The determination of nucleic acids

Alterations in nuclear anatomy by chemical modification of proteins in isolated rat liver nuclei

Whole rat liver nuclei were treated with citraconic anhydride, a reagent specific for primary amines. Dramatic changes were observed in nuclear morphology and light scattering properties. An analysis for DNA and RNA content suggested that DNA was released from the nuclei with a short half-time, approximately 2-4s demonstrating a biphasic release profile. RNA was similarly released but with a monophasic profile. Analysis of SDS-PAGE gels of modified nuclei demonstrated a progressive enrichment of nuclear matrix (lamins) polypeptides with extent of modification. H1 histone was quantitatively lost as a function of modification reagent concentration, while approx. 50% of the nucleosomal histones cosedimented with DNA- and RNA-free nuclei. Modification in the presence of 2 mM EGTA released all the DNA and RNA [less than or equal to 1% remaining) while retaining structures characteristic of nuclear matrix, nucleoli, and ribonucleoprotein (predominantly hnRNA group A and B). These nucleic acid-deficient structures have been termed nuclear fossils to differentiate them from high salt detergent-prepared empty nuclear sacks, nuclear remnants, or nuclear scaffolds. Modification in the presence of 2% Triton X-100 results in structures similar to the nuclear fossils (EGTA treatment), but missing the double bilayer and a 51K polypeptide that is a major component of the other structures. The use of chemical modification on the nucleus provides an experimental approach for examining the role of ionic interactions in controlling nuclear structure. Citraconylation may thus serve two functions: (a) as a protein-specific perturbant of nuclei capable of simply and rapidly preparing a range of structural variants for the analysis of nuclear interactions; (b) offer a paradigm for control of nucleic acid-polypeptide interactions based on post-translational alterations in protein charge.

Histone-like protein in the Archaebacterium Sulfolobus acidocaldarius

The Archaebacterium Thermoplasma acidophilum contains a basic chromosomal protein remarkably similar to the histones of eukaryotes. Therefore, it was of interest to examine a different Archaebacterium for similar proteins. We chose to examine Sulfolobus acidocaldarius because it is thermophilic, like T. acidophilum, but nevertheless the two organisms are not particularly closely related. Two major chromosomal proteins were found in S. acidocaldarius. The smaller of these was soluble in 0.2 M H2SO4 and had a molecular weight of 14500. The larger was acid-insoluble and had a molecular weight of about 36000. Together, the proteins protected about 5% of the DNA against nuclease digestion and stabilized about 50% against thermal denaturation. Overall, the properties of these proteins were intermediate between those of the Escherichia coli protein HU and T. acidophilum protein HTa.

Increased renal DNA synthesis in vivo after administration of low doses of gentamicin to rats

Kidney cortex DNA synthesis was studied in female rats treated with a low dose of gentamicin (10 mg/kg) up to 14 days. Synthesis was measured by incorporation of [3H]thymidine into DNA 1 h after intraperitoneal injection of the labeled precursor (200 muCi per animal). Gentamicin given in one injection per day resulted in a greater incorporation of [3H]thymidine into DNA after both 7 and 14 days of treatment as compared with control animals. When the daily dose was divided into three equal injections given at 8-h intervals, a statistically significant increase in thymidine incorporation was observed as early as 4 days after starting gentamicin administration. Excellent agreement was found between DNA specific radioactivity and kidney cortex nuclear labeling, as measured by histoautoradiography. The greatest amount of [3H]thymidine incorporation occurred within proximal tubular cells and interstitial cells. We conclude that a finite duration of gentamicin treatment at low dosage induces an increased DNA synthesis in vivo in rat kidney cortex. We suggest that this reaction results from cellular proliferation and could reflect a regenerative process after focal necrosis induced by gentamicin at low doses. The demonstrated early increase in DNA synthesis could be a useful tool to measure kidney cortex alterations caused by various aminoglycosides at low, therapeutic doses.

The neurotoxicity of aflatoxin B1 in the rat

The effects of repeated intraperitoneal administration of aflatoxin B1 on the peripheral and central nervous systems of rats were investigated. Biochemical markers of neurotoxicity were monitored in nervous tissues following aflatoxin B1 dosage and after the cessation of aflatoxin B1 administration. Aflatoxin B1 increased the activities of beta-glucuronidase and beta-galactosidase in the central and peripheral nervous systems. Repeated exposure of rats to aflatoxin B1 also activated Na+ K+-ATPase and inhibited Mg2+-ATPase. Nervous tissue levels of DNA and total protein increased while the concentrations of RNA and phospholipid were depressed by aflatoxin B1. The alterations in these parameters were specific for each of the tissues examined during the recovery of the rats. The findings indicate that the repeated administration of aflatoxin B1 to rats results in degeneration in the central and peripheral nervous systems that may be related to the overt toxicity observed following aflatoxin administration.

Inhibition of rat embryonic development by the intrauterine administration of alpha-difluoromethylornithine

Decarboxylation of L-ornithine by L-ornithine decarboxylase (ODC; E.C.4.1.1.17.) is the initial step in the biosynthesis of putrescine, ODC activity is generally low in most tissues, marked increases are associated with rapid tissue growth and particularly with mammalian embryogenesis. 0.5 mg/kg of DL-alpha-difluoromethylornithine (DFMO) (irreversible inhibitor of ODC) was administered to uterine horns of Long-Evans adult rats during the 4th day of pregnancy. As control material, saline (0.15 M) was administered to contralateral uterine horn. The animals were sacrificed on different days, the uterine horns were removed and the number of implant of implanted embryos were counted. DNA, RNA, protein and dry weight content in implantation sites (5th day of pregnancy) indicated that decidualization following DFMO took place normally but that embryonic growth was arrested in the treated horn. When 100 micrograms of putrescine were added together with DFMO, the embryotoxic effect was absent.

Synaptonemal complexes are integral components of the isolated mouse spermatocyte nuclear matrix

Synaptonemal complexes (SCs) have been isolated as integral components of the nuclear matrix from purified mouse pachytene spermatocytes. These nuclear synaptonemal complex-matrices are prepared by extracting Triton X-100-treated nuclei with low (0.2 M) and high (1.0 or 2.0 M) NaCl, DNase I, and RNase A to remove 85% of the nuclear proteins, 97% of the RNA, and 99% of the DNA. Studies with the light and electron microscopes indicate that these matrices, while lacking a distinct lamina, contain nuclear pores interconnected by a fiber network, residual nucleoli, and interchromatin fibers. In addition, the pachytene spermatocyte matrices contain residual XY heterochromatin and the principal components of the SCs, including two lateral elements, a central element, a presumptive centromere, and attachment plaques. These SCs are preserved within the matrix and retain their structural association with the pore-fiber complex, even when subjected to strong dissociating conditions. Nuclear matrices from pachytene spermatocytes and spermatids (steps 1-8), when analyzed by SDS PAGE, contain an array of polypeptides distinct from those of mouse liver nuclear matrices. Proteins of spermatogenic matrices range in Mr from 8,000 to approximately 150,000. The prominent lamina proteins (Mr approximately 60,000-70,000) of somatic nuclear matrices are either absent or represent only a minor part of the spermatogenic matrix. The polypeptide composition of the pachytene spermatocyte and spermatid matrices are similar, although minor quantitative and qualitative differences are evident. These observations suggest that the SC constituents may consist of a heterogeneous group of proteins present in low proportion relative to total matrix proteins, or they may be retained, but in a different form, within the spermatid matrix.

Benzylamine oxidase in normal and atherosclerotic human aortae

Assays of serum benzylamine oxidase (BzAO) have led some workers to postulate a relationship between elevated BzAO activity and diseases characterized by proliferating connective tissue. The present study was designed to determine whether BzAO activity of a cellular tissue is also affected. BzAO was assayed in homogenates of normal and atherosclerotic human aortae. Characterization done in normal aortae showed that BzAO is not a classical monoamine, diamine, polyamine, or lysyl oxidase, nor is it a ceruloplasmin. The enzyme is heat stable at 60 degrees C and is associated primarily with the microsomal fraction on density centrifugation. Compared with phenylethylamines and indoleamines, benzylamine is the best substrate. BzAO is sensitive to inhibition by hydrazines and chymotrypsin but not trypsin, and is insensitive to Triton X-100 and sulfhydryl-group blockade. BzAO activity of atherosclerotic plaque (expressed per gram wet weight or per milligram protein) was decreased markedly compared to that in adjacent, nonplaque regions and in normal aortae. However, on a per milligram DNA basis, the BzAO activity of plaque did not differ from that of nonplaque tissue. We conclude that there is a decreased cell population density in plaque, a contention supported by kinetic analysis. Plaque BzAO showed a decreased Vmax with no change in the Km of benzylamine compared with nonplaque tissue. Thus, if a relationship exists between BzAO activity and proliferating connective tissue, it is not apparent at the level of the cellular enzyme in atherosclerotic aortae of man.

Activities of key enzymes in relation to glucose flux in tumor-host livers

1. Isotope and non-isotope methods were used to study hepatic metabolism of glucose in tumor-host livers. 2. Glycogen synthase, phosphofructokinase activities (Vmax) were decreased, while glucose-6-phosphate dehydrogenase and lactate dehydrogenase activities were increased in tumor-host livers. 3. Glycogen phosphorylase, glucokinase and several mitochondrial enzymes, had normal maximum activity in tumor-host livers. Net flux of glucose was decreased in the Embden-Meyerhof and the pentose phosphate pathway in tumor animals. 4. The hepatic cycling of glucose-carbons in tumor animals was significantly decreased as shown by different [14C] [3H] ratios of radioactivity in RNA and lactate, determined from simultaneous incorporation of [U-14C]glucose and [2-3H]glucose. 5. This study demonstrates that previous reports of increased activities of rate limiting enzymes of glucose metabolism in tumor-host livers do not represent a general finding of high glucose metabolism in tumor-host livers.

Comparative changes in the 32P labeling of adenine and uracil nucleotides in the hypertrophying rat heart

The turnover of cardiac adenine and uracil nucleotides was studied in the hypertrophying rat heart by means of the kinetics of incorporation of labeled phosphate into the alpha-phosphate groups of nucleotides. Cardiac hypertrophy was induced either by chronic isoproterenol treatment (5 mg X kg-1 body wt. daily, s.c.) or by abdominal aortic constriction. In both experimental models, although the labeling of alpha-P groups of adenine nucleotides was at first unmodified, the incorporation of [32P]Phosphate into uracil nucleotides was accelerated early and the stimulation maintained for several days. The intramyocardial concentration of UTP and uracil nucleotides rose during the early phase of hypertrophy, while the ATP and adenine nucleotide pools were depleted. All of these alterations were more pronounced in isoproterenol-treated animals than in those with aortic stenosis. In this experimental model (isoproterenol treatment), the hypertrophy develops faster and is accompanied by a larger increase in cardiac RNA concentration. Thus, the increase in the rate of synthesis of uracil nucleotides may be interpreted as an adaptative change of nucleotide metabolism in response to an increased requirement of precursors for RNA synthesis. The possible limiting role of pyrimidine nucleotides in the hypertrophic process is discussed.

Effects of toxic doses of urethane on rat liver and lung microsomes

Administration of carcinogenic doses of urethane to male rats (for 30 days) and to females (for 45 days) caused degranulation of microsomes of livers and lungs to approx. 15 and 35%, respectively. The cholesterol levels also declined more than 50% in urethane-treated rats when compared with controls. Studies on structural components of microsomes have shown that urethane administration causes the depletion of phosphatidylinositol, phosphatidylcholine and phosphatidylethanolamine in microsomal preparations from lungs and livers with a concomitant loss of neutral lipids in lung microsomes. SDS gel electrophoresis has shown that with the administration of urethane, new proteins appeared in microsomal preparations from lungs whereas in livers disturbances in protein levels were observed.

Metabolism of 1,2-dimethylhydrazine by cultured rat colon epithelial cells

The colon carcinogen 1,2-dimethylhydrazine (DMH) was cultured with rat colon epithelial cells to determine if these cells have the ability to metabolize DMH. Colon epithelial cells isolated from conventional and germfree Sprague-Dawley rats were incubated in CMRL 1066 supplemented medium containing 14C-DMH. Cells from both groups of rats metabolized DMH to gaseous metabolites, to metabolites in the medium that were putatively identified as azoxymethane and methylazoxymethanol, and to products that bound to DNA. Cells from germfree rats metabolized DMH at an equal or greater rate than cells from conventional rats for the criteria examined. This report demonstrates that rat colon epithelial cells can metabolize DMH without previous metabolism by other tissues or colon bacteria.

Biologic activity and quantification of messenger RNA coding for human chorionic somatomammotropin in normal and intrauterine growth--retarded pregnancies

Total ribonucleic acid (RNA) from human placentas obtained from normal and intrauterine growth--retarded (IUGR) pregnancies was translated in a reticulocyte cell--free system. Synthesis of human chorionic somatomammotropin (hCS) was estimated as a ratio of specific immunoprecipitated protein over total newly synthesized proteins. There is no significant difference between in vitro hCS synthesis directed by placental RNA from normal and IUGR pregnancies. Measurements of messenger RNA sequences coding for hCS, with a hCS complementary DNA probe, indicated that the hCS messenger RNA (mRNA) concentrations were similar for both groups. Low plasma hCS levels in pregnancies associated with growth-retarded fetuses can be explained by their significantly lower placental weights which correlate with their total RNA content. The total capacity of in vitro hCS production per placenta is significantly lower in this type of abnormal pregnancy. There is a good parallelism between the amount of hCS mRNA, its biologic activity tested in a cell-free system, and the secretion of hCS in the maternal circulation. These data suggest that there is no basic intracellular disturbance in hCS synthesis in placentas from fetal growth--retarded pregnancies.

Liver hypertrophy in winter flounder following exposure to experimentally oiled sediments

1. Male winter flounder were exposed to sediments contaminated with Venezuelan crude oil in 3 laboratory experiments of 4-5 months duration. 2. Oil exposure resulted in significant increases in liver weight. This was particularly evident in fish weighing less than 400 g. 3. The enlarged livers of the oil-exposed flounder had reduced concentrations of DNA, protein, Na+ and Zn2+, and increased concentrations of lipid and phospholipid. 4. The reduced DNA and Na+ concentrations suggested liver hypertrophy rather than hyperplasia. 5. The increased phospholipid concentrations suggested growth of membrane structures such as endoplasmic reticulum.

Pregnancy stimulates DNA synthesis in R3230AC mammary adenocarcinoma

The transplantable R3230AC mammary adenocarcinoma was grown in virgin, pregnant and lactating rats and in vivo rates of [3H]-thymidine incorporation into DNA and acid-soluble dTTP were compared between tumor and host mammary glands. The tumor differed from the host gland in that the rates of uptake and phosphorylation of the injected thymidine remained unchanged throughout the lactation cycle, but the dTTP pool increased greatly during pregnancy and declined during lactation. In both tumor and host gland, DNA labeling rates were higher during pregnancy than during lactation. Tumor DNA synthesis rates, in terms of incorporated dTMP, increased markedly during pregnancy and returned to pre-pregnant rates following parturition and during lactation. This pattern was similar to host mammary glands, but the change was of a greater magnitude. The data illustrate the usefulness of growing a transplantable mammary tumor in rats of varying physiological states. This way, similarities and differences between a mammary tumor and the host mammary gland regarding their responses to the hormonal milieu of pregnancy and lactation can be assessed.

Quantitative liver functions after 70% hepatectomy

Following 70% hepatectomy on rats the galactose elimination capacity, taken as a measure of the cytosolic liver function, was reduced from 2.55 +/- 0.48 to 1.27 +/- 0.19 (mean +/- SEM) mumol/min. Six hours later it was restored to control values. The prothrombin index, representing the function of the endoplasmic reticulum, was reduced from 1.13 +/- 0.02 to 0.34 +/- 0.02 (arbitrary units) after 12 h, and it was restored after 96 h. The rapid normalization of the initial fall in the capacity to metabolize galactose reflects a two- to three-fold increase of the galactose metabolizing capacity of the remaining liver. This study demonstrates that liver functions are dissociated in time following 70% hepatectomy in the rat, and that the galactose elimination capacity is restored before regeneration can compensate for the loss in liver cell mass.

Distribution, quantification and biological activity of messenger RNA coding for human chorionic somatomammotropin during normal pregnancy

Synthesis of hCS by RNA fractions from human placentas obtained at different stages of pregnancy was estimated either by immunological or electrophoretical methods in wheat-germ and reticulocyte cell-free systems. hCS synthesis is preferentially associated with polyribosomes bound to the membrane of the endoplasmic reticulum, as is assumed for a secreted protein. In both translational systems we determined only one precursor form of this hormone of a molecular weight near 24 000. Full-term placentas synthesize hCS as the major protein. This conveniently allowed us to isolate the messenger RNA coding for the hormone and to synthesize a specific hCS complementary DNA which we used as a probe for quantifying sequences of RNA coding for hCS during pregnancy. In placentas from first-trimester pregnancy, the concentration of hCS mRNA was 4 times less than in the full-term organs, and the hCS synthesis per microgram of RNA added into the translational medium was diminished in the same order of magnitude. In placentas from second-trimester pregnancy, the concentration of hCS mRNA was similar to that obtained at term, and in vitro the hCS synthesis per microgram of translated RNA was also similar to that observed at the end of pregnancy. However, the hCS mRNA content per placenta from mid-term pregnancy was much lower than from full-term gestation. We established a good parallelism, as pregnancy progressed, between the hCS mRNA content, its capacity of hCS synthesis in vitro and the maternal plasma hCS level, indicating that hCS production is controlled essentially by the biological active mass of the placenta.

Alterations in glomerular RNA in diabetic rats: roles of glucagon and insulin

Incorporation in vivo of labeled orotate into RNA and total nucleotides was measured in isolated glomeruli and whole renal cortex. In 2-day diabetic animals, glomerular RNA was increased, and there was greater incorporation of orotate into total nucleotides and RNA as compared with controls. Insulin reversed the exaggerated incorporation at infusion rates that corrected hyperglucagonemia without reducing plasma glucose and with only minimal changes in insulin concentrations. The addition of glucagon to insulin infusions reproduced the increased incorporation observed in untreated diabetics. Similar changes occurred in renal cortex, where differences in orotate incorporation into nucleotide precursors seemed to be the main cause for alterations in RNA labeling. Isotope incorporation in glomeruli correlated positively with plasma glucagon, but not with insulin or glucose concentrations. Although in 7-month diabetic animals orotate incorporation into RNA was less than in controls, probably as a consequence of renal disease, 24-hour insulin infusion decreased it further. Our results confirm that in the diabetic kidney, abnormal uracil nucleotide metabolism and increased cellular content of RNA are demonstrable in glomeruli as in the renal cortex. These changes appear to be related directly to hyperglucagonemia.

Effect of polybrominated biphenyls on hepatic microsomal metabolism of estrogens and uterotropic action of administered estrogen in rats

Perinatal exposure to polybrominated biphenyls (PBBs) increased the hepatic microsomal metabolism of estradiol, estrone, and ethynylestradiol in vitro. Pretreatment with PBBs decreased the effect of estradiol administered exogenously on uterine estrogen cytosolic receptor concentration. The effect of exogenous estradiol on uterine weight and uterine RNA content was also reduced by perinatal exposure to PBBs. Therefore, metabolism of estrogens is altered by PBBs.

The effect of ethanol and acetaldehyde on DNA synthesis in growing cells and on fetal development in the rat

Incorporation of 3H-thymidine into DNA was significantly diminished by treatment with ethanol and acetaldehyde in regenerating rat liver, rat cells in culture, and rat fetal tissues. Reduced incorporation was especially marked in the fetal central nervous system and was observed with both compounds at levels similar to those reported to occur in human alcoholics. The reduced incorporation of 3H-thymidine into fetal DNA, together with the increased fetal mortality observed in dams treated specifically with acetaldehyde during pregnancy, suggests that acetaldehyde is implicated in the mechanism of teratogenesis associated with the fetal alcohol syndrome.

Isozyme differentiation of aldolase and pyruvate kinase in fetal, regenerating, preneoplastic, and malignant rat hepatocytes during culture

Aldolase and pyruvate kinase isozymes were investigated in cultured hepatocytes from fetal, regenerating, and 2-acetyl-aminofluorene-fed rat liver as well as in some epithelial liver cell lines. Our results show that: (a) cell proliferation and prolonged expression of specific isozymes were found only in cultured hepatocytes from 17-day old fetuses; (b) the fetal type of pyruvate kinase expressed in regenerating and carcinogen-treated liver was temporarily lost only in cultured hepatocytes from regenerating liver; (c) the adult type of aldolase and pyruvate kinase was absent in one epithelial cell line derived from a carcinogen-treated liver and in the hepatoma tissue cell (HTC) line but was found in the Faza clone of the Reuber H35 cell line during the 50 first passages in vitro; and (d) the isozyme pattern of pyruvate kinase was always more strongly shifted than that of aldolase. The observations suggest that: (a) hepatocytes from carcinogen-treated liver exhibit the same lack of ability to proliferate in primary culture as normal adult hepatocytes; (b) adult hepatocytes can produce fetal isozymes without prior cell division; (c) pyruvate kinase is a stronger marker of dedifferentiation (retrodifferentiation) than aldolase; and (d) regulatory processes of isozyme expression are different during ontogenesis, regeneration, and hepatocarcinogenesis.

Effect of triiodothyronine on renal growth and renal sodium reabsorption in hypothyroid rats

Experiments were carried out to compare temporal changes in the paraaminohippuric acid clearance (CPAH), renal sodium reabsorption (RNa+), ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) content in hypothyroid rats after a single injection of triiodothyronine (T3) (50 micrograms/100 g body wt). CPAH and RNa+ showed no changes at 24 and 48 h. At 72 h, however, significant increases of 41% and 42% (per g kidney wet wt) were observed in CPAH and RNa+, respectively. The cortex in T3-treated hypothyroid rats showed a significant increase in the protein/DNA and RNA/DNA ratios at 24 h and progressive increases to a level of 24%, and 37%, respectively, at 48 h. No changes in DNA content were observed at either time-points. The results show that the increases in RNA/DNA and protein/DNA ratios upon T3 treatment preceded the increases in CPAH and RNa+, suggesting a direct effect of T3 on renal cortical growth, rather than a secondary response to a primary increase in renal functions.

An enriched preparation of basal-lateral plasma membranes from gastric glandular cells

A procedure is described for the preparation of a membrane fraction enriched in basal-lateral plasma membranes from gastric mucosa. Gastric glands isolated from rabbit were employed as starting material, greatly reducing contamination from non-glandular cell types. The distribution of cellular components during the fractionation procedure was monitored with specific marker enzymes. (Na+ + K+)-ATPase, ouabain-sensitive K+-stimulated p-nitrophenyl-phosphatase and histamine-stimulated adenylate cyclase were used as markers for basal-lateral membranes. These three markers were similarly distributed during both differential and equilibrium density gradient centrifugation. The enriched membrane fraction contained more than 30% of the total initial activities of the three basal-lateral membrane markers which were purified better than 11-fold with respect to protein. (Na+ + K+)-ATPase activity was resolved from the activities of acid phosphatase, pepsin, Mg2+-ATPase, cytochrome c oxidase, NADPH-cytochrome c reductase, glucose-6-phosphatase, (K+ + H+)-ATPase, DNA and RNA.

Microsomal activation of chlordane isomers to derivatives that irreversibly interact with cellular macromolecules

Incubation of 14C-labeled cis and trans isomers of chlordane with cofactor-fortified mouse hepatic microsomes resulted in binding of insecticide-derived material to endogenous protein and RNA and to added DNA. The microsomes were prepared from male C57BL/6J mice. Chlordane is known to cause hepatocellular carcinoma in a similar strain. The highest concentrations of radioactive material bound to protein, followed by RNA and DNA. The cis isomer produced greater amounts of bound radioactivity, while binding from trans-chlordane was slight and, in the case of DNA, not detectable. Investigation of the effect of microsomal enzyme induction by chlordane isomers and phenobarbital on the yield of bound, chlordane-derived material gave mixed results. Generally, use of induced microsomes increased binding to protein and DNA and had no effect on binding to RNA. The inducers caused increased mixed-function oxidase activity, cytochrome P-450 content, and epoxide hydratase activity in experimental microsomes. Omission of the NADPH generating system from microsomal preparations had a variable effect on binding. Inhibition of epoxide hydratase reduced cis-chlordane-related binding to DNA to unmeasurable levels.

Effects of repeated administration of rat 2-diethylaminoethyl-2-2-diphenylvalerate-HCI (SKF 525 A) on liver

Repetitive administration to male rats of 2-diethylaminoethyl-2-2-diphenyl-valerate-HCI (SKF 525 A) (50 mg/kg, i.p.), decreases the intensity of [14C]-orotic acid incorporation/mg of RNA but not the 14C-incorporation/g liver. The RNA content/g liver is significantly higher in SKF-treated animals than in controls. Decay of label in liver RNA from [14C] orotic acid pretreated animals, is not significantly different in SKF 525 A treated animals than in controls. SKF 525 A repetitive administration, does not modify the rate of incorporation of 32P in liver microsomal lipid when results are expressed per microgram of inorganic phosphorus but it does when expressed in terms of per gram liver. There is a significant decrease in the decay rate of label from 32P-prelabeled liver microsomal phospholipids when animals are treated with SKF 525 A. There is a significant increase in the protein and phospholipid content in the smooth endoplasmic reticulum fraction. The electron microscopy of liver from SKF 525 A-treated animals, shows the presence of large areas of round vesicles of swollen endoplasmic reticulum, partly due to smooth component and part due to rough component, having detached the ribosomes from their membranes. Results suggest an inhibitory effect of SKF 525 A on RNA and phospholipid degradative processes.

Tyrosine aminotransferase sensitivity to bromodeoxyuridine during restricted intervals of S phase in hepatoma cells

Synchronized hepatoma tissue culture (HTC) cells, accumulated at the G1/S boundary with aminopterin, were released into S phase with either thymidine or 5-bromodeoxyuridine (BUdR). Tyrosine aminotransferase (TAT) activity was found to be unaffected by BUdR over the initial 3 h of S phase, but then to rapidly decline to a new basal level of 40% of control by 9 h. There was no corresponding response in the activities of alcohol dehydrogenase, malate dehydrogenase, acid phosphatase, and alkaline phosphatase, or in the rate of protein and RNA synthesis. If BUdR incorporation was restricted to limited periods of S phase, TAT was found to be maximally suppressed by incorporation into the initial 40% of the DNA. Incorporation of the analogue into the latter 60% of DNA synthesized during S phase had no effect on TAT. This is the first report that the effect of BUdR on TAT in HTC cells is associated with incorporation of the analog into DNA synthesized during a specific interval of S phase.

Influence of clofibrate administration on the rate of synthesis of macromolecules in regenerating rat liver

Administration of the antihypercholesterolaemic drug clofibrate stimulates the rates of synthesis of nucleic acids and proteins in rat liver. The biosynthesis of mitochondrial proteins also is enhanced by the drug. In drug-fed animals, the rates of incorporation in vivo of radioactive precursors into DNA, RNA and proteins are stimulated even when the liver undergoes regeneration following partial hepatectomy. The rate of synthesis of mitochondrial proteins in the regenerative phase is higher in clofibrate-fed animals. These effects are consistent with the hepatomegalic and mitochondria-proliferating property of the drug.

Transcriptionally active RNA polymerases from Morris hepatomas and rat liver. Elucidation of the mechanism for the preferential increase in the tumour RNA polymerase I

The amount and/or activity of DNA-dependent RNA polymerase I, Ii and III from resting liver, regenerating liver and a series of Morris hepatomas (5123D, 7800, 7777, 3924A) were determined after extraction of the enzymes from whole tissue homogenates and subsequent fractionation by DEAE-Sephadex column chromatography. When compared with resting liver, the tumours exhibited a characteristic enzyme pattern in which polymerase I, but not II, was increased. The increase in RNA polymerase I was proportional to the tumour growth rates. Alterations in polymerase III were confined to the most rapidly proliferating hepatomas. By contrast, all classes of RNA polymerase were found to be increased during liver regeneration. Relative to resting liver, the fastest growing tumour, 3924A, exhibited the highest activities and/or amounts of RNA polymerase I (8-fold) and III (5-fold) per g of tissue. These alterations in the tumour RNA polymerases were reflected in corresponding increases in the transcriptionally active (bound or chromatin-associated) enzyme population. The mechanisms underlying the augmented synthesis of RNA in vitro by bound polymerase I from hepatoma 3924A were elucidated by product analysis. The results indicated that, relative to liver RNA polymerase I, the tumour enzyme produced more nascent RNA chains and elongated these chains at a faster rate. The number of 3'-termini, as measured by incorporation into uridine, was higher in the hepatoma even under conditions which prevented re-initiation. suggesting increased amount of transcriptionally active RNA polymerase I in the tumour.

The effects of oestrogens and progesterone on oestrogen receptors in female rat liver

The administration of oestradiol-17 beta or ethynyloestradiol as well as the synthetic progestogen norethisterone acetate resulted in translocation of the oestrogen receptor. Progesterone and the synthetic progestogen (+)-norgestrel were ineffective. The increases in nuclear oestrogen receptor content 1 h after injection of each steroid were similar but different subsequently. The increase with oestradiol-17 beta extended for 3--6 h and for at least 9 h with ethynyloestradiol. With norethisterone acetate, nuclear content was still increased after 24 h. Oestrogen injection resulted in cytosol receptor depletion and a 'deficit' in receptor content extending for 6 h, whereas norethisterone acetate-induced translocation was quantitative. With injections of norethisterone acetate + ethynyloestradiol the increase at 1 h and retention of the nuclear receptors were similar to that with norethisterone acetate alone. In contrast, the depletion of cytosol receptor and its restoration were similar to that seen with ethynyloestradiol alone, suggesting that norethisterone acetate did not interfere with the oestrogen receptor replenishment. Specific binding in vitro of [3H]oestradiol-17 beta in liver cytosols was inhibited by (+)-norgestrel and norethisterone acetate, but not progesterone, at concentrations of 10--100 microM. Nuclear receptors present after norethisterone acetate injection bound oestrogen with high affinity (Kd = 1.52 nM), similar to receptors of oestrogen-injected animals. In the uterus, differential retention of nuclear receptors in response to oestrogens is associated with different cellular responses. The differences in the response of the receptor system in liver to the various steroids suggests that the corresponding tissue responses may also be dissimilar. These results are discussed in relation to the problems of liver dysfunction in oral-contraceptive users.

Nucleo-cytoplasmic relationships of oestrogen receptors in rat liver during the oestrous cycle and in response to administered natural and synthetic oestrogen

Oestrogen receptors were measured in the cytosolic and purified nuclear fractions of rat liver. Both cytosolic and nuclear receptors bind oestrogen with high affinity (Kd = 1.47 and 2.28 nM respectively) and specificity similar to that of receptors in order oestrogen-target tissues such as the uterus. During the 4-day oestrous cycle the receptor content and distribution between cytosol and nucleus did not vary; in particular, the content of nuclear receptor did not appear to fluctuate in concert with known cyclic changes in the concentration of plasma oestrogen. Injection of 50 micrograms of oestradiol-17 beta or 10 micrograms of ethynyloestradiol resulted in a 4--6-fold increase in the nuclear receptor content, with a concomitant decrease in the unoccupied-receptor content of cytosol 1 h after injection. The nuclear receptors present after injection bind oestrogens with similar affinity (Kd = 2.78 nM) and specificity to receptors present in uninjected animals. The administration of lower doses of either oestrogen was less effective in producing increases in nuclear receptor content. Hence there is apparently substantial translocation of receptor to the nucleus in response to hyperphysiological doses of oestrogen, but not to the physiological changes in plasma oestrogen concentrations during the oestrous cycle. The response to exogenous oestrogens is discussed in relation to the clinical use of synthetic oestrogens and progestogens.

The zinc and copper content of blood leucocytes and plasma from patients with benign and malignant prostates

Zinc and copper levels in plasma have been measured in 41 patients with benign prostatic hypertrophy and 44 patients with carcinoma of the prostate, 24 of whom were receiving some form of hormonal therapy. The zinc concentrations in the blood leucocytes of some of the patients were also examined. We were unable to detect any differences between the leucocyte zinc levels of the three groups examined. Similarly, plasma zinc levels were not affected by age or disease, whereas the plasma copper levels were significantly higher (p less than 0.01) in the benign and malignant categories (mean = 124 micrograms/100 ml) when compared to a younger normal population (mean = 84.0 micrograms/100 ml). Hormonal therapy induced a rapid rise in the plasma copper concentrations and a concomitant marginal fall in zinc levels of the carcinoma patients. The magnitude of these hormone-induced changes were dependent on the type of therapy prescribed to the patient.

Changes in the synthesis of ribosomal ribonucleic acid and of poly(A)-containing ribonucleic acid during the differentiation of intestinal epithelial cells in the rat and in the chick

Epithelial cells were isolated from rat and chick small intestine by techniques which separated subpopulations of differentiating villus and upper crypt cells from each other and from populations of mitotically dividing lower crypt cells. Incorporation of precursors into epithelial-cell DNA, cytoplasmic rRNA and cytoplasmic poly(A)-containing RNA occurred in the lower crypt cells in vivo when precursor was supplied from the vascular system of the intestine. Incorporation of precursor into 28S and 18S rRNA continued in the upper crypt cells, but occurred to only a very slight extent (if at all) in villus cells, whereas incorporation into poly(A)-containing RNA continued (at a diminishing rate) as the differentiating cells migrated along the villi. When precursor was supplied from the intestinal lumen, its incorporation into DNA and into rRNA of crypt cells was not very different from that observed with the other mode of precursor administration, but incorporation into villus-cell poly(A)-containing RNA then occurred at essentially the same rate in all intestinal epithelial cells in vivo. Cytoplasmic poly(A)-containing RNA appeared to turn over in rat crypt cells with a half-life not exceeding 24 h; crypt-cell rRNA showed no turnover and no evidence could be found for the presence of 'metabolic DNA'.

Upon the observation of superbeads in chromatin

There exist some indications that nucleases recognize "superbeads" in chromatin. We show that a chromatin extract of rat liver which contains so-called "superbead"-peaks can be separated in a Mg++ soluble and a Mg++ insoluble fraction. The Mg++ insoluble fraction contains the full complement of histones and the expected DNA fragments, but has lost the characteristic peaks in sucrosegradient profiles. These discrete peaks are found in the Mg2+ soluble fraction of the chromatin extract. We give evidence that these peaks are RNP particles on the basis of their protein- and nucleic acid contents.

Cell differentiation and flagellar elongation in Naegleria gruberi. Dependence on transcription and translation

This paper presents evidence that the phenotypic transformation of Naegleria gruberi from amebae to flagellates that occurs when cells are placed in a nutrient-free aqueous environment is dependent on transcription and translation. RNA and protein are synthesized during the hour-long differentiation. Actinomycin D and daunomycin selectively inhibit RNA synthesis, and cycloheximide selectively inhibits protein synthesis, throughout the time required for differentiation. These inhibitors prevent differentiation if added soon after the cells are transferred to nonnutrient buffer but cease to block specific differentiation events at subsequent, reproducible times, the transition points. After each transition point, morphogenesis can occur in the presence of the inhibitor and in the virtual absence of transcription or translation. A map of the transition points indicates that RNA synthesis is required until halfway through the temporal process from initiation to flagellum assembly, and that protein synthesis is required until three-fourths of the way through. Even when flagellum outgrowth can occur in the presence of cycloheximide, the length of the flagella formed is determined by the extent of synthesis of an unknown "limiting precursor." The transition points for formation of flagella and for formation of the streamlined flagellate body shape are temporally separate. These results indicate that differentiation in Naegleria involves a redirection of cell metabolism to produce new RNA and protein molecules that are essential for morphogenesis.

Biochemical mechanisms in the Killmann experiment: critique of the deoxyuridine suppression test

The degree of inhibition of [3H]thymidine incorporation into DNA by exogenous deoxyuridine is assayed in a procedure known as the deoxyuridine suppression test. We report studies of the biochemical basis of this phenomenon in phytohemagglutinin-stimulated lymphocytes, which suggest that its mechanism has not been fully understood. Results show that inhibition by deoxyuridine is caused only in part by expansion of the intracellular pools of nonradioactive dTMP and dTTP, which dilutes the specific radioactivity of the [3H]dTMP and [3H]dTTP derived from [3H]thymidine. Increased dTTP levels also inhibit thymidine kinase. In addition, thymidine kinase is competitively inhibited by intracellular deoxyuridine. Inhibition of thymidine kinase activity by both mebolites further decreases the specific radioactivity of [3H]dTMP and [3H]dTTP. Deoxyuridine also inhibits the incorporation of [3H]deoxyadenosine and [3H]deoxyguanosine into DNA in these cells. Exogenous deoxyuridine still inhibits [3H]thymidine incorporation in cells whose de novo thymidylate synthesis has been strongly inhibited by 5-fluorodeoxyuridine or methotrexate. In such drug-treated cells, exposure to high concentrations of exogenous deoxyuridine can partially overcome the inhibition of thymidylate synthetase with resulting increase in the severely depleted dTTP pools. This increase is associated with enhanced DNA synthesis, as measured by incorporation into DNA of labeled deoxyribonucleosides other than [3H]thymidine. We conclude that exogenous deoxyuridine has multiple effects on [3H]thymidine incorporation, which must be considered in interpretations of deoxyurindine suppression test results.

Experimental systolic and diastolic overloading in rats: total proteins turnover rate. Enzymatic and structural properties of myosin

The fractional turnover rate of the total cardiac proteins has been measured by using the continuous infusion technique with 3H lysine. It augments by a factor of 3 in systolic as well as in diastolic overloading, but in the former the peak was reached within the first week after operation and in the later the peak was not reached until the 14th day. The myosin structure and enzymatic properties have been studied in several huge hypertrophic hearts (around 100% hypertrophy). In this condition the burst size of myosin is normal, as well as its K+ ATPase, but there is a sharp decline in the Ca2+ ATPase activity. Moreover, antibodies against native or defolded heavy meromyosin exhibit, a vertical shift in microcomplement fixation when made to react with molecules extracted from hypertrophied hearts. The normal isozymic pattern of rat heart myosin, as shown in non dissociating electrophoresis, was reversed.

Partial hepatectomy reduces both metabolism and toxicity of benzene

Removal of 70--80% of the liver reduced both the metabolism and the toxicity of benzene in rats. Metabolism was evaluated by measuring the levels of urinary metabolites in both sham-operated and partially hepatectomized rats given 2200 mg/kg [3H]benzene sc. Toxicity was evaluated by measuring the incorporation of 59Fe into circulating erythrocytes according to the method of Lee et al. The observation that partial hepatectomy decreases benzene metabolism and protects against benzene toxicity indicates that the liver may play a primary role in the development of benzene-induced bone marrow toxicity. The fact that benzene administration also reduces the ability of the liver to regenerate after partial hepatectomy suggests that the regenerating liver may serve as a model system in lieu of the bone marrow for studying the mechanism by which benzene inhibits cell proliferation.