Immunoreactive Ornithine Decarboxylase Research Articles

Altered subcellular localization of ornithine decarboxylase in Alzheimer’s disease brain

The amyloid precursor protein can through ligand-mimicking induce expression of ornithine decarboxylase (ODC), the initial and rate-limiting enzyme in polyamine biosynthesis. We report here the regional distribution and cellular localization of ODC immunoreactivity in Alzheimer’s disease (AD) brains. In frontal cortex and hippocampus of control cases, the most pronounced ODC immunoreactivity was found in the nucleus. In possible and definite AD the immunoreactivity had shifted to the cytoplasm. In cerebellum of control cases, ODC staining was found in a small portion of Purkinje cells, mostly in the nucleus. In AD, both possible and definite, the number of stained Purkinje cells increased significantly and immunoreactivity was shifted to the cytoplasm, even though it was still prominent in the nucleus. In conclusion, our study reveals an early shift of the ODC immunoreactivity in AD from the nuclear compartment towards the cytoplasm.

Influence of Ovarian Ornithine Decarboxylase in Folliculogenesis and Luteinization

LH plays a relevant role in folliculogenesis, ovulation, and luteinization. Although ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, is a target of LH in the ovary, the functional significance of ODC induction has remained elusive. Our study reveals that the blockade of the induction of ovarian ODC by means of the specific inhibitor alpha-difluoromethylornithine (DFMO) affects folliculogenesis and luteinization. In immature female mice, DFMO was found to inhibit ovarian growth, the formation of Graafian follicles, and the secretion of progesterone and estradiol. In adult cycling females, the administration of DFMO on the evening/night of proestrus markedly decreased plasma progesterone levels at diestrus, which was associated to the decrease in the expression of steroidogenic factor 1, cytochrome cholesterol side chain cleavage enzyme, and steroidogenic acute regulatory protein in the ovary and to a reduced vascularization of the corpora lutea. These effects were not reverted by the administration of gonadotropins or prolactin. ODC immunoreactivity was also stimulated by LH in theca and granulosa cells of antral follicles but not in preantral follicles. Overall, these experiments demonstrate that elevated ODC values found in the ovary of immature and adult mice play a relevant function in ovarian physiology and that ODC/polyamines must be considered as important mediators of some of the effects of LH on follicular development and luteinization.

Immunocytochemical detection of ornithine decarboxylase.

Ornithine decarboxylase (ODC), a regulatory enzyme of polyamine biosynthesis, is involved in cell growth and differentiation. Lack of information about the exact cellular and subcellular localization of ODC is one of the main obstacles to precise interpretation of the biological roles of the ODC/polyamine system. Here we describe the development and optimization of an immunocytochemical method to detect ODC in cells and tissues. For this purpose a monoclonal antibody (MP16-2) against a defined epitope of ODC protein was developed. Specificity of the antibody for ODC was substantiated by Western blotting and ELISA analysis using cell and tissue homogenates. In cultured cells, optimal staining results were obtained after fixation with crosslinking fixatives followed by permeabilization with methanol. In rat tissues, ODC immunoreactivity was best preserved in paraffin sections fixed with Bouin's fixative. Antigen retrieval using SDS and citrate buffer substantially increased ODC immunostaining and decreased background staining. Localization studies of ODC in different cell lines showed that strongest staining for ODC was found in the nucleoplasm of mitotic cells, whereas confluent cells showed moderate perinuclear staining. Immunocytochemical studies of various rat tissues showed high cytoplasmic immunostaining of ODC in epithelial cells of kidney, prostate, and adrenal medulla of testosterone-treated rats, in glandular epithelium of small intestine, and in pancreas of neonatal and adult rats. (J Histochem Cytochem 47:1395-1404, 1999)

Dietary induction of ornithine decarboxylase in male mouse kidney

In male mouse kidney, ornithine decarboxylase (ODC) is induced after feeding, and the induction depends on dietary protein content. 24 h after feeding with 50% casein-containing meal, ODC activity and amount of immunoreactive ODC protein increased more than 10-fold, ODC mRNA level increased 2-fold, and the ODC half-life extended 7-fold. The renal ODC induction after feeding is, therefore, due mainly to stabilization of ODC protein. Urinary excretion of putrescine increased in response to the ODC induction, but the renal polyamine contents scarcely changed. Consistently, the level of antizyme, a polyamine-inducible protein, determined as the ODC–antizyme complex level, scarcely changed after feeding, and the antizyme/ODC ratio in the kidney largely decreased, resulting in the stabilization of ODC protein. The present results suggest that the strong excretion system of the kidney for newly synthesized polyamines enables renal ODC escape from antizyme-mediated feedback regulation.

Ornithine decarboxylase in developing brain of hydrocephalic rats. Effects of shunt operation.

We examined the changes in ornithine decarboxylase (ODC) immunoreactivity in the hydrocephalic cerebral cortex of HTX rats after decompression by shunt operation. The ODC immunoreactivity reached a very low level after the completion of cortical layer formation, and only faint staining was found on postnatal day (Pd) 11. The ODC immunoreactivity re-appeared after the shunt operation when the operation was done in the early days of life: the ODC immunoreactivity was first found on day 2 after shunting and persisted until day 8 after shunting. However, this was not apparent when the operation was not performed until Pd 14. The re-expression of ODC in hydrocephalic brain after shunting appears to cause resumption of the developmental process by relieving neurons from increased hydrostatic pressure. The dependence of ODC re-expression on the timing of the operation indicates that there may be a period of neocortical decompression that is critical for effective compensatory development, so that when delayed, decompression fails to re-activate the ODC-dependent development.

Ornithine decarboxylase in developing brain of normal and hydrocephalic rats. Biochemical and immunohistochemical studies.

Polyamines have various roles in cortical development. We examined the ontogenic changes in ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis, in cerebral cortices of normal and hydrocephalic rats. Both biochemical and immunohistochemical examinations revealed increased ODC protein and enzyme activity during the perinatal period. Apical dendrites of developing neuroblasts migrating from the superficial layer of cortical plate showed intense ODC immunoreactivity. Once they had settled at their final destination, ODC immunoreactivity weakened. Both ODC immunoreactivity and enzyme activity reached very low levels after completion of layer formation of cortex. The enzyme activity of ODC in hydrocephalic cortices exceeded that in normal cortex during the perinatal periods. ODC was rather overexpressed, but no characteristic distribution was observed in the hydrocephalic cortex. These findings indicate the participation of polyamines in the cortical development, especially in the layer formation. The overexpression of ODC in hydrocephalus appears to promote development despite increased hydrostatic pressure.

Long-term reduction of amplified ornithine decarboxylase sequences in human myeloma cells

(1) Human myeloma cell line Sultan, resistant to 20 mM difluoro-methylornithine (DFMO) owing to ornithine decarboxylase (ODC) gene amplification, was grown in the absence of DFMO for a period of 10 months. The gene copy number and methylation status of the ODC gene were monitored after withdrawal of DFMO. Moreover, levels of ODC mRNA, immunoreactive ODC protein, ODC activity and polyamine levels were recorded recurrently during the course of the study. (2) The results revealed that ODC gene copy number started to decrease after 4 weeks growth without DFMO, to a final level of less than 30% of the original gene dosage. The methylation status of the ODC gene, however, remained almost unaltered, displaying only a modest increase in methylation after 10 months without DFMO. The amount of ODC message dropped very rapidly to 75% of the original value, then started to decrease in a gene copy-number-dependent manner. The amount of ODC protein closely followed the levels of mRNA during the study, whereas the ODC activity, after a transient increase during the first week, decreased to half of the original level after 4 weeks. Between 6 and 16 weeks ODC activity stabilized to a fifth of the original value and no more changes were detected during the subsequent period of observation. (3) Due to the grossly elevated ODC enzyme activity, levels of putrescine and spermidine first peaked and then stabilized at 6 weeks after DFMO withdrawal. The final spermidine level was comparable with that of the parental Sultan cell line with only one copy of active ODC gene. However, putrescine content was strikingly elevated, being stabilized to a level that was 20 times higher than in parental cells. Spermine concentration was practically unchanged during the study. (4) According to the results obtained in this study, the abnormal level of ODC expression in human myeloma cells is suppressed partially at the level of transcription or post-transcriptionally, but it is not due to increased methylation of the gene. The major regulatory mechanism to compensate for a highly elevated ODC expression was modulation of the enzyme activity. After 10 months without DFMO, the cells still displayed about 20 times higher ODC activity and putrescine concentration than the myeloma cell line with a single copy of the ODC gene. They did not, however, show any signs of growth retardation or other features different from the parental cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of ornithine decarboxylase (ODC) in the cochlea of the immature rat

Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis, is important in cochlear development. Whereas tissue specific differences in cochlear ODC activity have been demonstrated, cellular localization of ODC protein in the inner ear of the immature rat has not. ODC was localized in inner ear structures using an ODC polyclonal antibody and the effects of cycloheximide on ODC immunoreactivity and enzymatic activity were determined. Tissues demonstrating elevated enzymatic activity contained cells with the strong immunoreactivity. ODC activity was highest in the organ of Corti and lateral wall followed by the cochlear nerve. Immunoreactivity was demonstrated throughout the cochlea with intense staining of the hair cells, pillar cells, Deiter's cells, inner sulcus cells, basilar membrane, stria vascularis, spiral ganglion cell bodies and cochlear nerve fibers. Cycloheximide rapidly diminished cochlear ODC activity and expression of ODC protein. The half-life of cochlear ODC was 30 min. Localization of cellular sites of ODC is important in understanding the role of the ODC-polyamine pathway in cochlear development and will be a valuable marker for tissue damage from ototoxic agents.

Post-transcriptional inhibition of ornithine decarboxylase induction by zinc in a difluoromethylornithine resistant cell line

Addition of Zn 2+_ to cell medium inhibited the induction of ornithine decarboxylase (ODC) activity in ODC overproducing L1210-DFMO r cells. A significant effect was observed at a concentration as low as 0.01 mM, however a more marked inhibition was caused by the addition of 0.1 mM Zn 2+. The inhibition of the induction of ODC activity was accompanied by a proportional decrease in the content of immunoreactive ODC protein, whereas the level of ODC mRNA, detemined by a solution hybridization RNase protection assay, was not affected signigicantly. Instead, some acceleration of ODC turnover was observed. the addition of 0.1 mM Co 2+ or Mn 2+, but not of other divalent metal ions, also inhibited ODC induction; differently from Zn 2+ however, these metals affected cell viability and/or cell growth. Removal of endogenous Zn 2+ by a chelator also provoked a strong decrease of ODC induction, which was reversed by Zn 2+. However, addition of Zn 2+ in excess of the chelator proved to be markedly inhibitory. These results indicate that both a restricted Zn 2+ availability and an enhanced presence of the metal can inhibit the induction of ODC in L1210-DFMO r cells.

Zinc is required for the expression of ornithine decarboxylase in a difluoromethylornithine-resistant cell line

Dilution of quiescent L1210-DFMOr (difluoromethylornithine-resistant) cells in fresh medium containing serum led to the induction of ornithine decarboxylase (ODC) and to the expression of its mRNA, as determined by a sensitive solution-hybridization-RNase-protection assay. Addition of the chelating agent diethylenetriaminepentaacetic acid (DTPA) at seeding time caused an inhibition of the induction of ODC activity by up to 90%, and only Zn2+ of the bivalent metal ions tested was effective in reversing this effect. The inhibition of the induction of ODC activity was accompanied by a marked decrease, prevented by Zn2+ supplementation, of the accumulation of immunoreactive ODC protein and ODC mRNA. DTPA treatment also caused a slight acceleration of ODC turnover. These results indicate that a restricted Zn2+ availability in L1210-DFMOr cells impairs ODC induction remarkably, mainly by affecting the expression of the messenger.

Induction of ornithine decarboxylase immunoreactivity in the male mouse kidney following testosterone treatment: an axial heterogeneity in the proximal tubule.

The effect of testosterone on the activity of ornithine decarboxylase (ODC), its protein level and immunocytochemical distribution were examined in the mouse kidney. Male BALB C mice at 8 weeks of age were used throughout. Fourteen hours before death, they received a subcutaneous injection of testosterone (1 mg/animal) or solvent to measure renal ODC activity or to detect the distribution of ODC immunoreactivity in the kidney. Renal ODC activity and the content of the enzyme were markedly increased after testosterone treatment. Histologically, few cells that were obviously immunoreactive to ODC were observed in the control animals and in the testosterone-treated animals a marked increase in ODC immunoreactivity was observed only in the cortex. ODC immunoreactive cells were located diffusely in the proximal tubule. In the pars recta, cells were stained weakly and homogeneously, while in the pars convoluta, the luminal surface of the cells showed stronger immunoreactivity. Moreover, many granule-like particles that were strongly ODC immunoreactive were observed inside the lumen of the pars convoluta. These results show that testosterone treatment induces an increase in ODC content in certain cells located in the proximal tubule of the cortex.

Differential mechanisms of induction of ornithine decarboxylase in rat intestine by l- and d-amino acids

A single intragastric administration of glycine, L- and D-alanine, and L-and D-serine into rats resulted in a more than 20-fold stimulation of intestinal mucosal ornithine decarboxylase (ODC) within 4 h. The stimulation of ODC activity was accompanied by an increase in the amount of immunoreactive ODC protein. The induction of ODC by D-amino acids was in all likelihood attributable to an enhanced accumulation of ODC-specific mRNA species as revealed by Northern blot and dot-blot hybridization analyses. However, the induction by glycine and L-amino acids was not explainable by changes of mRNA since the changes in mRNA contents were only marginal. Since the turnover rates of L-serine-induced and D-serine-induced intestinal ODC protein were the same as the non-induced control, we concluded that the induction by glycine and L-amino acids was brought about by an increased efficiency of translation of the ODC message.

Stimulation of putrescine production by epidermal growth factor in rat liver after partial hepatectomy

When epidermal growth factor was given to rats after partial hepatectomy, hepatic putrescine content was significantly increased at 4, 6 and 10 hr compared with control rats. Ornithine decarboxylase activity was also increased. Hepatic ornithine decarboxylase messenger RNA content was significantly greater than control levels at 2 hr after epidermal growth factor treatment, but not at 10 hr, when the amount of ornithine decarboxylase messenger RNA in control animals was four times that at 2 hr. When actinomycin D was administered 6 hr after partial hepatectomy, hepatic ornithine decarboxylase activity at 10 hr was reduced to half the control levels. This reduction was attenuated by epidermal growth factor treatment at 6 and 8 hr. Hepatic immunoreactive ornithine decarboxylase protein content showed a highly positive correlation with hepatic ornithine decarboxylase activity at 4, 6 and 10 hr, irrespective of epidermal growth factor treatment. Hepatic spermidine N1-acetyltransferase activity was significantly increased at 6 hr compared with control rats. These results suggest that, after partial hepatectomy in rats, exogenous epidermal growth factor may stimulate hepatic putrescine production by increasing ornithine decarboxylase messenger RNA content and altering posttranscriptional ornithine decarboxylase regulation, as well as enhancing spermidine N1-acetyltransferase activity.

Ornithine Decarboxylase Induction in Partially Hepatectomized Rat Liver and Modes of Its Stimulation by Glucagon and Insulin

Hepatic ornithine decarboxylase (ODC) activity increases after partial hepatectomy and this activity is further stimulated by pharmacologic doses of glucagon and insulin. We now present data suggesting that glucagon and insulin stimulate ODC activity by distinct mechanisms. ODC activity increased progressively after partial hepatectomy and reached an initial peak at 4 h. Activity decreased to 50% of its peak value at 6 and 8 h and then rose progressively to a maximum at 12 h. Enzymatic activity was well correlated with the amount of hepatic immunoreactive ODC protein, thus suggesting that increased enzyme activity was due to increased amount of enzyme protein. Hepatic ODC mRNA increased gradually and continuously, reaching the maximal value by 12 h. In rats receiving glucagon after partial hepatectomy, ODC mRNA increased significantly by 2 h and enzyme immunoreactive protein and activity by 2 to 4 h as compared to controls. In contrast, insulin administration only induced a significant increase in enzyme immunoreactive protein and activity 10 to 12 h after partial hepatectomy. No significant changes in ODC mRNA level were observed. Our data suggest that the regulation mechanism of ODC induction following partial hepatectomy differs depending on the time after operation. Our data also suggest that while glucagon appears to regulate ODC activity by a transcriptional mechanism, insulin appears to operate at a post-transcriptional level.

Modulation of insulin induced ornithine decarboxylase by putrescine and methylputrescines in H-35 hepatoma cells

The effect of several methylputrescines on the activity of insulin-induced ornithine decarboxylase (ODC) was examined in H-35 hepatoma cells. The induction involved both protein and m-RNA synthesis. Actinomycin D inhibited ODC activity when given up to 1 h after insulin treatment. When added to the medium 2 h or 3 h after the insulin, the activity was increased 100% and 80% respectively. Insulin-induced ODC from H-35 cells had a biphasic half-life, a shorter one of 46 min and a longer one of 90 min. 1-Methylputrescine and 2-methylputrescine were found to be competitive inhibitors of the ODC from H-35 cells with Ki values of 2.8 and 0.1 mM respectively. Putrescine itself was found to have a Ki = 2.4 mM. N-Methylputrescine was a very poor inhibitor of the cell free ODC while 1,4-dimethylputrescine did not show any inhibitory effect. When cellular ODC activity was measured, the four methylputrescines assayed as well as putrescine entirely abolished its activity in the H-35 cells when given at a 1 mM concentration together with insulin. 1-Methylputrescine and 1,4-dimethylputrescine abolished 60% of the activity at a 0.1 microM concentration. All the methylputrescines given at 0.1 mM concentrations decreased the putrescine content of the stimulated cells to the levels found in quiescent cells, but only 1-methyl and 2-methylputrescines decreased spermidine and spermine content. 1,4-Dimethyl and 1-methylputrescines showed a strong inhibition of ODC synthesis, while the other diamines were less inhibitory. At concentrations that abolished ODC activity, 1,4-dimethylputrescine decreased 70% of the total immunoreactive ODC bands, while 1-methyl and 2-methylputrescine decreased them by 50%, and N-methylputrescine and putrescine decreased them by 20%. The lack of decrease in immuno-reactive ODC with the latter two compounds was mainly due to the appearance of immunoreactive degradation products of ODC of low molecular weight. Putrescine and N-methylputrescine affected protein synthesis to a small extent in stimulated cells, while 1-methylputrescine decreased it to the level of non-stimulated cells. Insulin (1 microM concentration) stimulated DNA synthesis in the cells, and this stimulation was doubled in the presence of 2-methylputrescine or putrescine. It can be concluded that, among the methylputrescines assayed, 2-methylputrescine was the best inhibitor of cell-free ODC activity, while 1,4-dimethylputrescine and 1-methylputrescine were the best inhibitors of cellular ODC activity.

Superinduction of ornithine decarboxylase (ODC) by actinomycin D is due to stimulation of ODC mRNA translation

Inhibition of transcription by treatment with actinomycin D caused superinduction of the ornithine decarboxylase (ODC) activity in Ehrlich ascites tumor cells. Experiments with cycloheximide ruled out the possibility that this superinduction was due to stabilization of ODC. Instead the ODC activity exhibited a more rapid turnover in the presence of actinomycin D ( t 1 2 =36 min) than in its absence ( t 1 2 = 56 min). The superinduction was found to coincide with an increased rate of ODC synthesis, as determined by measuring the incorporation of [ 35S]methionine into immunoreactive ODC protein. The steady-state level of ODC mRNA was unchanged, indicating an effect on the translational efficiency.

Regulation of ornithine decarboxylase expression by anisosmotic shock in alpha-difluoromethylornithine-resistant L1210 cells.

Ornithine decarboxylase (ODC) activity is known to be strongly enhanced in mammalian cells by a sudden reduction in ambient osmolality. The effect of hypoosmotic shock on the regulation of ODC protein and mRNA levels was studied in a variant L1210 mouse leukemia cell line (D-R cells) which expresses ODC at greater than or equal to 100-fold higher levels than the parental cells. Hypoosmotic stress increased ODC activity in proportion with the osmotic gradient imposed to both D-R cells and their normal counterparts. A 60% decrease in medium osmolality increased ODC activity and the amount of immunoreactive ODC protein from 20- to 30-fold after 4 h without any detectable change in ODC mRNA contents in D-R cells. ODC induction was sustained up to 48 h after hypoosmotic shock, with maximal activity levels being observed at 24 h. Hypotonic shock dramatically increased (up to 36-fold) the rate of ODC synthesis as measured by 10-min pulses with 35S-labeled methionine, in agreement with kinetic constants predicted from the changes observed for the enzyme activity. Moreover, hypoosmotic stress extended the half-life of ODC activity from 35 +/- 10 to 212 +/- 67 min and blocked any degradation of the radiolabeled immunoreactive protein, which had a half-life of 28 +/- 6 min under isotonic conditions, for at least 120 min after addition of cycloheximide. The induction of ODC by hypoosmotic stress was quickly reversed by a sudden upshift of osmolality through a very rapid inhibition of ODC biosynthesis and an increase in the rate of enzyme degradation. Thus, hypoosmotic stress activates the expression of ODC exclusively through post-transcriptional mechanisms in D-R cells. The osmotically induced accumulation of ODC molecules is quite unique as shown by the fact that ODC is the major protein (approximately 25% of total) synthesized during the first 4 h following a 60% hypotonic shock, despite a 30-50% reduction of the rate of labeled precursor incorporation into soluble proteins.

Mucosal ornithine decarboxylase in the small intestine: localization and stimulation.

In most tissues increases in ornithine decarboxylase (ODC) are associated with growth. Refeeding fasted rats. a potent stimulus for mucosal growth, strongly increases ODC in both small and large intestinal mucosa. In the small bowel, almost all of this increase occurs in the mature villus cells rather than the proliferative crypt cells. Nevertheless, inhibition of ODC with difluoromethylornithine blocks the growth response. Using a highly specific, polyclonal antiserum to ODC, we have determined that in the fasted rat ODC is localized almost exclusively to the villus cells. Using antiserum dilution techniques, we have shown that, within 2 h, refeeding increases the amount of immunoreactive ODC in both villus and crypt cells. Furthermore, the trophic hormone gastrin also increases ODC, but only in the crypt cells. Epidermal growth factor increased ODC to a greater extent than gastrin, but stimulation was more general, including both crypt and villus cells. Perfusing an isolated segment of small bowel in situ with glycine for 2 h also increased immunoreactive ODC but only in the villus cells. Thus in the small intestine the effect of refeeding on ODC activity appears to be mediated by different types of stimuli: luminal nutrients increase enzyme levels in the absorbing villus cells, while trophic peptides stimulate ODC synthesis in the proliferative crypt cells.

Ornithine decarboxylase activity and immunohistochemical location in postischemic brain.

Ornithine decarboxylase, rate-limiting in polyamine formation, has been found to be necessary for the development of vasogenic edema after cryogenic cerebral injury and is postulated to be of importance in late ischemic brain edema formation. Ornithine decarboxylase activity and accompanying edema was studied after transient cerebral ischemia in Mongolian gerbils. Bilateral carotid artery occlusion was utilized to produce dense forebrain ischemia. After 4 h of reperfusion a significant elevation in ornithine decarboxylase activity was present (72.5 +/- 24.7 vs 8.5 +/- 2 pmoles/mg protein/h, p less than 0.05). Immunohistochemical localization of ornithine decarboxylase indicated its presence in cortical neurons of ischemic gerbils. This was typically located in the perinuclear cytoplasm and extended into proximal dendrites. Nonischemic animals did not contain ornithine decarboxylase immunoreactivity. These studies show the presence and location of ornithine decarboxylase in cerebral tissue subjected to transient ischemia. The increase in this marker of polyamine activity paralleled previous studies in this model of cerebral edema formation and reperfusion deficit in blood flow and evoked potential, suggesting that ornithine decarboxylase is a marker for and may be associated with those late metabolic events leading to progressive functional deterioration after incomplete cerebral ischemia.

Gastric mucosal ornithine decarboxylase: localization and stimulation by gastrin.

Gastrin injection and refeeding fasted rats are effective trophic stimuli for the oxyntic gland mucosa of the stomach. Neither stimulus increases detectable ornithine decarboxylase (ODC) activity in the tissue. Difluoromethylornithine (DFMO), a potent inhibitor of ODC, blocks the mucosal growth response, indicating that ODC activity is necessary for growth. Elevated levels of spermidine and spermine are detectable in the mucosa after gastrin administration. Using a highly specific, polyclonal antiserum to ODC, we determined that the enzyme is present in oxyntic gland mucosa confined to a narrow band of cells at the base of the gastric pits and openings of the glands. In antral mucosa, ODC is present throughout the lower 20% of the mucosa, which consists of the necks and pyloric glands. Using antiserum dilution techniques, we show that gastrin administration increases immunoreactive ODC in the oxyntic gland area but not in the antral mucosa, where it has no trophic effect. Elevated cellular content of ODC is apparent within 2 h after injection of gastrin, peaks at 4 h, and declines to basal levels by 12 h. Gastrin-stimulated increase in ODC is confined to the narrow band of cells in which low levels of the enzyme protein were detected in control animals. The decarboxylating activity detectable in oxyntic gland mucosal extracts is not inhibited by administration of DFMO or cycloheximide, each of which inhibits ODC activity in other tissues. Addition of unlabeled lysine to the decarboxylation assay reaction of oxyntic gland mucosa extract inhibits the decarboxylation of radiolabeled ornithine substrate. Thus it is likely that the stomach possesses nonspecific decarboxylase activity, which accounts for most of the measured activity.(ABSTRACT TRUNCATED AT 250 WORDS)