Receptor independent stimulatory effect of noradrenaline on Na,K-ATPase in rat brain homogenate. Role of lipid peroxidation

CCL2 Induces the Production of β2 Adrenergic Receptors and Modifies Astrocytic Responses to Noradrenaline

The decline in brain noradrenaline levels is associated with the progression of certain neurodegenerative diseases. This seems to be due, at least in part, to the ability of noradrenaline to limit glial activation and to reduce the damage associated with it. Our previous studies of the mechanisms involved in this process indicate that noradrenaline induces the production of the chemokine CCL2 in astrocytes. While CCL2 can protect neurons against certain injuries, its overproduction has also proven to be harmful and to prevent noradrenaline neuroprotective effects. Therefore, in this study, we analyze if the modifications caused to astrocytes by an excessive production of CCL2 may alter their response to noradrenaline. Using primary cultures of rat cortical astrocytes, we observed that CCL2 enhances the production of beta 2 adrenergic receptors in these cells. While this potentiates noradrenaline signaling through cAMP, the activation of the transcription factor CREB is inhibited by CCL2. Furthermore, although CCL2 potentiates noradrenaline induction of glycogenolysis, this does not translate into an augmented release of lactate, one of the processes through which astrocytes help support neurons. Additionally, other neuroprotective actions of noradrenaline, such as the production of brain derived neurotrophic factor and the inhibition of the inducible nitric oxide synthase in astrocytes were modified by CCL2. These data suggest that some of the central nervous system alterations related to CCL2 could be due to its effects on adrenergic receptors and its interference with noradrenaline signaling.

Sildenafil, a phosphodiesterase-5 inhibitor, offers protection against carbon tetrachloride-induced hepatotoxicity in rat

BACKGROUND

Elevation of phosphodiesterase-5 (PDE5) activity converts cyclic guanosine monophosphate (cGMP) to 5'-GMP, a mechanism that could be associated with drug-mediated hepatotoxicity. This study investigated whether selective inhibition of PDE5 by sildenafil could offer protection against hepatotoxicity induced by carbon tetrachloride (CCl4).

METHODS

CCl4 (0.5 mL/kg) was administered intraperitoneally to induce hepatotoxicity. The control group received normal saline. Sildenafil (5 mg, 10 mg, and 20 mg/kg, p.o.) was administered to CCl4-treated rats.

RESULTS

CCl4 significantly increased the serum levels of gamma glutamyl transferase (γ-GT), alkaline phosphatase (ALP), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) and reduced total protein (TP) (p<0.05). Pretreatment with sildenafil moderately reduced ALP, AST, and ALT activities with modest increase in TP level. CCl4-induced changes in the antioxidant status of the liver were significantly improved by sildenafil, especially at the lowest dose of 5 mg/kg by elevating the levels of reduced glutathione (GSH), glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) and preventing lipid peroxidation (p<0.05). Sildenafil did not significantly alter the total cholesterol and triglyceride levels. However, high-density lipoprotein (HDL) level was significantly increased by sildenafil (p<0.05).

CONCLUSIONS

The results from this study suggest that sildenafil, when used at low doses, may be a useful pharmacological protective agent against CCl4-induced hepatotoxicity.

Methyl jasmonate attenuated lipopolysaccharide-induced depressive-like behaviour in mice

Depression is a recurrent neuropsychiatric disorder that affects millions of individuals worldwide and impact negatively on the patients' social functions and quality of life. Studies have shown that i.p injection of lipopolysaccharide (LPS) induces depressive-like behavior in rodents via induction of oxidative stress and neuroinflammation. Methyl jasmonate (MJ), an isolated compound from jasmine plant has gained reputation in aromatherapy for treatment of depression, nervousness and memory deficits. This study was designed to evaluate the effects of MJ on LPS-induced depressive-like behavior in mice. Mice were given MJ (5-20 mg/kg), imipramine (10 mg/kg) or vehicle (10 mL/kg) intraperitoneally for 7 consecutive days. On day 7, treatment was carried out 30 min prior to i.p injection of LPS (830 μg/kg). Twenty four hours after LPS administration, tail suspension, forced swim and sucrose preference tests were carried out. Thereafter, serum corticosterone levels were determined using ELISA. The levels of malondialdehyde (MDA), glutathione (GSH) and tumor necrosis factor-alpha (TNF-α) were determined in brain tissue homogenates. LPS significantly increased immobility time in the tail suspension and forced swim tests when compared with vehicle (p < 0.05), which indicates depressive-like syndromes. However, the increased immobility time was significantly reduced by MJ (5-20 mg/kg) when compared with LPS-treated group. LPS administration also altered the levels of MDA, GSH, corticosterone and TNF alpha in mice, which was significantly reversed by MJ. These findings suggest that attenuation of LPS-induced depressive-like behavior by MJ may be related to suppression of oxidative stress and release of TNF alpha.

Anti-inflammatory and membrane stabilizing properties of methyl jasmonate in rats

The present investigation was carried out to evaluate anti-inflammatory and membrane stabilizing properties of methyl jasmonate (MJ) in experimental rat models of acute and chronic inflammation. The effects of MJ on acute inflammation were assessed using carrageenan-induced rat's paw edema model. The granuloma air pouch model was employed to evaluate the effects of MJ on chronic inflammation produced by carrageenan in rats. The number of white blood cells (WBC) in pouch exudates was estimated using light microscopy. The levels of biomarkers of oxidative stress, such as malondialdehyde (MDA), glutathione (GSH) and activity of antioxidant enzymes in the exudates, were determined using spectrophotometry. The membrane stabilizing property of MJ was assessed based on inhibition of hemolysis of rat red blood cells (RBC) exposed to hypotonic medium. Our results indicated that MJ (25-100 mg·kg^-1, i.p.) produced significant anti-inflammatory activity in carrageenan-induced paw edema in rats (P < 0.05). MJ reduced the volume of pouch exudates and the number of WBC in carrageenan-induced granulomatous inflammation. It also exhibited potent antioxidant and membrane stabilizing activities. In conclusion, these findings suggest the therapeutic potentials of methyl jasmonate in disease conditions associated with inflammation and its anti-inflammatory activity may be related to its antioxidant and membrane stabilizing activities.

Probable mechanisms involved in the antipsychotic-like activity of methyl jasmonate in mice

Psychosis is a chronic neuropsychiatric disorder that affects millions of individuals worldwide and impairs the quality of life and productivity of the patients. The clinical efficacy of antipsychotic drugs has been compromised by adverse effects, relapse, and therapeutic failures, thus necessitating search for alternative agents. Methyl jasmonate (MJ) is a bioactive compound reported to have beneficial effects in various neurological disorders. This study was undertaken to investigate the antipsychotic-like effects of MJ in mice. Male Swiss mice were pretreated intraperitoneally with MJ (25-100 mg/kg) or vehicle (10 mL/kg) 60 min prior to bromocriptine (5 mg/kg) or acute injection of ketamine (10 mg/kg). Thereafter, each mouse was observed for stereotype behaviors for 2 min at 10, 15, 20, 30, and 45 min post-bromocriptine injection. Another set of mice received MJ (25-100 mg/kg) or vehicle (10 mL/kg) 60 min after chronic ketamine injection (20 mg/kg, i.p) once daily for 14 consecutive days. Afterwards, locomotor activity and memory function in this sequence were evaluated using open field and Y-maze tests. The levels of malondialdehyde (MDA) and glutathione (GSH) and activity of catalase and superoxide dismutase (SOD) in the brain were determined. MJ significantly inhibited stereotypy behavior induced by bromocriptine or acute ketamine injection, which suggest antipsychotic-like activity. It also attenuated hyper-locomotion and memory deficits induced by chronic injection of ketamine in mice. The increased oxidative stress as shown by the altered brain levels of MDA, GSH, and activity of antioxidant enzymes induced by chronic injection of ketamine was reduced by MJ. Taken together, these findings suggest that MJ demonstrated antipsychotic-like property via mechanism related to its antioxidant property and interference with dopaminergic neurotransmission.

Methanol Extract of Adansonia digitata Leaf Protects Against Sodium Arsenite-induced Toxicities in Male Wistar Rats

BACKGROUND

Human and animal population exposure to arsenic through the consumption of arsenic contaminated water is rampant in many parts of the world. Protective agents of medicinal plants origin could provide maximum protection against toxicities of various kinds.

OBJECTIVE

The protective role of orally administered methanol extract of the leaves of Adansonia digitata (MELAD) on sodium arsenite (SA) - induced clastogenicity and hepatotoxicity in male Wistar rats was evaluated.

MATERIALS AND METHODS

Thirty male Wistar rats divided into six Groups (1-6) of five animals each were used for the study. Group 1 (negative control) received distilled water and normal diet only, Groups 2-6 received the extract (at 250 or 500 mg/kg body weight) and/or SA at 2.5 mg/kg body weight.

RESULTS

There was statistically significant (P < 0.05) increase in the number of micronucleated polychromatic erythrocytes and lipid peroxidation in the SA group as compared with the negative control and treated groups. Administration of the extract reduced the effects of SA on the above parameters. Activities of serum alanine and aspartate aminotransferases did not show statistically significant effects; however, the histological analyses revealed periportal cellular infiltration by mononuclear cells, whereas the MELAD treated groups show mild cellular infiltration and mild portal congestion.

CONCLUSIONS

MELAD protect against SA-induced toxicities in rats, and it may offer protection in circumstances of co-exposure and cases of arsenicosis.

SUMMARY

MELAD extract significantly reduce the lipid peroxidation induced by sodium arsenite in the liver of rats.MELAD did not show profound effects on the activities of serum alanine (ALT) and aspartate (AST) aminotranferases.MELAD offered significant protection against sodium arsenite-induced genotoxicity in the micronuclei induction assay.In the circumstances of co-exposure to arsenic contamination, MELAD may protect against sodium arsenite-induced toxicities. Abbreviations Used: MELAD: Methanol extract of the leaves of Adansonia digitata, SA: Sodium arsenite, nMPCEs: Number of micronucleated polychromatic erythocytes; ALT: Alanine aminotranferase; AST: Aspartate aminotranferase, TBARS: Thiobarbituric acid reactive substances, TBA: Thiobarbituric acid, MDA: malondialdehyde, Sodium arsenite (NaAsO2), IARC: International Agency for Research on Cancer.

Ashanti pepper (Piper guineense Schumach et Thonn) attenuates carbohydrate hydrolyzing, blood pressure regulating and cholinergic enzymes in experimental type 2 diabetes rat model

BACKGROUND

Ashanti pepper (Piper guineense Schumach et Thonn) seed is well known in folkloric medicine in the management of type 2 diabetes (T2DM) with little or no scientific documentation for its action. This study investigated the effect of Ashanti pepper seed on some enzymes relevant to carbohydrate hydrolysis, blood regulation and the cholinergic system, as well as the blood glucose level, lipid profile, antioxidant parameters, and hepatic and renal function markers in T2DM rats.

METHODS

T2DM was induced by feeding rats with high-fat diet (HFD) for 14 days followed by a single intraperitoneal dose of 35 mg/kg body weight of streptozotocin (STZ). Three days after STZ induction, diabetic rats were placed on a dietary regimen containing 2%-4% Ashanti pepper.

RESULTS

Reduced blood glucose level with decreased α-amylase, α-glucosidase and angiotensin I converting enzyme (ACE) activities were observed in Ashanti pepper seed and acarbose-treated rat groups when compared to that of the diabetic control rat group. Furthermore, the results revealed that inclusion of 2%-4% Ashanti pepper seed in diabetic rat fed group diets may ameliorate the lipid profile, antioxidant status, and hepatic and renal function in T2DM rats as much as in the acarbose-treated groups. In addition, a chromatographic profile of the seed revealed the presence of quercitrin (116.51 mg/g), capsaicin (113.94 mg/g), dihydrocapsaicin (88.29 mg/g) and isoquercitrin (74.89 mg/g).

CONCLUSIONS

The results from this study clearly suggest that Ashanti pepper could serve as a promising source of phenolic compounds with great alternative therapeutic potentials in the management of T2DM.

Ameliorative Activity of Ethanol Extract of Artocarpus heterophyllus Stem Bark on Pancreatic β-Cell Dysfunction in Alloxan-Induced Diabetic Rats

This study sought to investigate the ameliorative effects of ethanol extract Artocarpus heterophyllus (EAH) in alloxan-induced diabetic rats. The rats were divided into 6 groups, with groups 1 and 2 serving as nondiabetic and diabetic control, respectively; group 3 serving as diabetic rats treated with 5 mg/kg glibenclamide; and groups 4 to 6 were diabetic rats treated with 50, 100, and 150 mg/kg of EAH, respectively. Assays determined were serum insulin, lipid peroxidation, and antioxidant enzyme activities. EAH stem bark reduced fasting blood glucose and lipid peroxidation levels and increased serum insulin levels and activities of antioxidant enzymes. Data obtained demonstrated the ability of EAH stem bark to ameliorate pancreatic β-cell dysfunction in alloxan-induced diabetic rats.

Antidiabetic and antioxidant effects of Croton lobatus L. in alloxan-induced diabetic rats

BACKGROUND

Croton lobatus contains a high amount of antioxidant phytochemicals that probably account for its wide use as food and medicine in the traditional communities of West Africa.

METHODS

The study evaluated the modulatory role of methanol extract of Croton lobatus leaf on alloxan-induced diabetes and associated cardiovascular complications. Male rats were randomly selected and assigned to one of six groups (A to F) of eight animals each: A (distilled water); B (corn oil); C (Alloxan); D (Alloxan + 100 mg kg-1 Croton lobatus); E: (Alloxan + 200 mg kg-1 C. lobatus); and F (Alloxan + 100 mg kg-1 glibenclamide).

RESULTS

Acute toxicity studies revealed no mortality of rats at the administration of different doses of extract up to the 5,000 mg kg-1 dose. Histology of the pancreas showed focal area of necrosis, and fatty infiltration in diabetic untreated rats, but these lesions were absent in pancreas of rats treated with C. lobatus extract.

CONCLUSION

Methanol leaf extract of C. lobatus reduced arteriogenic risk factors, improved antioxidant status, restored the observable pathological lesions associated with experimental diabetes in rats, and thus offers a new therapeutic window as herbal therapy for the treatment of diabetes mellitus and associated cardiovascular complications.

Antioxidative and antidiabetic activities of watermelon (Citrullus lanatus) juice on oxidative stress in alloxan-induced diabetic male Wistar albino rats

Background:

The nutritional and medicinal importance of watermelon has been emphasized and its diseases preventive and curative power must be evaluated. Hence, this study was designed to evaluate the antioxidative and antidiabetic potentials of watermelon.

Materials and Methods:

The in vivo assay was carried out on 15 male albino rats which were divided into groups of three stages. In stage I, all animals received normal feeds and water for 1-week after, which five animals were selected and sacrificed for biochemical analyses which form the nondiabetic control, group. The remaining animals were fasted for 24 h before injected intra-peritoneally with a freshly prepared solution of alloxan at a dosage of 35 mg/kg body weight. Five out of the 10 rats were sacrificed as diabetic group while last five animals were fed with water melon juice for a week after, which they were sacrificed to form the treated group animals. In all the groups, body weights, fasting blood sugar, total protein level in the blood, and other biochemical parameters such as reduced glutathione (GSH), glutathione peroxidase (GPx), malondialdehyde (MDA) concentration; catalase, and superoxide dismutase (SOD) % inhibition activities were determined.

Results:

The results of the biochemical analyses showed a significant increase in the concentration of blood glucose level after treatment with alloxan, which indicates that diabetic was induced. Hence, watermelon juice caused increased in weight, hypoglycemia; and increases in GSH, GPx, catalase, and SOD % inhibition activities with reduced MDA concentration after treatments.

Conclusion:

The watermelon juice resulted in the restoration of impaired conditions of the rats.

Evidence of attenuation of intestinal ischemia-reperfusion injury following pre-treatment with methanolic extracts from Chromolena odorata in rats

BACKGROUND

Chromolena odorata is a tropical species of flowering shrub in the family Asteraceae, leaves of it have been reported to be widely used as herbal remedy for the treatment of various ailments. It is particularly reported to be useful in the healing of wounds.

METHODS

We investigated the possibility of amelioration of intestinal ischemia-reperfusion (IR) injury in rats treated with methanolic extract of C. odorata (MECO). Wistar albino rats were divided randomly into five groups of six animals each as control, IR-treated, IR+200 mg/kg MECO, IR+400 mg/kg MECO, and IR+200 mg/kg vitamin C. Pre-treatment with MECO or vitamin C was for 7 days.

RESULTS

The contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) were significantly reduced by MECO and vitamin C, while there were significant enhancements of the activities of superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), as well as the content of reduced glutathione (GSH) in pre-treated rats compared to IR-treated rats. Glutathione S-transferase (GST) activity was not significantly affected in all the groups. Histopathological examination of small intestinal mucosa revealed significant attenuation of intestinal pathology in animals pre-treated with MECO, while IR injury produced severe villi erosion, necrosis, and inflammatory cell infiltrations.

CONCLUSIONS

The present study highlights the antioxidant activities of MECO and its ability to inhibit inflammatory cell infiltration as mechanisms involved in its protection against IR injury in the intestine of rats, an effect that was largely comparable to that of vitamin C.

Comparative assessment of onion and garlic extracts on endogenous hepatic and renal antioxidant status in rat

BACKGROUND

Despite growing claims of functional health benefits in folkloric medicine, the safety of chronic/elevated intakes of onion and garlic cannot be assumed. Therefore, this study assesses oral administration of varied doses of onion and garlic on some biomarkers of hepatic and renal functions in rats.

METHODS

Animals were divided into five groups: control group received vehicle and extract-treated groups received varied doses of onion or garlic extract (0.5 mL and 1.0 mL/100 g bwt/day) for 6 weeks.

RESULTS

Both doses of onion caused marked (p<0.05) increase in hepatic and renal levels of glutathione (GSH), glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT) and marked (p<0.05) decrease in malondialdehyde (MDA). Treatment with low dose of garlic elicited similar trend except in hepatic CAT, renal SOD and GST levels. A high dose of garlic only caused marked (p<0.05) increase in hepatic GST, renal GST, and SOD. Both doses of onion and low dose of garlic significantly (p<0.05) enhanced renal Na+/K+-ATPase activity. Only a high dose of onion caused significant (p<0.05) increase in hepatic aspartate transaminase (AST), alkaline phosphatase (ALP), and decrease in plasma AST activities.

CONCLUSIONS

These findings suggest antioxidant enhancing capability for both doses of onion and low dose of garlic, while high dose of garlic elicited pro-oxidant conditions.

Oxidative stress indices in Nigerian pesticide applicators and farmers occupationally exposed to organophosphate pesticides

BACKGROUND

Reports have clearly indicated the role of oxidative stress in the pathogenesis of organophosphate pesticides (Op) toxicity. However, there is dearth of information on which group of the farm workers is more at risk of Op-induced oxidative stress.

AIM

This study determined serum levels of malondialdehyde (MDA), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH), myeloperoxidase (MPO), nitric oxide (NO), and serum activity of acetylcholinesterase (AChE) in farm workers exposed to Op.

SUBJECTS AND METHODS

A total of 60 (30 pesticide applicators and 30 farmers) and 30 apparently healthy non-farmers who were nonexposed to Op (controls) were recruited into this study. Serum activity of AChE was determined using high performance liquid chromatography (HPLC), while serum levels of MDA, GSH, and NO and serum activities of CAT, MPO, GPx, and superoxide dismutase (SOD) were determined colorimetrically.

RESULTS

Serum activities of AChE and CAT were significantly lower, whereas MPO activity was significantly higher in pesticide applicators compared with controls. Similarly, farmers had significantly reduced serum AChE activity and significantly raised MPO activity compared with controls. However, serum activities of AChE, CAT, and MPO were significantly lower, whereas mean level of MDA was significantly higher in pesticide applicators compared with farmers.

CONCLUSION

This study shows that Op applicators are more exposed to oxidative stress than farmers, thus Op applicators require increased antioxidant supplements than farmers.

A comparative evaluation of the biological effects of environmental cadmium-contaminated control diet and laboratory-cadmium supplemented test diet

This study was designed to examine the effects of a diet contaminated by environmental cadmium on organ/body weight ratio and selected toxicological indices. It was also designed to permit a comparative analysis of the effects of the diet contaminated by environmental cadmium and that of cadmium supplemented diet based on the same parameters. Our results show that even though the cadmium content of the environmental cadmium contaminated diet was 300% less than that of the cadmium supplemented diet, the former caused statistically significant changes in Superoxide dismutase (SOD) activity (P < 0.025), Na+/K+ ATPase activity (P < 0.005) and Malondialdehyde (MDA) level (P < 0.025) when values at the end of 1 month exposure were compared to the values at the end of 3 months exposure. These parameters were altered in the same manner by the cadmium content of the supplemented diet in addition to significant reduction in liver/body weight ratio (P < 0.005) within the exposure periods examined. By virtue of the very close nature of the values of these parameters in rats exposed to the two different diets, it appears that the background cadmium (cadmium from the environment) content of the diets is largely responsible for the observed changes, except in the case of liver/body weight ratio.

Changes in Carboxypeptidase A, Dipeptidase and Na+/K+ ATPase Activities in the Intestine of Rats Orally Exposed to Different Doses of Cadmium

The purpose of the present study was to evaluate the effect of cadmium on some protein digestive and absorption enzymes in rats. Thirty-six rats were grouped into three groups of 12 animals each; one group received deionised water and acted as control. One group received 445 microM Cd and the last group received 890 microM Cd in their drinking water for a period of one month. The results obtained indicate that increasing the level of cadmium from 445 microM to 890 microM in the drinking water of the rats led to 29% and 23% increase in accumulated cadmium in the proximal and distal small intestine respectively. The body weight gain of rats exposed to 445 microM and 890 microM Cd was decreased by about 24% and 43% respectively when compared with the control. The activities of carboxypeptidase A, dipeptidase and Na+/K+ ATPase were reduced in the mucosa of the proximal end of the small intestine of cadmium exposed rats. The reduction was dose dependent; with the 890 microM Cd exposed rats displaying the least activities. In the distal small intestine, the activities of these enzymes were restored in the 445 microM Cd exposed rats to levels that were not statistically different (P > 0.05) from those observed in the controls. In the 890 microM Cd exposed rats, dipeptidase activity improved by about 80% compared with the activity of the enzyme in the proximal small intestine. Likewise, Na+/K+ ATPase activity increased by about 125% compared with the observed level in the proximal small intestine. The study suggests that cadmium given to rats in drinking water compromise protein digestion and absorption of nutrients particularly in the proximal region of small intestine and could account for weight reduction associated with cadmium toxicity.

Influence of hypoosmolality on the blood-brain barrier permeability during epileptic seizures

Changes in the blood-brain barrier permeability to macromolecules were investigated during pentylenetetrazol-induced seizures, using Evans-blue as an indicator, in water-intoxicated and nonintoxicated Wistar albino (210-250 g) adult rats of both sexes. Evans-blue albumin extravasation was judged visually and estimated quantitatively with a spectrophotometer using homogenized brain to release the dye. Hypoosmolar treatment (water intoxication) was performed by the intraperitoneal administration of distilled water to a volume of 10% of the body weight; Six groups of rats were studied. Group I: female control (n=10), Group II: male control (n=10), Group III: nonwater-intoxicated female+seizure (n=15), Group IV: nonwater-intoxicated male+seizure (n=15), Group V: water-intoxicated female+seizure (n=15), Group VI: water-intoxicated male+seizure (n=15). Approximately 2 h after the injection of water, the plasma osmolarity had decreased by 25-30 mosm. Our results revealed that in female rats, the extravasation of Evans-blue albumin was greater in the brains of water-intoxicated rats compared to nonwater-intoxicated rats after pentylenetetrazol-induced seizures. In addition, hypoosmotic female rats were shown to have a larger increase in blood-brain barrier permeability than hypoosmotic male rats after pentylenetetrazol-induced seizures. This difference between male and female rats was found to be significant (P=.005).

Increased superoxide dismutase and Na+, K+-ATPase activities in aortic strips from potassium-adapted rats: implication for altered vascular reactivity

The contributions of superoxide dismutase (SOD) and Na(+), K(+)-ATPase to the altered vascular reactivity in potassium-adapted rats were investigated to test the hypothesis that smooth muscle hyperpolarisation may be involved. Isometric contractions to noradrenaline (NA), 5-hydroxytryptamine (5-HT), and relaxations to acetylcholine (ACh), levcromakalim (LEV) and sodium nitroprusside (SNP), were measured in aortic rings from potassium-adapted rats. Pieces of the aortae were also excised from the animals and assayed for SOD and Na(+), K(+)-ATPase. Maximum contractile responses were significantly attenuated (P<0.05) in aortic rings from the potassium-adapted rats to NA and 5-HT, while relaxations were also significantly augmented (P<0.05) in the same rings to LEV and SNP, but not to ACh. Both SOD and Na(+), K(+)-ATPase activities were significantly higher (P<0.05) in the aortae from the potassium-adapted rats compared to controls. It is concluded that the alteration in vascular smooth muscle reactivity may be due to hyperpolarisation caused by the activities of SOD and Na(+), K(+)-ATPase.

Modulation defect of sodium pump evidenced in diabetic patients by a microcalorimetric study

Sodium pump activity of intact erythrocytes in their own plasma was measured by microcalorimetry in 41 healthy subjects and 35 insulin-dependent diabetic patients. Results show that modulation of the sodium pump is altered in diabetic patients. Addition of insulin increases functioning of the Na(+)-K+ pump in controls but has no effect in diabetic patients. These subjects show a slower response of the Na(+)-K+ pump to the inhibitory effect of ouabain. Cross-incubation experiments suggest that these findings may be explained by the existence of a plasmatic factor that impairs the modulation of the sodium pump in diabetic patients.

Methylprednisolone and membrane properties of primary cultures of mouse spinal cord

The present study attempts to define the capacity of methylprednisolone sodium succinate (MP) to protect neuronal membranes against a free radical challenge in primary cultures of fetal mouse spinal cord. Incubation of these cultures with MP significantly increased the Na+,K(+)-ATPase activity, an effect that was blocked by the RNA synthesis inhibitor, actinomysin D and the protein synthesis inhibitor, cycloheximide, suggesting an induction of protein synthesis by MP. In contrast, incubation with FeCl2 for 1 or 2 h significantly inhibited Na+,K(+)-ATPase activity and elevated the levels of thiobarbituric acid-reactive substances (TBARS). Pretreatment with MP prevented the rise in TBARS and partially prevented the decrease in Na+,K(+)-ATPase activity for the first hour of FeCl2 incubation, an effect that was lost during the second hour. A second dose of MP after the first hour of incubation with FeCl2 partially restored Na+,K(+)-ATPase activity and reduced TBARS levels after the second hour of exposure to FeCl2. Co-incubation of MP with cycloheximide completely prevented the decrease in Na+,K(+)-ATPase activity seen after a 2-h incubation with FeCl2 and eliminated the need for a second dose of MP after the first hour of incubation with FeCl2. These findings suggest a capacity for rapid protein induction and antioxidant activity for MP in vitro.

Endogenous factor activating Na,K-ATPase induced by blockade of adrenoceptors

It was established that the regulatory factor released from the effector cells under the blockade of postsynaptic alpha- and beta-adrenoceptors by phentolamine and propranolol (0.5-1.0 microM) and activating noradrenergic uptake and synthesis increased the activity of Na,K-ATPase of isolated rat organs and partially purified Na,K-ATPase isolated from the rat brain. The regulatory factor is a protein with molecular mass 25-100 kDa, adsorbed on phenylsepharose CL-4B and eluated with 30 mM KCl. It consists of two active components with pI 5.1 and 5.9 which in admixture (1:1) activate Na,K-ATPase by 60%.

Brain Na+/K(+)-ATPase regulation by serotonin and norepinephrine in normal and kindled rats

In this work we confirmed the activation of rat brain Na+/K(+)-ATPase by norepinephrine (NE) and observed a variable response of the enzyme according to the brain region considered. In isolated neuronal or glial fractions from normal cerebral cortices, we studied the response of the enzyme to increasing concentrations of serotonin (5-HT) (10(-9)-10(-3) M). A dose-dependent response over basal values was present in glial fractions, beginning at 10(-6) M. No such response was obtained in the neuronal fractions. In amygdaloid kindled brains, the pattern of activation by NE was different than in controls: less pronounced (cortex, brainstem, and diencephalon), inhibition-activation (cerebellum), or no change (striatum). The activation of Na+/K(+)-ATPase by 5-HT observed in the control glial fraction was not present in the kindled glial fraction. In conclusion, 5-HT seems to activate Na+/K(+)-ATPase preferentially in glial cells, and the kindling process markedly modifies this regulation. The normal response to NE in brain homogenates is less altered by kindling than is the response to 5-HT in the same regions.

In vivo and in vitro effects of aldrin on rat brain synaptosomal Mg2+ and Na+,K(+)-adenosine triphosphatase

Aldrin, a chlorinated hydrocarbon, inhibited rat brain synaptosomal membrane-bound Na+,K(+)-adenosine triphosphatase (ATPase) and Mg2(+)-ATPase activities under in vivo and in vitro conditions. Na+,K(+)-ATPase was non-competitively inhibited whereas Mg2(+)-ATPase was inhibited uncompetitively. Arrhenius plots of both these ATPases without aldrin under in vivo and in vitro conditions were found to be linear. In the presence of aldrin, on the other hand, Arrhenius plots of the same ATPases were nonlinear. Slopes of Arrhenius plots of both ATPases under in vivo and in vitro condition were changed with change in temperature with aldrin. The activation energy (AE) of Na+,K(+)-ATPase and Mg2(+)-ATPase activities were changed over the temperature range 15-40 degrees in the presence of aldrin. These results thus suggest that aldrin increases the lipid fluidity of the synaptosomal membrane which may be a cause of inhibition of neuronal membrane-bound Na+,K+ and Mg2(+)-ATPase activities.

Opposite effects of methylene blue and ascorbate on lipid peroxidation in muscles. Correlation with the redox state. I. Experiments on satisfied frogs

Homogenates of heart, stomach and rectus abdominis muscles of the frog have shown different degrees of malondialdehyde (MDA) formation. MDA content was highest in heart, and lowest in stomach musculature. The resultant tissue redox-state potential (RSP) and redox potential (E'0) in homogenates determined potentiometrically also showed differences with opposite signs in relation to MDA levels. An electron acceptor, methylene blue (MB), decreased but an electron donor, ascorbate (Asc), increased the MDA level in each of the muscles. These effects were dependent upon the concentration of MB and Asc and proportional to the control MDA content in each muscle. Thus an inverse interdependence between MDA level and redox state existed even when a positive change in redox potentials was induced by MB, and also when a negative change was induced by Asc. Since there was a close negative correlation between the changes of MDA concentration and redox potential in the homogenates, it is strongly suggested that the changes of redox state in muscle are implicated in the processes leading to lipid peroxidation (LP).

Changes of salt intake and of (Na+K)-ATPase activity in brain after high dose treatment with deoxycorticosterone

Mineralocorticoids (MC) have a dual effect on salt intake: in adrenalectomized rats, they reduce previously elevated salt intake; and in intact rats a high MC dose increases salt intake. We have studied the activity of (Na+K)-ATPase and [3H]ouabain binding in rats treated with deoxycorticosterone (DOC) in doses that elicited a salt appetite. Brains were removed from control and treated animals, and 20 different areas were punched out from brain slices cut every 300 microns. DOC treatment significantly reduced (Na+K)-ATPase activity in the lateral hypothalamic area, anterior amygdaloid and lateral amygdaloid nuclei, while increasing it in the periventricular gray matter; changes in other regions were not significant. Binding of [3H]ouabain was not modified by DOC treatment. In parallel experiments, we determined MC receptors in adrenalectomized rats. Binding of [3H]aldosterone was preferentially found in hippocampus, followed by lateral septum, anterior, posterior and lateral amygdaloid areas, with lower levels in other regions. However, there was no correlation between [3H]aldosterone binding and (Na+K)-ATPase activity in brain punches from either control or DOC-treated rats. Further experiments are needed to ascertain if (Na+K)-ATPase changes in discrete areas of the brain containing moderate levels of mineralocorticoid receptors, are related to the behavioral effects of DOC.

Na+, K+-ATPase activity in cultured C6 glioma cells

Rat C6 glioma cells were cultured for 4 days in MEM medium supplemented with 10% bovine serum and Na+, K+-ATPase activity was determined in homogenates of harvested cells. Approximately 50% of enzyme activity was attained at 1.5 mM K+ and the maximum (2.76 +/- 0.13 mumol Pi/h/mg protein) at 5 mM K+. The specific activity of Na+, K+-ATPase was not influenced by freezing the homogenates or cell suspensions before the enzyme assay. Ten minutes' exposure of glioma cells to 10(-4) or 10(-5) M noradrenaline (NA) remained without any effect on NA+, K+-ATPase activity. Neither did the presence of NA in the incubation medium, during the enzyme assay, influence the enzyme activity. The nonresponsiveness of Na+, K+-ATPase of C6 glioma cells to NA is consistent with the assumption that alpha (+) form of the enzyme may be preferentially sensitive to noradrenaline. Na+, K+-ATPase was inhibited in a dose-dependent manner by vanadate and 50% inhibition was achieved at 2 x 10(-7) M concentration. In spite of the fact that Na+, K+-ATPase of glioma cells was not responsive to NA, the latter could at least partially reverse vanadate-induced inhibition of the enzyme. Although the present results concern transformed glial cells, they suggest the possibility that inhibition of glial Na+, K+-ATPase may contribute to the previously reported inhibition by vanadate of Na+, K+-ATPase of the whole brain tissue.

Stimulation of brain Na,K-ATPase by norepinephrine but not taurine

The effect of taurine on rat and hamster brain Na,K-ATPase was examined and compared to norepinephrine (NE) stimulation of the enzyme. Although NE stimulation of microsomal Na,K-ATPase was observed in the presence of the cell cytosolic fraction, taurine was without effect in the presence and absence of this fraction. Taurine also failed to modulate pubescent and mature hamster brain Na,K-ATPase. Presence or absence of ion chelators did not change taurine's effect. These results are discussed in relation to previous reports of taurine and catecholamine stimulation of Na,K-ATPase.

The effect of vanadate on Na+,K+-ATPase activity of mouse cerebral cortex during bicuculline-induced seizures

The effect of bicuculline-induced seizures on Na+,K+-ATPase activity of mouse cerebral cortex homogenates, using two different procedures of sample preparation (freezing in situ or decapitation of animals without freezing) is described. Regardless of tissue treatment Na+,K+-ATPase activities during bicuculline-induced seizures did not differ significantly from the appropriate controls when vanadate-free ATP was used as substrate. The response of Na+,K+-ATPase to K+ activation was also similar; the increase in potassium concentration from 2 to 20 mM caused a 33.0 and 32.3% increase of enzyme activity in cortical homogenates from control and convulsing mice, respectively. Vanadate added to the assay medium inhibited Na+,K+-ATPase activity in a dose-dependent manner; with both types of tissue treatment there was, however, a tendency towards lesser inhibition of the enzyme from convulsing mice and at 1 X 10(-7) M vanadate this difference, though slight, was statistically significant: -22.59 vs -27.55% (freezing) and -28.73 vs -38.42% (decapitation) for seizures vs controls, respectively. The reduced sensitivity of Na+,K+-ATPase towards vanadate inhibition in cortical homogenates prepared from mice with convulsions suggests that vanadate might play a role in the modulation of enzyme activity during seizures in vivo.

Effect of catecholamines and metal chelating agents on the brain and brown adipose tissue Na,K-ATPase

Catecholamines stimulate Na,K-ATPase activity in the microsomal membranes of the brain and brown adipose tissue. This stimulation is apparent in the absence of soluble, cytosolic inhibitors and exhibits the same characteristics in both tissues: it occurs at high concentrations (10(-6)-10(-4) M) only; there is no difference in potency between isoprenaline, norepinephrine and epinephrine (EC50 = 1-2 X 10(-5) M); the D-stereoisomer of isoprenaline is equally as effective as the L-form; stimulation of Na,K-ATPase may also be achieved by the metal chelators EDTA, EGTA and desferal; the hydrophobic beta-blockers, propranolol and alprenolol, inhibit both the norepinephrine-stimulated and basal levels of enzyme activity at concentrations of 10(-5)-10(-3) M; phenoxybenzamine, an irreversible alpha-adrenergic blocker, inhibits basal Na,K-ATPase as well as norepinephrine-stimulated enzyme activity (EC50 = 2.5 X 10(-5) M). Because none of these observations can be related to the properties of the stereospecific adrenergic receptor (alpha or beta), it may be concluded that the catecholamine-Na,K-ATPase interaction is not mediated by the receptor. More probably, catecholamines may antagonize the Na,K-ATPase inhibition caused by some tightly membrane-bound metals (but not vanadium) via the ortho-catechol moiety of the catecholamine molecule. The stimulation of brown fat Na,K-ATPase by catecholamines does not have much relevance to the norepinephrine-stimulated thermogenesis in this tissue.

Effect of insulin-induced hypoglycemia on blood-brain barrier permeability

The effects of hypoglycemia on cerebrovascular permeability to the Evans blue-albumin complex were studied in rats injected with 50 IU/kg, i.v. crystalline zinc insulin. One group of hypoglycemic animals was warmed to keep their body temperatures close to 37 degrees C, and the rats in the other group were allowed to become hypothermic by hypoglycemia. The arterial blood pressures of the hypoglycemic rats were continuously monitored during the coma and a significant rise in pressure was observed in most animals at the end of the coma. When glucose was administered i.v. to five animals of each group, this elevated pressure returned to normal values within 0.5 min and the animals slowly recovered normal behavior. At termination of the coma, most brains in the hypothermic hypoglycemic group showed an intensive and extensive staining by Evans blue; whereas only two brains in the normothermic hypoglycemic group showed any noticeable extravasation of Evans blue-albumin. Arterial PO2, PCO2, and pH were determined and no significant difference was found between values from animals in hypoglycemic coma and the controls. Four animals were surface-cooled and were used to examine the effects of hypothermia on blood-brain barrier permeability. These brains did not show any macroscopically evident Evans blue-albumin extravasation. The results indicated that prolonged, severe hypoglycemia with hypothermia caused a profound blood-brain barrier dysfunction whereas normothermic hypoglycemia resulted in few cases of any noticeable increase in blood-brain barrier permeability.

Vanadyl (VO2+) induced lipoperoxidation in the brain microsomal fraction is not related to VO2+ inhibition of Na,K-ATPase

Vanadyl (VO2+) is a potent inductor of the lipid peroxidation in brain microsomes. This effect, however, is obtained at concentrations by two orders of magnitude higher (10(-4)-10(-3)M) than those which effectively inhibit the brain microsomal Na,K-ATPase. At 10(-6)M VO2+ which inhibits 50% of the Na,K-ATPase activity there is no measurable malonyldialdehyde production. Vanadate (VO-3) which is an equally potent inhibitor of Na,K-ATPase as VO2+ has almost no capacity to induce the lipoperoxidation. The addition of 10(-4)M ascorbate to the brain microsomes stimulates the lipoperoxidation to the maximum level regardless of the presence or absence of exogenous vanadium ions. Ascorbate-induced inhibition of brain Na,K-ATPase which is known to be associated with lipoperoxidation is strictly additive with the vanadyl (VO2+) inhibition of this enzyme. Even at submaximal concentrations there is no indication for any potentiation between these two inhibitory systems. The disparity between the mechanisms of ascorbate and vanadyl-induced inhibition of Na,K-ATPase is also documented by the effect of EDTA which inhibits the former type only. It is concluded, that the vanadium-induced inhibition of brain microsomal Na,K-ATPase is not related to induction of lipoperoxidative capacity of the brain.