Biomedical subjects

J T Eells

Publications and source records attributed to J T Eells.

At least 19 recordsLinked to original sources

PubMed2006

Photobiomodulation partially rescues visual cortical neurons from cyanide-induced apoptosis.

Near-infrared light via light-emitting diode treatment has documented therapeutic effects on neurons functionally inactivated by tetrodotoxin or methanol intoxication. Light-emitting diode pretreatment also reduced potassium cyanide-induced cell death, but the mode of death via the apoptotic or necrotic pathway was unclear. The current study tested our hypothesis that light-emitting diode rescues neurons from apoptotic cell death. Primary neuronal cultures from postnatal rat visual cortex were pretreated with light-emitting diode for 10 min at a total energy density of 30 J/cm2 before exposing to potassium cyanide for 28 h. With 100 or 300 microM potassium cyanide, neurons died mainly via the apoptotic pathway, as confirmed by electron microscopy, Hoechst 33258, single-stranded DNA, Bax, and active caspase-3. In the presence of caspase inhibitor I, the percentage of apoptotic cells in 300microM potassium cyanide was significantly decreased. Light-emitting diode pretreatment reduced apoptosis from 36% to 17.9% (100 microM potassium cyanide) and from 58.9% to 39.6% (300 microM potassium cyanide), representing a 50.3% and 32.8% reduction, respectively. Light-emitting diode pretreatment significantly decreased the expression of caspase-3 elicited by potassium cyanide. It also reversed the potassium cyanide-induced increased expression of Bax and decreased expression of Bcl-2 to control levels. Moreover, light-emitting diode decreased the intensity of 5-(and -6) chloromethy-2', 7-dichlorodihydrofluorescein diacetate acetyl ester, a marker of reactive oxygen species, in neurons exposed to 300 microM potassium cyanide. These results indicate that light-emitting diode pretreatment partially protects neurons against cyanide-induced caspase-mediated apoptosis, most likely by decreasing reactive oxygen species production, down-regulating pro-apoptotic proteins and activating anti-apoptotic proteins, as well as increasing energy metabolism in neurons as reported previously.

Animals↗

PubMed2003

Therapeutic photobiomodulation for methanol-induced retinal toxicity.

Methanol intoxication produces toxic injury to the retina and optic nerve, resulting in blindness. The toxic metabolite in methanol intoxication is formic acid, a mitochondrial toxin known to inhibit the essential mitochondrial enzyme, cytochrome oxidase. Photobiomodulation by red to near-IR radiation has been demonstrated to enhance mitochondrial activity and promote cell survival in vitro by stimulation of cytochrome oxidase activity. The present studies were undertaken to test the hypothesis that exposure to monochromatic red radiation from light-emitting diode (LED) arrays would protect the retina against the toxic actions of methanol-derived formic acid in a rodent model of methanol toxicity. Using the electroretinogram as a sensitive indicator of retinal function, we demonstrated that three brief (2 min, 24 s) 670-nm LED treatments (4 J/cm(2)), delivered at 5, 25, and 50 h of methanol intoxication, attenuated the retinotoxic effects of methanol-derived formate. Our studies document a significant recovery of rod- and cone-mediated function in LED-treated, methanol-intoxicated rats. We further show that LED treatment protected the retina from the histopathologic changes induced by methanol-derived formate. These findings provide a link between the actions of monochromatic red to near-IR light on mitochondrial oxidative metabolism in vitro and retinoprotection in vivo. They also suggest that photobiomodulation may enhance recovery from retinal injury and other ocular diseases in which mitochondrial dysfunction is postulated to play a role.

Animals↗

PubMed2001

Differential recovery of retinal function after mitochondrial inhibition by methanol intoxication.

PURPOSE: The authors' laboratory has previously documented formate-induced retinal toxicity in a rodent model of methanol intoxication. These studies determined functional, bioenergetic, and structural recovery of the retina after methanol intoxication. METHODS: Rats were intoxicated with methanol, and retinal function was assessed by electroretinography 72 hours after the initial dose of methanol and after a 72-hour recovery period. Retinal energy metabolites, glutathione (GSH) concentrations, and histology were determined at the same time points. RESULTS: Both rod-dominated and UV-cone-mediated electroretinogram responses were profoundly attenuated in methanol-intoxicated rats. In rats allowed to recover from methanol intoxication, there was significant, although incomplete, recovery of rod-dominated retinal function. However, there was no demonstrable improvement in UV-cone-mediated responses. Retinal adenosine triphosphate (ATP), adenosine diphosphate (ADP), and GSH concentrations were significantly reduced after intoxication. Although retinal energy metabolites returned to control values after the recovery period, retinal GSH remained significantly depleted. Histopathologic changes were apparent in the photoreceptors after methanol intoxication, with evidence of inner segment swelling and mitochondrial disruption. In animals allowed to recover from methanol intoxication, there was no evidence of histopathology at the light microscopic level; however, ultrastructural studies revealed subtle photoreceptor mitochondrial alterations. CONCLUSIONS: These findings support the hypothesis that formate inhibits retinal mitochondrial function and increases oxidative stress. They also provide evidence for a differential sensitivity of photoreceptors to the cytotoxic actions of formic acid, with a partial recovery of rod-dominated responses and no recovery of UV-cone-mediated responses.

Adenosine Diphosphate↗

PubMed2000

Increased mitochondrial K(ATP) channel activity during chronic myocardial hypoxia: is cardioprotection mediated by improved bioenergetics?

Increased resistance to myocardial ischemia in chronically hypoxic immature rabbit hearts is associated with activation of ATP-sensitive K(+) (K(ATP)) channels. We determined whether chronic hypoxia from birth alters the function of the mitochondrial K(ATP) channel. The K(ATP) channel opener bimakalim (1 micromol/L) increased postischemic recovery of left ventricular developed pressure in isolated normoxic (FIO(2)=0.21) hearts to values (42+/-4% to 67+/-5% ) not different from those of hypoxic controls but did not alter postischemic recovery of developed pressure in isolated chronically hypoxic (FIO(2)=0.12) hearts (69+/-5% to 72+/-5%). Conversely, the K(ATP) channel blockers glibenclamide (1 micromol/L) and 5-hydroxydecanoate (5-HD, 300 micromol/L) attenuated the cardioprotective effect of hypoxia but had no effect on postischemic recovery of function in normoxic hearts. ATP synthesis rates in hypoxic heart mitochondria (3.92+/-0.23 micromol ATP. min(-1). mg mitochondrial protein(-1)) were significantly greater than rates in normoxic hearts (2.95+/-0.08 micromol ATP. min(-1). mg mitochondrial protein(-1)). Bimakalim (1 micromol/L) decreased the rate of ATP synthesis in normoxic heart mitochondria consistent with mitochondrial K(ATP) channel activation and mitochondrial depolarization. The effect of bimakalim on ATP synthesis was antagonized by the K(ATP) channel blockers glibenclamide (1 micromol/L) and 5-HD (300 micromol/L) in normoxic heart mitochondria, whereas glibenclamide and 5-HD alone had no effect. In hypoxic heart mitochondria, the rate of ATP synthesis was not affected by bimakalim but was attenuated by glibenclamide and 5-HD. We conclude that mitochondrial K(ATP) channels are activated in chronically hypoxic rabbit hearts and implicate activation of this channel in the improved mitochondrial bioenergetics and cardioprotection observed.

Adaptation, Physiological↗

PubMed2000

Ischemic preconditioning in rats: role of mitochondrial K(ATP) channel in preservation of mitochondrial function.

We examined the role of the sarcolemmal and mitochondrial K(ATP) channels in a rat model of ischemic preconditioning (IPC). Infarct size was expressed as a percentage of the area at risk (IS/AAR). IPC significantly reduced infarct size (7 +/- 1%) versus control (56 +/- 1%). The sarcolemmal K(ATP) channel-selective antagonist HMR-1098 administered before IPC did not significantly attenuate cardioprotection. However, pretreatment with the mitochondrial K(ATP) channel-selective antagonist 5-hydroxydecanoic acid (5-HD) 5 min before IPC partially abolished cardioprotection (40 +/- 1%). Diazoxide (10 mg/kg iv) also reduced IS/AAR (36.2 +/- 4.8%), but this effect was abolished by 5-HD. As an index of mitochondrial bioenergetic function, the rate of ATP synthesis in the AAR was examined. Untreated animals synthesized ATP at 2.12 +/- 0.30 micromol x min(-1) x mg mitochondrial protein(-1). Rats subjected to ischemia-reperfusion synthesized ATP at 0.67 +/- 0.06 micromol x min(-1) x mg mitochondrial protein(-1). IPC significantly increased ATP synthesis to 1.86 +/- 0.23 micromol x min(-1) x mg mitochondrial protein(-1). However, when 5-HD was administered before IPC, the preservation of ATP synthesis was attenuated (1.18 +/- 0.15 micromol x min(-1) x mg mitochondrial protein(-1)). These data are consistent with the notion that inhibition of mitochondrial K(ATP) channels attenuates IPC by reducing IPC-induced protection of mitochondrial function.

Adenosine Triphosphate↗

PubMed2000

Development and characterization of a rodent model of methanol-induced retinal and optic nerve toxicity.

Methanol is an important public health and environmental concern because of the selective actions of its neurotoxic metabolite, formic acid, on the retina, optic nerve and central nervous system. Humans and non-human primates are uniquely sensitive to methanol-induced neurotoxicity as a consequence of the limited capacity of primate species to oxidize and thus detoxify formic acid. The toxic syndrome in primates is characterized by formic acidemia, metabolic acidosis and blindness or serious visual impairment. Nonprimate species are normally resistant to the accumulation of formate and associated metabolic and visual toxicity. We have characterized retinal and optic nerve toxicity in a nonprimate model of methanol toxicity using rats in which folate-dependent formate oxidation has been selectively inhibited, allowing formate to accumulate to toxic concentrations following methanol administration. Methanol-intoxicated rats developed formic acidemia, metabolic acidosis and visual toxicity analogous to the human methanol poisoning syndrome. Visual dysfunction was manifested as reductions in the electroretinogram and the flash-evoked cortical potential which occurred coincident with blood formate accumulation. Histological studies revealed mitochondrial disruption and vacuolation in the retinal pigment epithelium, photoreceptor inner segments and optic nerve. The temporal relationship between methanol administration and the onset and development of ocular toxicity, as well as, the degree of metabolic acidosis and extent of formic acidemia in this rodent model are remarkably similar to that documented in human methanol intoxication. Moreover, the functional and morphologic findings in methanol-intoxicated rats are consistent with the hypothesis that formate acts as a mitochondrial toxin in the retina and optic nerve. The establishment and characterization of this nonprimate animal model of methanol intoxication will facilitate research into the mechanistic aspects of methanol toxicity and the development and testing of treatments for human methanol poisoning.

Animals↗

PubMed1999

Opioid-induced second window of cardioprotection: potential role of mitochondrial KATP channels.

Opioids have been previously shown to confer short-term cardioprotection against a prolonged ischemic insult. Therefore, the present study was designed to determine whether opioids can induce a delayed or "second window" of cardioprotection and to assess the potential involvement of the mitochondrial KATP channel. All rats were subjected to 30 minutes of ischemia and 2 hours of reperfusion (I/R). Control animals, injected with saline 24 hours before I/R, elicited an infarct size/area at risk (IS/AAR) of 62.9+/-3.4. TAN-67, a delta1-opioid receptor agonist, was administered 10 or 30 mg/kg IP 12, 24, 48, or 72 hours before I/R. TAN-67 (10 mg/kg) 12- or 24-hour pretreatment did not significantly reduce IS/AAR (62.1+/-6.3 and 43.3+/-7.3, respectively). Similarly, 12-hour pretreatment with TAN-67 (30 mg/kg) did not reduce IS/AAR (60.0+/-5.6); however, 24-hour pretreatment significantly reduced IS/AAR (34.5+/-5.9). Forty-eight-hour pretreatment with TAN-67 maximally reduced IS/AAR (29.2+/-7.0), and opioid-induced cardioprotection was lost after 72-hour pretreatment (61.7+/-3.8). TAN-67-induced cardioprotection could be abolished by pretreatment with the selective delta1-opioid receptor antagonist 7-benzylidenenaltrexone, BNTX, administered either 30 minutes before TAN-67 given 48 hours before I/R or 10 minutes before I/R in rats previously treated for 48 hours with TAN-67 (59.6+/-3.1 and 58.7+/-3.5, respectively). The involvement of the KATP channel was investigated with 2 inhibitors: glibenclamide, a nonselective KATP channel inhibitor, and 5-hydroxydecanoic acid, selective for the mitochondrial KATP channel in rabbits. Glibenclamide, administered 30 minutes before I/R in 48-hour TAN-67-pretreated rats, completely abolished cardioprotection (60. 4+/-3.2). Similarly, 5-hydroxydecanoic acid, administered 5 minutes before I/R in rats pretreated 48 hours previously with TAN-67, completely abolished cardioprotection (57.8+/-2.5). These results suggest that delta1-opioid receptor stimulation, 24 to 48 hours before an ischemic insult, produces a delayed cardioprotective effect that is possibly the result of mitochondrial KATP channel activation.

Analgesics↗

PubMed1999

Formate-induced inhibition of photoreceptor function in methanol intoxication.

Formic acid is the toxic metabolite responsible for the retinal and optic nerve toxicity produced in methanol intoxication. Previous studies in our laboratory have documented formate-induced retinal dysfunction and histopathology in a rodent model of methanol intoxication. The present studies define the time and concentration dependence of formate-induced retinal toxicity in methanol-intoxicated rats. Retinal function was assessed 24, 48, and 72 h after the initial dose of methanol by flicker electroretinographic measurements. Retinal histopathology was assessed at the same time intervals. Rod- and cone-mediated electroretinogram (ERG) responses were attenuated in a formate concentration- and time-dependent manner, and both retinal sensitivity and maximal responsiveness to light were diminished. Attenuation of UV-cone-mediated responses was temporally delayed in comparison to the functional deficits observed in the 15 Hz/510 nm responses, which have a rod-mediated component and occurred at significantly higher formate concentrations. Both 15 Hz/510 nm and UV-cone-mediated ERG responses were undetectable by 72 h; however, if light intensity was increased, a retinal ERG response could be recorded, indicating that photoreceptor function was profoundly attenuated, but not abolished, under these intoxication conditions. Functional changes preceded structural alterations. Histopathological changes were most pronounced in the outer retina with evidence of inner segment swelling, photoreceptor mitochondrial disruption, and the appearance of fragmented photoreceptor nuclei in the outer nuclear layer. The nature of both the functional and structural alterations observed are consistent with formate-induced inhibition of mitochondrial energy production, resulting in photoreceptor dysfunction and pathology.

Animals↗

PubMed1997

Mitochondria-mediated cell injury. Symposium overview.

Mitochondria have long been known to participate in the process of cell injury associated with metabolic failure. Only recently, however, have we come to appreciate the role of mitochondria as primary intracellular targets in the initiation of cell dysfunction. In addition to ATP synthesis, mitochondria are also critical to modulation of cell redox status, osmotic regulation, pH control, and cytosolic calcium homeostasis and cell signaling. Mitochondria are susceptible to damage by oxidants, electrophiles, and lipophilic cations and weak acids. Chemical-induced mitochondrial dysfunction may be manifested as diverse bioenergetic disorders and considerable effort is required to distinguish between mechanisms involving critical mitochondrial targets and those in which mitochondrial dysfunction is secondary and plays only a modulatory role in cell injury. The following paragraphs review a few important examples of chemical-induced cytotoxic responses that are manifested as interference with mitochondrial metabolism and bioenergetics, gene regulation, or signal transduction in the form of apoptosis and altered cell cycle control. Greater understanding of the molecular mechanisms of mitochondrial bioenergetics, ion regulation, and genetics will lead to numerous additional examples of mitochondria-mediated cell injury, revealing important new insight regarding the prediction, prevention, diagnosis, and treatment of chemical-induced toxic tissue injury.

Aging↗

PubMed1996

Formate-induced alterations in retinal function in methanol-intoxicated rats.

Formic acid is the toxic metabolite in methanol poisoning. Permanent visual damage in methanol-intoxicated humans and non-human primates has been associated with prolonged exposures (> 24 hr) to blood formate concentrations in excess of 7 mM; however, little information is available on the toxicity associated with chronic low-level or repeated exposure to methanol. The present studies compared the effects on retinal function and structure of rapidly increasing formate concentrations typical of acute methanol intoxication with low-level plateau formate concentrations more likely to be generated by subacute or chronic methanol exposure. Rats that accumulated formate concentrations of 8-15 mM developed metabolic acidosis, retinal dysfunction, and retinal histopathologic changes. Retinal dysfunction was measured as reductions in the a- and b-waves of the electroretinogram that occurred coincident with blood formate accumulation. Histopathologic studies revealed vacuolation in the retinal pigment epithelium and photoreceptor inner segments. Rats exposed to formate concentrations ranging from 4 to 6 mM for 48 hr showed evidence of retinal dysfunction in the absence of metabolic acidosis and retinal histopathology. These data indicate that formic acid generated from methanol oxidation acts as a direct retinal toxin. Formate-induced retinal dysfunction in methanol-intoxicated rats can be produced by steadily increasing concentrations of formate and importantly can also be produced by prolonged exposure to lower concentrations of formate. Our findings substantiate evidence based on clinical case reports and a small number of epidemiological studies and support the hypothesis that the visual system toxicity produced by acute, subacute, or chronic methanol poisoning share a common mechanism.

Animals↗

PubMed1993

Differences in the neuroexcitatory actions of pyrethroid insecticides and sodium channel-specific neurotoxins in rat and trout brain synaptosomes.

The effects of pyrethroid insecticides and other sodium channel-specific neurotoxins on synaptosomal membrane potential were investigated in rat and trout brain synaptosomes using the membrane-permeant lipophilic cation [3H]tetraphenylphosphonium (TPP+). Concentration-dependent and tetrodotoxin-sensitive decreases in TPP+ accumulation, indicative of membrane depolarization, were produced by veratridine, aconitine, scorpion (Leiurus quinquestriatus) venom, and type I and type II pyrethroids, in both species. Veratridine, aconitine, and Leiurus venom were more potent and efficacious membrane-depolarizing agents in rat synaptosomes than in trout synaptosomes. Type II (deltamethrin, cypermethrin) pyrethroids produced similar depolarizing responses in rat and trout synaptosomes; however, the 1R-cis-alpha R isomer of deltamethrin, which had no effect on membrane potential in rat synaptosomes, depolarized trout synaptosomes. This isomer of deltamethrin was also shown to produce toxicity in trout, but not in rats. The type I pyrethroids, permethrin and NRDC 157, exhibited significantly greater intrinsic activity in trout brain synaptosomes, producing maximal membrane depolarizations that were three times greater than those observed in rat brain synaptosomes. These results provide evidence of species-specific differences in the membrane-depolarizing properties of pyrethroid insecticides and sodium channel-specific neurotoxins. They also suggest that some of the neurotoxin binding domains of the voltage-sensitive sodium channel in trout brain differ from those in mammalian brain. The hypersensitivity of fish to the neurotoxic actions of pyrethroid insecticides may be related to these differences.

Alkaloids↗

PubMed1992

Pyrethroid insecticide-induced alterations in mammalian synaptic membrane potential.

The neuroexcitatory actions of two toxicologically distinct classes of pyrethroid insecticides were characterized in rat brain synaptosomes using [3H]tetraphenylphosphonium to measure changes in synaptosomal membrane potential and by measuring the release of [3H]acetylcholine. Both type I (permethrin) and type II (deltamethrin, cypermethrin and fenvalerate) pyrethroids produced a concentration-dependent tetrodotoxin-sensitive membrane depolarization which was stereospecific for the neurotoxic isomer of each pyrethroid. Deltamethrin was the most potent and efficacious pyrethroid in these studies, with an EC50 of 30 nM and a maximal estimated membrane depolarization of 27 mV, followed by cypermethrin, fenvalerate and permethrin. The phenoxybenzyl pyrethroids also increased the spontaneous release of [3H]acetylcholine from rat brain synaptosomes, further supporting a depolarizing action of these insecticides on nerve terminal membranes. Pyrethroid-induced release of [3H]acetylcholine was tetrodotoxin-sensitive and occurred over the same concentration range as membrane depolarization. These data indicate that type I and type II phenoxybenzyl pyrethroids act potently and stereoselectively on the voltage-sensitive sodium channel to increase sodium influx into synaptic terminals producing membrane depolarization and neurotransmitter release. Furthermore, they show that pyrethroid-induced alterations in synaptosomal membrane potential is a sensitive measure of pyrethroid action on the sodium channel and of pyrethroid toxicity.

Animals↗

PubMed1991

Methanol poisoning. A rodent model with structural and functional evidence for retinal involvement.

Methanol ingestion can lead to visual impairment, central nervous system dysfunction, or death. The extent of ocular involvement has been difficult to determine because the toxicity is restricted to humans and nonhuman primates due to species differences in methanol metabolism. A rodent model of methanol toxicity recently developed by us was used to evaluate retinal dysfunction in methanol poisoning. Formic acidemia and visual toxic reactions developed in methanol-intoxicated rats. Electroretinographic analysis indicated a significant early deficit in b-wave amplitude followed by a temporally delayed, lesser reduction in a-wave amplitude. Histologic evaluation of the eyes 60 hours after methanol administration revealed generalized retinal edema and vacuolation in the photoreceptors and retinal pigment epithelium. Ultrastructural examination showed swelling and disruption of the mitochondria in photoreceptor inner segments, optic nerve, and the retinal pigment epithelium. These studies document direct retinal involvement in this nonprimate model of methanol toxicity.

Animals↗

PubMed1991

Methanol-induced visual toxicity in the rat.

Human methanol poisoning is characterized by formic acidemia, metabolic acidosis and blindness or serious visual impairment. Nonprimate species are ordinarily resistant to the accumulation of formate and the associated metabolic and visual toxicity. A nonprimate model of methanol-induced visual toxicity was developed using rats treated with subanesthetic concentrations of nitrous oxide to inhibit the oxidation of methanol's toxic metabolite, formic acid. Methanol-intoxicated rats developed formic acidemia, metabolic acidosis and visual toxicity within 36 hr of methanol administration analogous to the human methanol poisoning syndrome. Visual dysfunction was measured as reductions in the flash-evoked cortical potential and electroretinogram, which occurred coincident with blood formate accumulation. Alterations in the electroretinogram occurred at formate concentrations lower than those associated with other visual changes and provide functional evidence of direct retinal toxicity in methanol poisoning.

Acidosis↗

PubMed1989

Effects of intraocular mescaline and LSD on visual-evoked responses in the rat.

The effects of mescaline and LSD on the flash-evoked cortical potential (FEP) were determined in unrestrained rats with chronically-implanted electrodes. Systemic administration of mescaline or LSD significantly attenuated the primary component of the FEP at three stimulus intensities with the greatest effect observed 60-90 minutes following drug administration. The magnitude and specificity of the effects of these agents on the primary response suggest that they produce deficits in conduction through the retino-geniculato-cortical system. The serotonin receptor antagonists, cyproheptadine and methysergide, antagonized the mescaline-induced depression of the FEP in accordance with neurochemical and behavioral evidence that mescaline acts as a partial agonist on serotonin receptors. Topical or intraocular administration of atropine antagonized the actions of systemically-administered mescaline. In addition, intraocular administration of mescaline or LSD attenuated the FEP indicative of an action of these hallucinogens on visual processing in the retina which is modulated by muscarinic receptor activity.

Administration, Topical↗

PubMed1988

Pyrethroid insecticides evoke neurotransmitter release from rabbit striatal slices.

The effects of the synthetic pyrethroid insecticide fenvalerate ([R,S]-alpha-cyano-3-phenoxybenzyl[R,S]-2-(4-chlorophenyl)-3- methylbutyrate) on neurotransmitter release in rabbit brain slices were investigated. Fenvalerate evoked a calcium-dependent release of [3H]dopamine and [3H]acetylcholine from rabbit striatal slices that was concentration-dependent and specific for the toxic stereoisomer of the insecticide. The release of [3H]dopamine and [3H]acetylcholine by fenvalerate was modulated by D2 dopamine receptor activation and antagonized completely by the sodium channel blocker, tetrodotoxin. These findings are consistent with an action of fenvalerate on the voltage-dependent sodium channels of the presynaptic membrane resulting in membrane depolarization, and the release of dopamine and acetylcholine by a calcium-dependent exocytotic process. In contrast to results obtained in striatal slices, fenvalerate did not elicit the release of [3H]norepinephrine or [3H]acetylcholine from rabbit hippocampal slices indicative of regional differences in sensitivity to type II pyrethroid actions.

Acetylcholine↗

PubMed1985

Role of hepatic tetrahydrofolate in the species difference in methanol toxicity.

The susceptibility of various species to methanol toxicity is inversely related to the rate of tetrahydrofolate (H4folate)-dependent formate oxidation to carbon dioxide. Thus, the levels of various folate derivatives and folate-dependent enzyme activities present in the livers of monkeys, which are sensitive to methanol, and rats, which are not, were compared in order to investigate the biochemical basis of this species difference. Hepatic H4folate levels in monkeys were 60% of those in rats, and formylated-H4folate derivatives were 2-fold higher in monkeys than in rats. No significant difference between monkeys and rats in the levels of total hepatic folate or 5-methyl-H4folate was observed. The activities of formyl-H4folate synthetase (EC 6.3.4.3) and formyl-H4folate dehydrogenase (EC 1.5.1.6) were 4- and 2-fold higher, respectively, in monkeys than in rats. There was no significant difference between monkeys and rats in methionine synthetase activity (EC 2.1.1.13). Dihydrofolate reductase activity (EC 1.5.1.3) in monkeys was 20% of that in rats. 5,10-Methylene-H4folate reductase (NADPH) activity (EC 1.1.1.171) in monkeys was 40% and 25% of that in rats when the rates of the forward and reverse reactions, respectively, were compared. Serine hydroxymethyltransferase activity (EC 2.1.2.1) was 2-fold higher in monkeys than in rats. The differences in the activities of methylene-H4folate reductase and serine hydroxymethyl-transferase between monkeys and rats may have contributed to the difference in hepatic H4folate levels. The 40% lower level of hepatic H4folate in monkeys, as compared to rats, relates well to the 50% lower maximal rate of formate oxidation in monkeys. Thus, the species difference in susceptibility to methanol may be explained by the difference in the level of hepatic H4folate.

Animals↗

PubMed1984

Nucleoside and oxypurine homeostasis in adult rabbit cerebrospinal fluid and plasma.

In adult New Zealand white rabbits, the effects of food deprivation and of massive elevations of plasma uridine or thymidine concentrations on CSF and plasma nucleoside and oxypurine concentrations were studied. Nucleoside and oxypurine levels were determined by high performance liquid chromatography using unequivocal methods of compound identification. After 48 and 96 h of food deprivation, the concentrations of uridine, cytidine, inosine, thymidine, deoxycytidine, deoxyuridine, hypoxanthine, xanthine, and uric acid in CSF and plasma were not different than in controls, except at 96 h, when the plasma uridine concentration was 35% lower (p less than 0.05). After elevation of the plasma and CSF thymidine concentrations to approximately 200 and 100 microM, respectively, with intravenous thymidine for 5 h, there was a large increase in CSF and plasma thymidine to approximately 100 microM and a smaller increase in plasma and CSF deoxyuridine concentrations. After elevation of the plasma and CSF uridine concentrations to 0.6 and 0.2 mM, respectively, there was a large increase in CSF and plasma uracil and a smaller increase in plasma and CSF deoxyuridine concentrations. Elevated plasma concentration of thymidine and uridine significantly decreased the CSF to plasma ratios of deoxyuridine and thymidine; however, only elevated plasma uridine concentrations decreased the CSF to plasma ratio of uridine. These results document the powerful homeostatic mechanisms that regulate the concentrations of the principal nucleosides and oxypurine bases in CSF.

Animals↗