and hippocampus at two nanomolar binding sites or states. To clarify the actions of carbamazepine at the A1 adenosine receptor, its inhibitory actions were compared with those of known adenosine agonists and xanthine antagonists using 0.1 nM[3H]CHA, in which almost all binding is to the higher affinity state, or 10 nM [3H]CHA, in which there is a substantial contribution of binding from both states. The ratios of the IC50 values (concentration that inhibits specific binding by 50%) at 10 nM [3H]CHA to the IC50 values at 0.1 nM [3H]CHA were 18-31 for the agonists and 4-10 for the xanthine antagonists. CBZ had a ratio of 3. The inhibitory effects of GTP on [3H]CHA binding were less in the presence of the adenosine agonist, 2-chloroadenosine than were inhibitory effects in the presence of the xanthine antagonist theophylline or CBZ in both cortex and hippocampus. These in vitro studies indicate that CBZ is an antagonist at A1 adenosine receptors in cerebral cortical and hippocampal membranes from rat brain. Agonist activity at A1 adenosine receptors would have been compatible with the sedative anticonvulsant effects of CBZ, but these data do not support a role of the anticonvulsant action of carbamazepine on A1 adenosine receptors in cerebral cortex or hippocampus.

[The role of gonadotropins, cyclic AMP, 22-R-hydroxycholesterol and cofactors in regulating endocrine functions of the Leydig cells in rats. II. Effects of LH, hCG, dbcAMP, 22-R-OH-cholesterol and cofactors on the synthesis of pregnenolone and testosterone in the interstitial gland of rats]. / Rola gonadotropin, cAMP, 22-R-hydroksycholesterolu i kofaktorów w regulacji funkcji endokrynnej komórek Leydiga u szczura. II. Wplyw LH, hCG, dbcAMP, 22-R-OH-cholesterolu i kofaktorów na synteze pregnenolonu i testosteronu w gruczole sródmiazszowym szczura.

The authors examined in vitro the influence of gonadotrophins, cAMP, 22-R-OH-cholesterol and cofactors on the synthesis of pregnenolon and testosterone in the interstitial gland of the rat. Sections of the nucleus were incubated with LH (100 ng/ml), hCG (1.0 j.m./ml), dbcAMP (1 mM), 22-R-OH-cholesterol (30 microM) and cofactors (NAD + NADP + G-6-P + G-6-PDH). It was found that an increase in concentrations of hCG above physiological values was not accompanied by an increase in secreting steroid hormones. LH, hCG and dbcAMP increased the synthesis of pregnenolon twice, and testosterone--three times. 22-R-OH-cholesterol as a substrate increased the synthesis three and four times respectively, and added cofactors five times and four and a half times respectively. Joining 22-R-OH-cholesterol or a cofactor with LH does not intensify a stimulating effect.

[The role of gonadotropins, cyclic AMP, 22-R-OH-cholesterol and cofactors in regulating endocrine functions of the Leydig cells in rats. III. Mechanisms responsible for "desensitization" of the Leydig cells of rats caused by high doses of hCG]. / Rola gonadotropin, cAMP, 22-R-OH-cholesterolu i kofaktorów w regulacji funkcji endokrynnej komórek Leydiga u szczura. III. Próba wyjasnienia mechanizmów odpowiedzialnych za "desensybilizacje" szczurzych komórek Leydiga, wywolana wysokimi dawkami hCG.

Two groups of rats (a control group and the group examined) were administered intraperitoneally supraphysiological doses of hCG in order to induce a "down regulation" effect on the level of receptors LH and to achieve the desensibilization of Leydig cells. The authors tried to find out at which stage of sequence of changes from receptor stimulation to hormone production there appears a state of cellular resistance to further stimulation. Sections of the nucleus were incubated with various substances influencing steridogenesis (LH, hCG, dbcAMP, 22-R-OH-cholesterol, NAD + NADP + G-6-P + G-6-PDH). An index of the influence of the above substances on the synthesis of androgens were amounts of pregnenolon as the first and testosterone as the final stage of hormonal changes marked radioimmunologically in nucleus homogenates and incubating media. It was shown that the resistance of Leydig cells to further stimulation in the group of animals that were given high doses of hCG is the result of enzymatic blocks in testosterone synthesis. The first block is "late" block of 17 alpha-hydroxylase and 17-20 desmolase, disturbing transforming of 21-carbon steriods into 19-carbon androgens. When the dose of hCG increases, there appears the second block, the so called "early" block, disturbing mitochondrial synthesis of pregnenolon. It was found that exogenic cofactors are in a position, at least partially, to restore the activity of blocked enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

[The role of gonadotropins, cyclic AMP, 22-R-hydroxycholesterol and cofactors in regulating endocrine functions of the Leydig cells in rats. I. Effect of cofactors on the synthesis of steroid hormones in the interstitial gland of rats]. / Rola gonadotropin, cAMP, 22-R-hydroksycholesterolu i kofaktorów w regulacji funkcji endokrynnej komórek Leydiga u szczura. I. Wplyw kofaktorów na synteze hormonów sterydowych w gruczole sródmiazszowym szczura.

The authors evaluated the influence of NAD, NADP, G-6-P and G-6-PDH on the synthesis of steroid hormones in the interstitial gland of the rat. The animals were killed by decapitation, and sections of the nucleus weighing altogether 20 mg were incubated with NAD (0.4 mM), NADP (0.4 mM), G-6-P (3.5 mM) and G-6-PDH (2 j.m./ml) for 4 hours in CO2 incubator. Then the tissue was homogenized, removed by centrifugation and then from the homogenous supernatant the authors extracted steroids which were in the incubating medium and in the tissue. Steroid hormones examined were marked radioimmunologically, they were: pregnenolon as the first and testosterone as the second stage of synthesis of nucleus androgens. The search carried out shows that the strongest stimulator in biosynthesis of pregnenolon was NADP together with the reducing system (G-6-P and G-6-PDH). On the other hand, in case of testosterone the highest effectiveness was achieved by simultaneous use of the cofactors examined. Applying cofactors separately the authors were able to find that both NAD and NADP together with the reducing system were responsible for testosterone synthesis and their simultaneous applying in the incubating medium leads to a synergistic effect.

Differential effects of adrenalectomy and starvation-refeeding on hepatic lipogenic responses to dehydroepiandrosterone and glucocorticoid in BHE and Sprague-Dawley rats.

The interaction of rat strain and glucocorticoid status on the dehydroepiandrosterone (DHEA)-mediated decrease in response to starvation-refeeding was studied. DHEA treatment of intact starved-refed Sprague-Dawley rats resulted in significantly lower hepatic lipid and glucose-6-phosphate dehydrogenase activity than observed in non-DHEA-treated rats. When Sprague-Dawley rats were adrenalectomized (ADX), the response to DHEA treatment was potentiated. If glucocorticoid was replaced, there was some amelioration of the DHEA effect in the ADX rats. Responses to DHEA in BHE rats subjected to the above paradigms were different. The responses of starved-refed BHE rats to DHEA were more pronounced and it appeared that glucocorticoid replacement was not as effective in overcoming DHEA in these rats. Thus, it appears that the comparative inhibition of the glucocorticoid-mediated response to starvation-refeeding by DHEA is strain dependent.