Polyamines and ornithine decarboxylase activity during growth and differentiation in Blastocladiella emersonii.

The activity of ornithine decarboxylase (EC 4.1.1.17, L-ornithine carboxy-lyase) was determined during the life cycle of Blastocladiella emersonii. The specific activity of the enzyme was found to be low in the zoospores, to rise 20-fold during germination and early growth, to fall during growth and to rise again during sporulation. This rise in enzyme activity was shown to be dependent on protein synthesis. Putrescine levels, on a per mg of protein basis, paralleled the fluctuation found in ornithine decarboxylase activity. Putrescine and spermidine were the only polyamines found in extracts of B. emersonii.     

Polyamines and ornithine decarboxylase activity during growth and differentiation in Blastocladiella emersonii

The activity of ornithine decarboxylase (EC 4.1.1.17, L-ornithine carboxy-lyase) was determined during the life cycle of Blastocladiella emersonii. The specific activity of the enzyme was found to be low in the zoospores, to rise 20-fold during germination and early growth, to fall during growth and to rise again during sporulation. This rise in enzyme activity was shown to be dependent on protein synthesis. Putrescine levels, on a per mg of protein basis, paralleled the fluctuations found in ornithine decarboxylase activity. Putrescine and spermidine were the only polyamines found in extracts of B. emersonii.     

Changes in ornithine decarboxylase activity in the developing parotid salivary gland

Ornithine decarboxylase activity in the rat parotid salivary gland was estimated during the early postnatal development. Regular alterations of enzymatic activity were found in different periods of gland development. The data obtained were compared with the evidence on the establishment of protein synthesis circahoralian rhythm of this organ in ontogenesis. The ornithine decarboxylase activity, being rather high in the parotid gland as long as up to the 20th-21st days, decreases during the termination of differentiation in this organ. It rises simultaneously with the emergence of circahoralian rhythm of protein synthesis.     

Arginase,ornithine decarboxylase and S-adenosylmethionine decarboxylase in chicken brain and retina

• 1.1. Arginase, ornithine decarboxylase and S-adenosylmethionine decarboxylase are active in both retina and brain. Activity is higher in cerebellum than in the cerebral hemispheres and optical lobes.
• 2.2. Arginase and ornithine decarboxylase are very active in the retina of very young chicks, while S-adenosylmethionine decarboxylase is poorly active. By contrast, S-adenosylmethionine decarboxylase is much more active in brain.
• 3.3. The pattern of activity during development is different; only ornithine decarboxylase is very active during embryonal life; S-adenosylmethionine decarboxylase, at all events in brain, is more active in adult life.
• 4.4. Ornithine decarboxylase is inhibited in vitro by α-difluoromethylornithine, but not in vivo. Diaminopropane inhibits brain ornithine decarboxylase, but does not induce an ornithine decarboxylase-antizyme.
• 5.5. Methylglyoxal bis(guanylhydrazone) promotes an increase of S-adenosylmethionine decarboxylase activity in both the brain and the retina in vivo.

     

Estrogen- and antiestrogen-induced ornithine decarboxylase activity and uterine growth in the rat

The estrogen antagonists tamoxifen and monohydroxytamoxifen are also classified as partial estrogen agonists. In infantile rats, estradiol induced a single peak of uterine ODC activity at 6h following injection regardless of the extent of induction by various estradiol doses. By contrast, the timing of the ODC activity peak induced by tamoxifen and monohydroxytamoxifen was highly dependent upon the dosing conditions and was delayed to 18 h at lower tamoxifen doses. In immature rats, tamoxifen and monohydroxytamoxifen induced two peaks of uterine ODC activity resembling those induced by estradiol. Both ODC activity peaks were delayed by 9 h, without decreases in peak heights, by a 50-fold tamoxifen dose reduction. In all experiments the initial appearance of antiestrogen- and estradiol-induced ODC activity corresponded to initial uterine wet weight gain regardless of dosing condition. Thus, when dose-related temporal shifts are taken into account, tamoxifen and monohydroxytamoxifen are complete agonists with respect to induction of uterine weight gain and ODC activity.     

Ornithine decarboxylase activity in developing rat brain

—Total ornithine decarboxylase (ODC) (EC 4.1.1.17) activity per rat brain was elevated markedly from 14 days after conception to 12 days postnatum. ODC activity in the brainstem was very low and changed little during postnatal development. Activity in the cerebral hemispheres declined from a high level at birth to the low adult level by 8 days postnatum. Conversely activity in the cerebellum increased markedly from 3 days until 11 days postnatum, then suddenly decreased. Hence, the periods of greatest ODC activity paralleled those of maximal cell proliferation in each brain region. During perinatal brain development ODC activity changed considerably; it declined at about one day prior to term, and then increased rapidly to its highest level of activity at 4 h postnatum. Premature birth by caesarian section or lack of maternal care and nutrition did not affect this early postnatal response. The postnatal burst in ODC activity appears to be unique for brain tissue, since this response did not occur in heart, skeletal muscle or liver. Data from studies in which portions of fractions characterized by high or low enzymatic activity, respectively, were mixed or in which the supernatant enzyme fraction was dialysed are not consistent with the presence of direct inhibitors or activators of the enzyme. In addition, administration of cycloheximide to newborn rats abolished the 4-h postnatal burst in ODC activity. Our results suggest that the increase in ODC activity reflects enzyme synthesis de novo.     

Zinc can influence ornithine decarboxylase activity in rat thymus cells

Summary The thymus of young rats contained a high basal activity of ornithine decarboxylase (ODC). Treatment with zinc sulphate caused a slight increase of thymic ODC activity within 6 hours and a more marked enhancement (three-fold) in the spleen 24 h after treatment. In spite of the high activity of thymic ODCin vivo, ODC was not detectable in primary cultures of rat thymocytes, but was early and largely induced after treatment with Concanavalin A (Con A). The presence of 0.1 mM zinc in the medium increased the response of ODC to Con A. This effect of zinc in mitogen activated thymocytes may be due to the stabilization of ODC, which was found to decay with a half life of 65 min after the block of protein synthesis with cycloheximide. On the contrary in absence of zinc the half life of the enzyme was 40 min, as in the rat thymus in vivo.Zinc alone, at 0.1 mM concentration, did not affect ODC activity in resting thymocytes during the early times, but the metal was able to cause an increase of the enzyme activity after 4–6 days of culture. Other heavy metals such as mercury, cadmium and copper provoked a late increase of ODC activity, but their action was evident only at dosages which were toxic for the cells.     

Polyamines in brain and heart of the neonatal rat: effects of inhibitors of ornithine decarboxylase and spermidine synthase

Daily administration of dicyclohexylamine (DCHA), an inhibitor of spermidine synthase, to neonatal rats produced a dose-dependent depletion of brain spermidine, accompanied by a rise in putrescine and spermine. Despite continued DCHA treatment, levels of all three polyamines returned toward normal within two weeks. alpha-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, had a much more profound and persistent effect on spermidine and also depleted putrescine throughout drug administration; furthermore, DFMO prevented both the elevation of putrescine caused by DCHA and the eventual restitution of spermidine levels. Although a similar pattern of effects was seen in the heart, the time course of onset of DCHA-induced alterations in polyamine levels and the rapidity of subsequent adaptation were considerably different from those in brain. The net activity of DCHA toward polyamines in developing tissues thus involves the direct actions of the drug on spermidine synthesis in combination with compensatory metabolic adjustments made by each tissue to polyamine depletion.     

Desensitization of ornithine decarboxylase activity to norepinephrine in the testis of rat

Injection of norepinephrine (NE) at a dose of 10 micrograms per testis caused the testis refractory in terms of ornithine decarboxylase (ODC) activity at 24 h. This desensitization was found to be both time and dose dependent. Injection with follicle stimulating hormone, luteinizing hormone, prostaglandin F2 alpha, cyclic AMP or epinephrine to norepinephrine desensitized testis caused stimulation of ODC activity. This indicates that the refractoriness caused by norepinephrine is specific to this agent alone.     

Regulation of ornithine decarboxylase activity by putrescine and spermidine in rat liver

The marked enhancement of the activity of ornithine decarboxylase (EC 4.1.1.17) in rat liver at 4 h following partial hepatectomy or the treatment with growth hormone could be almost completely prevented by intraperitoneal administration of putrescine. A single injection of putrescine to partially hepatectomized rats caused a remarkably rapid decline in the activity of liver ornithine decarboxylase with an apparent half-life of only 30 min, which is almost as rapid as the decay of the enzyme activity after the administration of inhibitors of protein synthesis. Under similar conditions putrescine did not have any inhibitory effect on the activity of adenosylmethionine decarboxylase (EC 4.1.1.50) or tyrosine aminotransferase (EC 2.6.1.5). Spermidine given at the time of partial hepatectomy or 2 h later also markedly inhibited ornithine decarboxylase activity at 4 h after the operation and, in addition, also caused a slight inhibition of the activity of adenosylmethionine decarboxylase.     

Lack of ornithine decarboxylase activity in isolated rat liver parenchymal cells

Polyamines are associated with fundamental metabolic and functional steps in cell metabolism. The activity of ornithine decarboxylase, the key enzyme in polyamine metabolism, was followed during the preparation of rat liver parenchymal cells and in the isolated cells during incubation. In experiments in which ornithine decarboxylase was not induced in vivo, enzyme activity dropped to barely measurable values during the preparation. An even more drastic loss of enzyme activity was noted in livers in which ornithine decarboxylase activity was stimulated in vivo 20-40fold by previous injection of bovine growth hormone, or thioacetamide or elevated because of circadian rhythmical changes of the enzyme activity. Within the first 20 min of liver perfusion to disintegrate the tissue, ornithine decarboxylase activity decreased by up to 80%. The presence of bovine growth hormone during cell preparation cannot prevent the loss of enzyme activity. Incubation of the isolated cells for periods of up to 240 min did not restore the enzyme activity. Furthermore, incubation of the cells with bovine growth hormone did not induce ornithine decarboxylase, even though the medium was supplemented with amino acids in physiological concentrations. During normal liver perfusion and in contrast to the situation with isolated cells, there is no loss of enzyme activity but a small rise. Following pretreatment of the animals with bovine growth hormone or thioacetamide the highly stimulated activity of ornithine decarboxylase declined slowly during liver perfusion, but never dropped to values lower than normal for perfusion periods of up to 240 min. Moreover, in the intact perfused organ ornithine decarboxylase remains responsive to bovine growth hormone. The experiments demonstrate that enzymatic tissue dispersion by collagenase in particular or the preparation of isolated cells in general drastically alters the metabolic and functional state of rat liver parenchymal cells.     

Effects of dexamethasone on the activity of histidine decarboxylase, ornithine decarboxylase, and dopa decarboxylase in rat oxyntic mucosa

Since accelerated turnover of histamine in oxyntic mucosa may be an important factor in the pathogenesis of peptic ulcers, the effect of dexamethasone and other glucocorticoids on the activity of gastric histidine decarboxylase (HDC) was studied in the rat. The activity of HDC in rat oxyntic mucosa increased significantly after dexamethasone was injected s.c. to rats at doses larger than 0.4 mg/kg body weight. The maximum response of the HDC activity to dexamethasone (4 mg/kg) was observed 8 h after the treatment. The activity of ornithine decarboxylase (ODC) increased at 4 h, while that of DOPA decarboxylase showed no significant change throughout the 16-h period following a single injection of dexamethasone. The mucosal levels of histamine, putrescine, and spermidine rose significantly after the steroid treatment, while the spermine levels remained nearly constant. There was no sex difference in these responses to dexamethasone. Betamethasone showed nearly the same effects as dexamethasone on the decarboxylase activities and the mucosal levels of diamines. Serum gastrin levels showed no significant change for the first 4 h and then rose significantly 8 and 16 h after dexamethasone treatment. Pentagastrin (0.5 mg/kg) increased the HDC activity, while it showed no significant effect on either the mucosal ODC activity or levels of polyamines and histamine. These data suggest that dexamethasone influences the metabolism of histamine and polyamines in rat oxyntic mucosa both directly and via stimulation of gastrin release.     

Modulation of ornithine decarboxylase activity and ornithine decarboxylase-antizyme complex in rat heart by hormone and putrescine treatment

Ornithine decarboxylase was present in a cryptic, complexed form in an amount approximately equivalent to that of free ornithine decarboxylase activity in adult rat heart. Addition of isoproterenol (10 mg/kg) caused a notable rise in ornithine decarboxylase activity and a simultaneous decrease in the amount of the complexed enzyme. During the period of ornithine decarboxylase decay, when cardiac putrescine content had reached high values, the level of the complex increased above that of the control. Administration of putrescine (1.5 mmol/kg, twice) or dexamethasone (4 mg/kg) produced a decrease of heart ornithine decarboxylase activity, while it did not remarkably affect the level of complexed ornithine decarboxylase, therefore raising significantly the ratio of bound to total ornithine decarboxylase. Putrescine also elicited the appearance of free antizyme, concomitantly with the disappearance of free ornithine decarboxylase activity after 3-4 h of treatment. These results indicate that a significant amount of ornithine decarboxylase occurs in an inactive form in the heart under physiological conditions and that its absolute and relative levels may vary following stimuli which affect heart ornithine decarboxylase activity.     

Effect of catecholamines on ornithine decarboxylase activity in the testis of immature rat

Intratesticular injection of epinephrine and norepinephrine caused stimulation of ornithine decarboxylase (ODC) activity in the testis of immature rat. The effect of epinephrine was time and dose dependant. The minimal effective dose for epinephrine was found to be 100 pg and optimal stimulation was observed with 500 ng of the drug. Maximal stimulation of ODC occurred at 2 h after the treatment and reduced significantly at 4 h reaching to control levels at 6 h. Simultaneous injection of epinephrine with dibutyryl cAMP, luteinizing hormone, follicle stimulating hormone or prostaglandin E₂ caused additional stimulation of the enzyme activity. Injection of epinephrine to norepinephrine treated animals caused additional effect. Both epinephrine and norepinephrine were found to stimulate the enzyme activity in leydig cell and seminiferous tubule fractions. These results suggest that catecholamines are also involved in the regulation of ODC activity in the testis of rat.     

Regulation of ornithine decarboxylase activity in rat ovarian cells in vitro.

Incubation of rat ovarian cell suspension with human choriogonadotropin (hCG) caused a marked enhancement of ornithine decarboxylase (EC 4.1.1.17) activity after a lag period of several hours. Even though ovarian ornithine decarboxylase could be induced in minimum essential medium by the hormone alone, supplementation of the medium with various sera greatly enhanced the stimulation of the enzyme activity. All the sera tested (human, fetal calf and horse) were able to stimulate ornithine decarboxylase activity even in the absence of hCG. Maximum stimulation of the enzyme activity by hCG and/or serum occurred in ovarian cell suspensions prepared from 30 to 33-day-old rats. There was a close correlation between the stimulation of ornithine decarboxylase activity and the accumulation fo cyclic AMP in response to the administration of the hormone (in the presence or absence of serum). However, while various sera alone markedly enhanced ovarian ornithine decarboxylase activity in vitro they, if anything, only marginally stimulated the accumulation of cyclic AMP and the secretion of progesterone in ovarian cells in the absence of gonadotropin. A similar dissociation of the stimulation of ornithine decarboxylase activity from the production of cyclic AMP and progesterone was likewise found when the ovarian cells were incubated in an enriched medium (M199) supplemented with albumin and lactalbumin hydrolysate in the absence of the hormone. Under these culture conditions ornithine decarboxylase activity was strikingly enhanced, greatly exceeding the stimulation obtained with various sera, while the accumulation of cyclic AMP and the secretion of progesterone remained virtually unchanged. Specific inhibition (up to 90%) of gonadotropin-induced ornithine decarboxylase activity by difluoromethyl ornithine or 1,3-diamino-2-propanol had little effect on the ability of the ovarian cells to respond to the hormone with increasing production of cyclic AMP and progesterone. While showing that rat ovarian ornithine decarboxylase can be induced in vitro by choriogonadotropin or various sera, our results indicate that the activation of the enzyme involves at least two different mechanisms: (i) One (in response to gonadotropin) involving a prior stimulation of cyclic AMP production, and (ii) another (in response to serum) that is not associated with increases in the accumulation of the cyclic nucleotide.