Slow Metabolic Rate Research Articles

Enhancement of Secondary Metabolite Production by Immobilized Gossypium arboreum Cells

AbstractA novel reactor with simultaneous use of plant cell immobilization, permeabilization, and elicitation was designed to enhance the productivity of secondary metabolites and to overcome limitations of plant cell culture, such as slow metabolic rate, low product yield, and sensitivity to shear stresses. Production of gossypol, an antifungal agent, from Gossypium arboreum was selected as a model system. The effects of immobilization, permeabilization, and elicitation on gossypol production were investigated in free suspension culture, immobilized plant cell reactor with recycled batch operation, and bioreactor with continuous operation. G. arboreum cells were effectively immobilized on a cotton matrix by entrapment with a spirally wound configuration. Permeabilization of immobilized cells provided a tool for a continuous process increasing the release of gossypol by 30%, while the elicitation technique played a major role to enhance productivity by more than 8‐fold. In comparisons of productivity, continuous operation and combined treatment gave productivity over 20‐fold higher than batch culture. Simultaneous use of immobilization, permeabilization, and elicitation was possible in continuous operation with an immobilized plant cell reactor.

Induction of MFO activity in the antarctic fish Pagothenia bernacchii: Preliminary results

The aim of this study was to determine the detoxication capacity and the sensitivity to pollutants of fish living in a pristine environment such as the Antarctic Ocean. Forty specimens of Pagothenia bernacchii collected during the Antarctic summer of 1991–1992 were divided into three groups, and were treated with 10 mg/kg of B(α)P, 50 mg/kg of PCBs and corn oil and sacrificed after 2, 4 and 10 days. The mixed function oxidase activity measured in these fish through the test of BPMO, EROD and BROD activities revealed that both B(α)P and PCBs are effective in inducing this enzyme system. Owing to the slow metabolic rate of this species, related to the low ambient temperature of its natural habitat, the highest level of induction was monitored after 10 days i.e. much later than in fish of temperate seas.

Properties of cold-adapted microorganisms and their potential role in biotechnology

Cold-adapted (psychrophilic and psychrotrophic) microorganisms are distinguished from mesophiles by their ability to grow at low temperatures. They are widely distributed in nature. Their response to high temperatures was shown to be disruption in protein synthesis by inability of RNA formation, alterations of the structure of nucleic acids, inactivation of thermolabile enzymes, activation of lytic enzymes, alterations of the cell morphology, inhibition of cell division and induction of heat shock proteins. At low temperatures, among other physiological characteristics, psychrophiles and psychrotrophs have slower metabolic rates and higher catalytic efficiencies than mesophiles. The genetic basis of cold adaptation is not cleared up. Cold-adapted microorganisms have a considerable potential in biotechnological application (waste treatment at ambient temperatures, enzymology, food industry, medicine).

Effectiveness and dropout rate of a very-low-calorie diet program

Severe obesity is a well-established health hazard (1). Many treatments are available, but few are effective because lost weight is quickly regained, followed by physiologic and psychological problems such as accelerated fat storage, slow metabolic rate, loss of muscle mass, fatigue, and depression (2–5).

Biphenyl and fluorinated derivatives: liver enzyme-mediated mutagenicity detected in Salmonella typhimurium and Chinese hamster V79 cells

Hepatocarcinogenic polychlorinated and polybrominated biphenyls usually show negative results in in vitro mutagenicity assays. Problems in their testing result from their low water solubility and their slow rate of metabolism. We therefore investigated better soluble model compounds, namely biphenyl and its 3 possible monofiuorinated derivatives. In the direct test, these compounds proved tobe nonmutagenic in Salmonella typhimurium TA98 and TA100 (reversion to histidine prototrophy) and in Chinese hamster V79 cells (acquisition of resistance to 6-thioguanine). However, when the exposure was carried out in the presence of NADPH-fortified postmitochondrial fraction of liver homogenate from Aroclor 1254-treated rats. all 4 compounds showed mutagenic activity in V79 cells. 3-Fluorobiphenyl produced strong mutagenic effects in S. typhimurium TA100 as well, whereas the other biphenyls were inactive. In strain TA9J8, 3- and 4-fluorobiphenyl showed mutagenic activity. This mutagenicity was enhanced in the presence of 1,1,1-trichloropropene 2,3-oxide, an inhibitor of microsomal epoxide hydrolase, thus suggesting that epoxides may be active metabolites.

The effects of ions on the conjugation of xenobiotics by the aralkyl‐coa and arylacetyl‐coa N‐acyltransferases from bovine liver mitochondria

The aralkyl-CoA:glycine N-acyltransferase and the arylacetyl-CoA:amino acid of N-acyltransferase were purified from bovine liver mitochondria and their response to a variety of ions investigated. The activity of the aralkyl transferase was inhibited by divalent cations with all substrates investigated. For benzoyl-coenzyme A (CoA), K+ was a competitive inhibitor, competing for binding at the benzoyl-CoA binding site. With salicylyl-CoA, K+ did increase the dissociation constant (KD) for acyl-CoA but it was not a competitive inhibitor and in addition, K+ increased the Michaelis constant for glycine (Kglym) tenfold. The data suggest that the increase in Kglym is due to bound K+ forcing reorientation of salicylyl-CoA at the active site so that it impinges on the glycine binding site. Inorganic anions and cations did not affect the extent of product inhibition by hippuric acid with either acyl-CoA and this was because they affected the binding of acyl-CoA and hippuric acid to the same extent. Ions did, however, greatly reduce the extent of product inhibition by CoA. This is critical because under approximate in vivo conditions (2.5 mM CoA), the salt-free enzyme would be almost completely inhibited by CoA. The arylacetyl transferase was activated by inorganic ions when assayed at saturating substrate concentrations. However, at physiologic concentrations of glycine certain salts were modestly inhibitory. The inhibitory effect of KCl was characterized by a large decrease in the affinity of the enzyme for phenylacetyl-CoA, suggesting that the arylacetyl-CoA region of the active site contained an inhibitory ion binding site. At low (physiologic) concentrations of substrate, the arylacetyl transferase was extensively inhibited by CoA and this inhibition was greatly reduced by ions. The 3'-phosphate group on CoA was found to be important for binding to the salt-free enzyme but in the presence of ions its importance was diminished. In the absence of inorganic ions the affinity of the enzyme for phenylacetyl-CoA and naphthylacetyl-CoA was so high that it could not be measured. In the presence of KCl the KD values for phenylacetyl-CoA and naphthylacetyl-CoA were similar, but the Km for glycine was extremely high for 1-naphthylacetyl-CoA conjugation, which accounts for its slow rate of metabolism. Conjugation with glutamine had a high Michaelis constant for glutamine (KGlum) and a low maximum velocity (Vmax) which accounts for the absence of glutamine conjugation in vivo.

Binding of Estradiol-17-Fatty Acid Esters to Plasma Proteins*

The C-17 fatty acid esters of estradiol are a unique family of long-acting estrogens that circulate in blood. The unusual duration of the estrogenic action of these esters has been shown previously to correlate with their very slow rate of metabolism. However, in striking contrast to their slow rate of metabolism, the clearance of these esters from blood is relatively rapid, not very different from that of estradiol (E2). Studies on the effect of the size of the carboxylic acid moiety on the rates of both metabolism and clearance have suggested that an active process might be involved in the cellular uptake of these circulating esters, and this, in turn, raised the question of how E2-fatty acid esters are transported in blood. The binding of representative E2-17-fatty acid esters to both human and rat plasma proteins known to bind either E2 or fatty acids was investigated. As expected, both E2 and 5 alpha-dihydrotestosterone bound to human sex hormone-binding globulin, whereas none of the E2 esters bound to this human plasma protein. Similarly, E2 bound to rat alpha-fetoprotein (AFP) and unsaturated fatty acids bound to both human and rat AFP, but none of the E2 esters bound to AFP of either species. These steroid esters bind to lipoproteins. Over 85% of a representative ester, E2-17-stearate, partitioned in the lipoprotein fractions of both human and rat serum, while the synthetic short chain ester, E2-17 beta-acetate, like E2 itself, partitioned predominantly in the nonlipoprotein fraction of blood. These results demonstrate the unusual binding of a family of steroid hormones to plasma lipoproteins and open the possibility that they are transported into target cells through the mediation of lipoprotein receptors.

Oxidative degradation of chlortoluron, propiconazole, and metalaxyl in suspension cultures of various crop plants

The metabolism of chlortoluron, ( N′-(3-chloro-4-methylphenyl)- N,N-dimethylurea), propiconazole (1-[2-(2′,4′-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl]- 1H-1,2,4-triazole), and metalaxyl ( dl- N-(2,6-dimethylphenyl)- N-(2′-methoxyacetyl) alanine methyl ester) was investigated in suspension cultures of crop species for which differences in metabolism had been demonstrated at the intact plant level. Uptake and metabolism of chlortoluron by cultures of Italian rye-grass ( Lolium multiflorum) was slow, the metabolites detected (42% of applied radioactivity after 13 days) being products of ring methyl oxidation and N-monodealkylation reactions. In sharp contrast, metabolism in a cotton ( Gossypium hirsutum) suspension culture was extremely fast (72% after 4 hr) and was attributed to extensive N-didealkylation in addition to rapid ring methyl oxidation. This rate of metabolism also implied a very rapid uptake of chlortoluron by the cotton culture. 14C-labelled propiconazole became rapidly associated with cells of wheat ( Triticum aestivum) and rice ( Oryza sativa) following treatment of suspension cultures. Uptake was initially more rapid in the rice culture (36% of applied radioactivity after 8 h compared to 19% for wheat) which, together with a slower rate of metabolism, resulted in more unchanged propiconazole being associated with rice cells. On a parts-per-million basis these results indicated an apparent 10-fold accumulation of propiconazole in rice cells compared to 5-fold in the wheat culture. Propiconazole metabolite patterns were similar in cultures of both species and indicated side-chain hydroxylation as the principal pathway. Uptake of metalaxyl was slow in suspension cultures of both lettuce and potato (≅ 20% after 17 days). Subsequent metabolism was also slow but appeared to be limited by the poor rate of uptake. Both cultures were found to be similarly versatile with respect to metabolic attack on metalaxyl, which included ring methyl hydroxylation, aryl hydroxylation, ester cleavage, ether cleavage ( O-dealkylation), and N-dealkylation (side-chain cleavage), the hydroxylation reactions being quatitatively the more important. The results for all three pesticides are compared to those obtained previously from studies with intact plants of the same species.

D(-)Lactic acid--a metabolism problem

The metabolization of D-lactate was examined in volunteers by means of renal excretion after intake of DL-lactate, and in rats as well as in rat liver in vitro by the oxidation rate of 14C-D-lactate to 14CO2. In five volunteers after intake of DL-lactate containing 1.60 to 6.5 mmol D-lactate per kg 0.75 (equiv. to 50-200 mg/kg) an average of 1.2-2.2 percent of the dose was eliminated in urine. The exponential decline of renal elimination during the first 15 hours after intake and the total excretion time up to 24 hours (and possibly more) suggested a quite slow rate of metabolism. Following intraperitoneal injection of 2.0 and 4.2 mmol per kg 0.75 in rats (equiv. to 62 and 131 mg per kg in man) the oxidation rate of D-lactate vs. L-lactate was significantly and strongly reduced. After intragastral dosage of DL-lactate containing 4.2 to 12.8 mmol D-lactate per kg 0.75 an average of 0.9 and 2.4 percent were excreted in urine as D-lactate and as metabolites. Even after the lowest dose D-lactate oxidation to CO2 extended far beyond 8 hours. Higher doses decreased the rate of D-lactate oxidation. In tissue samples of rat liver in vitro oxalate, L-lactate and pyruvate inhibited the oxidation of D-lactate. L-lactate in a physiological concentration was sufficient to effect an inhibition of 20 percent. A significant increase of D-lactate oxidation with increasing body weight and a significantly higher oxidation of D-lactate in conventionals vs. germ-free rats indicated the influences of age and gastro-intestinal flora on D-lactate metabolism. From these results it is concluded that D-lactic acid is only slowly metabolized if the concentration of one or other of the lactate isomers is elevated.

Child and Adolescent Nortriptyline Single Dose Kinetics Predict Steady State Plasma Levels and Suggested Dose

The use of nortriptyline single dose kinetics to predict steady state plasma levels and suggested dose was investigated in 33 pediatric subjects who were diagnosed as having major depressive disorder. The data were analyzed separately for the 11 subjects 5 to 9 years old who received a single dose of 25 mg and a fixed daily dose of 20 mg of nortriptyline, and for the 22 subjects 10 to 16 years old who received a single dose of 50 mg and a fixed daily dose of 50 mg of nortriptyline (N = 17) or a fixed daily dose of 20 mg (N = 5) because of a very slow rate of metabolism of the drug. Correlations within the group of 5 to 9 years olds between the steady state plasma levels and the five sampling points after the single dose were all highly significant. Correlations between the steady state plasma levels within the group of 10 to 16 year olds and the five sampling points after the single dose and a fixed daily dose of 50 mg (N = 17) were also highly significant. Similar correlations for the total group of 10 to 16 year olds (N = 22) were performed (prorating the steady state plasma levels of the slow metabolizers), and these too were highly significant. Suggested dose schedules for each age group were developed from the regression equations of nortriptyline steady state plasma levels versus 24-hour nortriptyline plasma levels after the single dose. The regression equation for the group of 5 to 9 year olds was highly significant.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro ruminal fermentation of organic acids common in forage.

Mixed rumen bacteria from cows fed either timothy hay or a 60% concentrate were incubated with 7.5 mM citrate, trans-aconitate, malate, malonate, quinate, and shikimate. Citrate, trans-aconitate, and malate were fermented at faster rates than malonate, quinate, and shikimate. Acetate was the primary fermentation product for all six acids. Quinate and shikimate fermentations gave rist to butyrate, whereas malate and malonate produced significant amounts of propionic acid. High-pressure liquid chromatography of fermentation products from trans-aconitate incubations revealed a compound that was subsequently identified as tricarballylate. As much as 40% of the trans-aconitate acid was converted to tricarballylate, and tricarballylate was fermented slowly. The slow rate of tricarballylate metabolism by mixed rumen bacteria and its potential as a magnesium chelator suggest that tricarballylate formation could be an important factor in the hypomagnesemia that leads to grass tetany.

EFFECTS OF PHOTOCYCLES AND PERIODIC AMMONIUM SUPPLY ON THREE MARINE PHYTOPLANKTON SPECIES. II. AMMONIUM UPTAKE AND ASSIMILATION1

ABSTRACTThe relative influence of the photoperiod and of periodic ammonium pulses in entraining the cell division cycle in nitrogen‐limited cyclostat cultures differs dramatically in Hymenomonas carterae Braarud and Fagerl, Amphidinium carteri Hulburt and Thalassiosira weissflogii Grun. We examined how each species processes an NH4+ pulse at various times during the cell cycle and the L/D cycle. Rates of NH4+ uptake and changes in cellular concentrations of NH4+, free amino acids, and protein were examined after the addition of an NH4+ pulse. Depletion of NH4+ from the medium occurred earlier when the pulse was given at the beginning of the light period than at the beginning of the dark period in H. carterae and A. carteri. Depletion took longer in the T. weissflogii cultures and the kinetics were similar during both stages of the photocycle in this species. Similarly, the temporal phasing and maximum pool sizes varied with timing of the NH4+ pulse in H. carterae and A. carteri but complete assimilation was relatively rapid. More persistent pools of NH4+ and free amino acids accumulated in T. weissflogii, and the patterns of assimilation varied little as a function of the timing of the pulse with respect to the photocycle. Although nitrogen metabolism occurred rapidly in nitrogen‐limited H. carterae and A. carteri, the entrainment of the cell division cycle by the photoperiod resulted in a large degree of uncoupling between completion of nitrogen assimilation and cell division. It is hypothesized that the strong entrainment of the cell division cycle of T. weissflogii by NH4+ pulses results from a relatively slow rate of nitrogen metabolism.

Distribution of Bratton-Marshall-positive material in mice following intravenous injections of nitrosoureas.

As determined by a colorimetric assay measuring parent compounds plus ether-extractable nitroso-containing metabolites, N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU) disappeared more rapidly than N-(2-chloroethyl)-N'cyclohexyl-N-nitrosourea (CCNU) and N-(2-chloroethyl)-N'-(4-transmethylcyclohexyl)-N-nitrosourea (MeCCNU) and their products from the tissues of mice injected IV. Assay of selected samples by high-pressure liquid chromatography revealed that the colorimetric assay for BCNU was specific in that the two assays gave equivalent results. Following IV-injections of CCNU and MeCCNU, however, levels of the parent compounds decreased much more rapidly than the total, color-producing material. Of seven tissues, the largest Cxt values for BCNU, as determined by the colorimetric assay, were noted for blood (442 microgram-min/ml) and large intestine (285 microgram-min/g). Liver (29 microgram-min/g) had the lowest Cxt value, reflecting rapid metabolism of the compound by this organ. Color-producing material related to CCNU disappeared from the solid tissues of mice in a manner generally parallel to that for blood. Of the Cxt values for this compound and its products, those for lung (1753 microgram-equivalents-min/g), kidney (1633 microgram-equivalents-min/g), and small intestine (1557 microgram-equivalents-min/g) were highest. Consistent with its slower rate of metabolism, MeCCNU and its color-producing metabolites remained in most tissues of mice for 12 h following injection. Except for brain (1434 microgram-equivalents-min/g), Cxt values for this nitrosourea and its metabolites in tissues were higher than those of blood (5485 microgram-equivalents-min/ml), with kidney (15,324 micrograms-equivalents-min/g), liver (12,921 microgram-equivalents-min/g), and large intestine (11,501 microgram-equivalents-min/g) being highest. For each nitrosourea, a fair correlation was observed between the Cxt values for tissues and the toxic and/or antitumor effects at those sites.

Low molecular weight intracellular iodocompounds with long intrathyroidal half-life: remnants of thyroglobulin hydrolysis?

In this paper additional information on low molecular weight, soluble, intrathyroidal iodocompounds with slow metabolic rate is provided. These compounds have previously been localized autoradiographically within the follicular cells. Radioiodide was administered to rats on a normal iodine intake (6--7 microgram/day) for 80 days to approach isotopic equilibration of the intrathyroidal iodine with the dietary radioiodide. When the isotope was omitted from the diet the intrathyroidal radioiodine was released with an apparent half-life of approximately 12 days. When the individual soluble components carrying radioiodine were analyzed after separation on Sephadex G-200, different apparent half-lives were found, the half-life of thyroglobulin (Tgb) being roughly 10 days and that of the low molecular weight iodocomounds being in the order of 60 to 100 days or more. In addition to the soluble low molecular weight iodocompounds, the radioactivity in the particulate fraction increased by 100% during the tracer washout when compared to Tgb and the total soluble fraction. The soluble slow turnover iodocompounds contained a higher percentage of carbohydrate and total iodine than Tgb, while the relative amounts of each sugar analyzed (hexoses, fucose, hexosamine and sialic acid) were close to those in Tgb. Sephadex G-25 chromatography of the low molecular weight iodocompounds obtained after Sephadex G-200 separation resulted in the separation of 4 peaks. Two peaks identified as iodopeptides could be further analyzed. The carbohydrate composition of these peptides was similar to that of 2 glycopeptides obtained after in vitro enzymatic hydrolysis of purified Tgb with pronase. Slow equilibration with radioiodine, long apparent intrathyroidal half-life and carbohydrate content similar to that of Tgb, taken together with previously published data on intracellular localization of soluble intrathyroidal iodocompounds, suggest that the low molecular weight iodocompounds are products of in vivo hydrolysis of engulfed Tgb droplets.

Metabolism of phenformin in the rat and guinea-pig.

1. Following administration of [2'-14C]phenformin to rat and guinea pig, the guinea-pig showed a slower rate of excretion of radioactivity than the rat, together with a slower rate of metabolism, which may partly explain the increased pharmacological response of the guinea-pig to the drug. 2. The rat eliminated 26% of an intraduodenal dose of [2'-14C]phenformin (20 mg/kg) in the bile in 6 h compared to 6% in the guinea-pig. 3. The rat excreted large amounts of 4-hydroxyphenformin (free and conjugated with glucuronic acid) and also some unchanged phenformin, but the extent of metabolism varied with dose and route of administration. 4. The guinea-pig excreted no 4-hydroxyphenformin after an oral dose (25 mg/kg) and only a small amount after i.p. administration (12.5 mg/kg). After oral administration, guinea-pig urine contained an unidentified metabolite, and its glucuronide, which may be a product of aliphatic C- or N-hydroxylation and which accounted for 47% of the 24 h urinary radioactivity (17% of the dose). Guinea-pig faeces contained an unidentified metabolite which had similar chromatographic properties to the novel urinary metabolite.

Gastrins in cat and dog: evidence for a biosynthetic relationship between the large molecular forms of gastrin and heptadecapeptide gastrin.

1. Extracts of antral, duodenal and jejunal mucosa contained the same concentrations and molecular forms of gastrin in cat and dog. In both species component III constituted 93%, component II 4% and components I and IV each 1% of the total immunoreactivity. 2. During electrical vagal stimulation or feeding in (a) anaesthetized cats with ligated kidney vessels and resected jejunum and ileum, (b) anaesthetized normal cats or (c) conscious normal cats, release of the large molecular forms of gastrin, components I and II, was not detectable. 3. Luminal perfusates of cat antrum contained only component III and occasionally less than 2% of component IV. 4. Intravenous injections into conscious cats of components I, II and III isolated from cat antrum revealed a significantly slower elimination of the large components (t1/2 approximately 4.2 and 4.0 min respectively) than of component III (t1/2 approximately 1.1 min). Thus the absence of components I and II in cat blood cannot be due to rapid degradation. 5. During feeding, components I and II constituted 20% of the total gastrin immunoreactivity in antral venous blood of dogs. This amount is sufficient to account for the predominance of large components in peripheral venous blood in dogs considering their slow metabolic clearance rates. 6. Luminal perfusates of dog antrum contained components I, II and III in proportions corresponding to those found in antrum. 7. The results indicate that components I and II are synthesized in the same proportions in gastrin cells of cat and dog. In the cat, components I and II are, however, never released from the cells. Since these components contain heptadecapeptide gastrin within their sequeaces, they probably represent biosynthetic precursors of the principal gastrin, the heptadecapeptide (component III). The predominance of component III in gastric juice suggests that the feline gastrin cell secretes only component III, which degrades to component IV in blood.

Evolution of thinking in fetal respiratory physiology

An outstanding characteristic of intrauterine life is the low oxygen pressure (Po2) of fetal blood. It seemed at one time that in order to tolerate the Po2 of the uterine environment the fetus must have a relatively slow rate of oxidative metabolism or depend upon anaerobic pathways of substrate utilization. Subsequent studies have shown that the fetus has a high rate of oxygen consumption and that lactic acid is a substrate rather than a net product of normal fetal metabolism. The circulatory response of the fetus to acute hypoxia is centered on the requirement of maintaining the arterial oxygen flow to the heart and central nervous system without increasing cardiac output. The arterial oxygen flow concept helps in understanding the physiologic meaning of the high oxygen affinity of fetal blood and the boundary conditions of the fetal defense against hypoxia.

The Mechanism of Hypergastrinemia in Achlorhydria

The effect of protein-rich food, intravenous calcitonin injections, and intragastric instillation of hydrochloric acid on serum gastrin concentrations and gastrin component pattern was studied in hypergastrinemic patients (pernicious anemia) and matched control subjects. Moreover, plasma secretin concentrations were measured during intragastric acidification. The intragastric acidification resulted in rapid fall in serum gastrin concentrations, although not below the upper limit of normal range. The small components, III (gastrin-17-like) and IV (gastrin-13-like), almost disappeared, whereas the concentrations of component I and component II (gastrin-34-like) were less affected. The increase in secretin concentrations after intragastric acidification was smaller in patients with pernicious anemia than in normal subjects, although the difference was not significant. In contrast to the results in normal control subjects, neither food nor calcitonin produced significant variations in serum gastrin concentrations and gastrin component pattern of pernicious anemia patients. The failure of food to stimulate and of calcitonin to inhibit release of gastrin in the majority of pernicious anemia patients might suggest that gastrin secretion in these patients is autonomous. However, considering the recently recognized slow metabolic clearance rate of big gastrins, the effect of intragastric acidification suggests that the mechanism for acid inhibition of the antral gastrin secretion is intact in patients with achlorhydria.

Medroxyprogesterone acetate: a steroid with potent progestational activity but low receptor affinity in the guinea pig uterus.

The guinea pig progestin receptor appears to be unique among mammalian receptors studied to date in that it displays a low binding affinity for some biologically potent 17 alpha-substituted progestinss. [3H]Medroxyprogesterone acetate (MPA) was synthesized and used to investigate this dichotomy between binding affinity and biological activity. The comparison of cytoplasmic and nuclear receptor binding characteristics suggested that progesterone and MPA were bound to the same receptor but with different affinities. Following an intravenous injection of 3H-steroids, the plasma level of progesterone was lower than that of MPA at all time points. Correspondingly, for up to 6 hours following steroid administration, progesterone levels were lower in uterine cytoplasm and higher in nuclei than those of MPA. However, by 24 hours, MPA nuclear levels were higher than those of progesterone, in accordance with plasma levels. We conclude that the potent biological activity of MPA relative to progesterone is due in part to its slower rate of metabolism and longer nuclear retention.

Auxin and Ethylene Control of Growth in Seedlings ofZea maysL. andAvena sativaL

The effects of applied ethylene on the growth of ooleoptiles and mesocotyls of etiolated monocot seedlings (oat and maize) have been compared with those on the epicotyl of a dicot seedling (the etiolated pea). Significant inhibition of elongation by ethylene ( 10 pi l1 for 24 h) was found in intact seed lings of all three species, but lateral expansion growth was observed only in the pea internode and oat mesocotyl tissue. The sensitivity of the growth of seedling parts to ethylene is in the decreasing order pea internode, oat coleoptile and oat mesocotyl, with maize exhibiting the least growth response. Although excised segments of mesocotyl and coleoptile or pea inter node all exhibit enhanced elongation growth in IAA solutions (10_6-2 x 10~5 mol 1_1), no consistent effects were found in ethylene. Ethylene production in segments was significantly enhanced by application of auxin (IAA, 10-5 mol 1_1 or less) in all tissues except those of the oat mesocotyl. Segments of maize show a slow rate of metabolism of applied [2-14C]IAA (30 per cent con verted to other metabolites within 9 h) and a high capacity for polar auxin transport. Ethylene (10 pi 1_1 for 24 h) has little effect, on either of these processes. The oat has a smaller capacity for polar transport than maize and the rate of metabolism of auxin is as fast as in the pea (90 per cent metabolized in 6 h). Although ethylene pretreatment does not change the rate of auxin metabolism in oat, there is a marked reduction in auxin transport. It is proposed that the insensitivity of maize seedlings to ethylene is related to the supply and persistence of auxin which could protect the seedling against the effects of applied or endogenously produced ethylene. Although the mesocotyl of oat is sensitive to applied ethylene it may be in part protected against ethylene in vivo by the absence of an auxin-enhanced ethylene production system. The results are discussed in relation to a model for the auxin and ethylene control of cell growth in the pea.