Ornithine Decarboxylase mRNA Research Articles

Control of ornithine decarboxylase in Chinese hamster ovary cells by polyamines. Translational inhibition of synthesis and acceleration of degradation of the enzyme by putrescine, spermidine, and spermine.

We have recently isolated, without using any inhibitors, a mutant of Chinese hamster ovary cell line which greatly overproduces ornithine decarboxylase in serum-free culture. Addition of polyamines (putrescine, spermidine, or spermine, 10 microM) or ornithine (1 mM), the precursor of polyamines, to the culture medium of these cells caused a rapid and extensive decay of ornithine decarboxylase activity. At the same time the activity of S-adenosylmethionine decarboxylase showed a less pronounced decrease. Notably, the polyamine concentrations used were optimal for growth of the cells and caused no perturbation of general protein synthesis. Spermidine and spermine appeared to be the principal regulatory amines for both enzymes, but also putrescine, if accumulated at high levels in the cells, was capable of suppressing ornithine decarboxylase activity. The amount of ornithine decarboxylase protein (as measured by radioimmunoassay) declined somewhat more slowly than the enzyme activity, but no more than 10% of the loss of activity could be ascribed to post-translational modifications or inhibitor interaction. Some evidence for inactivation through ornithine decarboxylase-antizyme complex formation was obtained. Gel electrophoretic determinations of the [35S]methionine-labeled ornithine decarboxylase revealed a rapid reduction in the synthesis and acceleration in the degradation of the enzyme after polyamine additions. No decrease in the amounts of the two ornithine decarboxylase-mRNA species, hybridizable to a specific cDNA, was detected, suggesting that polyamines depressed ornithine decarboxylase synthesis by selectively inhibiting translation of the message.

Induction of mouse epidermal ornithine decarboxylase by the tumor promoter 12- O-tetradecanoylphorbol-13-acetate: Dependence on calcium availability

The role of calcium in epidermal ornithine decarboxylase (ODC) induction by 12- O-tetradecanoylphorbol-13-acetate (TPA) was determined in adult mouse skin pieces incubated in serum-free minimal essential medium (MEM). Addition of TPA to skin pieces incubated in serum-free MEM, which contains 1.82 m m Ca 2+ and 0.83 m m Mg 2+, resulted in about a 200-fold increase in epidermal ODC activity at about 8 h after TPA treatment. TPA failed to induce epidermal ODC in skin pieces incubated in calcium-free medium. Similarly, chelation of extracellular calcium by ethyleneglycol bis(β-aminoethyl ether) N,N′-tetraacetic acid (EGTA) prevented ODC induction by TPA, which could be resumed upon calcium restoration in the medium. Furthermore, calcium ionophore A23187, which facilitates efflux of Ca 2+ across cellular membranes, induced ODC activity in incubated skin pieces. Epidermal ODC activity increased by TPA appears to be the result of an increase in both the amount of ODC protein and the level of hybridizable ODC messenger. Inhibition of the induction of ODC activity by EGTA was the result of the inhibition of the amount of active ODC protein and the level of ODC mRNA.

Two ornithine decarboxylase mRNA species in mouse kidney arise from size heterogeneity at their 3' termini.

Ornithine decarboxylase (OrnDCase; L-ornithine carboxy-lyase, EC 4.1.1.17) mRNA present in mouse kidney comprises two species with molecular sizes of approximately 2.2 and approximately 2.7 kilobases (kb). cDNA clones prepared from murine kidney OrnDCase mRNA were used to determine the reason for the size heterogeneity of these mRNAs. Two of the cDNA clones (pODC16 and pODC74) that differed at the 3' termini were isolated and sequenced. DNA sequencing indicated that each cDNA had a poly(A) tail; however, pODC74 was 429 nucleotides longer than pODC16 at the 3' end and contained two AATAAA signals for poly(A) addition. That the longer cDNA corresponded to the larger mRNA was confirmed by hybridization of a unique Pst I/Pst I fragment from the 3' terminus of pODC74 only to the 2.7-kb OrnDCase mRNA. The two cDNAs did not represent full-length copies of OrnDCase mRNAs and were 1199 (pODC16) and 1204 base pairs (bp) (pODC74) long. There were five mismatches in their 759-bp-long overlapping nucleotide sequence, suggesting that the 2.2- and 2.7-kb OrnDCase mRNAs may be products of two separate, yet very similar, OrnDCase genes. Androgen regulation of the accumulation of these two OrnDCase mRNAs appeared to occur coordinately, as testosterone administration brought about comparable increases in their concentrations in mouse kidney.

Ornithine decarboxylase: Its significance in toxicology.

Ornithine decarboxylase (ODC) is the first and rate-limiting enzyme involved in the biosynthetic pathway of polyamines. This review mainly surveys the literatures about the change in the levels of ODC in organs of mammals in response to a wide variety of drugs and chemicals, with respect to its toxicological implications. Emphasis is especially placed on the induction of ODC by drug-metabolizing enzyme inducers, hepatotoxins, chemical carcinogens, tumor promoters and metal ions, and the toxicological significance of this induction of ODC is discussed. In addition, the significance of the inhibitory effects of some drugs and chemicals on the tumor promoter-mediated inductions of ODC is discussed. This review also described briefly the role of polyamines in tissue growth and the reactions responsible for the biosynthesis and interconversion of the polyamines. Besides, the purification of ODC, the recent advances in the studies of ODC genes, mRNA and cDNA are briefly described. The regulation of ODC by its antizyme, and specific inhibitors of ODC such as α-difluoromethylornithine and their potentials for investigation of the cellular role of polyamines are summarized. The available evidence suggests that the changes in ODC activity in organs of mammals owing to the administrations of drugs and chemicals could be a useful pharmacological and toxicological marker.

Transcription of the speC (ornithine decarboxylase) gene of Escherichia coli is repressed by cyclic AMP and its receptor protein

The speC gene encoding ornithine decarboxylase (ODC) in Escherichia coli is negatively regulated by cAMP and the cAMP receptor protein (CRP). In minicells transformed with the plasmid pODC bearing speC, cAMP supplementation repressed ODC synthesis. In a cell-free protein synthesizing system directed by pODC, cAMP at 10 −5M repressed ODC synthesis by 90%. This repression required a functional CRP as cAMP failed to repress ODC synthesis in vitro in an extract prepared from a crp − strain; the addition of purified CRP to the crp − extract restored the ability of cAMP to repress ODC synthesis. In a prototroph transformed with the plasmid pCOD bearing a speC::tet chimeric gene, cAMP supplementation decreased tetracycline (Tc) resistance. In contrast, in crp − strains transformed with pCOD or pTET (Tc R), cAMP supplementation did not change their Tc resistance. When a cya − strain was supplemented with 2 mM cAMP, steady state levels of ODC mRNA were repressed by 80%. However, when a isogenic crp − strain was supplemented with 2 mM cAMP, no repression of ODC mRNA was observed. These results indicate that the cAMP-CRP complex exerts negative transcriptional control of ODC synthesis as a function of the speC promoter.

Human lung tumor sensitivity to difluoromethylornithine as related to ornithine decarboxylase messenger RNA levels

The differential response to polyamine depletion has been studied in two types of human lung tumor cells. Small cell lung carcinoma cells die following polyamine depletion by difluoromethylornithine treatment while non-small cell lines demonstrate a typical cytostatic response. We now report that a small cell line, NCI H82, has a lower apparent capacity for polyamine biosynthesis than does a representative non-small cell, NCI H157. In subconfluent cultures, the ornithine decarboxylase activity is 25 times lower in the small cell than the non-small cell and by comparison, the polyamines in the small cell line are markedly reduced. Most significantly, levels of mRNA coding for ornithine decarboxylase are approximately 100-fold lower in the small cell than the non-small cell line, and this difference does not appear to be a result of gene rearrangement. These results suggest that differential sensitivity to polyamine depletion is related to different steady-state levels of ornithine decarboxylase mRNA.

Induction of ornithine decarboxylase by 12-O-tetradecanoylphorbol 13-acetate in hamster fibroblasts. Relationship between levels of enzyme activity, immunoreactive protein, and RNA during the induction process.

Phorbol ester tumor promoters and growth factors rapidly stimulate ornithine decarboxylase activity in the transformed hamster fibroblast line HE68BP. We report here a close correspondence between the time courses and magnitudes of induction of ornithine decarboxylase activity and immunoreactive ornithine decarboxylase protein following treatment of HE68BP cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) and/or refeeding with fresh medium. Cycloheximide addition to induced cells caused a rapid fall in the levels of both ornithine decarboxylase activity and ornithine decarboxylase protein. Northern blot analysis of RNA isolated from HE68BP cells indicated that treatment with TPA and fresh medium increased the amount of two species of mRNA of lengths 2.4 and 2.1 kilobase. This increased accumulation of ornithine decarboxylase mRNA corresponded temporally to that observed at the protein level, with a 15-fold maximal induction 7 h after treatment followed by a rapid decline in hybridizable RNA. These data indicate that stimulation of ornithine decarboxylase activity by TPA or refeeding involves changes in levels of ornithine decarboxylase mRNA as well as changes in the rate of synthesis of ornithine decarboxylase protein.

Translational regulation of mammalian ornithine decarboxylase by polyamines.

Ornithine decarboxylase, which catalyses the formation of putrescine, is the first and rate-limiting enzyme in the biosynthesis of polyamines in mammalian cells. The enzyme is highly regulated, as indicated by rapid changes in its mRNA and protein during cell growth. Here we report that ornithine decarboxylase is regulated at the translational level by polyamines in difluoromethylornithine-resistant mouse myeloma cells that overproduce the enzyme due to amplification of an ornithine decarboxylase gene. When such cells are exposed to putrescine or other polyamines, there is a rapid and specific decrease in the rate of synthesis of ornithine decarboxylase, assayed by pulse-labeling. Neither the cellular content of ornithine decarboxylase mRNA nor the half-life of ornithine decarboxylase protein is affected. Our results indicate that polyamines negatively regulate the translation of ornithine decarboxylase mRNA, thereby controlling their own synthesis.

Nerve growth factor rapidly induces ornithine decarboxylase mRNA in PC12 rat pheochromocytoma cells.

The mechanism by which nerve growth factor (NGF) stimulates ornithine decarboxylase (OrnDCase; EC 4.1.1.17) activity in the rat pheochromocytoma cell line PC12 was investigated. As demonstrated previously, NGF rapidly induces OrnDCase activity in a dose-dependent manner, with maximal enzymatic activity at 4-6 hr after exposure to NGF. Activity subsequently returns to near basal levels. A cloned OrnDCase cDNA was used to analyze the levels of OrnDCase RNA. In response to NGF administration, OrnDCase RNA levels were induced. The time course of the OrnDCase RNA induction paralleled that of the enzyme activity induction, and the magnitude of both inductions was quantitatively the same. Increased concentration of OrnDCase RNA was clearly detected at the earliest time point examined, 2 hr. No change was observed in the size of OrnDCase RNA. The dose-response curves for both RNA and enzyme activity inductions were also similar. Thus, increased OrnDCase RNA levels fully account for, and are responsible for, the induction of activity. Further, one-third of the OrnDCase RNA induction was unaffected by cycloheximide treatment but was fully blocked by actinomycin D treatment, suggesting that NGF acts through at least two mechanisms to mediate the OrnDCase induction. The first mechanism is cycloheximide insensitive and the second is mediated through an event requiring ongoing protein synthesis. Both mechanisms require ongoing transcription, as evidenced by the complete sensitivity of the induction process to actinomycin D.

Ornithine decarboxylase inhibitors increase the cellular content of the enzyme: Implications for translational regulation

Ehrlich ascites tumor cells grown in the presence of inhibitors of ornithine decarboxylase (EC 4.1.1.17) exhibited an elevated content of this enzyme. The increase could not solely be explained by a decrease in the degradation rate of the enzyme. Instead a stimulation of enzyme synthesis, probably mediated via the polyamine-depleting properties of the inhibitors, is suggested. The enhancement of cellular ornithine decarboxylase content was not accompanied by any significant changes in the amount of ornithine decarboxylase mRNA, indicating a regulation at the level of translation.

Amplification of ornithine decarboxylase gene in response to polyamine deprivation in Chinese hamster ovary cells.

We have isolated from an arginase-deficient polyamine-dependent Chinese hamster ovary cell line a new mutant strain that has greatly increased ornithine decarboxylase activity. This enables the cells, in the absence of ornithine, to decarboxylate lysine into cadaverine (diaminopentane) that is further converted into N-(3-aminopropyl)cadaverine and N,N'-bis(3-aminopropyl)cadaverine. These unusual polyamines can support the growth of the cells without added polyamines derived from ornithine. Immunoreactive ornithine decarboxylase-like protein was clearly increased in the mutant cells but could not solely account for the greatly increased enzyme activity. Southern blot analysis of DNA hybridized to a plasmid carrying ornithine decarboxylase-cDNA revealed at least a 32-fold amplification of the ornithine decarboxylase gene. Ornithine decarboxylase-mRNA concentration was also highly increased in the cells. The half-life of the enzyme and the Km for ornithine were not altered from those of the parental cell line.

Mutant Strain of Chinese Hamster Ovary Cells with No Detectable Ornithine Decarboxylase Activity

We previously described an arginase-deficient, polyamine-dependent Chinese hamster ovary cell line which grows in serum-free medium. From this strain we isolated a new mutant strain that has no detectable catalytic ornithine decarboxylase activity. The mutant cells contain, however, immunoreactive ornithine decarboxylase-like protein roughly in the same quantity as the parent strain. The mutant and the parent cell line strains also contain similar amounts of ornithine decarboxylase-mRNA hybridizable to a specific cDNA. If polyamines are omitted from the medium, proliferation of the mutant cells is considerably retarded and ceases in 6 to 10 days. Addition of ornithine or alpha-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, has no effect on these cells. Putrescine and spermidine decreased in the mutant cells to undetectable levels during polyamine starvation, whereas spermine was reduced to 1/5th of that found in the control cultures. Polyamines appear to be indispensable for the mutant strain, but this was obvious only after the amount of polyamines, found as impurities in bovine serum albumin used in the medium, was reduced by dialysis to 10(-12) M. Because sera contain polyamines, the ability of the mutant strain to grow in serum-free medium is a great advantage in elucidation of the mechanisms of polyamine function.

Mutant strain of Chinese hamster ovary cells with no detectable ornithine decarboxylase activity.

We previously described an arginase-deficient, polyamine-dependent Chinese hamster ovary cell line which grows in serum-free medium. From this strain we isolated a new mutant strain that has no detectable catalytic ornithine decarboxylase activity. The mutant cells contain, however, immunoreactive ornithine decarboxylase-like protein roughly in the same quantity as the parent strain. The mutant and the parent cell line strains also contain similar amounts of ornithine decarboxylase-mRNA hybridizable to a specific cDNA. If polyamines are omitted from the medium, proliferation of the mutant cells is considerably retarded and ceases in 6 to 10 days. Addition of ornithine or alpha-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, has no effect on these cells. Putrescine and spermidine decreased in the mutant cells to undetectable levels during polyamine starvation, whereas spermine was reduced to 1/5th of that found in the control cultures. Polyamines appear to be indispensable for the mutant strain, but this was obvious only after the amount of polyamines, found as impurities in bovine serum albumin used in the medium, was reduced by dialysis to 10(-12) M. Because sera contain polyamines, the ability of the mutant strain to grow in serum-free medium is a great advantage in elucidation of the mechanisms of polyamine function.

Nucleotide sequence of murine ornithine decarboxylase mRNA.

Ornithine decarboxylase (OrnDCase; L-ornithine carboxy-lyase, EC 4.1.1.17) is the first and rate-limiting enzyme in the biosynthesis of polyamines in mammalian cells. During cell growth the enzyme is regulated by rapid changes in the level of its mRNA and protein. To explore the molecular basis of these changes, we cloned a full-length cDNA copy of the major 2.4-kilobase OrnDCase mRNA from mouse cells and determined its sequence. The cDNA contains 2465 nucleotides derived from OrnDCase mRNA, consisting of a 737-nucleotide-long 5' noncoding segment, a coding segment of 1383 nucleotides terminated by a TAG triplet, and a 342-nucleotide 3' noncoding segment. The encoded protein of 461-amino acid residues has a molecular weight of 51,105 and has a potential site for phosphorylation by casein kinase II. In the unusually long 5' leader sequence, there are four ATG triplets, each of which is followed by an in-phase termination signal; the presence of these upstream ATGs could explain the low in vitro translational activity of OrnDCase mRNA reported earlier. A restriction digest of mouse genomic DNA was probed with a defined OrnDCase coding sequence, revealing a multimembered family of OrnDCase-related genes.

Cell-free synthesis of ornithine decarboxylase. Changes in mRNA activity in the liver of thioacetamide-treated rats.

Ornithine decarboxylase (ODC)mRNA associated with free polysomes of rat liver was translated in a reticulocyte lysate cell-free system. Newly synthesized ODC protein was identified by specific immunoprecipitation, molecular size as determined by polyacrylamide gel electrophoresis with sodium dodecyl sulfate, and competition by excess unlabeled ODC in the immunoprecipitation. A single injection of thioacetamide was found to cause several fold increases in both immunotitratable ODC protein and polysomal ODC-mRNA activity, while it provoked a much larger increase in ODC activity in rat liver. The results indicate that the induction of hepatic ODC activity by thioacetamide treatment is due not only to an increase in the activity of polysomal ODC-mRNA but also to a translational and/or posttranslational control.

Androgen-regulated ornithine decarboxylase mRNAs of mouse kidney.

Ornithine decarboxylase, the first enzyme of the polyamine biosynthetic pathway, is induced by androgens in the mouse kidney. We have isolated from a kidney cDNA clone bank two plasmids, pODC1440 and pODC934 , that contain different cDNA inserts corresponding to ornithine decarboxylase mRNA. Identification was based upon the ability of plasmid-specific mRNAs to encode a 53,000-dalton polypeptide that reacts with antibody to purified mouse kidney ornithine decarboxylase. Plasmid pODC1440 hybridizes predominantly to a mRNA that is 2.1 kilobases (kb) long and is induced about 20-fold in the kidneys of female mice treated with testosterone. Plasmid pODC934 hybridizes to mRNAs of lengths 2.2 and 2.6 kb, which are induced about 8-fold by testosterone. There are probably no more than 1-2 copies of the pODC1440 -specific sequence in the mouse genome, while there may be as many as 12 copies of the pODC934 -specific sequence. That the two plasmids correspond to different ornithine decarboxylase mRNAs is suggested by two observations. First, several mouse strains express normal levels of pODC934 -specific RNA and little or no pODC1440 -specific RNA; furthermore, pODC934 -specific RNA is expressed in several tissues while pODC1440 -specific RNA is kidney-specific. Thus, androgen-mediated stimulation of kidney ornithine decarboxylase activity levels involves alterations in the concentrations of at least two distinct mRNAs.

Androgen induction of ornithine decarboxylase mRNA in mouse kidney as studied by complementary DNA.

To investigate the mechanisms by which androgens regulate ornithine decarboxylase (OrnDCase; L-ornithine carboxy-lyase, EC 4.1.1.17) in mouse kidney, a cDNA clone encoding OrnDCase mRNA was prepared. Purification of OrnDCase mRNA from kidneys of androgen-treated mice was accomplished by immunoadsorption of renal polysomes to a protein A-Sepharose column and enrichment for poly(A)-containing RNA by oligo(dT)-cellulose. Double-stranded cDNA synthesized from this mRNA was inserted into the Pst I site of plasmid pBR322 by using oligo(dG . dC)-tailing and was propagated in Escherichia coli. Plasmids containing cDNA sequences coding for OrnDCase were identified by differential colony hybridization, by radioimmunological detection of OrnDCase-like antigens in bacterial cultures, and by cell-free translation of hybrid-selected mRNA followed by immunoprecipitation with monospecific OrnDCase antiserum. A restriction endonuclease fragment of the selected plasmid DNA (pODC54) was labeled by nick-translation and used to study changes in OrnDCase mRNA concentration. After a single dose of testosterone, renal OrnDCase mRNA concentration increased as soon as 6 hr and peaked 24 hr after steroid injection, as measured by RNA blot hybridization. Continuous androgen treatment for 4 days resulted in a 10- to 20-fold increase in OrnDCase mRNA concentration in normal animals, but no induction of this mRNA was detected in mice that have an inherent defect of the androgen receptor (testicular feminization). These results indicate that androgens regulate OrnD-Case synthesis in mouse kidney, at least in part, by increasing OrnDCase mRNA accumulation.

A mouse lymphoma cell mutant whose major protein product is ornithine decarboxylase.

Mutant mouse lymphoma cells that overproduce ornithine decarboxylase have been generated by selection for resistance to difluoromethylornithine, an inhibitor of the enzyme. Starting with wild type S49 mouse lymphoma cells, sensitive to growth inhibition by 10 microM difluoromethylornithine, we obtained the Z.12 line, which is approximately 100 times more resistant to that drug (McConlogue, L., and Coffino, P. (1983) J. Biol. Chem. 258, 8384-8388). Subsequent selection for still higher levels of resistance was applied to the Z.12 cells and resulted in the generation of the D4.1 line, resistant to 10 mM difluoromethylornithine. The relative synthesis of ornithine decarboxylase in wild type, Z.12, and D4.1 cells was assessed by pulse labeling these cells with [35S]methionine and analyzing the radiolabeled proteins directly, or after immunoprecipitation, on sodium dodecyl sulfate-polyacrylamide gels. As shown previously, the rate of ornithine decarboxylase synthesis is augmented in Z.12 as compared to wild type. In D4.1 cells, the rate of synthesis of ornithine decarboxylase exceeds that of any other single protein; about 15% of total protein synthesis is devoted to the enzyme. The relative amounts of translatable ornithine decarboxylase mRNA in each cell line was determined by in vitro translation of extracted RNA. These results showed that the relative rate of synthesis in each cell line is a reflection of the cell's relative content of translatable ornithine decarboxylase mRNA. Examination of the chromosomes of wild type and D4.1 cells revealed that the former are pseudodiploid and the latter tetraploid. Two of the four chromosomes 14 in D4.1 contain large homogeneously staining regions, a finding consistent with the presence of regions of gene amplification.

A mutant of Chinese hamster ovary cells resistant to alpha-methyl- and alpha-difluoromethylornithine.

We describe a mutant of Chinese hamster ovary cells which is resistant to elevated levels of alpha-methylornithine and alpha-difluoromethylornithine, reversible and enzyme-activated irreversible inhibitors, respectively, of the enzyme ornithine decarboxylase (ODC). The mutant cells have significantly elevated levels of enzyme activity compared to wild-type cells, but several of the physical parameters of the enzyme are completely normal: Michaelis-Menten parameter, Km, affinity for the analog, and half-life. The temporal regulation of this activity in synchronized cells is not perturbed, and the suppression of ODC activity by the addition of putrescine is still observed. Indirect experiments suggest increased concentrations of ODC mRNA in the mutant cells.

Review of Cytology

Recently, we have shown that ornithine decarboxylase (ODC), a rate-controlling enzyme in the polyamine biosynthetic pathway, is overexpressed in prostate cancer (PCA) and prostatic fluid in humans (R. R. Mohan et al., Clin. Cancer Res., 5: 143–147, 1999). ODC is also characterized as an androgen-responsive gene, and the androgenic stimulation regulates the development and growth of both normal and tumorigenic prostate cells. Thus, chemopreventive approaches aimed toward the modulation of ODC could be effective against PCA. Green tea polyphenols (GTPs) possess strong chemopreventive properties against a variety of animal tumor models and in some human epidemiological studies. At least two epidemiological studies have suggested that people who consume tea regularly may have a decreased risk of PCA. In this study, we investigated the effect of GTPs against testosterone-mediated induction of ODC in human prostate carcinoma cells, LNCaP as an in vitro model, and in Cpb:WU rats and C57BL/6 mice as in vivo models. Treatment of LNCaP cells with testosterone resulted in induction of ODC activity in a dose-dependent manner. Pretreatment of the cells with GTPs resulted in a significant inhibition of testosterone-caused induction of ODC activity in a dose-dependent manner. Similar effects of GTPs were observed in anchorage-independent growth assay of LNCaP cells where pretreatment of the cells with GTP was found to result in dose-dependent inhibition of colony formation. Testosterone treatment of the cells resulted in a significant increase in the level of ODC mRNA, and this increase was almost completely abolished by prior treatment of the cells with GTPs. The administration of testosterone (10 mg/kg body weight, i.p.) to sham-operated and castrated Cpb:WU rats resulted in 2- and 38-fold increases in ODC activity, respectively, in the ventral prostate. Oral feeding of 0.2% GTPs in drinking water for 7 days before testosterone administration resulted in 20 and 54% decreases in testosterone-caused induction of ODC activity in sham-operated and castrated rats, respectively. Similar results were obtained with C57BL/6 mice, where testosterone treatment at similar dosage resulted in a 2-fold increase in ODC activity in the ventral prostate and prior oral feeding with 0.2% GTPs resulted in 40% inhibition in this induction.