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J Knopp

Publications and source records attributed to J Knopp.

At least 19 recordsLinked to original sources
PubMed2001

Endocrine responses to space flights.

Simultaneously with human space flights several series of observations were performed by using experimental animals--mainly rats--exposed to space flights on board of special satellites BION-COSMOS or in Shuttle Transportation Systems (STS). The aims of these experiments were to study in more details: the mechanisms of the changes in bones and skeletal muscle, the alterations of the function of immune system, the radiation effects on organism, the mechanism of the changes of endocrine functions, the evaluation of the role of hormones in alteration of metabolic processes in organism. The advantages of these animal experiments were the possibilities to analyze not only the plasma samples, but it was possible to obtain samples of organs or tissues: for morphological and biochemical analysis for studies of the changes in enzyme activities and in gene expressions, for measurement of metabolic processes and for investigation of the hormone production in endocrine glands and estimation of the response of tissues to hormones. It was also possible to compare the endocrine response to spaceflight and to other stress stimuli. These animal studies are interesting for verification of some hypothesis in the mechanism of adaptation of human organism to the changes of gravity. The disadvantage was, however, that the animals in almost all experiments could be examined only after space flight. The actual inflight changes were investigated only in two SLS flights. In this short review it is not possible to evaluate all hormonal data available on the response of endocrine system to the conditions of space flights. Therefore we will concentrate on the response of pituitary adrenocortical system, pituitary thyroid and pituitary gonadal functions.

Animals↗
PubMed2000

Nuclear all-trans retinoic acid receptor status in rat liver: a comparison of effects of three different stressors--immobilization, laparotomy, and 2-deoxy-D-glucose.

Retinoic acids and their cognate nuclear receptors exert a substantial regulatory role in cell growth and development as well as in the neuroendocrine system. These effects are primarily mediated by all-trans retinoic acid receptors (RARs), members of the steroid/thyroid hormone receptor superfamily of ligand inducible transcription factors. The present study was undertaken in order to compare the effects of immobilization stress (IMO), laparotomy, and 2-deoxy-D-glucose (2DG)-induced intracellular glucopenia on both nuclear RAR affinity and concentration in the rat liver. IMO when compared to non-stressed group of rats, significantly reduced the RAR maximal binding capacity (Bmax) in liver, with the equilibrium association constant (Ka) remaining unchanged. No significant changes of the RAR Bmax and the Ka, were observed in liver of rats that underwent laparotomy. In contrast, a single dose of 2DG (500 mg/kg) resulted in a significant increase of the RAR Bmax 10 h after 2DG application, with the Ka remaining unchanged. Shorter intervals, 1 or 5 h after 2DG application were ineffective on both the RAR Bmax and Ka. In the 2DG-adapted rats (6 doses of 2 DG, 500 mg/kg; 1 dose/day), decapitated 24 h after the last 2DG dose, the RAR Bmax was found significantly higher when compared to control group of animals. No further effect of the next dose of 2DG to repeatedly injected rats on the RAR Bmax and Ka was observed in animals killed 5 h after the seventh dose of 2DG. 2DG-induced intracellular glucopenia markedly up-regulates RARs in liver, but does not change the affinity of the receptor. Thus, the effect of 2DG on RAR concentration in liver specifically differs from that of IMO or laparotomy.

Animals↗
PubMed1999

Changes in plasma catecholamine and corticosterone levels and gene expression of key enzymes of catecholamine biosynthesis in partially hepatectomized rats.

OBJECTIVE: To reexamine the possible role of catecholamines and corticosterone in the early period of liver regeneration after partial hepatectomy (PH)in conscious cannulated rats under carefully controlled conditions which would allow to obtain reliable information about sympathetic-adrenomedullary function after PH in the rat in vivo. METHODS: Plasma levels catecholamines (epinephrine - EPI, norepinephrine - NE) were estimated by radioenzymatic assay and these of corticosterone by competitive protein binding assay. The total RNA was isolated from the adrenals and tyrosine hydroxylase (TH) mRNA expression was estimated by hybridisation with cDNA after Northern blot. The level of immunoreactive protein was measured by using a monoclonal antibody to rat TH, visualized by Western light chemiluminescent detection system and analyzed by densitometry. The level of TH in adrenals was estimated with the aid of 3H-tyrosine and TH cofactor DL-6-methyl-5,6,7,8-tetrahydropterine and the formed radioactive water was measured by scintillation spectometry. RESULTS: The plasma level of norepinephrine (NE), epinephrine (EPI) and corticosterone rapidly increased 20 min. after PH or sham operation (laparotomy). Although the increase of plasma NE was about the same after both PH and laparotomy, that of EPI and corticosterone in PH rats was significantly higher as compared to the laparotomy. One hour after the surgery plasma NE levels in both groups decreased to the basal value and remained still unchanged 4 and 24 h later. At the interval of 4h the plasma level of EPI was higher than in laparotomized controls, but after 24 h the EPI levels returned to basal values. Adrenal tyrosine hydroxylase (TH) mRNA level was significantly elevated in both PH and laparotomized rats, however 24 h after the surgery they returned to the baseline. Adrenal TH immunoprotein levels and TH activity were significantly elevated in both groups 4 h after the surgery, while 24 h later they returned to the baseline in laparotomized rats bur remained elevated in PH rats. Adrenal phenylethanolamine N-methyl-transferase (PNMT) mRNA levels were increased 4 h after both the PH and laparotomy and declined within 24 h. CONCLUSIONS: The first peak of catecholamine and corticosterone levels might result from unspecific stressor associated with the surgery. These levels could be accompanied with the mechanism of the rat liver regeneration. Prolonged elevations of EPI found after PH seems to be specific for liver regeneration indicating that the rise in the adrenal TH mRNA appears to be translated into immunoreactive protein which further leads to the elevation of TH activity. These results contrast markedly with previous studies indicating that the regeneration is modulated predominantly by norepinephrine.

Anesthesia↗
PubMed1998

Genetic and hormonal control of cytosolic malate dehydrogenase activity in Drosophila melanogaster.

The activity of Drosophila cytosolic malate dehydrogenase (MDH; EC 1.1.1.40), a key enzyme in the biosynthesis of lipids, was found to be regulated by both the sesquiterpenoid juvenile hormone (JH), and the steroid hormone ecdysone. The responsiveness of MDH to JH largely depended on the developmental stage or endogenous titre of ecdysone. During the early through middle period of the last larval instar, when ecdysone levels are low, MDH responded to JH rapidly by increasing activity, while little or no response was measured in mature larvae (postfeeding stage) and fresh pupae when the endogenous pulse of ecdysone is high. Activity of MDH in ecd1 and su(f)ts67g, two ecdysone-deficient mutants of Drosophila, was increased when compared to wild type controls, and was also sensitive to administration of JH. The differences in MDH activity between ecd1 and su(f)ts67g were negligible indicating a substantial role of ecdysone in the enzyme regulation and minimal or no effect of their genetic backgrounds. Accordingly, another Drosophila mutant, ap4 which is naturally deficient in JH production, displayed significantly reduced activity of MDH in heterozygotic combination, and almost undetectable MDH activity in null homozygote adults. The ap4 phenotype was more strongly manifested in the adult stage than in larvae which showed 7-times lower requirements for JH titre. In addition, high/low sucrose diet fed to wild types or mutants affected the activity of larval MDH, but the enzyme remained sensitive to administration of JH. These results corroborate those described for mammals and provide the first evidence that Drosophila MDH might be under differential hormonal and nutritional control. These data will serve as a basis for further molecular characterization of the Drosophila MDH gene and its regulation.

Animals↗
PubMed1997

Insulin and catecholamines act at different stages of rat liver regeneration.

Insulin and catecholamines are known to exert effects on hepatocyte growth and metabolism. The binding of insulin, the plasma levels of insulin (INS), and the plasma catecholamine levels of epinephrine (EPI) and norepinephrine (NE) were measured during liver regeneration after partial hepatectomy (PH). A significant decrease (p < 0.05) of INS receptor binding capacity was found at 1, 2, and 3 days after operation. A single insulin injection (2.5 IU/kg body weight) at 24 h after sham operation or partial hepatectomy did not affect these changes of INS binding to hepatocytes. The plasma insulin and glucose levels were similar in both hepatectomized and sham-operated rats. Within 20 min after liver resection or sham operation, plasma NE and EPI concentrations increased rapidly. Then, a significant decrease was observed in plasma catecholamine levels at 1 h after laparotomy and PH. In both groups, laparotomized and partially hepatectomized plasma levels of NE at 4 h reached control values and remained unchanged at the 4- and 24-h periods. After PH, the levels of EPI remained elevated at 4 h in comparison with laparotomy. Adrenal tyrosine hydroxylase mRNA levels were significantly elevated at 4 h in both PH and sham-operated groups. These results suggest that signals that are initiated by catecholamines and transduced through second messengers presumably participate in the trigger mechanism of liver regeneration, while insulin (considered as a secondary mitogen) enhances a stimulus for liver regeneration.

Animals↗
PubMed1997

Ecdysone-modulated response of Drosophila cytosolic malate dehydrogenase to juvenile hormone.

Recently, we found that the activity of malate dehydrogenase (MDH), one of the key enzymes in the biosynthesis of lipids, is regulated in Drosophila melanogaster by juvenile hormone (JH) and JH analogues. Here we report that the response of MDH to JH, however, depends on the developmental stage of the animal in relation to its endogenous titre of ecdysteroids. During the interecdysial period of the last instar, when endogenous ecdysteroids are low, MDH rapidly responded to JH by increasing activity, while little or no response was monitored in wandering (post-feeding) larvae, i.e., after a pulse of ecdysteroids. Activity of MDH in ecd1 and su(f)ts67g, two ecdysteroid-deficient mutants of Drosophila, increased during a temperature shift to 29 degrees C as compared to wild-type controls, and was sensitive to administration of JH. In contrast, when ecd1 or su(f)ts67g larvae during restrictive conditions were fed on a 20-hydroxyecdysone diet, JH was unable to increase the activity of the MDH enzyme. However, when JH was applied prior to 20-hydroxyecdysone feeding, the activity of MDH was significantly stimulated. Two phases of MDH response to JH, dependent on ecdysteroids, could be observed. The first phase was short and independent of RNA and protein syntheses. But activation of MDH in later stages of the response was inhibited by actinomycin D and cycloheximide, indicating that MDH might be regulated by JH at the transcriptional and/or translational level.

Animals↗
PubMed1996

Regulation of gene expression and activity of malic enzyme in liver of hereditary hypertriglyceridemic (hHTG) insulin resistant rat: effect of dietary sucrose and marine fish oil.

The effect of increased dietary intake of n-3 polyunsaturated fatty acids (PUFA) on hepatic malic enzyme (EC 1.1.1.40) gene expression and activity was investigated in either hereditary fixed or dietary induced hypertriglyceridemia after euglycemic hyperinsulinemic (6.4 mU/kg/min) clamp. The hereditary hypertriglyceridemic rats (hHTG) were fed for 2 weeks basal (B) or high (63 cal %) sucrose (HS) diet, with or without fish oil (FO, 30 wt % n-3 PUFA). The results were compared with the data obtained in control (C) animals subjected to identical protocol. In hHTG rats, increased gene expression [hHTG: 1.7 +/- 0.1 vs. C: 0.5 +/- 0.05 arbitrary units (AU), P<0.02] for malic enzyme (ME) was not accompanied by increased activity of this enzyme in liver [hHTG: 1.1 +/- 0.1 vs. C: 3.1 +/- 0.4 nkat/mg, P<0.001]. HS feeding raised the activity [HS-hHTG: 4.2 +/- 0.3 nkat/mg, P<0.001; HS-C: 7.5 +/- 0.9 nkat/mg, P<0.001] and mRNA levels [HS-hHTG: 10.4 +/- 0.3 AU, P<0.001; HS-C: 7.7 +/- 0.3 AU, P<0.001] in liver of both hHTG and control rats. The supplementation of HS diet with FO led to striking suppression of activity by 63 % [2.8 +/- 0.5 nkat/mg, P<0.001] and gene expression [2.9 +/- 0.2 AU, P<0.001] for ME in liver of control rats. Such inhibitory effect was not as pronounced in hHTG rats and reached about 50 % in the ME activity [HS+FO: 2.0 +/- 0.06 nkat/mg vs. HS:4.2 +/- 0.3 nkat/mg, P<0.001] or 30 % decrease in ME mRNA levels [HS+FO: 7.5 +/- 0.8 Au vs. HS:10.4 +/- 0.3 AU, P<0.001]. Thus, hHTG rats have markedly elevated levels of mRNA for malic enzyme in liver accompanied by decreased enzymatic activity. Dietary manipulations leading to alteration of hypertriglyceridemia (HS diet, omega-3 PUFA) influenced both the activity of malic enzyme and its transcription in the liver.

Journal Article↗
PubMed1995

Expression of S14 protein gene in rat liver in response to partial hepatectomy, and its regulation with T3 and sucrose.

In rat liver a significant decrease in the expression of the protein S14 gene was observed 4 h after partial hepatectomy compared to sham operation performed after overnight fasting. After 24 h a decrease was recorded after partial hepatectomy or sham operation and this low level persisted for 120 h. A single i.p. dose of 3,5,3,'-L-triiodothyronine (10 micrograms/100 g body wt), a potent inducer of gene S14, reversed the inhibition of gene expression at each time interval studied in both the partially hepatectomized and sham-operated rats. Sucrose administration to rats 24 h after partial hepatectomy or to sham-operated rats restored the induction of hepatic mRNA S14 gene expression in approx. 60% of controls as recorded after 4 and 24 h. These data suggest that the expression of gene S14 was altered in the liver after partial hepatectomy or sham operation by food restriction, and no compensatory effect of the increased lipid metabolism was found in rat remnant liver. Our findings indicate that thyroid hormone and sucrose administration exert similar effects on hepatic expression of the protein S14 gene both in the regenerating liver and in the intact liver of sham-operated animals. In spite of the increased lipid metabolism of the liver after resection, sensitivity of mRNA S14 expression to triiodothyronine and sucrose was unchanged and its regulation was operative in a positive manner. These results also suggest that the treatment of a regenerating liver containing both the parent and the daughter hepatocytes with sucrose and/or triiodothyronine resulted in a fully restored response.

Animals↗
PubMed1994

Changes of insulin and glucagon binding to receptors in hepatocytes during liver regeneration.

The binding of insulin (INS) and glucagon (GL) on isolated rat hepatocytes during the process of liver regeneration after partial hepatectomy was determined. Adult male rats were subjected to 65-70% partial hepatectomy, control animals were sham-operated. The binding of radioiodine labelled INS and GL to isolated hepatocytes was determined 1, 2, 3 and 5 days after the surgery. The plasma levels of INS and glucose and microviscosity of liver plasma membranes were also measured. The decrease of INS receptor binding capacity was found 1, 2, and 3 days after operation. No differences in sham and partially hepatectomized groups in INS binding were noted 5 days after operation. A single insulin injection during the process of regeneration did not affect these changes of INS binding to hepatocytes. The increase of GL binding was observed on the third day after partial hepatectomy, however, on the 5th day no changes of GL binding to its receptors were noted. The plasma insulin and glucose levels were similar in both hepatectomized and sham-operated rats. The increase of plasma membrane microviscosity of hepatocytes during the process of liver regeneration and a negative correlation between INS binding and membrane microviscosity were found. These results demonstrated significant changes in binding parameters of both INS and GL receptors in hepatocytes during liver regeneration induced by partial hepatectomy.

Animals↗
PubMed1994

Effect of 3,5,3'-L-triiodothyronine on hepatic ornithine decarboxylase and thymidine kinase activity in rat after partial hepatectomy.

Partial hepatectomy (60%) led to the biphasic increase (first one at 4 h and second one at 48 h) of ornithine decarboxylase activity in the remnant rat liver. Daily administration of 3,5,3'-L-triiodothyronine (T3) (10 micrograms/100 g) to rats for 7 days before partial hepatectomy had little effect on the enzyme activity. At five days, ornithine decarboxylase activity declined to control level (sham operated controls) and its activity was significantly enhanced by T3. Ornithine decarboxylase gene expression in the rat liver (examined by Northern blot analysis using poly A+ mRNA) started to increase 4 h after partial hepatectomy, remained elevated for 48 h and decreased after 5 days. Its activity was not altered by T3 treatment. The activity of thymidine kinase increased progressively after partial hepatectomy, but its peak value was delayed by T3 administration. Plasma prolactin levels increased within 5-15 min after liver resection, then declined to control values and increased 24 h after the surgery. The data demonstrate that the changes in ornithine decarboxylase activity in the rat liver after partial hepatectomy might result from the direct effect of prolactin on the activity of enzyme rather than from its induction by hormone. Triiodothyronine administration altered both ornithine decarboxylase and thymidine kinase activities suggesting that T3 appears to regulate ornithine decarboxylase activity at post-translational level.

Animals↗
PubMed1993

Inhibition of 3,5,3'-triiodothyronine binding to its receptor in rat liver by protease inhibitors and substrates.

Various protease inhibitors (e.g. phenylmethanesulfonyl fluoride (PMSF), tosyl-phenylalanine chloromethyl ketone (TosPheCH2Cl)) and substrates (e.g., tosyl-arginine methyl ester (TosArgOMe), tryptophan methyl ester (TrpOMe)) inhibit the binding of adrenal and sex steroids to their cognate receptors (Hubbard and Kalimi (1985) Mol. Cell. Biochem. 66, 101-109). Here we extend this finding to the receptor for 3,5,3'-triiodothyronine (T3) in rat liver nuclei. We find that PMSF, TosPheCH2Cl and other protease inhibitors as well as TosArgOMe, TrpOMe, tyrosine methyl ester (TyrOMe) and tyrosine ethyl ester (TyrOEt) inhibit binding of 125I-T3 to its receptor in rat liver nuclei. Inhibition by protease substrates appears to be at or close to the hormone binding domain. By analogy with the known mechanism of binding of protease inhibitors and substrates to enzymes, we suggest that the T3 receptor contains a nucleophilic site at or close to the hormone binding domain.

Animals↗
PubMed1993

Cross-linking of iodinated prolactin to rat liver nuclear protein.

The specific binding of prolactin (PRL) in rat liver nuclei have been examined. Following cross-linking with the use of 125I-rat prolactin and autoradiography the evidence is presented for the specific binding of PRL to a nuclear protein with low Mr of about 7000. This study shows that the PRL binder in rat liver nuclei is a small protein and probably differs from molecular form of the rat liver membrane prolactin receptor.

Animals↗
PubMed1992

Thyroid hormone responsiveness of the L1210 murine leukemia cell line.

The presence of saturable and high affinity 3,5,3'-triiodothyronine (T3) binding sites was demonstrated in L1210 murine leukemia cell nuclei. Scatchard analysis revealed one class of receptors for T3 with Ka = 2.187 x 10(9) l/mol and a maximum binding capacity (Bmax) of 3.96 fmol/10(6) cells. The effects of T3 on protein phosphorylation and growth rate of L1210 cells were investigated in a medium containing T3-depleted fetal calf serum. T3 was observed to be effective in enhancing protein phosphorylation (153.06% +/- 5.99 SD) compared to cells grown in the absence of T3 (81.49% +/- 13.50 SD). Moreover, in the presence of high T3 concentration (11.15 nmol/l) T3 was found to significantly increase the cell growth rate. In addition, the T3 receptor-associated alterations during the cell cycle, as measured by flow cytometry, suggest that the presence of T3 receptors becomes evident during the late G1 phase of the cell cycle, and T3 receptor numbers increase during the S phase. These results suggest that in in vitro conditions representing high T3 concentration, the number of L1210 leukemia cells may be increased by T3 via nuclear receptors. The L1210 leukemia cell line may serve as a convenient tool for in vitro studies of nuclear receptors and/or mechanism of action of T3. The binding affinity of T3 receptors is similar to that found in rat hepatocytes or human lymphocytes.

Animals↗
PubMed1992

Effect of protease inhibitors and substrates on 3,5,3'-triiodothyronine binding to rat liver nuclear receptors.

The effect of protease inhibitors N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and N-carbobenzoxy-L-phenylalanine chloromethyl ketone (ZPCK) at concentrations ranging from 1.5 x 10(-6) mol/l to 1.5 x 10(-4) mol/l on the specific binding of 3,5,3'-triiodothyronine (T3) to rat liver nuclear receptors was evaluated. Both TPCK at 1.5 x 10(-5) mol/l (P < 0.001) and ZPCK at 1.5 x 10(-6) mol/l (P < 0.05) showed the inhibition of T3 binding to nuclear receptors. The evaluation of T3 binding data following separation of unbound TPCK from treated nuclear receptors on a Sephadex G-25 column showed that the inhibition of T3 binding was irreversible, since a substantial decrease of the equilibrium association constant (Ka) was found when compared to the mock samples lacking TPCK. In addition, similar inhibitory effect on T3 specific binding to rat liver nuclear receptors was found at 5.0 x 10(-4) mol/l by protease substrates L-tyrosine benzyl ester (P < 0.001), L-tyrosine ethyl ester (P < 0.02), L-tryptophan methyl ester (P < 0.02) and L-tryptophan ethyl ester (P < 0.05). The data suggest that: 1. both protease inhibitors and substrates tested inhibited T3 specific binding to T3 nuclear receptors; 2. this may support the hypothesis that T3 receptors like other receptors encoded by c-erbA gene possess a site that recognize both serine protease inhibitors and substrates in its hormone binding domain.

Amino Acid Chloromethyl Ketones↗
PubMed1992

Effect of triiodothyronine on rat liver polysome profiles and translational activity of mRNA after partial hepatectomy.

The administration of 3,5,3'-L-triiodothyronine (T3) (200 micrograms/100 g) to rats immediately after partial hepatectomy led to an increase in total polysome content of residual hepatocytes (as measured 18 h postoperatively) which exceeded that observed after partial hepatectomy in the absence of hormone. The percentage of free ribosome pool remained the same after partial hepatectomy irrespectively on the absence or presence of T3. After partial hepatectomy the sedimentation pattern of total polysomal fraction (isolated 18 h postoperatively) shifted towards smaller aggregates as compared with that isolated from sham operated animals. T3 did not affect this pattern. The translational capacity of mRNA isolated from regenerating liver after 18 h was higher than that of mRNA isolated from sham operated animals. T3 increased the translational capacity of mRNA isolated from regenerating liver if administered immediately after surgery. Two dimensional electrophoresis of translated products showed that one of the typical proteins recently characterized with Mr 25,000 pI 6.9 appeared after partial hepatectomy and was significantly increased when T3 was administered immediately after surgery. These results show that thyroid hormone can enhance some of the characteristics features of liver regeneration involved in the synthesis of proteins typical for the process of liver regeneration.

Animals↗
PubMed1991

Qualitative changes of total cytoplasmic RNA size patterns in estrogen-induced adenoma in female rats.

Estradiol was administered 2.5 mg once a week for 4, 8 and 16 weeks to female Wistar rats. Hyperprolactinemia corresponding to the size of the pituitary developed along the pituitary enlargement after 4 weeks and macroscopically apparent pituitary adenomas after 8 and 16 weeks of treatment. The total pituitary cytoplasmic RNA was isolated from treated and control animals and the size distribution pattern of total RNA was obtained by sucrose gradient centrifugation. Estrogen treatment did not change that pattern in the first 4 weeks of treatment, but considerable RNA size distribution changes mainly in the medium size molecular range occurred after 8 and 16 weeks of estrogen administration. It can be hypothesized that an effect of estrogens on pituitary lactotroph hypersecretion and proliferation is not identical with events of irreversible adenomatous cell transformation which occurs later on during chronic estrogen administration.

Animals↗
PubMed1991

Partial hepatectomy alters serum hormone levels in rats.

The level of thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), thyroxine (T4), 3,5,3'-L-triiodothyronine (T3), corticosterone, testosterone and insulin in serum were measured at 1, 12, 48 and 120 h after partial hepatectomy (PH) or sham operation in rats. After PH the level of ACTH and corticosterone was significantly elevated while that of TSH, T4 and testosterone was decreased and returned to the values found in sham operated animals within 5 days. The level of T3 was unchanged. These results show an increase in the function of pituitary-adrenal axis and a decrease in that of pituitary-thyroid axis shortly following PH with the tendency to return to normal function within five days.

Adrenocorticotropic Hormone↗