Fluoride Compromises Testicular Redox Sensor, Gap Junction Protein, and Metabolic Status: Amelioration by Melatonin

The excess fluoride intake has been shown to adversely affect male reproductive health. The aim of the present study was to investigate the key mechanism underlying fluoride-induced testicular dysfunction and the role of melatonin as a modulator of testicular metabolic, oxidative, and inflammatory load. The present results indicated that sodium fluoride (NaF) exposure to adult male golden hamsters severely impairs reproductive physiology as evident from markedly reduced sperm count/viability, testosterone level, androgen receptor (AR), testicular glucose transporter (GLUT-1), gap junction (connexin-43), and survival (Bcl-2) protein expression. NaF exposure markedly increased testicular oxidative load, inflammatory (NF-kB/COX-2), and apoptotic (caspase-3) protein expression. However, melatonin treatment remarkably restored testicular function as evident by normal histoarchitecture, increased sperm count/viability, enhanced antioxidant enzyme activities (SOD and Catalase), and decreased lipid peroxidation (LPO) level. In addition, melatonin treatment upregulated testicular Nrf-2/HO-I, SIRT-1/ FOXO-1, and downregulated NF-kB/COX-2 expression. Further, melatonin ameliorated NaF-induced testicular metabolic stress by modulating testicular GLUT-1expression, glucose level, and LDH activity. Furthermore, melatonin treatment enhanced testicular PCNA, Bcl-2, connexin-43, and reduced caspase-3 expression. In conclusion, we propose the molecular mechanism of fluoride-induced testicular damages and ameliorative action(s) of melatonin.

Foxo1 Attenuates NaF-Induced Apoptosis of LS8 Cells through the JNK and Mitochondrial Pathways

Fluoride-induced ameloblast apoptosis is a key event in dental fluorosis development. Forkhead box o1 (Foxo1) is a transcription factor involved in cell apoptosis. The present study aims to investigate the effect of Foxo1 on ameloblast apoptosis induced by fluoride in vitro and to explore its possible mechanism. Ameloblast-like cells (LS8 cells) were exposed to various concentrations of NaF for up to 48 h. Foxo1 activation was modulated using lentiviral vectors, and cell apoptosis was measured by flow cytometry. The expression levels of Foxo1, c-Jun N-terminal kinase (JNK), and some well-known regulators of the mitochondrial pathway of apoptosis (cytoplasmic cytochrome c, cleaved caspase-9, cleaved caspase-3, Bcl-2, and Bax) were detected by quantitative real-time PCR, western blot, and immunofluorescence assay. The results showed significantly decreased expression and increased phosphorylation of Foxo1 in NaF-treated LS8 cells. Further investigation revealed that forced Foxo1 activation with lentiviral vectors attenuated NaF-induced apoptosis of LS8 cells, markedly decreasing protein levels of cytoplasmic cytochrome c, cleaved caspase-9, and cleaved caspase-3 while increasing the Bcl-2/Bax ratio and JNK expression level. These findings suggest that Foxo1 attenuated NaF-induced apoptosis of LS8 cells via inhibiting the mitochondrial pathway and activating JNK.

Melatonin-mediated upregulation of Sirt3 attenuates sodium fluoride-induced hepatotoxicity by activating the MT1-PI3K/AKT-PGC-1α signaling pathway

Mitochondrial reactive oxygen species (ROS) production has been implicated in the pathogenesis of fluoride toxicity in liver. Melatonin, an indolamine synthesized in the pineal gland, was previously shown to protect against sodium fluoride (NaF)-induced hepatotoxicity. This study investigated the protective effects of melatonin pretreatment on NaF-induced hepatotoxicity and elucidates the potential mechanism of melatonin-mediated protection. Reducing mitochondrial ROS by melatonin substantially attenuated NaF-induced NADPH oxidase 4 (Nox4) upregulation and cytotoxicity in L-02 cells. Melatonin exerted its hepatoprotective effects by upregulating Sirtuin 3 (Sirt3) expression level and its activity. Melatonin increased the activity of manganese superoxide dismutase (SOD2) by promoting Sirt3-mediated deacetylation and promoted SOD2 expression through Sirt3-regulated DNA-binding activity of forkhead box O3 (FoxO3a), thus inhibiting the production of mitochondrial ROS induced by NaF. Notably, increased peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) by melatonin activated the Sirt3 expression, which was regulated by an estrogen-related receptor (ERR) binding element (ERRE) mapped to Sirt3 promoter region. Analysis of the cell signaling pathway profiling systems and specific pathway inhibition indicated that melatonin enhances PGC-1α expression by activating the PI3K/AKT signaling pathway. Importantly, inhibition of melatonin receptor (MT)-1 blocked the melatonin-activated PI3K/AKT-PGC-1α-Sirt3 signaling. Mechanistic study revealed that the protective effects of melatonin were associated with down-regulation of JNK1/2 phosphorylation. Our findings provided a theoretical basis that melatonin mitigated NaF-induced hepatotoxicity, which, in part, was mediated through the activation of the Sirt3 pathway.

Caffeic acid, a phyto polyphenol mitigates fluoride induced hepatotoxicity in rats: A possible mechanism

Fluoride induced hepatotoxicity has been extensively studied in both humans and animals. However, the mechanism underlying in the hepatotoxicity of experimental fluorosis remains obscure. The severity of fluoride toxicity was reduced by oral administration of certain plant derived antioxidants. Caffeic acid (CA) a polyphenolic compound has diverse range of pharmacological activity in the biological system. Therefore, the present study was aimed to investigate the protective mechanism of CA, against fluoride induced hepatotoxicity in rats. The rats were treated with 300 ppm of NaF via drinking water ad libitum alone and in combination with CA at a dose of 50 mg/kg daily for 30 days by oral intubation. CA treatment significantly prevented fluoride induced hepatic damage as evident from the histopathological studies and declined levels of serum fluoride and liver marker enzymes. A significant decrease in the levels of enzymatic (SOD2, CAT, GPx, and GSTpi class) and nonenzymatic (GSH and Vitamin C) antioxidants along with increased ROS, lipid peroxidation, protein carbonyl content, and nitrate levels by fluoride were also prevented in these groups. In addition, CA inhibits fluoride induced apoptosis by altering the Bax and caspase-3p20 expressions. Further, fluoride induced upregulation of Nox4, p38α MAPK, Hsp60, and downregulation of Hsp27 are the indicators for the detection of oxidative damage, apoptosis, and mitochondrial stress was also modulated by CA. These findings reveal that CA supplementation has a protective effect against fluoride induced hepatotoxicity in rats.

Prophylactic effect of N-acetylcysteine against sodium fluoride-induced blood oxidative stress in mice

Ninety female Balb/c mice were used. The animals were allocated to evenly six groups. While the first group was maintained as control, Groups 3, 4, 5, and 6 were administered 750 ppm, 1500 ppm, 3000 ppm, and 6000 ppm of N-acetylcysteine, respectively, for a period of 15 days. After day 15, Groups 2-6 were administered sodium fluoride, containing 100 ppm fluoride in drinking water, for another 15 days. Plasma malondialdehyde (MDA) levels and erythrocyte superoksid dismutase (SOD) and catalase (CAT) activities were determined at the beginning of the trial and on days 15 and 30. According to the data obtained in the present study, N-acetylcysteine, when administered at the indicated doses, did not produce a significant alteration in any of the three parameters investigated. On the other hand, while the plasma MDA level was determined to have increased significantly, erythrocyte SOD and CAT activities were ascertained to have decreased significantly in the group, which was administered sodium fluoride alone on day 30. In the groups, which were administered N-acetylcysteine prior to sodium fluoride, however, it was observed that, after sodium fluoride administration, plasma MDA levels and erythrocyte SOD and CAT activities drew closer to the values of the control group.

Vitamin E supplementation protects oxidative stress during arsenic and fluoride antagonism in male mice

Arsenic and fluoride are common environmental contaminants. Coexposure to these elements can occur through groundwater. We investigated the effects of sodium meta arsenite (50 mg/L in drinking water) and sodium fluoride (50 mg/L in drinking water) individually and in combination. Biochemical parameters suggestive of alterations in heme synthesis pathway, oxidative stress in liver and kidneys, and concentration of essential metals in blood and soft tissues were studied in Swiss albino male mice given the chemicals for 3 weeks. The possible beneficial effect of vitamin E administration (25 mg/kg, oral, alternate days after arsenic/fluoride exposure) on the above variables was investigated. Exposure to arsenic or fluoride caused a significant depletion in blood delta-aminolevulinic acid dehydratase (ALAD) activity, platelet counts (PLT), and glutathione (GSH) level. Blood white blood cell (WBC) counts also decreased. These changes were accompanied by increased reactive oxygen species (ROS) levels. Arsenic and fluoride exposure led to a significant depletion of super oxide dismutase (SOD) activity with no effect on catalase and glutathione peroxidase (GPx) activities. Combined exposure to these toxicants had no synergistic effect on blood ALAD activity and WBC counts, and the effects seen appeared to result predominantly from arsenic. Hepatic catalase activity, on the other hand, increased significantly on exposure to arsenic and fluoride. There was only moderate antagonistic effect on arsenic and fluoride concentration in blood and liver, and kidney arsenic concentration was less pronounced during coexposure compared with arsenic alone. Interestingly, fluoride concentration showed less pronounced uptake during concomitant exposure compared with fluoride exposure alone. Vitamin E supplementation during coexposure to arsenic and fluoride provided only moderate recovery in the altered antioxidant enzymes and in depleting ROS level, but the altered essential metal concentration, particularly calcium level, responded more favorably to vitamin E administration. It can be concluded from the current study that (i) coadministration of arsenic and fluoride was less toxic to the animals compared with individual toxic effects of these toxicants, and (ii) vitamin E supplementation during coexposure had only limited additional beneficial effects in restoring altered biochemical variables, maintaining pro-oxidant/antioxidant balance, and reducing body arsenic store but plays a significant role in maintaining essential metal balance.

Protective effects of vitamins C and E against endometrial damage and oxidative stress in fluoride intoxication

1. Fluoride (F) is an essential trace element that has protective effects against bone mineral loss. However, it becomes toxic at higher doses and induces some adverse effects on a number of physiological functions, including reproduction. The aims of this study were to examine F-induced oxidative stress that promotes production of reactive oxygen species (ROS) and to investigate the role of vitamins C and E against possible F-induced endometrial impairment in rats. 2. Rats were divided into three groups: control, F and F plus vitamins. The F group was given 100 mg/L orally for 60 days. Combined vitamins were also administered orally. Fluoride administration to control rats significantly increased endometrial malondialdehyde (MDA) but decreased superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) activities. Endometrial glandular and stromal apoptosis were investigated by DNA nick end-labelling (TUNEL) method on each sample and the mean endometrial apoptotic index (AI) was calculated. 3. Vitamin administration with F treatment caused endometrial MDA to decrease, but SOD, GSH-Px and CAT activities to increase, all to significant levels. Vitamins showed a histopathological protection against F-induced endometrial damage. There was a significant difference in the AI between the groups. Lymphocyte and eosinophil infiltration in stroma in F-treated rats were more than those in the control and F + Vit groups. 4. It can be concluded that oxidative endometrial damage plays an important role in F-induced endometrial toxicity, and the modulation of oxidative stress with vitamins reduces F-induced endometrial damage both at the biochemical and histological levels.

Effects of selenium and zinc on renal oxidative stress and apoptosis induced by fluoride in rats

OBJECTIVE

To study the effects of selenium and zinc on oxidative stress, apoptosis, and cell cycle changes in rat renal cells induced by fluoride.

METHODS

Wistar rats were given distilled water containing sodium fluoride (50 mg/L NaF) and were gavaged with different doses of selenium-zinc preparation for six months. Four groups were used and each group had eight animals (four males and four females). Group one, sham-handled control; group two, 50 mg/L NaF; group three, 50 mg/L NaF with a low dose of selenium-zinc preparation (0.1 mg/kg Na2 SeO3 and 14.8 mg/kg ZnSO4 x 7H2O); and group four, 50 mg/L NaF with a high dose of selenium-zinc preparation (0.2 mg/kg Na2 SeO3 and 29.6 mg/kg ZnSO4 x 7H2O). The activities of serum glutathione peroxidase (GSH-Px), kidney superoxide dismutase (SOD), and the levels of malondialdehyde (MDA) and glutathione (GSH) in the kidney were measured to assess the oxidative stress. Kidney cell apoptosis and cell cycle were detected by flow cytometry.

RESULTS

NaF at the dose of 50 mg/L increased excretion of fluoride in urine, promoted activity of urine gamma-glutamyl transpeptidase (gamma-GT), inhibited activity of serum GSH-PX and kidney SOD, reduce kidney GSH content, and increased kidney MDA. NaF at the dose of 50 mg/L also induced rat renal apoptosis, reduced the cell number of G2/M phase in cell cycle, and decreased DNA relative content significantly. Selenium and zinc inhibited effects of NaF on oxidative stress and apoptosis, promoted the cell number of G2/M phase in cell cycle, but failed to increase relative DNA content significantly.

CONCLUSION

Sodium fluoride administered at the dose of 50 mg/L for six months induced oxidative stress and apoptosis, and changes the cell cycle in rat renal cells. Selenium and zinc antagonize oxidative stress, apoptosis, and cell cycle changes induced by excess fluoride.

[Influence of combined iodine and fluoride on phospholipid and fatty acid composition in brain cells of rats]

OBJECTIVE

Investigating the influence of combined iodine and fluoride on phospholipid and fatty acid composition in brain cells of rats.

METHODS

Five groups of rats were provided with deionized drinking water containing 0 and 150 mg/L NaF, and containing both 150 mg/L NaF and 0.003, 0.03 or 3 mg/L KI respectively for 5 months. Then phospholipid and fatty acid composition were determined using liquid chromatography.

RESULTS

The phospholipid composition had no obvious change. The high concentration fluoride (150 mg/L) and high concentration Iodine (3 mg/L) with high concentration fluoride could cause significant changes of the fatty acid composition in brain cells of rats, the proportion of unsaturated fatty acid (C18:2) was significantly decreased and the saturated fatty acid (C12:0) increased obviously. The antagonistic action of 0.03 mg/L KI drinking water on this kind of influence induced by 150 mg/L NaF was the most evident, whereas that of 3 mg/L KI was action of synergetic toxicity.

CONCLUSION

Fluorosis had obvious influence on phospholipid and fatty acid composition in brain cells of rats, and its mechanism might be associated with action of lipid peroxidation, and 0.03 mg/L KI is the optimal concentration for the antagonistic action with this influence from fluorosis.

Amiodarone attenuates fluoride-induced hyperkalemia in vitro

Poisoning by hydrofluoric acid or fluoride salts results in hypocalcemia, hypomagnesemia, and hyperkalemia with subsequent cardiac dysrhythmias. In previous studies, quinidine attenuated fluoride-induced hyperkalemia in vitro, and enhanced survival in animals. Like quinidine, amiodarone is a potassium channel blocker, although amiodarone is more familiar to clinicians due to its recent inclusion in advanced cardiac life support (ACLS) protocols.

OBJECTIVES

This in-vitro study of human erythrocytes was designed to determine whether amiodarone could attenuate fluoride-induced hyperkalemia.

METHODS

Six healthy volunteers each donated 60 mL of blood on three occasions. Each specimen was divided into 12 tubes, incubated at 37 degrees C, and oxygenated with room air. An aqueous sodium fluoride (F(-)) solution was added to tubes 1-9. Incremental amounts of quinidine were added to tubes 1-4 (Q(1)-Q(4)) to attain calculated concentrations of 0.73 microg/mL, 1.45 microg/mL, 2.9 microg/mL, and 5.8 microg/mL, respectively. Incremental amounts of amiodarone were added to tubes 5-8 (A(1)-A(4)) to attain calculated concentrations of 0.38 microg/mL, 0.75 microg/mL, 1.5 microg/mL, and 3.0 microg/mL, respectively. Tubes 9-12 were controls for each of F(-), amiodarone, quinidine alone, and no additive, respectively. Extracellular potassium concentration ([K(+)]) was followed, and an objective endpoint was defined as the rise in potassium concentration at 6 hours.

RESULTS

Fluoride produced a significant change in [K(+)] by 6 hours in all samples. Quinidine produced a J-shaped curve in its ability to attenuate the rise in [K(+)], with only one concentration, Q(3), demonstrating significance versus tube 9 (control). Amiodarone also demonstrated a J-shaped dose-response effect, with statistical significance at A(1), A(2), and A(3) versus tube 9 (control). There was no significant difference among the effective concentrations (Q(3), A(1), A(2), and A(3)) of both drugs.

CONCLUSIONS

In this in-vitro model using human blood, amiodarone and quinidine both attenuated F(-)-induced hyperkalemia. Further study is indicated to determine whether amiodarone enhances survival in F(-)-poisoned animals.

High-fluoride drinking water. A health problem in the Ethiopian Rift Valley 1. Assessment of lateritic soils as defluoridating agents

PURPOSE

High-fluoride drinking water represents a health hazard to millions of people, not least in the East African Rift Valley. The aim of the present project was to establish a simple method for removing excessive fluoride from water.

MATERIAL AND METHODS

Based on geological maps and previous experience, 22 soil samples were selected in mountainous areas in central Ethiopia. Two experiments were performed: 1. After sieving and drying, two portions of 50 g were prepared from each soil and subsequently mixed with solutions of NaF (500 mL). Aliquots (5 mL) of the solutions were taken at pre-set intervals of 1 hour to 30 days for fluoride analysis--using an F-selective electrode. 2. After the termination of the 30-days test, liquids were decanted and the two soil samples that had most effectively removed fluoride from the NaF solutions were dried, and subsequently exposed to 500 mL aqua destillata. The possible F-release into the distilled water was assessed regularly.

RESULTS

Great variations in fluoride binding patterns were observed in the different soils. The percent change in F-concentration in the solutions, as compared to the original absolute value(F-), varied: at 1 hour from a decrease of 58% to an actual increase of 7.7%, while--at 30 days--all soil samples had caused a decrease in the F-concentration, varying from 0.5% to 98.5%. Only minute amounts of fluoride would leach from the fluoride-enriched soils.

CONCLUSION

Lateritic soils may remove excessive fluoride from drinking water. Methods for practical application of this principle should be tested at household level.

Magnesium sulfate inhibits the oxytocin-induced production of inositol 1,4,5-trisphosphate in cultured human myometrial cells

OBJECTIVE

The purpose of this study was to determine the effects of magnesium sulfate on inositol trisphosphate production and the mechanism of these effects.

STUDY DESIGN

Myometrium was obtained at the time of cesarean delivery from women before labor at term. Inositol trisphosphate was measured in the primary myometrial cell cultures after stimulation with oxytocin, sodium fluoride, or Bay K 8644 with or without preincubation with magnesium sulfate or nifedipine. Experiments were performed in either calcium-containing or calcium-free medium that contained egtazic acid and after preincubation with the intracellular calcium chelator BAPTA-acetoxymethylester. Inositol trisphosphate production was measured by radioreceptor assay. In separate experiments, changes in intracellular calcium concentrations ([Ca(2+)](i)) were measured with the use of Fura-2 and spectrophotofluorometry.

RESULTS

Oxytocin, sodium fluoride, and Bay K 8644 increased inositol trisphosphate production 2- to 4-fold. Preincubation with magnesium sulfate (3 x 10(-3) mol/L) for > or = 5 minutes decreased oxytocin-, sodium fluoride-, and Bay K 8644-induced inositol trisphosphate production in either calcium-containing or calcium-free media. Preincubation with BAPTA-acetoxymethylester decreased oxytocin-stimulated inositol trisphosphate production by 78% in calcium-containing media and completely prevented the oxytocin response in calcium-free media. Magnesium sulfate decreased inositol trisphosphate production in calcium-containing media but had no additional effect in calcium-free media. Oxytocin and Bay K 8644 increased [Ca(2+)](i) in either calcium-containing or calcium-free media, and magnesium sulfate reduced this in both cases.

CONCLUSION

Magnesium sulfate appears to inhibit phosphatidylinositol-4, 5-bisphosphate-specific phospholipase C activity and subsequent calcium release in cultured myometrial cells by a direct effect on phospholipase C.

[Effects of selenium on the damage of learning-memory ability of mice induced by fluoride]

Sodium fluoride added with or without sodium selenite in deionized water was administered to male mice for 8 weeks. The influences of fluoride on learning-memory behavior were tested on Y-maze, and the ultrastructure of Gray I synaptic interface in the CA3 area hippocampus was quantitatively analyzed by electron microscopy and computer image processing appliance. The main results showed that the learning capability of mice drinking higher concentration of fluoride presented remarkable deterioration. The thickness of post-synaptic density (PSD) was decreased. The width of the synaptic cleft was remarkably increased. It was found that combined administration of fluoride and proper concentration of selenium could decrease the toxic effect of fluoride. There were synergetic toxicities if the concentration of selenium was too high. The results suggested that selenium might antagonize the neurotoxicity of fluoride on behavior and morphology.

[Study on antagonistic effects of selenium and zinc on the renal impairments induced by fluoride in rats]

Wistar rats were provided with distilled water containing NaF(100 mg/L), and were administered through gavage with Na2SeO3[0.1 mg/(kgBW.d)] and/or ZnSO4[14.8 mg/(kg BW.d)]. The results of biochemical, pathological and ultrastructural examinations showed that fluoride could cause serious renal impairments. The major damage induced by fluoride was epithelia of proximal renal tubules. The lipid peroxidation might be one of the mechanisms of fluoride toxicity. Na2SeO3 and ZnSO4 could antagonize the renal impairments induced by fluoride through their antioxidation. The cooperative effect of Na2SeO3 and ZnSO4 was more powerful than either Na2SeO3 or ZnSO4 alone.

[Study of the phenomenon and substantiation of the mechanism of antimutagenesis under conditions of action of sodium fluoride]

Transplanted human amnion cells have been used in experiments differing in the regularity of the sodium fluoride and alpha-tocopherol action to determine a considerable antimutagenic efficiency of the mutagenic process modifier, the efficiency being dependent on the treatment variability.

Fluoride stimulates in vitro vascular prostacyclin synthesis: interrelationship of G proteins and protein kinase C

The role of G proteins in mediating adrenoceptor-prostacyclin synthesis coupling was investigated using the G protein activator, sodium fluoride. Sodium fluoride (NaF) stimulated in vitro rat aortic prostacyclin (PGI2) synthesis (EC50 = 5 x 10(-3) mol.l-1), an action inhibited completely by the presence of EDTA (10(-2) mol.l-1). The NaF-PGI2 dose-response curve was moved to the left by the presence of adrenaline, phorbol 12,13-dibutyrate (PDBU) and the Ca2+ ionophore A23187 in the incubation media. NaF-stimulated (5 x 10(-3) mol.l-1) PGI2 synthesis was inhibited by the Ca2+ channel blockers, verapamil and nifedipine, the protein kinase C inhibitor, H7, and lanthanum. Prazosin and yohimbine were without effect on NaF action, but partially inhibited adrenaline-potentiated NaF-stimulated PGI2 synthesis. Cyclic adenosine-3',5'-monophosphate (cAMP) and dibutyryl cAMP were without effect on de novo or NaF-, adrenaline-, PDBU- or A23187-stimulated PGI2 synthesis. Since fluoride is known to stimulate adenyl cyclase and phospholipase C, these data suggest that: (1) NaF stimulates in vitro rat aortic PGI2 synthesis by initiating Ca2+ influx; (2) this Ca2+ influx is mediated by protein kinase C, probably through G protein activation of phospholipase C and the generation of the protein kinase C activator, diacyl glycerol; and (3) adenyl cyclase and protein kinase A are not involved in NaF-stimulated PGI2 synthesis by the rat aorta.

Functional uncoupling of the platelet alpha 2-adrenergic receptor-adenylate cyclase complex in the elderly

Elderly humans demonstrate decreased responsiveness in several hormone-receptor systems, including adrenergic receptors. Studies of the beta-adrenergic receptor (beta-AR) system have shown that reduced beta-adrenergic sensitivity in the elderly may be due to reduced beta-AR affinity for agonists. To determine the mechanisms underlying altered alpha-adrenergic sensitivity in the elderly, we assessed the relationships between age and platelet membrane alpha 2-adrenergic receptor (alpha 2-AR)-binding properties, receptor-linked adenylate cyclase (AC) activity, and the affinity of the alpha 2-AR-AC complex for agonists in 18 young (mean age, 24 yr; range 19-34) and 13 elderly (mean age, 69 yr; range, 63-85) normal subjects. In platelet membrane preparations from elderly compared to young subjects, we found similar antagonist-binding properties and similar activity of the catalytic unit of platelet AC, as indicated by the cAMP response to sodium fluoride stimulation. However, mean epinephrine-mediated inhibition of sodium fluoride-stimulated platelet AC activity was less in the elderly [20 +/- 4% (+/- SEM) vs. 31 +/- 2% inhibition; P less than 0.005). In addition, platelet alpha 2-AR affinity for agonist was lower in the elderly, as indicated by the higher concentration of epinephrine needed to inhibit 50% of specific [3H]yohimbine binding (IC50, 3.2 +/- 0.6 vs. 1.4 +/- 0.3 microM; P less than 0.02). These data provide evidence that platelet membranes from elderly humans have decreased responsiveness to alpha-adrenergic stimulation, which can be attributed to reduced alpha 2-AR-AC affinity for agonists. Similarly to reported age-related alterations in beta-adrenergic receptor function, these results suggest that there is also functional uncoupling of the alpha 2-AR-AC complex in elderly humans.

Phosphatidylserine vesicles increase rat brain synaptosomal adenylate cyclase activity

Phosphatidylserine vesicles incubated in hypotonic conditions with rat brain synaptosomes increased basal adenylate cyclase activity but did not modify the response of the enzyme to norepinephrine. Moreover, phosphatidylserine antagonized the stimulation of adenylate cyclase activity by NaF. We suggest that in present experimental conditions the effect of phosphatidylserine vesicles is at the level of the GS regulatory protein of adenylate cyclase.

Synthesis of 2',3'-O-(2,4,6-trinitrocyclohexadienylidine)guanosine 5'-triphosphate and a study of its inhibitory properties with adenylate cyclase

A fluorescent GTP analog 2',3'-O-(2,4,6-trinitrocyclohexadienylidine) guanosine 5'-triphosphate (TNP-GTP) has been prepared and some of its physical properties characterized. TNP-GTP was found to be a potent inhibitor of chick embryo heart adenylate cyclase as activated by guanyl 5'-(beta,gamma-imido)triphosphate (GppNHp), F-, and forskolin with Ki values in the 8-15 microM range. It also appeared to inhibit substantially basal adenylate cyclase in this system. TNP-GTP demonstrated an effective competition with [3H]GppNHp, binding to membranes equivalently to GppNHp and about three times better than GTP. 8-Azidoguanosine 5'-triphosphate (8N3GTP) mimics GTP activation of chick embryo heart adenylate cyclase and [gamma-32P]8N3GTP is effectively photoincorporated into a 42,000- to 44,000-Mr doublet when proteins are separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. TNP-GTP effectively prevents this photoincorporation, as does GTP, at concentrations that agree with their respective apparent inhibition and activation binding constants. The data suggest that TNP-GTP could prove to be a valuable tool for studying the mechanisms of GTP regulation of adenylate cyclase and other GTP-regulated systems.

Inhibition of pituitary adenylate cyclase by atrial natriuretic factor

The effect of synthetic rat atrial natriuretic factor (ANF) on adenylate cyclase activity was studied in rat anterior and posterior pituitary homogenates. ANF (Arg 101-Tyr 126) inhibited adenylate cyclase activity in anterior and posterior pituitary homogenates in a concentration dependent manner. The maximum inhibitions observed were 42% in anterior pituitary with an apparent Ki of 10(-10) M, and 25% with an apparent Ki of 10(-11) M in posterior pituitary. Corticotropin-releasing factor (CRF), vasoactive intestinal peptide (VIP) and prostaglandins (PGE1) stimulated adenylate cyclase to various degrees in anterior pituitary homogenates and ANF inhibited the stimulatory effect of all these hormones. In addition ANF was also able to inhibit the stimulation exerted by NaF and forskolin which activate adenylate cyclase by receptor independent mechanism. Similarly, the stimulatory effects of N-Ethylcarboxamide adenosine (NECA), NaF and forskolin on adenylate cyclase in posterior pituitary homogenates were also inhibited by ANF. This is the first study demonstrating the inhibitory effect of ANF on pituitary adenylate cyclase.

[Morphofunctional characteristics of certain rat liver hepatocytic ultrastructures during prolonged exposure to sodium fluoride]

This paper deals with studying ultrastructural changes in hepatocytes of rats caused by long introduction of sodium fluoride separately and in combination with glutamine, glutaminic acid and riboflavin. Sodium fluoride promotes the development of significant changes in hepatocytes ultrastructure. An attempt was made to reduce effect of the long-period influence of sodium fluoride by means of preliminary introduction of some agents...