Low Levels of Serum Cholesterol/Phospholipids are Associated with the Antiphospholipid Antibodies in Monoclonal Gammopathy

A decrease in cholesterol blood level, not due to a decrease synthesis by the liver, has been observed in patients suffering from tumors. In this work cholesterol blood was evaluated in patients affected by monoclonal gammopathy who were not subjected to any treatment. The blood of 25 patients were analyzed for protein and lipid content. Patients were divided according to the gamma protein content into three groups, and it was demonstrated that the group with high levels of gamma proteins presented a strong decrease in blood cholesterol and phospholipids. In these patients the presence of antibodies against phospholipids by using cardiolipin and phosphatidylinositol as antigens has also been demonstrated. The antibodies were rare in patients with a low content of gamma proteins and normal level of lipids, but the frequency was more than 80% in patients with low blood lipid levels.

An analysis of DNA loss and synthesis in the rat adrenal medulla nuclei upon cold stimulation

The peculiar changes previously observed in DNA content of rat adrenal medulla cell nuclei upon intermittent cold exposure (15 hr at +4°C followed by 9 hr at room temperature) have been further studied with the aid of Feulgen histophotometry and H₃-thymidine radioautography. The amount of DNA decreases progressively with increasing length of cold exposure until 300 hr (-32%). Later a rapid change takes place, whereby DNA content per nucleus returns to values which are slightly, but consistently lower than normal. At termination of a period of cumulative exposure to cold, an analysis of a whole-day experimental cycle shows that the DNA decrease is due to loss of DNA during cold exposure and that DNA synthesis occurs upon return to room temperature. The balance between these two processes can be divided into three stages: (a) loss of DNA up to 300 hr of cumulative cold exposure; (b) marked increase in DNA by 350 hr; (c) oscillation around zero or slightly negative at 400 hr and beyond. These variations are due to: (1) the extension of DNA synthesis into the period of cold exposure as clearly demonstrated by radioautography (stage b), and (2) a later still greater DNA loss (stage c) which partly offsets the increased synthesis. A complex pattern of adaptation of the adrenal medulla cells, as regards DNA content, to the repetitive cold stimulus is thus demonstrated.

Chromatin-associated sphingomyelin: metabolism in relation to cell function

After the first histochemical demonstration by Chayen and Gahan of the presence of phospholipids and especially of sphingomyelin in chromatin, this became the object of long debate and of contradictory results. The general conclusion was that the presence of phospholipids may due to contamination during the isolation of chromatin. More recently the existence of a phospholipid chromatin fraction was confirmed by demonstrating that isolated hepatocyte nuclei, labelled by saturated and unsaturated radioiodination method, showed the presence of radioactivity only in the membrane and not in the isolated chromatin. The phospholipid composition showed an enrichment in sphingomyelin which increased during hepatocyte maturation or erythroleukemic cell differentiation induced by DMSO. A decrease in sphingomyelin was observed at the beginning of the S-phase in regenerating liver or in cultured proliferating cells. These changes were due to the presence of sphingomyelinase and sphingomyelin synthase in the chromatin, the activity of which paralleled the variation in sphingomyelin content. The sphingomyelin was co-localized with RNA as shown by biochemical and electron microscopy methods. Using bromo-uridine it was demonstrated that labelled RNA and sphingomyelin were present in actively transcribing nuclear regions. Isolated nuclear complexes after DNase and RNase digestion contained not only protein, but also RNA and sphingomyelin. After hydrolysis of sphingomyelin the RNAse-resistant RNA becomes RNAse sensitive. It can therefore be concluded that sphingomyelin and the related enzymes are present in the chromatin; sphingomyelin may have a role in RNA transcription protecting RNA by RNAse digestion before its transfer to the cytoplasm.

Antiphosphatidylinositol antibody in deep venous thrombosis patients

Antiphospholipid antibodies are a heterogeneous group of immunoglobulins with specificity for a number of phospholipids, phospholipid-binding proteins and phospholipid-protein complexes. The association between antiphospholipid antibodies and a variety of pathologic disorders, such as arterial and venous thrombosis and recurrent pregnancy loss is recognized as Antiphospholipid Syndrome. The immunoassay currently used to detect antiphospholipid antibodies is the anticardiolipin test. Anticardiolipin antibodies are believed to be polyspecific antibodies that cross-react with all the anionic phospholipids. Therefore, testing only for anticardiolipin antibodies does not always permit detection of all antiphospholipid antibodies, specially when only IgG are evaluated. In a selected population of 74 idiopathic and secondary deep venous thrombosis patients, IgG anticardiolipin, antiphosphatidylinositol and antiphosphatidylserine antibodies were detected by solid-phase immunoassays. Our results show that by testing for each antiphospholipid family, many patients, not evidenced by the standard anticardiolipin assay, were found to be antiphospholipid-positive. The anticardiolipin positive patients have always low, moderate or high levels of antiphospholipid antibodies, suggesting that the antiphospholipid positivity is predictive of anticardiolipin positivity. It should be noted that the patients with only antiphosphatidylinositol positive antibody have a story of nervous system pathology. The meaning of these results is at present under discussion.

In utero partial liver resection in the rabbit model: a study on fetal tissue regeneration

In this study we developed a model of in vivo intrauterine partial liver resection in the fetal rabbit to analyze fetal liver regeneration. After intravenous anesthesia, 12 time-dated pregnant, California rabbits underwent a midline laparotomy and minimal hysterotomy at 24-25 days of gestational age. One fetus was exposed from each pregnant doe and the fetal liver was partially resected. Cesarean sections were performed 24, 48 and 72 h and 4 days after surgery. Three fetuses operated at 24 days of gestational age and 3 fetuses operated at 25 days were alive at retrieval. The fetuses and the sampled livers were weighed at retrieval and fetal liver weight showed a well-maintained value in all cases. Fetal livers were processed for the common histologic stains. Lymphocytes, polymorphonuclear leukocytes and phagocytes were counted from sections obtained in areas close to the edge of resection. Inflammatory cells showed a peculiar pattern of infiltration at different stages of repair, with a constantly increased number of phagocytes peaking 48 h after resection. Fetal liver seems to present a specific pattern of repair that differs from both the adult liver and other fetal tissues healing after injury.

Choline base exchange activity in rat hepatocyte nuclei and nuclear membranes

Previous investigations have demonstrated the presence of phospholipids as a component of chromatin; however the mechanism of their synthesis, namely if they are synthesized in the nuclei or in the cytoplasm (microsomal fraction), from where they may eventually be transported to the nucleus, has not yet been clarified. The phosphatidylcholine, for example, can be formed, albeit in a limited amount, by an interconversion reaction between bases. The aim of the present research was to ascertain the presence of the enzyme complex responsible for this reaction in hepatocyte nuclei and in isolated nuclear membrane. The incorporation of [14C]-choline in phosphatidylcholine was assayed in microsomes, hepatocyte nuclei, liver nuclei and nuclear membranes of rat liver. The reaction was Ca(2+)-dependent and the specific activity was higher in microsomes but was present, albeit at a low level, also in nuclei and in nuclear membranes. Possible contaminations were excluded by specific microsomal markers and by the reaction time course. In fact, the nuclear reaction reached the maximum level slowly with respect to microsomes. Since the phosphatidylcholine extracted from the nuclei show an enrichment in unsaturated fatty acids of monoenoic fraction, such as oleic acid, the difference in reaction kinetics has been tentatively explained as due to the phosphatidylcholine fatty acid content. The presence of this base exchange enzyme complex may allow a fast change in chromatin phospholipid composition.

[Hepatic resection in the fetal rabbit. Histologic comparison of tissue regeneration in the fetus versus the adult]

Fetal tissues present peculiar features of repair after injury. Although the development of fetal hepatocytes have already been studied in vitro and in transplant models, an in vivo study of fetal liver regeneration is still missed in the literature, to the best of our knowledge. Eight time-dated pregnant California rabbits (23, 24, 25, 30 days of gestational age) and 2 adult male California rabbits were anesthetized following a standardized i.v. protocol (ketamine 50 mg/kg; xilazine 5 mg/kg; propiopromazine 0.75 mg/kg; spontaneous breathing; no anesthetic gas). All the pregnant does underwent a midline laparotomy and a minimal hysterotomy to approach a fetus per each animal. In 2 cases, 1 fetus was delivered and prior to sacrifice the fetal liver was sampled in toto (30 days of gestational age). These pregnancies were allowed to continue to term and were uneventful with a full-term spontaneous delivery of the remaining fetuses. In the other 6 pregnancies, after the hysterotomy, the fetal abdomen was entered through a right-sided longitudinal incision and the liver was partially resected by thermocauterization. Fetal abdomen was closed in 1 layer (non absorbable suture 7-0). The fetus was then returned in the uterus and, after amniotic fluid restoration with warmed saline, the hysterotomy was sutured in double layer (polyglycolic 5-0). Maternal abdomen was closed in 1 layer (polyglycolic 4-0) and the skin in a continuous overlying fashion (silk 3-0). The abdominal cavity of the 2 adult male rabbits was entered through a right subcostal incision. Partial liver resection was performed, and abdominal and skin closure followed the same techniques used for the pregnant does. The treated livers were then sampled in toto at 24, 48, 72 hrs and 4 days after surgery from the fetuses, and at 7 days from the adult rabbits. Histological stains were: H & E; Van Gieson; Masson; Alcian Bleu; PAS. Fetal histology showed a low inflammatory reaction poor in PMN cells with minimal deposition of collagen and a high amount of glycogen in the hepatocytes. The inflammatory response to resection was much more evident in the adult samples as much as the abundant intra and extra-cellular deposition of collagen associated to a minor amount of intracellular glycogen. The peculiar features of liver regeneration in the fetus, deserve further experimental studies.

Rat liver chromatin phospholipids

To shed light on the question whether the phospholipids present in chromatin are native or are due to contamination from nuclear membranes, we labeled the phospholipids of isolated nuclei and determined the amount of phospholipids (PL) and PL fatty acid composition in nuclei and chromatin. The hepatocyte nuclei were isolated and radioiodinated by the lactoperoxidase method under saturating and nonsaturating conditions, and the radioactivity associated with chromatin extracted from these nuclei was monitored. Whereas 97% the label was recovered in the nuclear membranes, only 0.08-0.6% was found in chromatin. The PL present in chromatin were relative to the amounts present in the entire nuclei and calculated as percentage of total, phosphatidylethanolamine (10%), phosphatidylserine (22%), phosphatidylinositol (19%) phosphatidylcholine (14%), and sphingomyelin (35%). In sphingomyelin of chromatin-associated PL an enrichment in polyunsaturated fatty acids was seen. The data indicated that the PL found in isolated chromatin do not seem to be due to contamination from the nuclear membrane.

Changes in oncogene expression in ascite tumour cells during ageing

The expression of two oncogenes, c-myc and c-fos, was studied in an ascitic tumour (ATPC+) at different times after implantation. The specific mRNA synthesis was analysed by Northern blot analysis. The presence of the oncogene proteins was shown by immunofluorescence using flow cytometry and referred to the distribution of the cells in the different cell phases. The results show that both oncogenes are expressed by ATPC+ tumour cells. c-myc is expressed 5, 8 and 12 days after implantation, although with a different intensity, and the protein is mainly present in S or S+G2 phase cells. The c-fos oncogene is expressed only 12 days after tumour implantation and the cells labelled with the specific antibody are mainly in G1 phase. We conclude that c-myc is principally correlated with proliferative activity, whereas c-fos is expressed by non-cycling cells.

Different expression of beta-N-acetylhexosaminidase in mouse tissues

The expression of genes encoding for the alpha and beta-subunits of the lysosomal enzyme beta-N-acetylhexosaminidase was investigated in different mouse tissues. It was found, using fluorogenic substrates, that the amounts of alpha and beta subunits were not the same in different tissues: alpha-subunit was more abundant in the brain, beta-subunit in epididymis and brain. The different isoenzyme patterns and specific activities in mouse tissues are due to the differences in the amount of hexosaminidase subunits. The mRNA, evaluated by Northern blotting analyses, revealed a greater expression of alpha-subunit in the testis and of beta-subunit in the brain and epididymis. The results indicate, therefore, that gene expression and the amount of subunits are in good relationship for beta-subunit, whereas there is no correlation for alpha-subunit.

TEM cytochemical study of the localization of phospholipids in interphase chromatin in rat hepatocytes

The electron microscopy cytochemical detection of phospholipids in well-defined areas in the interphase nuclei of hepatocytes has been obtained by the acid haematein test, modified for electron microscopy and by the phospholipase A2-colloidal gold method. The specificity of both methods were controlled by enzymatic digestion with phospholipase. The main intra-nuclear localization of phospholipids is at the border between the condensed and dispersed chromatin, where non-ribosomal RNA is also revealed by RNase-gold labelling. Phospholipids are detected, too, over the clusters of interchromatin granules and in the fibrillar component of the nucleolus.

Age-related changes in the cell proliferation of ATPC+ mouse ascites tumour

The growth of ATPC+, an ascites tumour derived from a spontaneous mammary carcinoma in BALB/c+ mice, was studied at different ages. It was observed that the number of cells increases rapidly during the first 5 days after implantation. Thereafter, the cell number increases more slowly, reaching a plateau after 8 days. This slowing-down is not due to a reduction in the growth fraction but to a lengthening of the cell cycle. Between 5 and 8 days the duration of all phases increases, including the S phase, which increases from 5.2 h in 5-day tumours to 8.2 h in 8-day tumours. In 12-day tumours both the cell cycle and S phase are only slightly longer than in 8-day tumours whereas the growth fraction is reduced. The slowing-down of cell growth can be attributed to growth fraction reduction rather than cell loss, which is maximal in the 5-day tumour. At this age the time course of the percent labelled cells and of the number of grains/nucleus suggests reutilization of [3H]-thymidine. Incorporation of [3H]-thymidine/cell decreases sharply in 12-day tumours due to a reduced availability of thymidine, which is degraded to thymine in the in vivo ascitic fluid faster than in 8-day tumours. This indicates an age-related change in the ascitic fluid composition.

Phospholipids in chromatin: incorporation of [32P]O4(2-) in different subcellular fractions of hepatocytes

Nuclear, chromatin and microsomal fractions were isolated from hepatocytes prepared from rats injected with [32P]O4(2-) and killed subsequently at times between 1 and 48 h. Specific activities of the total phospholipids (PL) were determined for each subcellular fraction. The major points noted were the initial specific activity of the chromatin PL was half that of both nuclear and microsomal PL at 1 h; the first peak of labelling occurred at 6 h in both nuclear and microsomal PL, but was 3 h later (9h) in the chromatin PL; and a second peak of labelling occurred in the chromatin and microsomal PL, but not in those of the nuclei. On fractionation of the PL, the major and most metabolically active components were phosphatidylcholine + phosphatidylethanolamine, whilst sphingomyelin accounted for only about 8 per cent of the total PL. The chromatin and microsomal fractions were somewhat similar in their labelling patterns though with a delayed peaking of activity in the chromatin. This is indicative of a synthesis and transport of PL from the microsomes to the chromatin.

Phospholipids in plant and animal chromatin

Isolated hepatic nuclei and hepatic chromatin have been analysed for their DNA, RNA, protein and phospholipid content. The protein/DNA ratio is 3 for nuclei and 1.95 for chromatin extracted from Triton X-100 treated nuclei. The phospholipids, (2.36 +/- 0.91 (S.D.) per cent of the total nuclear material), are lost during the chromatin preparation mainly during the Triton X-100 washings of the nuclei. Nevertheless, 10 per cent of the total nuclear phospholipids remain bound to the chromatin. The comparative analysis of both nuclei and chromatin shows a difference in phospholipids and fatty acid composition. Thus, the chromatin-associated phospholipid cannot be attributed simply to contaminating nuclear membrane. This is supported by the autoradiographic study of semi-thin sections of interphase nuclei from root apices of Vicia faba in which [3H] ethanolamine is clearly localized in the chromatin and nucleolar regions of the nuclei.

Behaviour of tyrosine amino transferase and convertase during the first hours after hepatectomy in rats

The activity of rat liver tyrosine amino transferase (TAT) increases after hepatectomy with a first prominent peak at 8 h and a second peak at 18 h. This change in activity is probably due to de novo enzyme synthesis since it is prevented by actinomycin-D (AMD). In the same period an increase of the lysosomal converting enzyme (convertase) which catalyses the in vitro transition of TAT from form I to form III, has been observed; this is not accompanied by changes of other lysosomal enzymes, such as acid phosphatase and cathepsin L. The activity of convertase is equal to that of the controls (sham operated animals) 2 h after hepatectomy, increases three times at 5 h, maintains the same value at 8 h and then decreases slowly to control level after 24 h. The correlation between the activity changes of the two enzymes strongly suggests a physiological role of convertase in TAT turnover.

Changes in endonuclease activity and in chromatin structure of rat hepatocytes during fetal and neonatal life

A developmental study of rat hepatic endonuclease has been performed. Nuclei, from different stages of hepatocyte maturation, were analyzed for endogenous endonuclease activity. The chromatin extracted from these nuclei does not show any fragmentation during the first 17 days of fetal development. On the 18th day of fetal life there is a massive increase in specific endonuclease activity. At birth this activity reaches a maximum level (3.5 units/mg DNA); thereafter it undergoes a gradual decrease. The size of the basic DNA repeats produced by the endonuclease action is 218.9 +/- 1.6 in 18-day-old fetuses and decreases to 204.9 +/- 2.5 in 19-day-old fetuses, a value which remains constant in the following fetal and postnatal life. This difference in monomer size is due to changes in the chromatin structure. Micrococcal nuclease digests show that the "nucleosome core" does not change during hepatocyte development. Therefore, the difference in size of the endonuclease DNA fragments must be due to the linker regions.

Base composition changes in hepatocyte nuclei DNA of rats at different ages

DNA extracted from isolated hepatic nuclei of rats at different aged (1 h, 6 and 30 days of life) has been characterized by (i) melting temperature, (ii) buoyant density, (iii) thermal denaturation on hydroxyapatite and (iv) nucleoside composition. The melting midpoint (Tm) determined spectrophotometrically in 0.1 X SSC (0.15 M NaCl/0.0015 M sodium citrate) is 71.9 +/- 0.4 for 1-h-old rats and decreases to 70.7 +/- 0.3 in 6-day-old animals. The buoyant densities of DNAs determined by CsCl on both native and alkaline-denaturated and reneutralized DNA were also found to decrease with age. Hydroxyapatite thermal denaturation of sonicated DNA confirmed the significant difference between the Tm values of 1-h-old and 6-day-old rats (86.5 +/- 0.5 and 85.2 +/- 0.1, respectively). The possibility that these differences in Tm values could be due to an increase in methyl bases, has been ruled out by the finding that the amount of [3H]methyl incorporated in relation to the DNA synthesis is constant at these two ages. The alternative possibility of a change in base composition has been tested by the chromatographic analysis of nucleosides. The dG + dC content is 0.433 +/- 0.003 in 1-h-old rats and decreases to 0.411 +/- 0.002 and to 0.403 +/- 0.005 in 6-day- and 30-day-old rats, respectively. The physiological significance of the different base composition is discussed in relation to the possibility that specific DNA sequences are synthesized during the non-premitotic synthesis which has been found to take place during the first 6 days of life.

Regulatory mechanisms of hepatic phosphorylase in fetal and neonatal livers of rats

Active phosphorylase was determined in rat livers during the end of the fetal period and the first days of life. This enzyme increases between the 16th day of gestation and birth. After birth, another increase in observed that takes place with 6 h. In the neonatal liver, the rapid increase in active phosphorylase, is inhibited by high levels of blood glucose, but is unaffected by actinomycin D. In fetal liver glucagon administration is followed after 5 h by an increase in total phosphorylase with only a small increase in active phosphorylase; this effect is blocked by actinomycin D. The fetal changes are interpreted as de novo synthesis, whereas the neonatal increase is due to an activation of inactive phosphorylase. Both enzymatic changes appear to be regulated by glycogen. The role of phosphorylase in the regulation of glycogen metabolism in neonatal liver is discussed.

Metabolic DNA in the hepatocyte nuclei in newborn rats

The behaviour in time of labelled nuclear DNA in the hepatocytes of newborn rats was studied using autoradiographic and biochemical techniques in two groups of experiments. In the first group H-3-thymidine was injected to the mothers at the 16th day of pregnancy and the amount of labelled DNA was evaluated in the newborns after delivery. In the second group H-3-thymidine was injected to the newborns two hours after birth and the labelled DNA was studied at the same time intervals as the first group. The amount of labelled thymidine incorporated into the first group of animals remains constant for the first three days of life, thereafter a reduction in specific activity of DNA is observed concomitant with an increase of the percentage of labelled nuclei and a decrease of the number of grains per nucleus. These results show that mitotic divisions, which are absent during the first three days of life, take place between the third and sixth days of life. The decrease of the specific activity is therefore due to dilution and not to loss of labelled DNA. In the second group of experiments the DNA labelled with H-3-thymidine shows a decrease by about 30--40% per day during the first three days of life accompanied by a decrease in the number of grains per nucleus without changes in the percentage of labelled nuclei. These data show that DNA synthesized during the first day after birth is metabolically unstable, unlike that synthesized during foetal life.

Catecholamine synthesis and excretion in rats exposed intermittently to cold

Previous findings have shown a turnover of nuclear DNA, a condition related to the functional activity of these cells, in the adrenal medullae of rats intermittently exposed to cold. Striking differences have been observed between various strains of rats, particularly Italico and Wistar rats. In order to evaluate the function of the adrenal medullary cells, the content of catecholamines in the organ and their urinary excretion have been evaluated, with the fluorimetric method, in rats of Italico and Wistar strains kept at room temperature and exposed intermittently to cold. The results show that (i) at room temperature the levels of excretion are lower in Italico than in Wistar rats in spite of the equal amine contents of the adrenal medullae, (ii) the first exposure to cold causes a large increase in the urinary excretion and a decrease of adrenaline and noradrenaline content of the adrenal glands in both strains, (iii) after 3 days the catecholamine content in the organ was higher than normal in Wistar rats, whereas in the Italico strain it continued to decrease, and (iv) a new steady state at higher levels is reached after 20 days of exposure, when not only the catecholamine content but also the urinary excretion is equal in both strains. These differences between the two strains of rats during intermittent cold exposure are discussed in relation to the behaviour of DNA.

I. Quantitative determination of the amount of DNA per nucleus by interference microscopy

A method for the determination of the DNA content of isolated nuclei of different ploidy has been developed. It is based on measurement of the nuclear dry mass, with an integrating microinterferometer, before and after DNase treatment. The values found are slightly low, because, as indicated by biochemical determinations, consistently 5% to 8% of DNA is not extracted by DNase under these conditions. The average DNA values thus obtained for diploid and tetraploid nuclei of adult rat liver are 7.7 and 15.6 pg (10(-12) g), respectively. Definite advantages of this procedure are: i) comparisons with biochemical determinations to give DNA values for each class of ploidy, ii) comparisons with histophotometry of the Feulgen dye-DNA complex to give absolute values instead of arbitrary units.

3. Decrease of labeled DNA in cells of the adrenal medulla after intermittent exposure to cold

Italico rats were injected with thymidine-(3)H 6 hr after the end of 300 hr of intermittent cold treatment. This plan of experiment ensured replacement in the adrenal medulla of lost DNA which is specifically sensitive to cold treatment and has a labeling index sufficiently high for statistical evaluation. The labeling index in the adrenal medulla decreases to one-half of the initial value within 10 days in animals subjected to further intermittent cold treatment and within 32 days in animals kept at room temperature. The very low mitotic index and the absence of doubling of the labeling index show that the observed labeling cannot be ascribed to pre-mitotic DNA synthesis. The concept of metabolic DNA adequately explains the findings.

II. Differences in adrenal medulla nuclear DNA content among rats of different strains following intermittent exposure to cold

The amount of DNA per nucleus in the adrenal medulla cells of four different strains of rats (Wistar, Sprague-Dawley, Long-Evans, and Italico) is determined both under control conditions and after 300 hr of intermittent exposure to cold. The adrenal medulla nuclei of the four strains of rats contain the same amount of DNA; however, the loss of DNA observed after the same experimental treatment differs markedly in the different strains. The loss is small in Wistar and Sprague-Dawley rats (8-13%), larger in Long-Evans rats (20%) and still larger in Italico rats (45%). The DNA loss in Wistar rats increases if the animals are fed the same diet as the Italico rats, and the DNA loss in Italico rats is reduced if the animals are fed the same diet as the Wistar rats. The different behavior of the four strains is discussed in terms of turnover of DNA.

A radioautographic study with H3-thymidine on adrenal medulla nuclei of rats intermittently exposed to cold

A considerable decrease (24 to 40%) of DNA content per nucleus previously observed in the adrenal medulla of rats exposed intermittently to cold is followed by restoration to normal and supranormal values. This phenomenon has now been studied by use of H(3)-thymidine, which was given to normal rats, to rats exposed to cold, and to animals brought to room temperature after cold exposure. In the first two conditions, no significant labeling of nuclei was observed. In the third, labeling took place clearly in the 1st 3 days. The grain counts showed that the early labeled nuclei had more grains than those labeled later, indicating differences in the rate of DNA synthesis. A statistically significant correlation was found, on the same nuclei, between amount of Feulgen dye and number of grains. It is concluded that net synthesis of DNA takes place in the phase of recovery from cold. This fact is not related to cell division, as no mitoses could ever be detected, but rather to the cold-induced loss of DNA. Clear demonstration is thus given of a marked variation in the amount of DNA per nucleus in relation to the functional conditions of adrenal medulla cells.

Changes in the DNA content of adrenal medulla nuclei of rats intermittently exposed to cold

In the adrenal medulla of rats exposed intermittently to cold (+4 degrees C) for 100 and 300 hours, a considerable decrease (24 to 40 per cent) of the DNA content per nucleus was observed, followed by restoration to normal or above normal values within 10 days after the withdrawal of the stimulus. The findings were obtained with a scanning integrating histophotometer, and confirmed by microinterferometric investigations (on the basis of the measurement of total dry mass of nuclei isolated in aqueous medium before and after treatment with DNase) and by microchemical determinations, combined with the count of the nuclei in the homogenates. The observed decrease of DNA content cannot be attributed to errors of the methods used, nor to consequences of cellular degeneration. The available evidence seems to indicate a real decrease rather than a change in the state of a part of DNA in the nucleus in vivo whereby it becomes extractable by aqueous solutions. The restoration cannot be due to mitotic processes, which were actually never detected even with the use of colchicine, since the adrenal medulla cells in the adult rat are known to be irreversible, postmitotic cells. A correlation between the functional activity of the adrenal medulla cells and the content or state of DNA in their nuclei is demonstrated.