Effect of a single dose of T3 on the uptake of (2-14C)-ethanolamine into chicken liver phospholipids

The effect of a single dose of 3,3',5-triidothyronine (T3) on the (2-14C)-ethanolamine uptake into liver phosphatidylethanolamine (PE) and lysophosphatidylethanolamine (LPE) were determined in chicken over a period of 0.25 to 6 h after radioactive precursor injection. In all cases animals received the T3 dose intraperitoneally 5 h before the injection of the labeled compound. T3 enhances the incorporation of (2-14C)-ethanolamine into liver PE and LPE. The maximum uptake takes place at 0.25 h for LPE and 0.5 h for PE after the precursor administration. A great and significant hormone-dependent increase in the incorporation of labeled compound is observed in LPE. Lipid P associated to PE and LPE remains constant throughout the experiment, and does not vary with hormone treatment. It is suggested that T3-injection increases, either directly or through other metabolic processes, PE and LPE turnover in chicken liver cells.     

Metabolism of liposomes prepared from a labelled ether analog of 1,2-dioleoyl-sn-glycero-3-phosphocholine in the rat

To synthesize the ether analog of 1,2-diacyl-sn-glycero-3-phosphocholine (PC), 1-O-cis-9'- octadecenyl -2-O-cis-9'-[9',10'(n)-3H] ocatadecenyl -sn-glycero-3- phosphocholine, we have adapted available methodology and have obtained a product of high specific activity and purity. The labelled dioleyl ether phosphatidylcholine ( DOEPC ) was used to prepare 250-350 A unilamellar liposomes, which contained also PC and free cholesterol. Following intravenous injection into rats, labelled PC was cleared from the plasma at a faster rate than DOEPC . The uptake of both labelled compounds by the liver increased up to 3 h, at which time there was about 40% of injected PC and 60% of DOEPC . The PC disappeared more rapidly than the DOEPC , so that 17 and 48% of injected label were present in the liver 24 h after injection of PC and DOEPC , respectively. Ten days after injection of DOEPC , about 10% of the label was still present in the liver. During the first 5 days after injection of DOEPC , 10% of radioactivity was found in the gastrointestinal tract and about 20% in the carcass; no increase in carcass radioactivity occurred during the loss of label from the liver. 24 and 48 h after injection of DOEPC , 40% of liver radioactivity was present in a neutral lipid, which on TLC comigrated with triacylglycerol. Since after alkaline hydrolysis this compound comigrated with diacylglycerol, it appears that the ether bond of DOEPC was not hydrolyzed, but after removal of phosphocholine, presumably by phospholipase C, the diether glycerol was reacylated . In experiments in vitro, the rate of exchange of labelled PC with red blood cell phospholipids exceeded that of DOEPC . Incubation of cultured hepatocytes with liposomes containing PC and/or DOEPC resulted in uptake of both phospholipids and metabolism of DOEPC to neutral lipids. The present findings indicate that DOEPC undergoes slow metabolism and can be eliminated from the body. These properties could prove advantageous for the use of DOEPC as a carrier of drugs and possibly as a carrier of free cholesterol in reverse cholesterol transport.     

Uptake and degradation of vitamin D binding protein and vitamin D binding protein-actin complex in vivo in the rat.

We have labelled the rat vitamin D binding protein (DBP), DBP-actin and rat albumin with 125I-tyramine-cellobiose (125I-TC). In contrast with traditional 125I-labelling techniques where degraded radioactive metabolites are released into plasma, the 125I-TC moiety is trapped intracellularly in the tissues, where the degradation of the labelled proteins takes place. By using this labelling method, the catabolism of proteins can be studied in vivo. In this study we have used this labelling technique to compare the tissue uptake and degradation of DBP, DBP-actin and albumin in the rat. DBP-actin was cleared from plasma at a considerably faster rate than DBP. After intravenous injection of labelled DBP-actin complex, 48% of the radioactive dose was recovered in the liver after 30 min, compared with 14% when labelled DBP was administered. Only small amounts of DBP-actin complex were recovered in the kidneys. In contrast with the results obtained with DBP-actin complex, liver and kidneys contributed about equally in the uptake and degradation of DBP determined 24 h after the injection. When labelled DBP was compared with labelled albumin, the amount of radioactivity taken up by the liver and kidneys by 24 h after the injection was 2 and 5 times higher respectively. In conclusion, liver and kidneys are the major organs for catabolism of DBP in the rat. Furthermore, binding of actin to DBP enhances the clearance of DBP from circulation as well as its uptake by the liver.     

Enhanced lutein bioavailability by lyso-phosphatidylcholine in rats

The bioavailability of lutein solubilized in mixed micelles containing either phosphatidylcholine (PC) or lysophosphatidylcholine (lysoPC) was evaluated in male rats. Mixed micelles contained 2.5 mM monooleoylglycerol, 7.5 mM oleic acid, 12 mM sodium taurocholate and 200 μM lutein either with 3 mM PC or lysoPC. To study lutein bioavailability, single and repeated dose experiments were conducted. For single dose study, group of rats (n = 30/group) were fed single dose of lutein solubilized in lysoPC (LPC group), PC (PC group) and no phospholipids (NoPL group) in micellar form. Each group was further divided in to five sub-groups (n = 6/sub group) to measure lutein bioavailability over time up to 9 h. For repeated dose study, group of rats (n = 6/group) were fed daily for 10 days a dose of lutein in mixed micelles with NoPL, PC and LPC. A separate group (n = 6) not fed mixed micelles was considered as zero-time control. In both the experiments, mixed micelles (0.2 ml/rat) were fed to the rat by direct intubation to the stomach. Results of single dose studies showed that the mean lutein levels in the plasma and liver of the PC group was significantly lower (p < 0.05) than those of the other two groups. Moreover, the average lutein level in the plasma and liver was significantly (p < 0.05) different among the groups in the order LPC > NoPL > PC. But, repeated dose experiment followed the order LPC > PC > NoPL. The level of lutein excreted through urine and feces of PC group was significantly higher (p < 0.05) than those of the other two groups. Thus, the results indicate that the PC in the mixed micelles suppressed the intestinal uptake of lutein after single dose but not after repeated dose and that lysoPC enhanced the absorption. In both the experiments, plasma and liver level of lutein was higher in LPC compared with PC group. Results also suggest that the luminal hydrolysis of PC to lysoPC is necessary for intestinal uptake of lutein solubilized in mixed micelles.     

The synthesis of bile acids in perfused rat liver subjected to chronic biliary drainage

1. Isolated rat liver was perfused with heparinized whole blood under physiological pressure resulting in the secretion of bile at about the rate observed in vivo. 2. The preparation remained metabolically active for 4h and was apparently normal in function and microscopic appearance. 3. When the perfusate plasma and liver cholesterol pool was labelled by the introduction of [2-(14)C]mevalonic acid the specific radioactivity of the perfusate cholesterol increased. The biliary acids (cholic acid and chenodeoxycholic acid) were labelled and had the same specific radioactivity. 4. Livers removed from rats immediately after, and 40h after, the start of total biliary drainage, were perfused; increased excretion rates of both cholic acid and chenodeoxycholic acid were found when the liver donors had been subjected to biliary drainage. 5. The incorporation of [2-(14)C]mevalonic acid or rat lipoprotein labelled with [(14)C]cholesterol into bile acids was studied. 6. A dissociation between the mass of bile acid excreted and the rate of incorporation of (14)C was found. This was attributed to the changing specific radioactivity of the cholesterol pool acting as the immediate bile acid precursor.     

Direct evidence of the role of propionate in choline synthesis in rats

Wistar rats were injected with 2-14C-propionate in a dose of 30 mu Ci/100 g bw, 2 h after food intake. Two hours after isotope injection the rats were decapitated to determine specific radioactivity (SR) in liver and brain lipids, in liver phosphatidylcholine (PC) and its structural components. The label was incorporated in liver lipids in a far greater amount. In liver PC, SR appeared the highest in glycerin and less higher in the fraction of higher fatty acids. The least amount of the label from 2-14C-propionate was incorporated in choline. The fact of the label incorporation in choline was recorded for the first time.     

Synthesis of ribonucleic acid in the venom gland of Crotalus durissus terrificus (Ophidia, Reptilia) after manual extraction of the venom

1. The incorporation of [5-(3)H]uridine into RNA of the venom gland of Crotalus durissus terrificus was studied after manual extraction (;milking') of the venom. The labelled precursor was injected immediately after milking. 2. The RNA was extracted 1, 2, 4, 6 and 8h after injection of the label and analysed by sucrose-density-gradient centrifugation. 3. The sedimentation analysis showed that 18S rRNA synthesis is higher than 28S rRNA at all time-intervals. The specific radioactivities of both ribosomal components did not reach a plateau even at 8h after injection. 4. An RNA fraction was detected sedimenting between 18S rRNA and 4S tRNA and was called the 10-14S fraction. The specific radioactivity was always higher than that of both classes of rRNA and reached the maximum value at 6h of labelling. 5. The incorporation of the precursor was also studied by radioautography, which helped to elucidate the intracellular origin of the RNA analysed by sucrose-density-gradient centrifugation.     

Hepatocyte-specific distribution of catalase and its inhibitory effect on hepatic ischemia/reperfusion injury in mice

To explore the possibility of using catalase for the treatment of reactive oxygen species (ROS)-mediated injuries, the pharmacokinetics of bovine liver catalase (CAT) labeled with ¹¹¹In was investigated in mice. At a dose of 0.1 mg/kg, more than 70% of ¹¹¹In-CAT was recovered in the liver within 10 min after intravenous injection. In addition, ¹¹¹In-CAT was predominantly recovered from the parenchymal cells (PC) in the liver. Increasing the dose retarded the hepatic uptake of ¹¹¹In-CAT, suggesting saturation of the uptake process. This cell-specific uptake could not be inhibited by coadministration of various compounds which are known to be taken up by liver PC, indicating that the uptake mechanism of CAT by PC is very specific to this compound. The preventive effect of CAT on a hepatic ischemia/reperfusion injury was examined in mice by measuring the GOT and GPT levels in plasma. A bolus injection of CAT at 5 min prior to the reperfusion attenuated the increase in the levels of these indicators in a dose-dependent manner. These results suggest that catalase can be used for various hepatic injuries caused by ROS.     

The mechanism of hepatic iron uptake from native and denatured transferrin and its subcellular metabolism in the liver cell.

Hepatic iron uptake and metabolism were studied by subcellular fractionation of rat liver homogenates after injection of rats with a purified preparation of either native or denatured rat transferrin labelled with 125I and 59Fe. (1) With native transferrin, hepatic 125I content was maximal 5 min after injection and then fell. Hepatic 59Fe content reached maximum by 16 h after injection and remained constant for 14 days. Neither label appeared in the mitochondrial or lysosomal fractions. 59Fe appeared first in the supernatant and, with time, was detectable as ferritin in fractions sedimented with increasingly lower g forces. (2) With denatured transferrin, hepatic content of both 125I and 59Fe reached maximum by 30 min. Both appeared initially in the lysosomal fraction. With time, they passed into the supernatant and 59Fe became incorporated into ferritin. The study suggests that hepatic iron uptake from native transferrin does not involve endocytosis. However, endocytosis of denatured transferrin does occur. After the uptake process, iron is gradually incorporated into ferritin molecules, which subsequently polymerize; there is no incorporation into other structures over 14 days.     

Tissue Distribution, Metabolism, Anticonvulsant Efficacy, and Effect on Brain Amino Acid Levels of the Glia-Selective γ-Aminobutyric Acid Transport Inhibitor 4,5,6,7-Tetrahydroisoxazolo[4,5-c]pyridin-3-ol in Mice and Chicks

Using tritium-labelled 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) its tissue distribution and metabolism were investigated in adult mice and 4-day-old chicks after systemic administration of the drug. It was found not to be significantly metabolized in the brain since metabolites of THPO corresponding to only approximately 8% of the parent compound could be detected 30 min after administration of the drug intramuscularly in mice. In the liver, however, THPO was found to be metabolized to a considerable extent. In chicks THPO metabolites were found in the brain but they accounted for less than 35% of the radioactivity. The brain concentration of THPO in mice and chicks corresponded to respectively 10 and 50% of the dose injected intramuscularly and the tissue level was essentially constant for at least 3 h after injection. Following systemic administration of THPO to mice and chicks the contents of aspartate, glutamate, glutamine, and gamma-aminobutyric acid (GABA) in whole brain and in synaptosomes was determined. It was found that only GABA contents were affected being increased in synaptosomes from mice and decreased in whole brain in chicks. Doses of THPO, which in chicks but not in mice led to brain levels that were sufficient to inhibit glial GABA uptake, were found to protect chicks but not mice against isonicotinic acid hydrazide-induced seizures. The findings are compatible with the notion that THPO exerts its anticonvulsant activity by inhibition of astrocytic GABA uptake.     

Some biochemical effects of triamcinolone acetonide on rat liver and muscle

1. The powerful anti-inflammatory glucocorticoid triamcinolone acetonide, administered to rats at 20 and 2.5mg/kg, leads to a decrease in the incorporation in vivo of [(3)H]uridine and [(32)P]orthophosphate into hind-limb skeletal muscle. 2. At the higher dose, this decrease in the rate of incorporation of precursors into RNA precedes a decrease in the incorporating ability of muscle ribosomes, which commences about 4-5h after drug administration, but is unaccompanied by any changes in the concentration of tissue ATP or free amino acids. 3. The ribosomal dysfunction extends to polyribosomes, which can only be successfully isolated from the muscle of triamcinolone-treated animals after the addition of alpha-amylase to the tissue homogenate to remove glycogen. 4. The specific radioactivity of muscle protein labelled in vivo with (14)C-labelled amino acids does not decrease progressively after triamcinolone administration. After 2h there is an apparent stimulation of incorporation which leads to an overall discrepancy between measurements of protein-synthetic activity made in vivo and in vitro. 5. There is a significant increase in muscle-glycogen concentration between 8 and 12h after the administration of triamcinolone acetonide (20mg/kg), although a significant decrease occurs after 4h. The fall in glycogen concentration may be due to a decrease in the rate of synthesis of protein essential for glucose uptake into the tissues. 6. As judged by (a) incorporation of (14)C-labelled amino acids into protein, (b) [(3)H]uridine and [(32)P]-orthophosphate incorporation into RNA, (c) the rate of induction of tryptophan pyrrolase and (d) changes in the pool sizes of taurine and tryptophan, the responses in liver followed the same time-course as those in muscle after administration of the drug.     

Hepatocyte-specific distribution of catalase and its inhibitory effect on hepatic ischemia/reperfusion injury in mice

To explore the possibility of using catalase for the treatment of reactive oxygen species (ROS)-mediated injuries, the pharmacokinetics of bovine liver catalase (CAT) labeled with ¹¹¹In was investigated in mice. At a dose of 0.1 mg/kg, more than 70% of ¹¹¹In-CAT was recovered in the liver within 10 min after intravenous injection. In addition, ¹¹¹In-CAT was predominantly recovered from the parenchymal cells (PC) in the liver. Increasing the dose retarded the hepatic uptake of ¹¹¹In-CAT, suggesting saturation of the uptake process. This cell-specific uptake could not be inhibited by coadministration of various compounds which are known to be taken up by liver PC, indicating that the uptake mechanism of CAT by PC is very specific to this compound. The preventive effect of CAT on a hepatic ischemia/reperfusion injury was examined in mice by measuring the GOT and GPT levels in plasma. A bolus injection of CAT at 5 min prior to the reperfusion attenuated the increase in the levels of these indicators in a dose-dependent manner. These results suggest that catalase can be used for various hepatic injuries caused by ROS.     

Metabolism of Serine in Growing Rats and Chicks at Various Dietary Protein Levels

The metabolic fate of the carbon skeleton of l-serine-U-¹⁴C has been investigated, in vivo and in vitro, in growing rats and chicks fed the diets with various protein calories percents (PC%) at 410 kcal of metabolizable energy.

The incorporation of ¹⁴C into body protein at 12 hr after the injection of serine-¹⁴C was about 49% of the injected dose in rats fed the 10 or 15 PC % diet, though the value was reduced in rats fed lower and higher protein diets. The ¹⁴CO₂ production was smaller in rats fed the 10 and 15 PC% diet, and it showed an inverse pattern to that of the ¹⁴C incorporation into body protein. Urinary excretion of ¹⁴C was higher in rats fed 10 and higher PC% diets, whose growth rate and net body protein retention were maximum.

In contrast to the case of rats, the incorporation of ¹⁴C into body protein of chicks at 6 hr after the injection was rather reduced in the 15 PC% group. The proportion of ¹⁴C excreted as uric acid was remarkably increased above the 10 PC% group, and about 19% of the injected dose was recovered in the 50 PC% group.

The catabolic rate of serine in the liver slices of rats and chicks was increased by high protein diets.

These results support the concept that the nutritional significance of metabolism of the carbon skeleton of serine in growing rats and chicks is different from each other, especially at high protein diets.     

Effect of alcohol on the metabolic conversion of 14C erucic acid in the liver of rats receiving rapeseed or peanut oil]

The effects of addition of ethanol to diets containing rapeseed or ground nut oil on the metabolic conversions of 14 14C erucic and 9-10 3H oleic acid were studied in the rat liver. 1. Whatever the diet more 14C than 3H radioactivity was recovered in liver lipids 2 and 19 hours after injection of labelled fatty acids. Ethanol has little effect on this incorporation. 2. Only small amounts of 3H oleic acid were converted. 3. In all cases, the metabolic conversion of erucic acid was identical: the main part of 14C was not recovered as erucic acid but was present in other monounsaturated fatty acids n-9: oleic acid (18 : 1), which was the most labelled acid, 16 : 1, 20 : 1 and nervonic acid (24 : 1). 4. The amount of erucic acid converted to shorter chain fatty acids was unchanged by addition of ethanol but the alcohol increased the proportion of 14C radioactivity recovered as nervonic acid. This latter effect was opposite to the effect of rapeseed oil diet, which consisted in a decrease in the conversion of erucic to nervonic acid. 5. A high amount of 14C radioactivity was recovered in the F.F.A. fraction of the liver as an unknown compound (13 and 80% of 14C radioactivity respectively after 2 and 19 h.) Its identification is presently under investigation.     

The uptake and metabolism of plasma lysophosphatidylcholine in vivo by the brain of squirrel monkeys

1. Adult squirrel monkeys were injected intravenously with doubly labelled lysophosphatidylcholine (a mixture of 1-[1-(14)C]palmitoyl-sn-glycero-3-phosphorylcholine and 1-acyl-sn-glycero-3-phosphoryl[Me-(3)H]choline; (3)H:(14)Cratio 3.75) complexed to albumin, and the incorporation into the brain was studied at times up to 3h. 2. After 20min, 1% of the radioactivity injected as lysophosphatidylcholine had been taken up by the brain. 3. Approx. 70% of the doubly labelled lysophosphatidylcholine taken up by both grey and white matter was converted into phosphatidylcholine, whereas about 30% was hydrolysed. 4. The absence of significant radioactivity in the phosphatidylcholine, free fatty acid and water-soluble fractions of plasma up to 30min after injection of doubly labelled lysophosphatidylcholine rules out the possibility that the rapid labelling of these compounds in brain could be due to uptake from or exchange with their counterparts in plasma. 5. The similarity between the (3)H:(14)C ratios of brain phosphatidylcholine and injected lysophosphatidylcholine demonstrates that formation of the former occurred predominantly via direct acylation. 6. Analysis of the water-soluble products from lysophosphatidylcholine catabolism revealed that appreciable glycerophosphoryl-[Me-(3)H]choline did not accumulate in the brain and that radioactivity was incorporated into choline, acetylcholine, phosphorylcholine and betaine. 7. The role of plasma lysophosphatidylcholine as both a precursor of brain phosphatidylcholine and a source of free choline for the brain is discussed.     

Ethanol inhibits phosphatidylcholine and phosphatidylethanolamine biosynthesis in human leukemic monocyte-like U937 cells

The effect of ethanol (ETOH) on the incorporation of [¹⁴C]oleic acid (18:1) into lipid in human monocyte-like U937 cells was investigated. With increasing time of exposure to ETOH, the percentage of the label distributed into neutral lipid (NL) declined from 35 per cent (3 h) to 10 per cent (24 h) accompanied by increased incorporation into phospholipid (PL). [¹⁴C] 18 : 1 was preferentially incorporated into triglyceride (TG) and phosphatidylcholine (PC), comprising over 65 per cent and 50 per cent of the label associated with NL and PL, respectively. Low concentrations of ETOH (⩽ 1·0 per cent; v/v) had no effect. At concentrations greater than 1·5 per cent, there was enhanced incorporation into TG and diacylglycerol (DAG) in a 24-h incubation period, while at 16 h the label in phosphatidylethanolamine (PE) was decreased. The effect of ETOH on the CDP-choline or ethanolamine pathway was examined by monitoring the incorporation of [³H]choline or [¹⁴C]ethanolamine into PC or PE, respectively. At low concentrations ETOH had no effect on either choline uptake or the incorporation into PC. Higher concentrations (≥ 1·5 per cent) for 3 and 6 h resulted in a slightly decreased choline uptake, and the reduction (40–50 per cent) of incorporation into PC suggests that the CDP-choline pathway was inhibited. There was a similar inhibition of the incorporation of [¹⁴C]ethanolamine into PE. When the cells were incubated for 3 h in the presence of 2 per cent ETOH and with labelled 18 : 1 and PL-base, the ratios of incorporation (base/18 : 1) into PC and PE fractions decreased, indicating that the major inhibition lay in blockage of the availability of the base moiety for PL formation. Analysis of the distribution of the label into metabolites revealed that ETOH inhibited the conversion of [¹⁴C] ethanolamine into [¹⁴C]phosphorylethanolamine. The reduction in incorporation was not due to the enhanced breakdown of base-labelled PL. Our results indicate that ETOH has an inhibitory effect on the CDP-choline or ethanolamine pathway.     

The incorporation of isotopic carbon (14C) into the cerebral glycogen of rabbits

1. The incorporation of (14)C into the brain glycogen of conscious rabbits with labelled glucose, bicarbonate and glutamate as precursors has been studied. 2. Substantial incorporation from all these precursors was demonstrated after an interval of 5hr. from their injection. 3. With [(14)C]glucose maximal incorporation occurred at about 8hr. from the time of injection. 4. Hydrocortisone led to increased incorporation of (14)C from labelled glucose. 5. Some comparisons between the turnover of brain glycogen and that of skeletal and cardiac muscle are reported.     

Stimulation of metamorphosis in Hydractinia echinata involves generation of lysophosphatidylcholine

Summary Whilst the significance of the phosphoinositide cycle in the activation of developmental events by extra-cellular signals is well established, the involvement of the phosphatidylcholine (PC) cycle is a matter just emerging. In the present study, the metabolism of phosphatidylcholine in early metamorphosis of Hydractinia echinata (Coelenterata; Hydrozoa) was investigated by incubation of planula larvae with ³H-choline, extraction of the metabolites and isolation of the metabolites by thin-layer chromatography (TLC). Phosphatidylcholine (PC), lysophosphatidylcholine (LPC), acetylcholine and glycerophosphocholine were the labelled metabolites. Induction of metamorphosis did not stimulate an increased incorporation of choline into PC. In larvae preincubated with ³H-choline to a steady state level of incorporation, a significant transient elevation of the radioactive label in LPC was observed 90 min after addition of metamorphosis stimulating agents. LPC probably derived from PC by the action of a phospholipase A₂ (PLA₂). LPCs from bovine and soybean origin as well as isolated larval LPC did not influence metamorphosis. PLA₂ from bee venom promoted Cs⁺-induced metamorphosis but did not influence phorbol ester-induced metamorphosis. The data suggest that a PLA₂ is activated during metamorphosis. This PLA₂ activation does not occur in those putative receptor cells which receive the primary external inducing stimulus but in the many larval cells which resume proliferation or differentiation in response to a second, internally propagated signal. Offprint requests to: T. Leitz     

Effect of a single dose of dimethylnitrosamine on biosynthesis of nucleic acid and protein in rat liver and kidney

1. Administration of a single dose of dimethylnitrosamine to rats temporarily fed on a protein-deficient diet causes a high incidence of kidney tumours. The effect of such a dose of dimethylnitrosamine (40mg/kg body wt.) on metabolism of nucleic acids and protein in rat liver and kidneys was examined during the week immediately after administration. 2. Incorporation of [(14)C]leucine and [(14)C]orotate into hepatic macromolecules was inhibited within 5h of injection of dimethylnitrosamine, and did not recover for at least 5 days. Interpretation of these results is complicated by the concomitant extensive hepatic necrosis. 3. Renal RNA synthesis was assayed by incorporation of [(14)C]orotate in vivo and measurement of DNA-dependent RNA polymerase activity in vitro. Both systems indicate biphasic inhibition; minimal activity was recorded 9h and 3 days after treatment. Changes in incorporation of [(14)C]leucine into renal protein were similar but less marked. 4. Sucrose-density-gradient analysis of renal cytoplasmic RNA indicated increased synthesis of rRNA 24h after injection of the nitrosamine. The rate of loss of radioactivity from kidney ribosomes pre-labelled with [(14)C]orotate was not modified by dimethylnitrosamine. 5. Dimethylnitrosamine increased incorporation of [(3)H]-thymidine into renal DNA. The three distinct periods of stimulated synthesis observed are discussed, with particular reference to recently published morphological studies of the sequential development of kidney tumours induced by dimethylnitrosamine in protein-depleted rats.     

Studies on the radiosensitivity of the function of the Golgi complex.

The uptake of 3H-glucosamine into primary human-embryo fibroblasts and into the Golgi-rich fraction isolated from liver of mice labelled in vivo was studied, after various doses of X-radiation, by autoradiography and biochemical methods. A dose of 90 rad resulted in an increased precursor uptake in interphase cells at 24 hours and in mitotic cells at 48 hours after irradiation; 226 rad had virtually no effect on the grain counts of interphase cells, but reduced the labelling of mitotic forms. The characteristic intracellular localization of the grains were not influenced by these doses. Although no immediate radiation-induced reaction could be observed in liver cells either, significant stimulation of the 3H-glucosamine incorporation was measured in isolated Golgi-rich fractions 24 hours after whole-body irradiation with 90, 450, or 905 rad. This phenomenon is discussed as a part of the somatic regeneration of membrane structures.