Effects of Estradiol and Nicotinamide Adenine Dinucleotide Phosphate on the Rate of Synthesis of Uterine Glucose 6-Phosphate Dehydrogenase

Effect of estradiol and progesterone on long chain fatty acyl-coenzyme A levels in the rat uterus

Fatty acyl-CoAs are potential in vivo inactivators of glucose-6-phosphate dehydrogenase (G6PD). Ovariectomized mature rats (n = 74) were given 5 micrograms of estradiol intravenously, then killed 0, 24, 36, 48 and 72 h later. Control levels of myristoyl-, palmitoyl-, stearoyl-, arachidonoyl-, oleoyl- and linoleoyl-CoA were 0.6, 3.2, 4.7, 3.4, 2.4 and 3.0 micrograms/uterus and were increased 39, 110, 146, 100, 84 and 69% at 36-48 h, respectively. Levels of fatty acyl-CoAs in the rat uterus become elevated 36 h after estradiol treatment. At the same time G6PD changes from a stable enzyme to one that is irreversibly inactivated, possibly due to being rapidly degraded. Progesterone (2 mg subcutaneously every 12 h, n = 30), administered beginning at either 24 or 36 h after estradiol treatment, had no effect on estradiol-induced changes in myristoyl-, palmitoyl-, or stearoyl-CoA. Compared to the groups of rats treated with estradiol alone, animals treated with combinations of estradiol and progesterone exhibited higher levels of arachidonoyl-CoA after 48 h, and oleoyl-CoA and linoleoyl-CoA were greater after 72 h. Progesterone increased the estradiol-induced levels of unsaturated fatty acyl-CoAs suggesting that progesterone may induce uterine fatty acid desaturase activity and/or uptake of dietary fatty acids. Addition of fatty acyl-CoAs, at concentrations seen in vivo at 36-48 h after estradiol, to purified G6PD, causes irreversible G6PD inactivation.

The pentose phosphate pathway in skeletal muscle under patho-physiological conditions. A combined histochemical and biochemical study

Over the last 30 years, research into the neuromuscular apparatus, has expanded greatly. Multidisciplinary investigations have rapidly advanced our understanding both of diseases and of the basic neuromuscular mechanisms. The mode of pathological reaction of the neuromuscular apparatus is now quite well understood. The most notable aspect of the reaction of the injured neuromuscular apparatus is the remarkably stereotyped character of the resulting pathological changes as demonstrated by a wide variety of harmful causes, producing surprisingly similar effects. The findings of our combined histochemical and biochemical investigations presented in this monograph, are in complete harmony with the stereotyped character of the pathological changes. For example, it is particularly striking that many affected muscle fibres of patients with muscular dystrophies, congenital myopathies, inflammatory myopathies, metabolic myopathies, endocrine myopathies, or with diseases of the lower motor neuron, display an enhanced activity of both oxidative enzymes of the pentose phosphate pathway. Likewise, we found that experimental animals with disordered skeletal muscles, provoked by different types of agents or treatments, reveal the same marked rise in activity of GPDH and PGDH in the muscle fibres, with a positive correlation between the activity of both enzymes. Other findings of our investigations point to a positive correlation between the activity of GPDH and PGDH on the one hand and that of the non-oxidative enzymes of the pentose phosphate pathway, the enzymes TA, TK, RPI and RPE on the other hand. The rise in activity of PGDH and, in particular, of GPDH is regulated by two different mechanisms. The first represents a rapid control mechanism based on the stimulation of both oxidative enzymes of the pentose phosphate pathway by NADP+ and on their inhibition by NADPH. The other mechanism represents a long-term effect directed at the synthesis of the enzymes. It is this type of mechanism which is responsible for the rise in activity of GPDH and PGDH we observed. The findings obtained with the applied enzyme histochemical techniques clearly demonstrated that the rise in activity of both enzymes is not homogeneously distributed in the disordered skeletal muscles of man and experimental animals. For that reason, in order to obtain reliable quantitative information about enzyme activities in the muscle fibres themselves, the application of biochemical assays on a micro-scale was indispensable. The biochemical assay of enzyme activities was performed on histologically and histochemically selected dissected muscle specimens.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of hepatic glucose-6-phosphate dehydrogenase activity in male and female rats by estrogen

The effect of estradiol-17 beta on the activity of glucose-6-phosphate dehydrogenase was studied in both male and female rats to further characterize the sex differences in the activity of this enzyme. Four groups of intact and castrated rats were implanted subcutaneously with graded doses (2.4, 4.8 and 7.2 micrograms/day) of pelleted estradiol in a physiologically relevant experimental system. After fourteen days the rats were sacrificed and their livers were assayed for G6PD activities. The result indicated that: (i) the enzyme activity was 3-fold higher in normal adult female than in male rats, (ii) low doses of E2 (2.4, 4.8 and 7.2 micrograms/day) increased the activity of G6PD 6-fold in castrated males and over 2-fold in female castrates as well as intact rats (iii) E2 stimulation of G6PD activity appears to be more effective in castrated males than in female rats (IV) sex difference in the activity of G6PD disappeared after treatment with E2 in castrated rats. It is concluded that the activity of G6PD in rats is markedly enhanced by low doses of E2, which appears to be largely responsible for the sex differences in the activity of this enzyme in rats.

Estradiol regulation of reactions involved in turnover of the amino acid acceptor terminus of tRNA in the rat uterus

Estradiol (E2) increases the specific amino acid acceptor activity of rat uterine tRNAs by increasing the proportion of certain tRNAs with intact and functional 3'-CCA acceptor termini. Activities of tRNA nucleotidyltransferase and 3'-exoribonuclease which synthesize and degrade this terminus, respectively, were measured and neither enzyme was modified by hormone treatment. Since cytidine triphosphate (CTP) levels are below reported Km values for nucleotidyltransferase, changes in CTP concentrations may regulate nucleotidyltransferase activity. An E2-induced 3-fold increase was seen in CTP synthetase activity (conversion of uridine triphosphate, UTP, into CTP). Uterine CTP levels in controls are minute (9 nmol/uterus, approx. 90 microM), and are increased 2.5-fold in E2(12 h)-treated rats. The rate of incorporation of [3H]UTP into the 3'-CCA terminus of tRNA was measured as coupled CTP synthetase-nucleotidyltransferase reactions and a 2.5-fold increase in incorporation occurred 8-12 h after E2 treatment. Injection of azaserine, (inhibitor of CTP synthetase) reduced E2-induced increases in CTP levels, CTP synthetase activity, and leucine acceptor activity of tRNAs. These results indicate that E2 regulates CTP levels by modulation of CTP synthetase activity, and that regulation of synthesis and/or repair of the 3'-CCA terminus of tRNA is proportional to E2-induced uterine cytosolic CTP levels.

Enzyme activities in the androgenized rat uterus refractory to oestrogenic stimulation

Uterine enzymes involved in the intermediary metabolism of glucose have been measured in the androgenized rat in which there is evidence of diminution of the oestrogenic responses despite raised glycogen and glucose typical of maximal oestrogenic stimulation. Phosphofructokinase and isocitrate dehydrogenase (NADP, cytosolic) activities were significantly decreased in the androgenized rat and were elevated following treatment with natural progesterone and synthetic progestins which partially reverse the uterine abnormalities of the androgenized rat. Mitochondrial protein was decreased in the uterus of the androgenized rat but there was an apparent sparing effect on isocitrate (NAD) and malate (NAD) dehydrogenase. The data suggest that selective effects on specific enzymes involved in intermediary metabolism are a feature of the refractory state associated with constant oestrogenic stimulation. The possible cellular mechanisms underlying these effects are discussed.

Isolation of a precursor and a nascent chain form of glucose-6-phosphate dehydrogenase from rat uterus and regulation of precursor processing by estradiol

SDS-polyacrylamide gel electrophoresis of anti-glucose-6-phosphate dehydrogenase immunoprecipitates from radiolabeled uterine tissue extracts previously revealed three proteins: A, B and C, which were tentatively identified as a 60-64 kDa precursor form, a 57 kDa predominant form, and a 40-42 kDa nascent peptide form of the enzyme, respectively. A peptide-mapping technique was used to examine structural homologies among A, B and C. Following the labeling of uterine proteins with [35S]methionine, labeled proteins A, B and C were isolated by immunoprecipitation and electrophoresis. Each protein was individually co-digested with authentic, [3H]methionine-labeled glucose-6-phosphate dehydrogenase using papain, the resulting peptides were resolved by isoelectric focusing and the peptides from the two sources on each gel were compared using double-label counting methods. Proteins A, B and C had at least eight peptides in common, both proteins A and C had two additional peptides in common that were not present in protein B, and B protein had two peptides that were either absent or present in reduced amounts in digests of proteins A and C. The extensive structural homology and immunoreactivity of these proteins indicated that proteins A, B and C were all related to glucose-6-phosphate dehydrogenase. The presence of two extra peptides in proteins A and C suggested that these peptides may be derived from a common NH2-terminal leader sequence which was present in both the precursor and nascent peptide chains. The presence of two peptides that were present in protein B and absent from proteins A and C is easiest to explain if they are derived from the two ends of the molecule, with the corresponding peptides in proteins A and C containing additional peptide sequences that are 'normally' removed by endogenous proteolytic processing enzymes. Based on the relative time-course of synthesis of the three glucose-6-phosphate dehydrogenase-related proteins in control and estrogen-treated uteri, it appears that estradiol promotes an increase in the relative rate of transfer of label from protein A into B by stimulating the rate of processing of the precursor to the predominant form of the enzyme and enhances the rate of translational conversion of protein C into higher molecular weight forms.

The inhibitory effect of actinomycin D and cycloheximide on the increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in experimentally induced diseased skeletal muscles

The myotoxic effect of the subcutaneous administration of N,N1-dimethyl-p-phenylenediamine (DPPD) in rats was enhanced by the simultaneous administration of hyaluronidase. The resulting myopathy was associated with an early and dramatic increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Administration of actinomycin D or cycloheximide prior to the combined DPPD and hyaluronidase treatment prevented the increase in activity of both pentose phosphate pathway enzymes, indicating that the increase in activity requires RNA synthesis and protein synthesis. The possibility that the increase in activity of both NADPH-regenerating enzymes results from the modification by effectors of existing less active forms of these enzymes leading to more highly active forms was refuted.

Glucose-6-phosphate dehydrogenase: partial characterization of the rat liver and uterine enzymes

Some properties of rat liver and uterine glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP+ oxidoreductase, EC 1.1.1.49) have been determined. A procedure has been used for the purification of rat liver glucose-6-phosphate dehydrogenase to homogeneity (spec. act. 210-225 units/mg protein) from large amounts of liver (0.5-2 kg) with yields of up to 30%. Uterine glucose-6-phosphate dehydrogenase was obtained by immunoprecipitation methods and the properties of radioactively-labeled forms of this enzyme were then determined. The amino acid composition of the liver enzyme was found to be similar to that for the enzyme from other mammalian tissues. The liver and uterine enzymes have a subunit molecular weight of 57000 and a pI of 6.5. The NH2-terminal amino acid of both enzymes was found to be pyroglutamate.

The increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in skeletal muscles of rats after subcutaneous administration of N,N'-dimethyl-para-phenylenediamine

After subcutaneous administration of N,N'-dimethyl-para-phenylenediamine (DPPD) in rats, a myogenic myopathy was produced in the skeletal muscles. In this communication, the results of the application of various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases and biochemical techniques for the estimation of activities of oxidoreductases in the experimental skeletal muscles are presented. The most striking results was the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase which increased dramatically during the early phase of the muscle disease. The increase in activity of the pentose phosphate shunt enzymes was the first pathological alteration and was present as early as 8 h after a single injection of DPPD. Histochemical techniques for demonstration of activity of both enzymes are therefore highly suited for the detection of minor diseases and the early onset of major diseases of the neuromuscular system. Some glycolytic enzymes as well as some enzymes of the aerobic part of the metabolism showed an early decrease or increase in activity indicating a metabolic imbalance in the muscle fibres. There were more fibres with an intermediate pattern of the energy yielding enzymes in the experimental muscle specimens then in specimens from the control groups. The activity of the catabolic hydrolytic enzymes was strongly increased in pathological muscles. The aerobic muscles were more vulnerable to DPPD than the anaerobic muscles.

Isolation of ribonuclease-free polysomes from human placenta

Human placenta is known to have a high level of polysome-bound ribonuclease which has hindered the isolation of intact polyribosomes from this tissue. We describe conditions for preparing polysomes devoid of apparent ribonuclease activity from both first trimester and term placenta. This stable preparation was achieved by utilizing buffer at low pH containing 300 mM LiCl and precipitating the polysomes chemically with 200 mM MgCl2. The yield of polysomes obtained by this procedure is 2-2.5 fold greater than that obtained by the conventional method of preparing placental polysomes. The polysomes are considered pure as judged by the ratios of absorbance 260/280 and 260/235. Moreover, the yield of polysomes obtained is greater than 95% of the tissue content and the profile of the polysomes is probably representative of the in vivo population. This is concluded from experiments in which a known amount of labelled chick polysomes was added to fresh placental tissue and the recovery of label and its distribution was analyzed.

Effect of sex hormones on glucose-6-phosphate dehydrogenase in rat levator ani muscle

We studied the influence of sex hormones using the hormone-sensitive levator ani muscle as a model tissue and glucose-6-phosphate dehydrogenase as an indicator of hormone action. Injection of testosterone or estradiol cause a 50% increase in the specific activity of glucose-6-phosphate dehydrogenase. The effect was dose-dependent, and was maximal at a dose of 2.5mg/100g body weight. Estradiol increased glucose-6-phosphate dehydrogenase as early as 8 h after injection, while testosterone required 12 h. Injection of estradiol on 2 successive days increased enzyme activity by 80%. The effect of estradiol was abolished by actinomycin D, suggesting enzyme induction. The results indicate a direct effect of estrogen on striated muscle.

Effect of estrogens on glucose phosphate dehydrogenase activity of liver and oviduct in the amphibian Bufo arenarum

Glucose- 6phosphate dehydrogenase (G-6PDH) stimulation by estradiol- 17beta has been studied in oviduct and liver of Bufa arenarum. OviducalG-6PDH has been found to be stimulated by a single dose of estradiol- 17beta (100 mug/100 g body weight), the stimulation being dependent on season. Hepatic G-6PDH of females is susceptible to hormonal stimulation, without seasonal variation, while in males the enzymatic activity is not modified under the same conditions. The stimulating effect of estrogen on oviducal and hepatic G- 6PDH was inhibited by Actynomicin D. The susceptibility of G- 6PDH to estrogenic action would assure NADPH production, indispensable for the biosynthesis of lipids which are required for cell growth and for hepatic vitellogenesis.

Effect of sodium fluoride on glucose-6-phosphate dehydrogenase activity in the rat uterus

Intrauterine administration of 50 mumol of NaF to the ovariectomized mature rat causes a 2--3-fold increase in the total uterine glucose-6-phosphate dehydrogenase activity within 24 h. The response is characterized by a 4--6 h lag with a maximum effect from 24 to 36 h after a single treatment. Uterine glucose-6-phosphate dehydrogenase activity continues to increase with daily administration of NaF through 4 days. The NaF-induced response is blocked by prior intrauterine administration of cycloheximide but not actinomycin D suggesting that the enzyme activity increases by a post-transcriptional effect of NaF on de novo enzyme synthesis. Direct measurement of the effect of NaF on the rate of incorporation of [14C] leucine into immunoprecipitable uterine glucose-6-phosphate dehydrogenase indicates that NaF causes a 9-fold increase in the rate of enzyme synthesis during the interval from 12 to 16 h after treatment. The half-life of the enzyme as measured by the rate of loss of [1-14C] glutamate from previously labeled utreine glucose-6-phosphate dehydrogenase is decreased from 27 to 10 h by NaF. The NaF response does not seem to be mediated by activation of uterine adenylyl cyclase since theophylline does not potentiate the response and since intrauterine application of cyclic AMP does not mimic the response. The increase in enzyme activity is preceded by an increase in the rate of utilization of the hexose monophosphate shunt pathway as determined by the ratio of the the rates of oxidation of [1-14C]glucose to [6-14C] glucose to CO2 by uterine slices in vitro. The action of NaF on this pathway most likely resutls from inhibition of the glycolytic enzyme, enolase, and increased pathway utilization may be the factor which controls enzyme synthesis. When given in combination with other known inducers of uterine glucose-6-phosphate dehydrogenase such as estradiol and NADP+, NaF acts synergistically.

A significant lag in the induction of ovalbumin messenger RNA by steroid hormones: a receptor translocation hypothesis

Although ovalbumin and conalbumin mRNA accumulate in the same tubular gland cells of the chick oviduct in response to estrogen or progesterone treatment, the kinetics of induction are markedly different. Conalbumin mRNA begins to accumulate within 30 min after estrogen administration, whereas there is a lag of approximately 3 hr before ovalbumin mRNA begins to accumulate, as measured by three independent assays. The kinetics of estrogen-receptor binding to chromatin indicate that these sites are saturated within 15 min of estrogen administration to the chicks, demonstrating that the lag is not due to slow uptake of the steroid. Suboptimal doses of estrogen produce the same lag, but the resultant rate of ovalbumin mRNA accumulation is lower than with an optimal dose. Partial induction of ovalbumin mRNA by a low dose of estrogen does not shorten the lag with an optimal dose. With progesteone, there is a lag of about 2 hr before either ovalbumin or conalbumin mRNA begins to accumulate. Treatment of chicks with hydroxyurea shortens the lag for ovalbumin induction with either hormone. Inhibition of protein synthesis with emetine does not prevent the accumulation of either ovalbumin or conalbumin mRNA. With cycloheximide, however, ovalbumin mRNA accumulation can be prevented. The existence of a lag suggests that there are intermediate steps between the binding of steroid receptors to chromatin and the induction of ovalbumin mRNA. There are basically two models to explain these delays in response: one involving the accumulation of an essential intermediate, and the other involving a rate-limiting translocation of steroid receptors from initial nonproductive chromatin-binding sites to productive sites. Several aspects of the kinetics of ovalbumin mRNA induction are more consistent with the latter model.