Studies on regulatory factors of ornithine decarboxylase activity during development of mouse mammary epithelium in vitro

Early weaning induces jejunal ornithine decarboxylase and cell proliferation in neonatal rats

Increased ornithine decarboxylase (ODC) activity is associated with rapid cell proliferation in many cell types. The cellular effects of early weaning on intestinal development are not well established. To investigate whether ODC is involved in intestinal growth after early weaning, we precociously weaned suckling rats on postnatal d 15 and followed through d 21 (6 d after early weaning). Age-matched suckling pups served as controls. Rat pups were killed 1, 2, 3 and 6 d after early weaning and jejunal mucosa was assayed for ODC and sucrase activities, and protein and DNA contents. Jejunal cell proliferation was monitored by bromodeoxyuridine immunohistochemistry. Elevated jejunal ODC activity 1 d after early weaning was the earliest cellular event that was detected in the current study. ODC activity peaked at d 3 (about 15-fold greater than age-matched unweaned suckling controls). Sucrase activity was elevated at d 2 after weaning and peaked at d 3 (about 10-fold greater than controls). Greater bromodeoxyuridine immunostaining in early weaned rats occurred on d 3. Protein and DNA contents were greater in jejunal mucosa of early weaned rats at d 6. Serum corticosterone levels were elevated on d 1 and d 2 after early weaning compared to controls. To explore whether the intake of nonpurified diet played a role, we also compared the induction of jejunal ODC activity in early weaned pups and pups that were food-deprived for 1 d. ODC activity was not greater in the food-deprived group compared to suckling controls while the early weaned group had 6-fold greater activity 1 d after early weaning. Early weaning stimulates jejunal cell proliferation and differentiation. The temporal sequence of increased ODC activity followed by increases in other growth variables suggests that the induction of ODC activity may act as an early marker of intestinal growth during early weaning.

Effect of difluoromethylornithine (DFMO) on NSAID-induced intestinal injury in rats

Combination therapy with difluoromethylornithine (DFMO) and a nonsteroidal antiinflammatory drug (NSAID) has been proposed for the chemoprevention of colonic neoplasia. The purpose of this study was to examine whether DFMO would affect NSAID-mediated intestinal injury. Male Sprague-Dawley rats were gavaged with 20 mg/kg of indomethacin, after seven days of exposure to drinking water with or without 2% DFMO. The rats were killed 24 or 48 hr later, and the small intestine removed for macroscopic and microscopic quantitation of intestinal injury by computerized image analysis. Seven days of DFMO alone had no effect on overall mucosal thickness, but did increase the depth of proximal intestinal crypts. Forty-eight hours after indomethacin, DFMO treatment decreased the number of indomethacin-induced ulcers and percent of the surface area ulcerated. However, DFMO also decreased the mucosal thickness, villus height, and crypt depth in indomethacin-treated rats. Thus although DFMO decreases macroscopic intestinal ulceration by indomethacin, the reduction in villus and crypt height suggests that it also impairs the mucosa's ability to recover from microscopic indomethacin-induced damage. This study shows DFMO does impact NSAID-mediated intestinal injury and therefore human trials with combinations of DFMO and NSAIDs should include monitoring for small intestinal injury.

Adaptive response of ileal mucosa to malnutrition in the rat: role of polyamines

Mucosal disaccharidases and ornithine decarboxylase activities were measured in malnourished, preweaning (19 days), post weaning (24 days) and young adult (37 days) rats. Malnutrition resulted in decreased body weight, intestinal weight, DNA and protein content. Mucosal Prot/DNA ratios were elevated in the ileal segments of the 24 and 37 day rats. Preweaned malnourished rats had significantly enhanced lactase specific activity in both jejunal and ileal segments. Adult malnourished rats showed enhanced jejunal lactase and sucrase activities which were not accompanied by elevated ornithine decarboxylase values. Mucosal sucrase and ornithine decarboxylase specific activities were significantly elevated in the ileal segment of the 24 and 37 day old malnourished rats. Studies of adult rats showed that these increased specific activities were located in the mature enterocytes at the villus tip, and persisted during a 24 h diurnal cycle. DFMO administration for 4 days completely inhibited mucosal ornithine decarboxylase and abolished the rise of ileal sucrase activity. We concluded that the intestinal response to reduced food intake is age related and differs in the jejunum and ileum: ornithine decarboxylase and polyamines are involved in ileal adaptation to malnutrition in postweaned and adult rats.

Essential role for polyamine biosynthesis in thyroxine stimulated pancreatic development in neonatal rats

Administration of thyroxine to rat pups leads to precocious development of the pancreas. The role of ornithine decarboxylase (ODC) and polyamines in thyroxine-induced pancreatic maturation was examined. Rat pups (aged 5 days) were given daily subcutaneous injection of thyroxine (0.1 micrograms/g body wt.) until the day before death. Serial ODC activities were measured in pancreatic homogenates after 1, 2, 3, 4, 5, 6, 7 and 10 days of thyroxine treatment. There was a biphasic induction of ODC activities by thyroxine: an early peak appeared on day 2 of treatment followed by a decrease on day 4; a second peak was evident on day 5 and then a decrease to control values by day 7. Significant increases in tissue concentrations of putrescine and spermidine were observed concomitant with two peaks of ODC activity. Pancreatic amylase concentration, DNA and protein also showed a significant increase after thyroxine treatment. Difluoromethyl ornithine (DFMO), a specific ODC inhibitor, given orally (8% in drinking water) to nursing dams at postnatal day 5 for 5 days caused an 83% inhibition of pancreatic ODC activity in thyroxine-treated pups when compared to thyroxine-treated pups not exposed to DFMO. Concomitantly, the thyroxine-induced increases in pancreatic weight, protein and amylase activity were suppressed. Our results suggest that increases in ODC activities and polyamine levels are critical intermediary steps in the precocious induction of pancreatic development by thyroxine.

Proliferation-related responses in rat astrocytes to epidermal growth factor

The signals which regulate the proliferation of astrocytes have relevance to both normal developmental processes and abnormal states of gliosis or glial tumor formation. We have extended studies of astrocyte proliferation and related responses in primary cultures of rat telencephalic cortical astrocytes as a result of treatment with epidermal growth factor. Epidermal growth factor stimulates the rate of DNA synthesis five fold and maintains the rate of protein synthesis. The stimulation occurs at a dose of 2 ng/ml and is greater in higher density cultures than in lower density cultures, perhaps representing a relative starvation for the growth factor. The astrocyte response is still present even after being cultured 3 1/2 weeks in serum-free and non-growth factor or hormone-supplemented media. Combined immunofluorescence and thymidine autoradiography disclose that glial fibrillary acidic protein containing cells are the cells synthesizing DNA in response to the growth factor, and combined rhodamine and fluorescein-linked stains disclose that epidermal growth factor is in the glial fibrillary acidic protein containing cells. Proliferation-related 2-deoxyglucose uptake is stimulated at approximately the same dose as DNA synthesis is stimulated, but the time course is relatively slow, maximizing at 48 hr. Ornithine decarboxylase is stimulated in 6 hr indicating more rapid nuclear stimulation by the signal. In conclusion, epidermal growth factor has a clear direct interaction with glial fibrillary acidic protein-containing cells which is greater in higher density cultures, is still present in long-quiescent cells, and includes DNA synthesis, cell cycle progression, hexose uptake, and polyamine synthesis.

Role of protein kinase C in the prolactin-induced responses in mouse mammary gland explants

Recently, the protein kinase C (PKC) activator 12-O-tetradecanoylphorbol 13-acetate (TPA) was found to have prolactin (PRL)-like actions on specific metabolic processes in mouse mammary gland explants. Since TPA is known to stimulate PKC, these observations suggest that PKC may have a role in the PRL stimulation of lactogenic processes. The present studies provide further evidence for this by demonstrating a transient, time-dependent translocation of PKC to the particulate fraction in response to PRL. Particulate-associated PKC reached a maximum between 15-30 min and returned to control values within 1-2 h after PRL treatment. PRL treatment for 16 h also induced a down-regulation of total cellular PKC. Inhibition of PKC function, either by a 30 h pretreatment with TPA (PKC down-regulation) or 2 h with 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7), resulted in an attenuation of PRL-stimulated effects on ornithine decarboxylase activity and synthesis of RNA, caseins, and lipids.

Additive stimulation of hepatic putrescine production by glucagon and insulin after partial hepatectomy in rats

When rats received glucagon or insulin every 2 h after partial hepatectomy (Hx), hepatic putrescine content was increased above control levels at 6 and 12 h, respectively. When the two hormones were combined, the increased levels were additive. Hepatic ornithine decarboxylase activity was above control levels at 12 h after insulin treatment. Hepatic spermidine N1-acetyltransferase activity was enhanced at 6 h only when glucagon was dosed. Putrescine administration from 0 to 4 h or from 6 to 10 h increased hepatic DNA synthesis to similar levels 22 h after Hx. These results suggest that glucagon and insulin additively stimulate hepatic putrescine production after Hx. This may explain the cooperative stimulation of liver regeneration by both hormones.

Decreased levels of nerve growth factor receptor on dexamethasone-treated PC12 cells

Treatment of PC12 cells with dexamethasone leads, in a period of days, to a 60% decrease in the binding of (125I)nerve growth factor. The decrease was maximal after 3 days of treatment with 1 microM dexamethasone, but some decrease was seen after 6 hr and at concentrations as low as 10 nM. The effect was specific for the glucocorticosteroids. Scatchard plots confirmed the overall loss of nerve growth factor binding, and studies with trypsin digestion and Triton X-100 extraction indicated that the decrease in binding was largely due to a decrease in the number of low-affinity receptors. Nerve growth factor-induced changes, such as the induction of ornithine decarboxylase and the generation of neurites, were inhibited, but only minimally, in dexamethasone-treated cells.

Ornithine decarboxylase activity, prolactin blood levels, and estradiol and progesterone receptors in human breast cancer

Ornithine decarboxylase (ODC) activity in human breast cancer tissues was correlated with prolactinemia (Prl), estradiol and progesterone cytosol receptors (ER and PR), and histopathologic pattern. Ninety-two cases of breast cancer, six benign mammary disease, and three normal breast tissues were studied for ER, PR, and ODC. Prolactinemia was assessed in 59 cancer patients, 14 of whom showed hyper-Prl along with significantly higher ODC than in patients with normal-Prl [(20.01 +/- 6.33) 10(-2) vs (5.20 +/- 0.90) 10(-2) pmol CO2/micrograms protein/h; P less than 0.0125]. A direct correlation was found between Prl and ODC in postmenopausal women (n = 40). Prl was assayed in seven of 13 ER-PR breast cancer patients; a highly significant, direct correlation was found between Prl and ODC in this group (r = 0.934, P less than 0.0025). ODC did not correlate with ER or PR. Carcinomas with higher ODC (n = 17) had higher cellularity, lower histologic differentiation, and higher nuclear anaplasia than those in which ODC was not detectable (n = 13). In normal breast and five of six benign mammary disease tissues, ODC was not detectable. These findings suggest that ODC could be a reliable marker for prognosis.

Effect of difluoromethyl ornithine (DFMO) on small intestine of adult and weanling rats

Oral feeding of DL-difluoromethyl ornithine (DFMO) (2% in water ad libitum) for 14 days has no detectable effect on the small intestine of adult rats. Similar feeding of DFMO to weanling rat pups caused diarrhea in three to four days accompanied by a decrease in food consumption and body weight compared to age-matched controls. Significant decreases in small intestinal mucosal weight, total protein, DNA, enterokinase, leucine amino peptidase, sucrase, and maltase contents were observed in the DFMO-treated group four days after treatment. Extending the treatment to seven days led to a more severe reduction in these parameters. Villous atrophy of the mucosa was demonstrable by light microscopy and morphometric measurements. The mucosa of the DFMO-treated rat pups showed a reduction in total thickness and villous height but no change in crypt depth. A significant reduction in villus-crypt ratio was also seen. Changes in small intestinal mucosal parameters were not due to a decrease in food intake since pair-fed, age-matched rat pups showed no biochemical changes compared to control pups. DFMO-treated weanling rats showed less than 5% of ornithine decarboxylase (ODC) activity when compared to age-matched control animals. The effects observed on the small intestinal mucosa are presumably due to inhibition of ornithine decarboxylase activities by DFMO which prevents the proliferation, regeneration, and maturation of epithelial cells. The relative insensitivity of the adult rat small intestine to DFMO treatment suggests a lesser dependence of its intestinal mucosa to ODC activities.

Prolactin selectively stimulates ornithine decarboxylase in the lateral lobe of the rat prostate

In androgenized-hypophysectomized rats, ovine prolactin stimulated the activity of the ornithine decarboxylase (ODC) of the lateral lobes, but not the ventral and dorsal lobes of the prostate glands in a time- and dose-dependent fashion. High degrees of enzyme stimulation were associated with significant elevations in the endogenous levels of its product, putrescine. The relative response to prolactin over basal activities was relatively unaffected by indomethacin but decreased with cycloheximide, suggesting that prostaglandins do not mediate the effects of the hormone, but that a high rate of protein synthesis is a prerequisite for its expression. Indomethacin alone significantly increased the basal activity of the enzyme above control levels, suggesting that prostaglandins may normally exert a degree of inhibition on the ODC. The selective activation of the lateral lobe ODC supports previous reports of a differential response of the various prostatic lobes to prolactin, and also provides a convenient biochemical response for examining details of prolactin action on this organ.

Prolactin desensitizes the prostaglandin E1-dependent adenylyl cyclase in the rat prostate gland

Prior exposure of the rat ventral prostate to a high dose of ovine prolactin in vivo or in vitro caused the specific desensitization of the prostaglandin E1-dependent adenylyl cyclase. Maximal desensitization was achieved in vivo 6 h after exposure to 100 micrograms prolactin and complete resensitization occurred after 7 days. No heterologous desensitization of the response of the cyclase to other hormones tested was observed. Incubation of isolated secretory cells with prolactin and prostaglandin E1 desensitized the subsequent response to the same prostaglandin. Simultaneous exposure of the cells to indomethacin prevented the prolactin-induced effect. Prolactin could also induce similar changes in the prostaglandin E1-dependent cyclase of rat Leydig cell tumour cells in vivo, suggesting that this may represent a phenomenon shared by other prolactin target organs. This study supports the hypothesis that prostaglandins may constitute second messengers for prolactin effects on the prostate gland.

Effects of various kinds of stimulation on ornithine decarboxylase activity in superior cervical sympathetic and nodose ganglia of rats

Levels of cyclic nucleotides and ornithine decarboxylase (ODC) activity were examined following the application of various kinds of stimuli to superior cervical sympathetic ganglia (SCG), nodose ganglia, and vagus nerve fibers excised from the rat. The level of cyclic GMP in the SCG rose rapidly to about 4.5- to 7.5-fold the unstimulated control with 10 min of incubation after applications of preganglionic electrical stimulation (10 Hz), acetylcholine (ACh; 1 mM), or high extracellular K+ ( [K+]0, 70 mM). The cyclic GMP level in nodose ganglia was increased less than in the SCG by either ACh or high [K+]0 but was not affected by ACh in vagus fibers. Cyclic AMP in the SCG was also increased about 4- to 5.5-fold over the control within 10 min with the addition of ACh, norepinephrine (NE; 0.05 mM), or high [K+]0. Although NE caused a small increase in cyclic AMP, neither ACh nor high [K+]0 produced any appreciable change in nodose ganglia or vagus fibers. The ODC activity in the SCG was increased by preganglionic stimulation of 3- to 4-hr duration but not by a shorter period. A similar change in ODC activity was caused by the addition of oxotremorine (1 mM), isoproterenol (0.1 mM), NE, cyclic AMP (1 mM), or dibutyryl cyclic GMP (1 mM). The effect was exaggerated by the further addition of 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor. The increase in ODC activity caused by ACh was abolished by a muscarinic cholinergic antagonist, atropine (0.01 mM), and following axotomy for a week, but not by a nicotinic antagonist or by denervation in the SCG. A similar increase in ganglionic ODC activity by NE was inhibited by an adrenergic blocker, propranolol (0.01 mM), and following axtotomy for a week, but not by denervation. Cholinergic or adrenergic stimulation did not cause an increase in ODC activity in nodose ganglia or vagus fibers. These results suggest that the stimulation-induced increase in ODC activity occurs in postganglionic neurons rather than in satellite glial cells and is mediated by muscarinic cholinergic or adrenergic receptors. The process appears to involve cyclic nucleotide-mediated protein biosynthesis in the SCG.

Effects of denervation and axotomy on nervous system-specific protein, ornithine decarboxylase, and other enzyme activities in the superior cervical sympathetic ganglion of the rat

The time courses of changes of three enolase isozymes (alpha alpha, alpha gamma, and gamma gamma), S-100 protein, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), ornithine decarboxylase (ODC), beta-galactosidase, and glucose-6-phosphate dehydrogenase (G6PDH) were examined from 1 to 14 days after cutting of the preganglionic nerve (denervation) or the postganglionic nerve (axotomy) of the superior cervical sympathetic ganglion (SCG) of the rat. The wet weight and protein content in the axotomized SCG increased continuously, to nearly twice those of the denervated SCG for 1-2 weeks after the operations. Among enolase isozymes in the SCG, neuron-specific gamma gamma-enolase decreased rapidly after denervation and stayed at a low level for 2 weeks, whereas the isozyme remained almost unchanged after axotomy. On the contrary, ganglionic alpha alpha-enolase and the alpha gamma-hybrid form increased remarkably to reach a maximum at the second day after axotomy, and remained above control for 1 to 2 weeks; these two enolase isozymes showed little change after denervation. Denervation caused a much larger increase than did axotomy in the ganglionic S-100 protein, an astrocyte-specific protein, during the first week after the operation, while the protein content decreased after 2 weeks of either denervation or axotomy. CNPase, a myelin-associated enzyme, rose suddenly 2 days after axotomy, and remained at a rather high level compared with the denervated ganglion, which showed little variation.(ABSTRACT TRUNCATED AT 250 WORDS)

The neurite-promoting effect of fibroblast growth factor on PC12 cells

Treatment of PC12 cells with fibroblast growth factor(s) from either brain or pituitary caused neurite outgrowth comparable to that produced by nerve growth factor. The neurite outgrowth was preceded by a substantial rise in the activity of ornithine decarboxylase.

Polyamine inhibition of gastric ulceration and secretion in rats

The effect of polyamines on gastric ulceration and secretion in rats was studied. Stress-induced gastric ulceration and ulceration in pylorus-ligated rats were inhibited by subcutaneous or oral administration of spermine; spermidine's inhibitory effect was somewhat less. Histamine-induced ulceration was also inhibited by the subcutaneous injection of spermine. In addition, the daily oral administration of spermine for 10 days was therapeutic against an acetic acid-induced ulcer (chronic ulcer). Gastric secretion in pylorus-ligated rats and in rats with fistulae and stimulated by histamine injection was decreased by the subcutaneous injection of spermine.

The effects of nerve growth factor on polyamine metabolism in PC12 cells

Nerve growth factor treatment produces a large increase in the activity of ornithine decarboxylase and a moderate decrease in the activity of S-adenosylmethionine decarboxylase in PC12 cells. These changes are reflected weakly, if at all, in the levels of putrescine, spermidine, and spermine in the cells. The rates of polyamine synthesis are increased somewhat more than the overall levels, but still are not comparable in extent to the increase in the ornithine decarboxylase activity. Inhibitors of ornithine decarboxylase and S-adenosylmethionine decarboxylase have their expected effects on the induction of ornithine decarboxylase and on the activities of both enzymes. Neither inhibitor alone, nor a combination of inhibitors, altered the rate or extent of nerve growth factor-induced neurite outgrowth in the cells.

Effects of cyclic nucleotides on ornithine decarboxylase activity in mammary gland explants from mid-pregnant mice

Dibutyryl cAMP and prolactin stimulated ornithine decarboxylase activity in mouse mammary gland explants which had been preincubated with insulin and cortisol for 1 day; maximally stimulatory concentrations of dibutyryl cAMP and prolactin produced a response which was greater than the sum of the responses of prolactin and dibutyryl cAMP when tested alone. 8-Bromo-cGMP inhibited ornithine decarboxylase activity whereas other derivatives of cyclic nucleotides were without effect. Cortisol concentrations were found to be important for optimizing the dibutyryl cAMP and prolactin responses. Optimal prolactin responses were obtained with cortisol concentrations greater than 10(-7) M, whereas optimal dibutyryl cAMP responses were observed with cortisol concentrations less than 10(-7) M. Despite the differing optimal cortisol concentrations for the prolactin and dibutyryl cAMP responses, it is concluded that prolactin and dibutyryl cAMP probably stimulate ornithine decarboxylase activity in the mammary gland via the same mechanism.

Prostaglandin stimulation of ornithine decarboxylase activity in mammary gland explants from mid-pregnant mice

The effects of various prostaglandins on ornithine decarboxylase (ODC) activity in mammary gland explants from mid-pregnant mice have been tested. PGE1, E2 and I2 elicit a concentration-dependent stimulation of ODC activity. The minimally effective concentrations are 0.5 ug/ml for PGE1 and E2, and 50 ug/ml for PGF2 alpha and 6-keto-PGF1 alpha. The PGE1 effect had a time course identical to that of prolactin. The prolactin action on ODC activity was attenuated by indomethacin, an inhibitor of prostaglandin biosynthesis. Arachidonic acid stimulated ODC activity and its effect was abolished by indomethacin. The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, potentiated the PGE1 effect on ODC activity. The results suggest that the prostaglandins may modulate prolactin's action on ODC activity via a cAMP dependent mechanism.

Induction of ornithine decarboxylase in guinea pig lymphocytes by the divalent cation ionophore A 23187. Effect of dibutyryladenosine 3',5'-monophosphate

The divalent cation ionophore, A23187, at a concentration of 0.25 microgram/ml, enhanced influx of Ca2+, activity of ornithine decarboxylase and incorporation of [3H]thymidine into DNA of guinea pig lymphocytes. Combined treatment of cells with A23187 and dibutyryladenosine 3',5'-monophosphate (Bt2cAMP) augmented these three events. A23187 at a concentration of 0.06 microgram/ml was insufficient for induction of ornithine decarboxylase stimulated neither Ca2+ influx nor [3H]thymidine incorporation, but stimulated Ca2+ efflux. A23187 (0.06 microgram/ml) in combination with Bt2cAMP caused a marked induction of ornithine decarboxylase and stimulation of [3H]thymidine incorporation into DNA. When the time of Bt2cAMP addition was delayed after A23187, the stimulation of ornithine decarboxylase activity decreased. Washout of Bt2cAMP from cell culture earlier than 4 h of incubation caused a reduction in the stimulatory effect of Bt2cAMP. These results suggest that raising concentrations of cytoplasmic Ca2+ and cellular cAMP are important to some initial events leading to induction of ornithine decarboxylase and these biochemical changes are obligatory sequential steps for stimulation of DNA synthesis.

Effects of 12-0-Tetradecanoylphorbol-13-acetate (TPA) on rat pheochromocytoma (PC12) cells: interactions with epidermal growth factor and nerve growth factor

The phorbol ester tumor promotor 12-0-tetradecanoylphorbol-13-acetate (TPA) specifically inhibited the binding of radioiodinated epidermal growth factor (125I-EGF) to rat pheochromocytoma (PC12) cells in a noncompetitive fashion with an apparent Ki of 11-26 nM. Both TPA and EGF elicited similar biological responses in PC12 cells including enhanced incorporation of 3H-choline and 32 P-orthophosphate into macromolecules, induction of ornithine decarboxylase, and stimulation of the phosphorylation of a 30,000 MW nonhistone, chromosome-associated protein. These effects were also elicited by nerve growth fact (NGF) which, in contrast to the former agents, is a differentiating stimulus for PC12 cells. The effects of TPA were additive or more than additive to the effects of NGF and EGF. When PC12 cells were induced to differentiate by treatment with NGF for 72 hours, the binding of 125I-EGF and responses to EGF were reduced by approximately 70%. The response of PC12 cells to the tumor promoter TPA was unaffected by treatment with NGF. Thus, the qualitatively similar effects of TPA and EGF seemed to be mediated through separate receptor systems with only the EGF receptor system reduced by NGF treatment.

Regulation of ornithine decarboxylase activity by cyclic AMP in guinea pig lymphocytes: transcriptional and post-transcriptional control

Induction of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in phytohemagglutinin-stimulated lymphocytes was suppressed by the administration of dibutyryl cyclic AMP and 3-isobutyl-1-methylxanthine. This inhibition of ornithine decarboxylase induction was overcome by removing the chemicals from the lymphocyte culture. However, the recovery of ornithine decarboxylase induction by washout of the chemicals did not occur when actinomycin D, cordycepin or alpha-amanitin was added to the cultures, suggesting that the synthesis of mRNA directed to ornithine decarboxylase was reduced in dibutyryl cyclic AMP- and 3-isobutyl-1-methylxanthine-treated cells. Moreover, the decay of ornithine decarboxylase activity in the cells treated with phytohemagglutinin plus dibutyryl cyclic AMP and 3-isobutyl-1-methylxanthine was significantly slower than that of control cells stimulated with phytohemagglutinin alone. The difference of the decrease in ornithine decarboxylase activity between dibutyryl cyclic AMP- and 3-isobutyl-1-methylxanthine-treated and control cells was observed when actinomycin D was added to the culture, but not when cycloheximide was added. Therefore, prevention of ornithine decarboxylase decay by cyclic AMP may be post-transcriptional events, but not post-translational events.

The action of adenosine analogs on PC12 cells

PC12 cells, a nerve growth factor-responsive clone of rat pheochromocytoma, contain a membrane-bound adenylate cyclase, which can be activated by adenosine analogs. The characteristics of the cyclase response indicate the presence of stimulatory adenosine receptors. Adenosine analogs also produce a marked increase in the ornithine decarboxylase levels of the cells, and the characteristics of this response suggest that it is linked to the adenylate cyclase-stimulatory adenosine receptors. The ornithine decarboxylase response elicited by 5'-N-ethylcarboxamideadenosine (NECA), a potent stimulatory adenosine analog, is synergistic with that produced by nerve growth factor. Differentiation of the cells with nerve growth factor, however, does not substantially alter either the response of cyclase to the adenosine analog or the magnitude of the adenosine-evoked ornithine decarboxylase response. Treatment of the cells with NECA produces an increase in the phosphorylation of a specific non-histone nuclear protein. While causing little or no morphological alteration by itself, NECA is synergistic with nerve growth factor in producing neurite outgrowth in PC12 cells. NECA does not cause an induction of acetylcholinesterase in the cells. NECA does not cause an induction of acetylcholinesterase in the cells, nor does it appear to affect the induction of this enzyme by nerve growth factor.

Multihormonal regulation of ornithine decarboxylase activity in highly differentiated porcine granulosa cells in vitro

Purified luteinizing hormone, but not follicle-stimulating hormone, elicited time- and dose-dependent stimulation of the cytosolic enzyme, ornithine decarboxylase, in highly differentiated, porcine granulosa cells maintained in vitro in chemically defined medium. Enzymatic induction was susceptible to inhibitors of protein and RNA synthesis, and was suppressed by selective direct and indirect inhibitors of ornithine decarboxylase. Physiologic concentrations of prostaglandin E2 and L-epinephrine also enhanced enzymatic activity in a dose-dependent and saturable manner. Systematic comparison of the hormonal induction of ornithine decarboxylase in highly differentiated versus poorly differentiated granulosa cells revealed distinctive patterns of enzymic responsivity in relation to the degree of cytodifferentiation attained in vivo. This in vitro model is likely to permit further detailed examination of the molecular mechanisms subserving the hormonal control of ovarian ornithine decarboxylase activity in spontaneously differentiated granulosa cells maintained under chemically defined conditions in vitro.

The induction of ornithine decarboxylase by nerve growth factor and epidermal growth factor in PC12 cells

Both nerve growth factor and epidermal growth factor cause an induction of ornithine decarboxylase in the rat pheochromocytoma clone PC12. The induction by nerve growth factor is transcription-dependent and occurs within 4 to 6 h. Antibody studies indicate that nerve growth factor must be present for 2-3 h to obtain full induction. Nerve growth factor is synergistic with either N6, O2-dibutyryl cyclic 3',5'-adenosine monophosphate (dBcAMP) or 3-isobutyl-1-methylxanthine (IBMX) in the induction. The magnitude of ornithine decarboxylase induction is influenced by the density of the culture. Synchronized cell populations show the greatest sensitivity to nerve growth factor just before, or immediately upon, entering S phase. The induction of ornithine decarboxylase by epidermal growth factor appears to be quite similar to that exhibited by nerve growth factor. Epidermal growth factor is active in the range of ng/ml. The time course of the induction is the same, as is the need for the peptide to remain in contact with the cells for several hours. Putrescine inhibits the induction and dBcAMP and IMBX accentuate it. Cells appear to be sensitive to epidermal growth factor also near the G1/S border. In spite of the marked similarities in these inductions, a maximal level of nerve growth factor plus a maximal level of epidermal growth factor yields greater induction than either alone, indicating the inductions occur by somewhat different mechanisms.

Increased activity of ornithine decarboxylase in goldfish following optic nerve crush

Ornithine decarboxylase (ODC) activity increased in goldfish retina, brain, and kidney several days following unilateral intraorbital optic nerve crush. Activity in both retinas followed a similar time course, an elevation being first detectable 3 days following crush, maximal on day 5 and returning to control levels by day 7. Increases were significantly higher in the retina on the lesioned side than in control retina. If one eye was surgically removed, a more prolonged elevation of ODC activity was seen in the remaining eye than was observed in control retinas following contralateral nerve crush. Sham operation or behavioral stress secondary to aversive electrical shock did not lead to significant increases in ODC activity in brain or retina. Explants of retinas whose optic nerve had been crushed 10--14 days prior to explantation, as well as those derived from the unlesioned side, showed increases in ODC activity following addition of beta-NGF to the medium. The response was greater in post-crush retinas than in control retinas. These results taken together suggest an increased responsiveness of the regenerating retina to stimuli that lead to increased ODC activity. While the nature of the in vivo signal(s) may be complex, it is inferred that degenerative changes in the distal stump play a significant role.

Effects of insulin on cultured rat brain cells: stimulation of ornithine decarboxylase activity

Growth-promoting peptide hormones, including growth hormone and insulin, stimulate rat brain ornithine decarboxylase (ODC; EC 4.1.1.17) activity in vivo (Roger et al., 1974; Roger and Fellows, 1980). To determine if this is a result of a direct action on brain, we have investigated the effect of peptide hormones in primary cell cultures of brain from fetal rats of 20 days gestational age. Significant stimulation of ODC activity was observed 4 h after administration of porcine insulin and bovine growth hormone. On a molar basis, growth hormone was less potent than insulin. By contrast, glucagon, enkephalin, and angiotensin II did not stimulate ODC in this system. At 25 ng/ml, insulin stimulated ODC activity approximately threefold, with maximum stimulation of five- to sevenfold reached at 1 microgram/ml. After a 1-h lag, insulin-stimulated ODC activity increased to a maximum between 5 h and 8 h and returned to basal levels by 24 h. The apparent Km of ODC, 5.66 +/- 1.16 microM, was not significantly altered by insulin treatment, nor was any enzyme activator found in mediating insulin actions. Additional evidence suggests that insulin stimulation of ODC activity involves both de novo synthesis of the enzyme and a prolongation of ODC half-life by 50%. These findings, implicating insulin as a regulator of ODC activity in brain cells, suggest the possible involvement of insulin or an insulin-like peptide in the control of growth and development of the CNS.

Retrogradely transported nerve growth factor increases ornithine decarboxylase activity in rat superior cervical ganglia

Nerve growth factor (NGF) transported intraaxonally from the adrenergic nerve terminals in the iris to the cell bodies in the superior cervical ganglion resulted in an increase in the activity of the enzyme ornithine decarboxylase in the ganglion. This occurred in both six-day-old and adult rats with the relative effect of the retrogradely transported NGF being greater in adult animals. These results suggest that the induction of ornithine decarboxylase by NGF may be due to the stimulation of intracellular receptors.

Ornithine decarboxylase in bovine corpora lutea

The ornithine decarboxylase (ODC) activity in cytosol and in dispersed cells of bovine corpora lutea was characterized in detail. The enzyme activity was maximal at an assay temperature of 38 C and was linear with respect to both duration of incubation and the amount of cytosol protein or cell number added. The pH optima for the enzyme was rather broad, i.e. 7.2 to 8.5. The apparent Km for ornithine (140-280 micro M) was similar for cytosol and cell ODC. Thiol compounds were required for the maximal enzyme activity and there was an absolute requirement for pyridoxal phosphate as a cofactor, with an apparent Km of 15 micro M. There was a modest competitive inhibition of ODC activity by the end products of ornithine catabolism. Human chorionic gonadotropin (hCG), prostaglandin (PG)E1, PGF2 alpha and cyclic nucleotides had no direct effect on ODC activity. There was no consistent response of ODC in cells and tissues slices pretreated with hCG and PGs. Only the corpus luteum part of bovine ovary of pregnancy contained ODC and this enzyme activity was unchanged throughout pregnancy.

Role of spermidine in casein gene expression in the rabbit

Spermidine concentration in rabbit mammary gland was estimated during pregnancy, lactation and after the induction of milk synthesis by prolactin and glucocorticoids in vivo and in vitro. It was observed that mammogenesis and lactogenesis during preganancy and the initiation of milk secretion at parturition are accompanied by an enhancement of spermidine concentration in the mammary gland. By contrast, the initiation of these phenomena by hormone injections does not require such variations of spermidine concentration. In organ culture, a slight increase in spermidine concentration was obtained under the influence of an hormonal combination including insulin, prolactin and cortisol. Spermidine added to the culture medium was unable to mimic cortisol action. An amplification of casein synthesis and a parallel increase of casein mRNA concentration was provoked by cortisol even when spermidine synthesis was blocked. Thus, one of the major actions of glucocorticoids during lactogenesis in the rabbit is not mediated through an increase in spermidine concentration in the mammary gland.