Retention Of 14C Research Articles

Metabolic Utilization of Pyridoxine-β-Glucoside in Rats: Influence of Vitamin B-6 Status and Route of Administration

[3H]5'-O-(beta-D-glucopyranosyl) pyridoxine (PN-glucoside) and [14C]pyridoxine (PN) were administered orally or intraperitoneally to vitamin B-6-adequate or -deficient rats. Analysis of intestinal contents and feces indicated effective intestinal absorption of PN-glucoside relative to PN. There was greater retention of 14C than 3H in the liver and carcass regardless of the route of administration of the radiolabeled vitamins. There was no major difference in the relative distribution of 3H and 14C among the vitamin B-6 metabolites in the liver between the treatment groups, and no [3H]PN-glucoside was detected in any of the livers. For all groups, the majority of the 3H administered was detected in the urine within 24 h. Less excretion of both 3H and 14C in the urine was observed for the deficient rats. There was no major difference in the relative proportion of urinary [3H]PN-glucoside or [3H]4-PA between rats fed or injected with the radiolabeled vitamins. These results indicate that vitamin B-6 status influences the clearance of metabolites derived from PN and PN-glucoside, as well as the clearance of intact PN-glucoside. Vitamin B-6 status, however, has little or no effect on the utilization of PN-glucoside. This study also suggests that the intestine is the primary site of the limited conversion of PN-glucoside to biologically active PN in the rat.

Effect of Phosphorus Deficiency on Source-Sink Interactions Between the Flag Leaf and Developing Grain in Barley

Chapin, F. S. Ill and Wardlaw, I. F. 1988. Effect of phosphorus deficiency on source-sink interactions between the flag leaf and developing grain in barley. —J. exp. Bot. 39: 165-177. Photosynthetic rate and stomatal conductance of P-deficient barley plants were increased by manipulations that increased plant demand for carbohydrates (shading of the ear or removal of other leaves). This was associated with retarded senescence of the flag leaf. Similarly, small flag leaves (i.e. those having large sinks relative to their own size) had high rates of photosynthesis. These relationships were most pronounced under conditions of P deficiency. Distribution of 32P and 14C from the flag leaf was determined by the carbohydrate demand of a plant part and was unaffected by altering the sink strength for P. Thus, ear shading increased accumulation by developing grains of 32P and 14C applied to the flag leaf, grain removal reduced accumulation by grain of both radioisotopes, and removal of lower leaves increased movement of both radioisotopes to vegetative plant parts; in contrast, P addition to the ear had no effect upon 32P or 14C distribution. P deficiency reduced the amount of tillering and, therefore, the movement of 32P and 14C to developing tillers and increased retention of 14C and 32P in the sheath of the flag leaf but otherwise had no major effect on patterns of carbon and phosphorus distribution. We conclude that the major effects of P deficiency upon source-sink interactions are (1) to reduce the number or activity of sinks in the shoot (grains and daughter tillers) and (2) to increase the sensitivity with which photosynthesis responds to demand for carbohydrate. The strengthened source-sink interaction under conditions of P deficiency provides a regulatory mechanism for reducing carbohydrate accumulation under conditions where carbohydrates do not strongly limit growth.

Effects of Sulfur Dioxide on Nitrogen Fixation, Carbon Partitioning, and Yield Components in Snapbean

AbstractThe air pollutant SO2 is known to affect plant biochemistry and physiology, although very little is known about its effects on N2‐fixation in legumes. This study sought to determine if N2‐fixation, C partitioning, and plant productivity of snapbean (Phaseolus vulgaris L.) were affected under short‐term, low‐level SO2 exposures. Plants were exposed, 29 d after planting (7 d before anthesis), to 0, 18, and 36 µmol SO2 m−3 for 4 h d−1 for 5 d in a fumigation chamber. On the last day of SO2 treatment, plants were also exposed to 14CO2 to determine changes in C partitioning patterns. At these concentrations, there was no visible damage to plant tissue and no significant changes in dry weight or yield components. Only the 36 µmol SO2 m−3 treatment reduced C2H2 reduction rates, but recovery to near control rates occurred within 24 h after SO2 removal. Leaves of plants treated with 18 µmol SO2 m−3 exported more of their total assimilated 14C than control plants, while those treated with 36 µmol SO2 m−3 retained greater amounts. Retention of 14C at the 36 µmol SO2 m−3 level may account for the inhibition of C2H2‐reduction because of less photosynthate arriving at the root nodules. These data suggest that SO2 levels that do not cause visible injury may interfere with C metabolism and transport in snapbean.

Ration and toxicant preexposure influence dieldrin accumulation by rainbow trout (Salmo gairdneri)

Whole body accumulation and tissue distribution of dieldrin in rainbow trout were studied through oral-dose disposition tests and subchronic exposures via water (0.04 and 0.08 μg dieldrin/L) and/or diet (0.087 μg dieldrin/g fish/d). Growth and no-growth (maintenance) rations of 4 and 2% body weight per day were employed. In subchronic tests, apparent steady-state residue concentrations depended on ration and exposure concentration after 8 weeks of exposure. At 16 weeks, mean whole fish residue concentrations ranged from 120 to 1,400 ng dieldrin/g fish. Combination food and water exposures at a growth ration produced the highest accumulation values (1,300–1,400 ng dieldrin/g fish). Maintenance rations apparently limited accumulation to a maximum of 360 ng dieldrin/g fish. Whole body dieldrin concentration, calculated on the basis of total lipids, greatly reduced the differences in residue levels due to ration. Tissue distribution of a single oral dose of [14C]dieldrin was determined in naive (no pretreatment) fish and those preexposed via the diet for 2, 4 or 6 weeks. Tissue concentrations of the tracer dose were determined 48 h following administration. Retention of the [14C]dieldrin was similar in most tissues of naive, 2- or 6-week dieldrin-pretreated fish with a slight downward trend with duration of pretreatment. Retention of 14C in the bile of fish receiving maintenance and growth treatments increased two- and five-fold, respectively, in 6-week pretreated as compared with naive fish. After 4 weeks of pretreatment, 14C concentrations peaked in all tissues except the bile, gut, and gut contents.

Sensory electroneurographic parameters and clinical recovery in sutured human nerves

The tissue distribution of toxic doses of 14C-acid-, 14C-alcohol-, and 14C-cyano-labeled deltamethrin was followed after iv administration to rats. All three radiolabeled preparations were found in every tissue examined within 1 min of injection. Peak central nervous system (CNS) levels were achieved within 1–5 min, but did not correspond to the onset of choreoathetosis. In the majority of the tissues examined the levels of deltamethrin label were similar, proportionately, to those found after administration of alcohol-labeled cismethrin. A major exception was the CNS which contained approximately 20% of the anticipated level of radiolabel suggesting that the CNS threshold for deltamethrin was approximately 0.5–1.0 nmol/g. Progressive accumulation of radioactivity in the erythrocyte fraction of the blood was observed following administration of cyano-labeled deltamethrin. This may contribute to the selective retention of 14C with this radiolabeled preparation.

Distribution of radiolabel in rats after intravenous injection of a toxic dose of 14C-acid-, 14C-alcohol-, or 14C-cyano-labeled deltamethrin

The tissue distribution of toxic doses of 14C-acid-, 14C-alcohol-, and 14C-cyano-labeled deltamethrin was followed after iv administration to rats. All three radiolabeled preparations were found in every tissue examined within 1 min of injection. Peak central nervous system (CNS) levels were achieved within 1–5 min, but did not correspond to the onset of choreoathetosis. In the majority of the tissues examined the levels of deltamethrin label were similar, proportionately, to those found after administration of alcohol-labeled cismethrin. A major exception was the CNS which contained approximately 20% of the anticipated level of radiolabel suggesting that the CNS threshold for deltamethrin was approximately 0.5–1.0 nmol/g. Progressive accumulation of radioactivity in the erythrocyte fraction of the blood was observed following administration of cyano-labeled deltamethrin. This may contribute to the selective retention of 14C with this radiolabeled preparation.

Distribution of 14C Photosynthetic Assimilates in ‘Valencia’ Orange Seedlings at 10° and 25°C1,2

Abstract The distribution of 14C-photosynthate was determined in 8-month-old potted ‘Valencia’ orange seedlings [Citrus sinensis (L.) Osbeck] during 25° and 10°C temperature regimes. Seedlings were pulse-labeled with 14CO2 for 3 hr after equilibration with ambient air. Radioactive assimilates were extracted at selected intervals, from leaves, stems, and roots and separated into several biochemical fractions. Low-temperature (10°) exposure resulted in a greater retention of 14C in the sugar fraction of leaves and a lower rate of 14C incorporation into organic and amino acid fractions. Data indicate a lower rate of metabolism of photosynthate and a reduced distribution of 14C in citrus seedlings at 10° than at 25°C.

EFFECT OF LEAF AGE AND SHADING ON THE MOVEMENT OF 14C THROUGH A SOYBEAN LEAF

Experiments were conducted to evaluate the effect of leaf age and shading on the movement of 14C assimilates through soybean (Glycine max (L.) Merr.) leaves. Leaves on plants at initial bloom and mid-podfill were pulse-labelled with 14CO2 for 2 min and the distribution of 14C in the leaf was followed for 24 h. Initially, 90% of the 14C activity was in the 80% ethanol-soluble fraction; this decreased rapidly, and by 7 h after labeling only 10% of the initial activity was in this fraction. The 14C in starch and perchloric-acid-soluble fractions increased to a maximum level (approx. 30% of initial activity) 30 min after labeling and declined slowly over the rest of the period. After 24 h, approximately 80% of the 14C had moved out of the leaf. There was no effect of leaf age on the pattern of movement of 14C through the leaf. Completely shading the plant immediately after labeling resulted in a rapid cessation (within 30 mm) of 14C movement into starch with an accompanying retention of 14C in the 80% ethanol-soluble fraction.

The dose-dependent metabolism of [ 14C]methylene chloride following oral administration to rats

[ 14C]Methylene chloride ( 14CH 2Cl 2) was administered to Sprague-Dawley rats in a single oral dose of 1 or 50 mg/kg. The disposition of radioactivity was followed for 48 hr after dosing. The major metabolites of CH 2Cl 2 were CO and CO 2, both of which were found in expired air. The fate of 14CH 2Cl 2 was dependent upon the administered dose. Rats given 1 mg 14CH 2Cl 2/kg metabolized approximately 88% of the dose, whereas those given 50 mg/kg metabolized only about 28%. Although all tissues examined 48 hr after dosing contained 14C activity, the overall tissue retention of 14C was low (< 10%) after either dose of 14CH 2Cl 2. The highest concentrations of 14C activity were found in the liver and the lowest in the fat. The data indicate that the observed dose-dependency was due to saturation of metabolic pathways for CH 2Cl 2 by the 50-mg/kg dose.

Dietary fat saturation and cholesterol turnover in aging rats

Aging has been shown to result in changes in cholesterol metabolism resulting in Increased concentration in the serum. The turnover of cholesterol is regulated, in part, by its retention in peripheral tissues. Conversion of cholesterol to acidic form in peripheral tissues has been reported. This report examines the retention of 4-14C-cholesterol in the livers and carcasses of male and female rats fed diets containing fats of polyunsaturated to saturated ratio 0.2 (BT diet) or 1 (M diet)until they were 9, 12, 15, 18, or 21 months of age. The tracer cholesterol was given 28 days prior to necropsy and tissues were analyzed for neutral and acidic 14C, cholesterol and cholanoic acids. Age beyond 1 year resulted in an increase of retention of 14C-cholesterol in the carcass while concentration remained constant, indicating slower turnover of cholesterol. There was no consistent diet effect, but males had greater retention than females. Retention of 14C which had been transformed to an acidic form followed an age pattern similar to that of cholesterol, except M diet caused greater retention of acidic 14C after 15 months than did BT diet. Carcasses contained about 1 mg cholesterol per gm and 30–100 μg/gm of cholanoic acids regardless of weight, age, sex or diet. Changes in sterol turnover and peripheral tissue catabolism of cholesterol are concluded to be affected by age and to contribute to the mechanism of increase in serum cholesterol with advancing age.

Root Development and Source-Sink Relations in Carrot,Daucus carotaL

Physiological responses to root pruning were investigated by comparing 14CO2 fixation rates, the partitioning of 14C-labelled assimilate, and soluble and insoluble carbohydrate levels in the leaves of carrot plants following the removal of some of the fibrous roots, or fibrous roots and part of the tap root. Root pruning reduced 14CO2 fixation by 28–45% but leaf specific activity (14C assimilation g-1 leaf fresh weight) was unchanged. The proportion of total assimilate exported to the root system increased following root pruning and this was at the expense of the developing leaves. In younger plants (where the tap root received 10% of the assimilate) the supply of 14C to the tap root was maintained in spite of root pruning. However, shortening the tap root to 3 cm in older plants (in which 30% of the fixed 14C was normally exported to the developing storage organ), reduced its sink capacity and resulted in slightly greater retention of 14C in the mature leaves. Greater concentrations of insoluble carbohydrate were found in the mature leaves following root pruning but soluble sugar content was unaffected. Only small differences were observed in the distribution of 14C between soluble and insoluble carbohydrate fractions when plants were fed 14CO2 several days after the root pruning operations. These physiological responses were mainly associated with the removal of fibrous roots and support the view that the fibrous root system is more important than the developing storage organ in regulating growth in young carrot plants.

Metabolism of budralazine, a new antihypertensive agent, III.

1. [14C]Budralazine (I) administered orally to normotensive and spontaneously hypertensive rats showed no significant difference in metabolic fate between the two groups. 2. Peak plasma levels of 14C were 3.6 microgram equiv. of I per ml in both normotensive and hypertensive rats. Approx. 5% of total 14C in the plasma consisted of I within 4 h, but thereafter the parent drug was not detected. Approx. 15% of 14C in the plasma consisted of 1-hydrazinophthalazine within 16 h after the administration. 3. 45% and 37% of the dose of 14C was excreted into urine and faeces within 24 h, respectively. 4. A high retention of 14C in the aorta wall was found and the time course of 14C in the aorta wall was compatible with that of the reduction in blood pressure. The radioactive materials retained in the aorta wall were likely to be I or 1-hydrazinophthalazine, probably the latter, following macroautoradiography in hypertensive rats.

Retention of acyl groups in LM cell fibroblasts with altered phospholipid composition

Incorporation and loss of membrane lipids were measured in murine fibroblasts grown in suspension culture with [2- 14C]acetate in a chemically defined medium devoid of serum or lipid. Greater than 98 and 94% of the 14C present in the phospholipids and neutral glycerides respectively was found in the fatty acyl groups. During a 3-day growth period LM fibroblasts lost 65% of their 14C-labelled acyl groups from the phospholipids and 36% from the neutral lipids. Selective retention of 14C in individual isolated phospholipid and neutral lipid species occurred only in phosphatidylethanolamine. Retention of acyl groups in the phospholipids or neutral glycerides was not a property of LM suspension cultured fibroblasts. Supplementation of the LM cells with choline analogues, such as N, N′-dimethylethanolamine, N-monomethylethanolamine, or ethanolamine instead of choline, decreased the loss of 14C-labelled fatty acids from phospholipid and neutral lipid. Ethanolamine supplementation resulted in increased loss of 14C from desmesterol as well as decreased incorporation of 14C into desmosterol. Thus, polar head group manipulation affected acyl group composition, acyl group retention, and sterol metabolism in suspension cultured LM cells.

De novo synthesis of d-alanine in germinating Pisum sativum seedlings

The amounts of d-alanine derivatives, γ- l-glutamyl- d-alanine and N-malonyl- d-alanine, increase rapidly during the early growth of pea seeds. Pyruvate-[1− 14C], l-alanine-[U− 14C], d-alanine-[U− 14C], l-alanine-[ 15N] and 15NH 4Cl were therefore fed to the seedlings and the incorporation investigated. Labelling results revealed that pea seedlings can utilize these erogenous compounds to form d-alanine and that labelled l-alanine is effectively converted to the d-enantiomer with retention of 14C and, largely, 15N label. Enzyme analyses in vitro provided additional evidence that the extract of pea seedlings catalyzes the direct conversion of l-alanine to d-alanine. The data suggest that the de novo synthesis of d-alanine in pea seedlings occurs by a racemase reaction.

Variations in the progress of 14C uptake as a source of error in estimates of primary production

The progress curves of 14C retention for samples of phytoplankton from the Irish Sea incubated at contrasting light intensities have been obtained by two methods. The first method (A) involved the incubation of the samples for various periods up to 6 h, while the second method (B) consisted of making a series of short-term incubations over the same 6 h period. Over this period, the cumulative uptake was tenerally less when estimated by Method A than by Method B. The difference was greater in the samples incubated at the lower light intensity, the light history of the samples having no effect on the difference. The differences has a kinetic basis, with two combinations of progress curves obtained by use of the two methods. The first combination was associated with samples collected in the early morning, while the second combination was exhibited by samples taken in the afternoon irrespective of sampling depth. In certain samples, no increase in the 14C retained by the cells as measured by Method A was observed after 4 h. The cumulative retention of 14C by the cells after 2 h was generally greater when estimated by Method A than by Method B, this situation being reversed after 4 h. This reversal indicated a change in uptake kinetics between 2 and 4 h and it is suggested that this interval represents the time necessary for the 14C to work through the cellular pool of carbon. The findings are discussed in relation to the methodology for obtaining both estimates of primary production and 14C uptake-light intensity curves for marine phytoplankton.

Loss of radiocarbon in direct use of Aquasol for liquid scintillation counting of solutions containing 14C‐NaHCO31

Carbon‐14 activity was lost when 14C‐NaHCO3 in aqueous solution was added to Aquasol. Phenethylamine can be used to form carbamates which are stable in Aquasol in order to achieve complete retention of 14C in the liquid scintillation cocktail.

Export of 14C‐Assimilates in Cotton Leaves1

AbstractA study was made of the export of 14C‐assimilate in mature leaves of ‘Stoneville 213’ cotton (Gossypium hirsutum L.). Fruiting branches and subtending leaves of field grown plants were pulse‐labeled with 14CO2 for 5 min at about mid‐day. The amount of 14C‐assimilate transported to the cotton boll from the subtending leaves, bracts or boll wall, as well as the amount of 14C‐assimilate remaining in the leaves and bracts, were determined over a 22‐hour period. During this translocation period, leaves and bracts export 14C‐assimilate to the boll wall, ovules and lint; whereas the boll wall does not export 14C. assimilate. The leaves are the dominant source of assimilate for cotton bolls throughout the season.There is a differential rate of export and retention of H2O soluble and insoluble (starch) assimilate from the leaves and bracts. There is an initial rapid phase of transport of H2O soluble compounds from both leaf and bract sources. About 80% of these compounds disappear 6 hours after exposin the sources to 14CO2. After 22 hours, over 90% of this pool is depleted. In contrast, there is a retention of 14C in the starch fraction up to 6 hours after pulse‐labeling the sources with 14CO2. After 6 hours, there is a slow export of 14C‐assimilate from the starch fraction stored in the sources. Cotton leaves export assimilate stored as starch slowly. At the end of 22 hours, 90 to 95% of the 14C‐assimilate disappears from mature leaves and bracts.

Effect of phenacetin on the uptake and elimination of salicylate by the rat.

The blood levels of 14C, emanating from 14C-acetyl-salicylic acid (14C-ASA) p.o. and 14C-salicylic acid i.v., were decreased and unchanged, respectively, by the concomitant oral ingestion of phenacetin. Subsequent investigation showed that phenacetin: (a) did not affect the total renal excretion of 14C or ASA metabolites; (b) enhanced the retention of 14C, from either 14C-ASA or 14C-phenacetin, in the stomach contents and stomach tissues; (c) delayed stomach emptying, and (d) did not form undialyzable or insoluble complexes with ASA. It was concluded that phenacetin reduced the blood levels of salicylate by inhibiting stomach emptying.

In Vivo Studies on the Introduction of the 4-t-Double Bond of the Sphingenine Moiety of Rat Brain Ceramides

Abstract Erythro-dl-[3-3H]sphinganine was injected directly into the brains of 14- to 15-day-old rats. After 2 hours, 2.0% of the injected radioactivity could be recovered in the ceramide fraction of the brain lipid extract. The ceramide material was fractionated by thin layer chromatography into the classes of N-acylsphinganine and N-acylsphingenine, containing approximately equal amounts of radioactivity. Free 3H-labeled long chain bases were recovered after alkaline hydrolysis of the two ceramide classes and confirmed to be sphinganine and sphingenine. The presence of tritium in the unsaturated base sphingenine indicates a direct conversion of sphinganine to sphingenine or an acylated sphinganine to acylated sphingenine. No free [3H]sphingenine could be demonstrated in the lipid extract indicating either that it is present in very small amounts, due perhaps to rapid acylation, or that it is not produced as the free base but rather through acylated sphinganine. A time study over 145 min of the incorporation of [3-3H]sphinganine into ceramides showed an initial rapid production of N-acyl-[3H]sphinganine, which stayed at a steady level for the duration, while N-acyl-[3H]sphingenine appeared more slowly but was the predimonate ceramide at the final set time. This suggests N-acylsphinganine may be the precursor of N-acylsphingenine. When N-[1-14C]stearoyl-[3-3H]sphinganine, with an isotope ratio of 2.22 (3H:14C), was the injected substrate, ceramide containing [3H]sphingenine and 14C fatty acid could be isolated. The observed isotone ratio for the N-acylsphingenine was 2.52, indicating an 87% retention of 14C compared to 3H. The similarity of ratios suggests a direct conversion of the injected ceramide to the isolated compound; the small loss of 14C due perhaps to some hydrolysis followed by resynthesis.

Membrane filter retention—a source of error in the 14C method of measuring primary production

The relationship between volume of water filtered and apparent specific activity of phytoplankton in which the latter decreases (cpm 14C ml−1) with increasing volume filtered, previously attributed to cellular damage to phytoplankton during vacuum filtration, is now considered mainly due to retention of unfixed radiotracer on the membrane filter. The retention capacity for 14C by the filter, expressed as radioactivity per milliliter filtered, is maximum for small sample volumes (&lt; 1 nil), decreasing to a constant value when sample volumes are larger than 100 ml. This is attributed partially to absorption in the filter and probable retention of 14C bound to unknown substances in the water or on the filter which are eluted or exchanged by passage of volumes of water of 100 ml or greater. This “washing” effect permits almost all of the 14C not fixed in organisms to pass through the filter.