Cystamine inhibits transglutaminase and caspase-3 cleavage in glutamate-exposed astroglial cells.

Although the precise role of transglutaminase in cell death is unknown, several findings demonstrate that tissue transglutaminase selectively accumulates in cells undergoing apoptosis both in vivo and in vitro. Calcium-dependent transglutaminase reactions are also implicated in several neurodegenerative diseases, including alterations in the release of excitatory amino acids. One prevalent theme in cell damage induced by excitotoxic stimuli in different regions of the CNS is that apoptosis may be executed by intracellular caspase proteases. Furthermore, the presence of functional ion channel-gated receptors in glial cells suggests that also astrocytes can be susceptible to glutamate's toxic effects. In this study, we demonstrated that prolonged exposure to glutamate (100 microM) of cultured astrocytes caused an increase in the expression of tissue transglutaminase (tTG). This effect was prevented by preincubation with GYKI 52466, an antagonist of AMPA/KA receptors. Glutamate exposure also promoted an increase in caspase-3 compared with control cultures. Confocal laser microscopy analysis demonstrated the presence of activated caspase-3 in the cytoplasm as well as in the nucleus. The inhibition of TG-catalyzed reactions by cystamine (1 mM) blocked the activation pathway of caspase-3, with an evident reduction of enzyme cleavage. These results suggest that glutamate increased both TG and caspase-3 in astroglial cells early in the excitotoxin-induced events.

Glutamate-induced increases in transglutaminase activity in primary cultures of astroglial cells.

Glutamate exposure of astroglial cells caused ligand-gated channel receptor activation, associated with excitotoxic cell response. We investigated the effects of 24 h glutamate exposure on transglutaminase in astrocytes primary cultures at 7, 14, and 21 days in vitro (DIV). Increases in enzyme activity were observed as a function of cell differentiation stage in glutamate-treated cultures. These effects were significantly reduced when GYKI 52466, an AMPA/KA receptors inhibitor, was added to the culture medium prior to incubation with glutamate. Microscopy observation on transglutaminase-mediated, fluorescent dansylcadaverine incorporation in living cells was consistent with these results. Western blotting analysis with monoclonal antibody showed that glutamate also up-regulated tissue transglutaminase expression, which reached the highest values in 14 DIV cultures. Confocal laser scanning microscopy analysis of immunostained astroglial cells showed a mainly cytoplasmic localisation of the enzyme both in control and treated cultures; nevertheless, counterstaining with the nuclear dye acridine orange demonstrated the presence of tissue transglutaminase also into the nucleus of glutamate-exposed and 21 DIV cells. The increases in enzyme expression and localisation in the nucleus of glutamate-treated astroglial cells may be part of biochemical alterations induced by excitotoxic stimulus.

NMDA-evoked excitotoxicity increases tissue transglutaminase in cerebellar granule cells.

In neuronal cells, excessive activation of glutamate receptors causes excitotoxic damage culminating in apoptotic and necrotic cell death. The molecular mechanism of excitotoxicity has been associated with excessive Ca(2+) influx and overload, triggering biochemical events that lead to cell death and tissue degeneration. Following mild insults via NMDA-receptor activation, central neurons undergo several biochemical modifications recognizable as early events in apoptotic machinery.Tissue transglutaminase, the most ubiquitous among cell transglutaminases, catalyzes the Ca(2+)-dependent protein cross-linking probably associated with morphological changes in several neurodegenerative disorders. The possible involvement of this enzyme in excitotoxicity-mediated events was investigated in primary cultures of cerebellar granule cells exposed for 30 min to NMDA (100 microM) in Locke's buffer. Under these conditions time-dependent increases in transglutaminase activity were observed. Tissue transglutaminase expression reached the highest levels within 3-4 h of NMDA exposure. Similarly, high levels of incorporation of fluorescent substrates were observed in living cells. Confocal laser microscopy analysis showed that fluorescein-labelled structures were distributed within the cytoplasm and close to the membranes of NMDA-exposed cells. These effects were dependent on the Ca(2+) influx triggered by the excitotoxic stimulus. Morphological changes in NMDA-treated cells gave evidence of significant cell damage which appeared within 5-6 h of NMDA exposure. These results suggest that increases in tissue transglutaminase may be associated to the effects of NMDA-induced excitotoxicity. Therefore, it is reasonable to hypothesize that if tissue transglutaminase levels and activity are up-regulated under such conditions, the protein cross-linking could be likely involved in excitotoxic response.

Apoptosis and necrosis occurring in excitotoxic cell death in isolated chick embryo retina.

Excitotoxic studies using isolated chick embryo retina indicated that such an in vitro model provides a valid tool to characterize the effect of different agonists for subtypes of glutamate ionotropic receptors. In retinas maintained for 24 h in a Krebs medium, after a brief exposure (30 min) to glutamate agonists, we compared the effects produced by NMDA and non-NMDA-agonists, such as kainic acid (KA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Delayed retinal damage was assessed by measuring lactate dehydrogenase (LDH) present in the medium after exposure to the previously named agonists. Although at high concentrations, both KA and AMPA produced more relevant release than NMDA, 7-8% of total retinal LDH was released after exposure to a 50 microM concentration of non-NMDA agonists. These values were similar to those obtained after 100 microM NMDA. In this regard, retinal tissue appeared to be less sensitive to excitotoxicity based on the activation of NMDA receptor subtype. All three agents produced histopathological lesions typical for excitotoxic damage. A delayed form of excitotoxicity observed in retina segments was predominated by necrotic features. However, the activation of apoptotic machinery early during the incubation period subsequent to brief exposure to NMDA (100 microM) was also present. The activation of caspase enzymes was studied by a fluorometric protease activity assay as well as by western blot analysis. Caspase-3-like activity reached the highest value within 3 h of incubation after exposure to excitotoxin, then the level of enzyme activity declined to lower values. As confirmed by a time-related appearance of TUNEL-positive nuclei, apoptotic features appeared to be specific for retina response to NMDA. In contrast, the exposure to a 50 microM concentration of KA or AMPA induced necrotic cell damage which was evident through the incubation, leading to a delayed mechanism of excitotoxicity. These observations provide evidence that in the retinal model, with regard to agonist concentrations and subtype of glutamate receptors, the cascade of events leading to excitotoxicity may result in either apoptotic or necrotic neuronal cell damage.

Serum ionized magnesium levels in type 2 diabetic patients with microalbuminuria or clinical proteinuria.

BACKGROUND/AIMS: The association between microalbuminuria and magnesium depletion is a controversial issue, and serum ionized magnesium levels have not been previously studied in patients with different grades of diabetic nephropathy. Therefore, the aim of this study was to evaluate circulating ionized magnesium concentrations in patients with non-insulin-dependent diabetes mellitus (NIDDM) and incipient or overt diabetic nephropathy. METHODS: We measured fasting plasma glucose, creatinine, creatinine clearance estimate, total cholesterol and triglycerides, and serum ionized magnesium (ion-selective electrodes, ISE) in 30 NIDDM patients with urinary albumin excretion rate (UAER) <20 microg/min (normoalbuminuria), 30 NIDDM patients with microalbuminuria (20 < UAER < 200 microg/min), 30 NIDDM patients with clinical proteinuria (UAER >200 microg/min), and 20 healthy subjects. RESULTS: Serum ionized magnesium levels were significantly reduced in diabetic patients when compared to control subjects (0.39 +/- 0.06 vs. 0.58 +/- 0.05 mmol/l, p < 0.001). Moreover, diabetic patients with microalbuminuria or clinical proteinuria showed a significant decrease in serum ionized magnesium with respect to normoalbuminuria group (normoalbuminuria: 0.45 +/- 0. 02 mmol/l; microalbuminuria: 0.36 +/- 0.05 mmol/l, p < 0.001; clinical proteinuria: 0.35 +/- 0.04 mmol/l, p < 0.001). Serum ionized magnesium showed a significant negative correlation with plasma HbA1c and triglycerides in both microalbuminuria and clinical proteinuria groups. Multiple linear regression analysis showed that circulating ionized magnesium levels decrease together with the increase of plasma HbA1c and triglycerides in NIDDM patients with incipient or overt nephropathy, also after adjusting for age, sex, BMI, diabetes duration, systolic and diastolic blood pressure, hypoglycemic therapy, plasma creatinine, creatinine clearance, plasma cholesterol and fasting glucose. CONCLUSIONS: Microalbuminuria and clinical proteinuria, as well as poor glycometabolic control and hypertriglyceridemia, are associated to relevant alterations in magnesium metabolism, and the measurement of serum ionized magnesium seems to represent a useful biochemical tool for the study of magnesium disturbances in patients with different grades of diabetic nephropathy.

Platelet magnesium depletion in normotensive and hypertensive obese subjects: the role of salt-regulating hormones and catecholamines.

We measured plasma and platelet magnesium concentrations, plasma epinephrine and norepinephrine, and plasma aldosterone and renin concentrations in normotensive (NT-Ob, n = 19, BMI 35.7 +/- 7.4 kg/m2, WHR 0.92 +/- 0.05) and hypertensive (HT-Ob, n = 11, BMI 35.2 +/- 3.6 kg/m2, WHR 0.93 +/- 0.07) obese subjects, and in a group of age- and sex-matched lean controls (n = 14, BMI 23.1 +/- 1.8 kg/m2, WHR 0.79 +/- 0.05). Plasma aldosterone and renin concentrations were significantly higher in obese subjects with respect to controls. Moreover, plasma norepinephrine and epinephrine levels were significantly increased in obese subjects, and plasma norepinephrine was higher in HT-Ob when compared to NT-Ob group. Platelet magnesium concentrations were significantly reduced in both normotensive and hypertensive obese subjects with respect to controls (controls 2.65 +/- 0.35 mumol/10(8) cells, NT-Ob 2.02 +/- 0.19 mumol/10(8) cells--p < 0.001, HT-Ob 1.98 +/- 0.18 mumol/10(8) cells--p < 0.001), while a slightly significant decrease in plasma magnesium levels was only detectable in HT-Ob group. Urinary magnesium and magnesium fractional excretion were significantly increased in hypertensive obeses. Pearson's correlation analysis, separately performed in each group of subjects, showed that plasma aldosterone, renin, epinephrine, norepinephrine and magnesium fractional excretion were negatively correlated to platelet magnesium levels in NT-Ob and HT-Ob groups, but not in lean controls. The multiple linear regression analysis performed in the whole group of obese subjects considering platelet magnesium as a dependent variable showed that platelet magnesium decrease together with the increase in plasma epinephrine (p = 0.046) and norepinephrine (p = 0.020), also after adjusting for age, sex, BMI, WHR, HOMA IR and diagnosis of hypertension. Furthermore, platelet magnesium showed a trend for negative association (p < 0.1) to plasma aldosterone and magnesium fractional excretion in multivariate analysis. The impairment in platelet magnesium handling observed in normotensive and hypertensive obese patients seems to be associated to a rise in renin-angiotensin-aldosterone and sympathetic systems activity. Our results suggest that platelet magnesium depletion, together with disturbances of salt-regulating hormones and catecholamines, may be involved in the pathophysiology of cardiovascular complications from obesity.

Changes in plasma, erythrocyte, and platelet magnesium levels in normotensive and hypertensive obese subjects during oral glucose tolerance test.

We evaluated the 75-g oral glucose tolerance test (OGTT)-induced modifications in glucose, insulin, and norepinephrine plasma concentrations, and in plasma, erythrocyte, and platelet magnesium levels in two groups of obese subjects (normotensive obese, NT-Ob, N = 19; hypertensive obese, HT-Ob, N = 15), and in a group of healthy control subjects (N = 12). During OGTT we detected a reduction in plasma magnesium concentrations and an increase in erythrocyte and platelet magnesium levels in the controls, whereas in both normotensive and hypertensive obese subjects, there was a reduction in plasma, erythrocyte, and platelet magnesium levels. Furthermore, no statistically significant difference was detected among the groups studied as regards delta-plasma magnesium. On the other hand, delta-erythrocyte magnesium and delta-platelet magnesium were negative in the NT-Ob (delta-erythrocyte magnesium: -0.24+/-0.08 mmol/L; delta-platelet magnesium: -0.49+/-0.09 micromol/10(8) cells) and HT-Ob (delta-erythrocyte magnesium: -0.20+/-0.10 mmol/L; delta-platelet magnesium: -0.50+/-0.11 micromol/10(8) cells) groups, and positive in control subjects (delta-erythrocyte magnesium: 0.40+/-0.08 micromol/L; delta-platelet magnesium: 0.47+/-0.09 mmol/ 10(8) cells). Finally, a direct correlation was found between delta-norepinephrine and delta-erythrocyte magnesium (r = 0.80, P < .01) in the control group, and a negative correlation was detected between delta-norepinephrine and delta-platelet magnesium (r = -0.58, P < .05) in the HT-Ob group. Our results seem to indicate that the insulin resistance status, the hyperglycemia, and the disregulation of the adrenergic system in obese subjects could be involved in the pathogenesis of the magnesium homeostasis impairment observed in the obese subjects.

Intracellular polyamine levels are involved in NMDA-evoked nitric oxide production in chick retina cells.

The NMDA-sensitive glutamate receptor complex can be modulated by numerous drugs and endogenous substances such as polyamines. We studied the pathway of arginine/nitric oxide/cyclic GMP in cultured chick retina cells through NMDA receptor activation, seen as a function of both differentiation stages of culture and intracellular polyamine levels. In our experimental conditions, the nitric oxide synthase activity was stimulated by NMDA from three to four times between embryonic day (E) 8 plus 5 days in vitro (C) and E8C7. The NMDA response was blocked by MK-801 (10 microM) by >60% at stage E8C5. During culture differentiation, the NMDA-induced increase in nitric oxide synthase activity at the E8C5 stage was blocked by preliminary incubation (24 h) of the cells with alpha-difluoromethylornithine, the inhibitor of polyamine biosynthesis. This effect was assessed by a reduction of NMDA-evoked cyclic GMP formation in polyamine-depleted retina cells. Thus, intracellular polyamine levels are involved in NMDA-evoked nitric oxide production. Our results indicate that (a) the developmental pattern of polyamine levels can be associated with the modulation of NMDA-evoked events and (b) the NMDA-mediated effects have been reduced in alpha-difluoromethylornithine-treated cell cultures. These observations provide evidence for a physiological interaction between polyamines and NMDA-sensitive glutamate receptors during differentiation stages of cultured chick retina cells.

[Obesity and hypertension: the role of magnesium]. / Obesità ed ipertensione: ruolo del magnesio.

We focus on the recent "ionic hypothesis", in which an alteration of ionic metabolism represents a peculiar event in the pathogenesis of obesity and hypertension. We report the results from our original studies in which we evaluated intraplatelet magnesium levels. In a study on normotensive and hypertensive patients with non insulin-dependent diabetes mellitus and healthy control subjects, we showed a common reduction of plasma, erythrocyte and platelet magnesium levels in both normotensive and hypertensive diabetics with respect to control. Anyway, hypertensive diabetics showed a greater reduction of intraplatelet magnesium concentrations when compared to normotensive diabetics. Using the same technique, we found reduced erythrocyte and platelet magnesium concentrations in patients with essential hypertension with respect to the control group. In a successive study, we found, in the group of normotensive obese, that erythrocyte and platelet magnesium levels were significantly lower than those of the control group, while in hypertensive obese patients a reduction of plasma magnesium levels has been also detected. In conclusion, in these studies has been confirmed the existence of a reduction of the intracellular magnesium concentrations, which is common in hypertensive and obese patients.

Plasma (total and ionized), erythrocyte and platelet magnesium levels in renal transplant recipients during cyclosporine and/or azathioprine treatment.

We evaluated total and ionized plasma magnesium levels, and erythrocyte and platelet magnesium concentrations from two groups of renal transplant recipients treated either with cyclosporine, azathioprine and prednisolone (group CAP, n = 8) or with azathioprine and prednisolone (group AP, n = 13), and in a group of age- and sex-matched healthy subjects (n = 10). Reduced plasma (total and ionized), erythrocyte and platelet magnesium concentrations were found in both CAP and AP groups with respect to controls (CAP: total plasma Mg median 0.61 vs 0.86 mmol/L, p < 0.01, ionized plasma Mg median 0.43 vs 0.58 mmol/L, p < 0.001, erythrocyte Mg median 2.18 vs 2.56 mmol/L, p < 0.05, platelet Mg median 1.75 vs 2.84 mmol/10(8) cells, p < 0.001; AP: total plasma Mg median 0.62 vs 0.86 mmol/L, p < 0.01, ionized plasma Mg median 0.48 vs 0.58 mmol/L, p < 0.001, erythrocyte Mg median 2.30 vs 2.56 mmol/L, p < 0.05, platelet Mg median 1.75 vs 2.84 mumol/10(8) cells, p < 0.001), while no difference was found between the two groups of transplant recipients as regards plasma and intracellular magnesium levels. Magnesium fractional excretion was higher in transplant recipients than in the control group (Mg fractional excretion median AP 18.6 per cent and CAP 12.8 per cent vs controls 3.5 per cent), whereas no difference was found between patients and control subjects for urinary magnesium 24h excretion. Moreover, in the whole group of transplant recipients (n = 21), urinary magnesium showed an inverse correlation with platelet (rs = -0.54, p < 0.05) and ionized plasma magnesium (rs = -0.48, p < 0.05), and time after transplantation showed a negative correlation with platelet magnesium concentrations (rs = -0.73, p < 0.001), and a direct correlation with fractional magnesium excretion (rs = 0.53, p < 0.05). Finally, a direct relationship between platelet magnesium and ionized plasma magnesium was also detected in the whole group of transplant recipients (rs = 0.47, p < 0.05). Both intraplatelet magnesium depletion and ionized plasma magnesium reduction induced by immunosuppressive therapy could be involved in the increased risk from atherosclerotic disease in renal transplant recipients.

Nitric oxide mediates NMDA-evoked [3H]GABA release from chick retina cells.

The stimulation of NMDA receptor increased [3H]GABA release from preloaded cultured retina cells. This effect appears to be mediated by NO production, since addition of L-NA reduces NMDA-evoked [3H]GABA release. Spermine/NO complex, an NO donor, mimics the effect produced by NMDA. The addition of zaprinast, a phosphodiesterase inhibitor, as well as 8-Br-cGMP enhances the NMDA-evoked [3H]GABA release. These results agree with the existence in chick retina cells of NO/cGMP pathways and support a role for NO in NMDA-evoked events. The activation of this receptor complex through maturative stages of the retina together with the NO-mediated increase in GABA release may account for NMDA differentiative effect in culturing retina cells.

beta-Endorphin enhances polyamine transport in human lymphocytes.

Opioid peptides, such as beta-endorphin (beta-end), are capable of modulating in vitro proliferative response of lymphocytes. We attempted to determine the role of extracellular polyamines in the regulation of immune responses to opioid peptides by measuring the extent of polyamine uptake as adaptional response to cell activation. beta-end dose-dependently enhanced the incorporation of radioactive spermidine and spermine. When the cells were depleted of spermidine, with addition of specific inhibitors of both biosynthesis and interconversion pathway, a large increase in the incorporation of radioactive spermidine was observed. This effect appeares to be specific for beta-end, although a non-opiate-specific receptor could be involved, since beta-end-enhanced incorporation of radioactive spermidine is not blocked by naloxone. We conclude that the enhancement of polyamine incorporation may be considered as an integral component of lymphocyte activation by beta-end.

Nitric oxide enhances amino acid release from immature chick embryo retina.

Nitric oxide (NO) was investigated for its ability to induce amino acid release from immature chick retina. The production of endogenous NO by activation of NO synthase after stimulation of N-methyl-D-aspartate (NMDA) subtype of glutamate receptor caused a significant increase in basal release of gamma-aminobutyric acid (GABA) and glutamine, whereas a more modest increase in the glutamate release was also observed. The exposure of chick retina from 9-day-old embryos to NO-generating compounds, S-nitroso-N-acetylpe-nicillamine (SNAP) and sodium nitroprusside (SNP) produced a dose dependent increase in GABA, glutamine, and glutamate release. This effect was reduced by about 80% by haemoglobin. These results indicate that NO has a stimulatory effect on amino acid release from chick embryo immature retina. However, this effect does not appear to involve a cGMP-related mechanism because 8-bromo-cGMP, a stable analogue of cGMP, failed to affect spontaneous amino acid release and because zaprinast did not enhance NMDA-stimulated release. In conclusion, our present observations may account for a role of NMDA-mediated events in the biochemical maturation under depolarizing conditions.

Nitric oxide synthase in chick embryo retina during development.

High levels of nitric oxide synthase were found in the early stages of developing chick embryo retina. The enzyme activity sharply decreased up to 13-day-old chick embryo retina, when the level of the last embryonic day was reached. The results show that nitric oxide is synthesized in chick embryo retina prior to synaptogenesis. The incubation of chick embryo retinas in presence of NMDA increased the synthesis of nitric oxide, thus, the appearance of nitric oxide production before the synaptogenesis in the retina as well as in the brain may be considered as signal for the development and shaping of neuronal and non-neuronal cells.

Putrescine, polyamines, and N1-acetylpolyamine levels in retina, visual cortex and cerebellum of free-running mice kept under continuous light or darkness.

Putrescine, spermidine and spermine levels were detected in the retina, visual cortex, cerebellum and parietal cortex of CD1 mice exposed to 36h continuous light or darkness. Retinal putrescine and polyamine concentrations were found to be highest in dark-adapted mice, and the stimulation of dark-adapted retina with flicker illumination was also accompanied by a significant decrease in putrescine, spermidine and spermine levels. In visual cortex as well as in cerebellum spermidine and spermine contents were higher in dark-adapted mice in comparison to light-exposed animals, while in parietal cortex no significant change was found neither in spermidine nor spermine levels. In the brain areas studied flicker illumination produced no significant decreases in putrescine and polyamine contents. The total polyamines expressed as putrescine equivalents were noticeably decreased in retina, visual cortex and cerebellum of light-adapted mice. In the retina spermine/spermidine molar ratio was significantly higher than in dark-adapted mice. The administration of N1, N2-bis-(2,3-butadienyl)-1,4-butanediamine (MDL 72527) produced a strong decrease of retinal putrescine and spermidine concentrations in both dark-adapted and light-exposed mice, and in the retina of mice exposed to continuous light a significant decrease in the spermine level was also observed. According to the influence on polyamine reutilization, after the irreversible inhibition of polyamine oxidase by MDL 72527, in the retina N1-acetylspermidine and N1-acetylspermine accumulation was highest in light-adapted mice. On the contrary in visual cortex, cerebellum and parietal cortex the MDL 72527 administration produced a more marked decrease of putrescine and spermidine contents in mice kept in continuous darkness.

Polyamines are involved in retinoic acid-mediated induction of tissue transglutaminase in human peripheral blood monocytes.

The differentiation of human peripheral blood monocytes (HPBM) into macrophages, when cultured in vitro, has been associated with an increase in the expression of tissue transglutaminase (TGc). Retinoic acid (RA) addition to 5-day-old cultured monocytes, 36 h later induced about 5-folds increase of TGc content. The preliminary exposure of cultured monocytes to alpha-difluoromethylornithine (DFMO) significantly reduced TGc induction caused by RA. DFMO alone does not induce significant changes in the time-course of TGc activity. In cultured monocytes exposed to DFMO, putrescine and spermidine, but not spermine were significantly depleted. The supplementation of putrescine (1 mM) or spermidine (0.5 mM) to culture medium reversed the inhibiting effect of DFMO on RA-mediated induction of TGc. However, the addition of polyamines in the absence of RA or DFMO did not mimic the induction of TGc by RA. We conclude that TGc induction by RA during in vitro maturation of monocytes to macrophages may be modulated by polyamine availability.

Excess of taurine supplementation in rat: effects on GABA-related amino acids in developing nervous tissues.

The effects of taurine supplementation on GABA-related amino acid homeostasis in developing nervous tissues of suckling rats were studied. In the first two weeks of postnatal growth, cerebral cortex and cerebellum appear more accessible to taurine supplementation in comparison to retina; in addition, different changes in excitatory/inhibitory amino acids were observed. After the 5th day of life, in the retina and cerebellum of taurine-supplemented pups a decrease in GABA levels was found; in contrast, in cerebral cortex GABA content significantly increased throughout 20 days of postnatal growth. In all nervous tissues studied (except for cerebellum) glutamine concentration increased at the 5th day; then in cerebellum and in retina, but not in cerebral cortex, a significant decrease until the 20th day occurred. Furthermore, in cerebellum and retina taurine supplementation decreased glutamate levels, in comparison to controls, at the 10th and until the 20th day of postnatal life, respectively, whereas in cerebral cortex an increase in glutamate level was observed only at the 5th day. In conclusion, taurine supplementation, in excess to the usual amount from the mother's milk, affected the glutamate compartments in various cell types. The changes in GABA-related amino acid concentrations in cerebral cortex, cerebellum, and retina may depend on the different pattern of the metabolic processes at different maturative stages.

Glucocorticoid regulation of spermidine acetylation in the rat brain.

The effect of glucocorticoids on polyamine metabolism has been elucidated further by measuring putrescine, spermidine, and spermine levels as well as ornithine decarboxylase, S-adenosylmethionine decarboxylase, and N1-acetylspermidine transferase activities in the hippocampus, cerebellar cortex, vermis, and deep nuclei of adrenalectomized rats. At 6 h after corticosterone or dexamethasone administration, the specific activities of ornithine decarboxylase and N1-acetylspermidine transferase showed the greatest increases in all brain tissues examined, and at 12 h, S-adenosylmethionine decarboxylase activity was not increased significantly. The hippocampus and cerebellar regions displayed different responses to corticosterone and dexamethasone, corresponding to the distribution of glucocorticoid and mineralocorticoid receptors. Corticosterone and dexamethasone increased ornithine decarboxylase and N1-acetylspermidine transferase activities in a dose-dependent manner, with dexamethasone being more active than corticosterone in all tissues. However, estradiol, progesterone, testosterone, and aldosterone were only active at doses greater than 5 mg/kg. The great increases in ornithine decarboxylase and N1-acetylspermidine transferase activities were accompanied by a marked increase in putrescine level and a small decrease in spermidine level. Our data confirm that the hippocampus and cerebellum are glucocorticoid target tissues and suggest that the increase in the content of putrescine, following acute treatment with glucocorticoids, is dependent on ornithine decarboxylase as well as N1-acetylspermidine transferase induction.