Biomedical subjects

J DiMattio

Publications and source records attributed to J DiMattio.

11 recordsLinked to original sources

PubMed1992

Decreased ascorbic acid entry into cornea of streptozotocin-diabetic rats and guinea-pigs.

High L-ascorbic acid (AA) levels in aqueous humor and intraocular tissues including lens and cornea are thought to protect against the harmful effects of the photochemical and ambient oxidation reactions involving oxygen and its radicals. Our pulse-chase studies follow a bolus of radiolabeled test molecules including [14C]L-ascorbic acid and [3H]L-glucose (L-glu) introduced into the blood at time t = 0, and determine the time-dependent concentrations of these labeled molecules as they move into aqueous humor, corneal endothelium and stroma tissues. Calculated entry and exit rate constants provide a representative measure of the functional state of passive and carrier mediated transport mechanisms in situ in normal and diabetic animals. Diabetic rats were categorized in terms of length of time exposed to a uniform, monitored streptozotocin (stz) diabetes as: short term (10-20 days); mid-term (40-60 days); and long term (100+ days). In the rat, we observed little change in entry rate of L-glu (a passive marker) into aqueous humor [control Ki = 0.0216 +/- 0.0021 (n = 14)/mid-term stz-diabetes Ki = 0.0202 +/- 0.0027 (n = 10)] and a modest decrease in the entry rate of AA into aqueous humor [control KAi = 0.0231 +/- 0.0022 (n = 14)/mid-term stz-diabetes KAi = 0.0201 +/- 0.0034 (n = 10)]. At corneal endothelium, we noted a significant decrease in the active movement of AA [control KE = 0.614 +/- 0.053 (n = 14)/mid-term stz-diabetes KE = 0.220 +/- 0.026 (n = 9)] while the passive L-glu entry rate remained essentially unchanged.+

Animals↗

PubMed1992

Ascorbic acid entry into cornea of rat and guinea pig.

The transport rates of radiolabeled ascorbic acid (AA), 3-O-methyl-D-glucose (mD-glu) and L-glucose (L-glu) from blood into the aqueous humor, corneal endothelium, and stroma compartments were studied in male Sprague-Dawley rats and English short-haired guinea pigs. In vivo pulse chase kinetic studies supplied transport entry rate constants, Ki (min-1), and used L-glu as a passive internal control. Results in the rat indicate that AA enters the aqueous humor at rates similar to L-glu and likely via simple passive diffusion. Rate constants for entry into endothelium for both L-glu and mD-glu were high, indicating a quick equilibrium with the aqueous humor. Endothelium AA levels continued to increase to levels higher than in the aqueous humor. Although all three test molecules quickly entered the endothelium, L-glu and mD-glu levels were soon found to decrease, whereas levels of AA or its metabolites remained high. AA entered the stroma of the rat cornea slower than either L-glu or mD-glu, suggesting that no special transport mechanism for AA is present. mD-glu moves into the stroma quickly, but high levels are not maintained. The guinea pig maintains AA levels in the cornea about 10 times higher than that of the rat by first accumulating AA in the aqueous humor and again by actively accumulating AA in the endothelium. Data at 24 h postbolus suggests that both the rat and guinea pig maintain high corneal AA levels for extended periods. Thus, whereas both glucose analogues enter and leave the cornea via the aqueous humor relatively quickly, AA appears to be actively taken up by the endothelium and thus maintained high in both species. Metabolic roles for ascorbate in the eye could conceivably be similar in both nocturnal rats and diurnal guinea pigs, even though the means of supply differ. Because the guinea pig does not produce AA, it conserves and stores a supply in the aqueous humor via active transport. The rat instead could rely on a steady supply of AA to meet intraocular needs.

3-O-Methylglucose↗

PubMed1992

Alterations in ascorbic acid transport into the lens of streptozotocin-induced diabetic rats and guinea pigs.

High ascorbic acid (AA) levels in the aqueous humor and intraocular tissues, including the lens, are thought to protect against the harmful effects of photochemical and ambient oxidation reactions involving oxygen and its radicals. In addition, AA may have various metabolic functions, including structural collagen formation in intraocular tissues. Recent work showed that, in the guinea pig, reduced AA was concentrated in the aqueous and lens epithelium. These in vivo studies were extended to streptozotocin-induced diabetic rats and guinea pigs to explore the state of AA transport and passive L-glucose movement in the diabetic lens. A bolus dose of radiolabeled test molecules, including 14C-AA, 3H-L-glucose (L-glu), and 14C-3-O-methyl-D-glucose, was injected into the blood at time zero, and the time-dependent concentrations of these labeled molecules were determined as they move into the aqueous humor, lens epithelium and capsule, and interior compartments. These kinetic studies provided a unique measurement of the functioning state of passive and carrier transport mechanisms in situ in normal and diabetic animals. Diabetic animals (blood glucose, greater than 300 mg/dl) were categorized in terms of the length of time of uniform monitored drug-induced diabetes as short term (10-20 days); midterm (40-60 days), and long term (100+ days). In the rat lens epithelium, significant decrease occurred in the active movement of AA (control KEi, 0.693 +/- 0.062 [n = 12]; midterm drug-induced diabetes Ki, 0.192 +/- 0.054 [n = 10]; t-test P less than 0.001). The passive L-glu entry rate increased (control KEi, 0.0268 +/- 0.0053 [n = 12]; midterm drug-induced diabetes KEi, 0.0421 +/- 0.075 [n = 10]; t-test P less than 0.005). Thus, it was suggested that the drug-induced diabetic rat lens epithelium had lost some of its ability to concentrate AA to high levels and achieved epithelial levels only one- to twofold those of aqueous; control animals concentrated AA to levels of five- to eightfold those of aqueous within 20 min. By contrast, the rate of movement of L-glu from epithelium to stroma increased minimally (control KSi, 0.0116 +/- 0.021 [n = 12]; midterm drug-induced diabetes KSi, 0.0136 +/- 0.034 [n = 10]; t-test P less than 0.05). In addition, AA entry rate into lens cortex increased fourfold (control KSi, = 0.0018 +/- 0.0003 [n = 12]; midterm drug-induced diabetes KSi, 0.0081 +/- 0.024 [n = 10]; t-test P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

3-O-Methylglucose↗

PubMed1991

In vivo use of neutral radiolabelled molecular probes to evaluate blood-ocular barrier integrity in normal and streptozotocin-diabetic rats.

Evidence suggests that the consequences of diabetes mellitus are numerous and that net changes in ocular barrier permeability are necessarily complex functions of changes at specific anatomical loci. In this study we explore changes in blood-aqueous and vitreous permeability in streptozotocin-diabetic rats using five stable radiolabelled probes. Three probes, (3H)-L-glucose, (14C)-sucrose and (14C)-carboxylinulin are relatively large molecules and are expected to move into ocular humours via paracellular routes. Two probes, (14C)-urea and (14C)-glycerol, are small and likely have a trans-cellular component to permeability. Pulse-chase kinetic studies follow the appearance of test molecules into ocular humours with rate constants estimated via linear modelling. Larger neutral probes L-glucose, sucrose and carboxylinulin entered the aqueous humour of control rats slowly via routes that presumably circumvent tight-junctioned barriers. These slow-entry rates were found to increase in diabetic animals suggesting an increase in passive paracellular permeability with significant variation among animals. In contrast, aqueous entry rates of smaller probes urea and glycerol were decreased in diabetic animals suggesting that these probes cross membranes and cells less efficiently in diabetic animals. The magnitude of these changes increased with the length of exposure to diabetes. Paralleling the aqueous humour studies, we found a significant but variable increase in vitreous entry rate with L-glucose, sucrose and carboxylinulin, but a decrease in entry rates with small probes urea and glycerol. These results suggests that diabetes-related blood-ocular permeability changes are complex and depend on the size and properties of the probe as well as the degree of diabetes exposure.

Animals↗

PubMed1991

Active transport of ascorbic acid across the retinal pigment epithelium of the bullfrog.

Known functions of the RPE include glucose, water and retinoid transports; an ion transport mechanism utilizing a Na(+)-K(+)-ATPase pump located in the apical membrane has been proposed. Recent studies with cultured RPE cells of cat and bovine indicate that the RPE takes up ascorbate by an active mechanism. In this study we use a mounted bullfrog RPE preparation to study unidirectional and net fluxes of radiolabeled (14C)-ascorbic acid (AA), (14C)-dehydroascorbic acid, (3H)-L-glucose(L-glu) and (14C)-3-O-methyl-D-glucose(mD-glu) in an effort to explore the mechanism whereby AA moves across this tissue. Comparative flux studies with AA indicated that the retina to blood side (apical to basal:AB) flux of AA was more than 6x that of L-glu, a passive marker of comparable size. The reverse BA flux of AA was not significantly different from that of L-glu. Flux studies of L-glu, mD-glu and dehydroascorbic acid revealed no "net" flux across the mounted RPE; significantly, only AA demonstrated a net flux from retina to choroid (AB). The AB flux of reduced ascorbate was significantly greater than that of dehydroascorbic acid indicating specificity of carrier mediation. Apical ouabain (10(-4) M) and sodium replacement in the bathing medium reduced the AB and net flux of AA significantly suggesting the requirement of a functioning Na(+)-K(+)-ATPase on the apical side membrane of the RPE. Energy blocker, dinitrophenol decreased unidirectional AB and net AA fluxes.(ABSTRACT TRUNCATED AT 250 WORDS)

3-O-Methylglucose↗

PubMed1989

Active transport of ascorbic acid into lens epithelium of the rat.

The transport rates of radiolabeled ascorbic acid (AA) and dehydroascorbic acid, as well as 3-O-methyl-D-glucose and L-glucose from blood into aqueous humor, lens epithelium and lens 'cortex' compartments were studied in male Sprague-Dawley rats. In vivo pulse chase kinetic studies and modeling of transport from plasma and aqueous and on into idealized water compartments of lens epithelium and cortex allowed for the calculation of transport rate constants, Ki (min-1), in experiments utilizing L-glucose as a passive internal control. TLC chromatography was used to monitor intraocular labeled molecules deriving from labeled test molecules introduced via blood. Results indicate that AA enters aqueous humor at rates similar to L-glucose and likely via simple passive diffusion. In contrast, an active uptake of AA by lens epithelium was found with the calculated entry constant for ascorbate being more than 21 times faster than that of L-glucose. Concentrations in lens epithelium were found to be more than twice that of aqueous humor within only 7 min from the introduction of a [14C]AA bolus into blood. It was also found that very little AA continued on past the epithelium to the interior lens cortex compartment. Our data suggest no special uptake of AA by lens fiber cells. The non-metabolizable analog of D-glucose, 3-O-methyl-D-glucose, however, readily moves past the lens epithelium into fiber cells at much faster rates than the passive L-glucose marker and in a manner consistent with facilitated diffusion. The data suggest that even in a nocturnal species, such as a rat, which demonstrates relatively low circulating levels of ascorbic acid in plasma and aqueous humor, special mechanisms exist for moving ascorbic acid into intraocular tissues. More specifically, the lens epithelium actively takes up ascorbate for some, as yet unclear purpose while the interior fiber cells appear to have no special uptake mechanism for this molecule.

Animals↗

PubMed1989

A comparative study of ascorbic acid entry into aqueous and vitreous humors of the rat and guinea pig.

The transport rates of radiolabeled ascorbic acid and dehydroascorbic acid, as well as, labeled 3-O-methyl-D-glucose and L-glucose from a central plasma compartment into aqueous and vitreous humors and cerebrospinal fluid were studied in vivo. Normal, male albino Sprague-Dawley rats and English Short Haired guinea pigs were used to explore the mechanism of ascorbic acid entry into ocular humors in a species that can produce ascorbate (the rat) and one that cannot and, like humans, is dependent on dietary sources (the guinea pig). In vivo kinetic studies allowed for the calculation of entry rate constants, Ki (min-1), in double-labeled experiments using L-glucose as an internal passive control. Parallel TLC chromatographic studies were performed to monitor intraocular labeled molecules deriving from the plasma-introduced test molecule. In addition, resting levels of ascorbic acid and D-glucose were determined in order to obtain more reliable data than previously available. Resting levels of D-glucose revealed a consistent pattern of lower levels in aqueous and vitreous humors and CSF than found in plasma for both rat and guinea pig. However, ascorbate levels differed significantly, with the guinea pig demonstrating high ascorbate levels in the aforementioned humors: 58, 77 and 22, respectively, times the circulating plasma value of 0.2 +/- 0.2 mg/dl. In contrast, the rat, like the guinea pig, had low plasma ascorbate levels (3.3 +/- 0.8 mg/dl) compared to glucose (162 +/- 8 mg/dl), with even lower aqueous and vitreous values in a pattern similar to that of D-glucose. In vivo aqueous, vitreous and CSF transport results from the guinea pig indicate active transport mechanisms for ascorbic acid that prefer the ascorbate over the dehydroascorbate moiety and are probably different from the carrier-facilitated diffusion mechanisms for D-glucose, which do not move molecules against a concentration gradient. TLC studies, performed under nitrogen, revealed that only (14C)-ascorbic acid was present in aqueous or vitreous humors regardless of whether the radiolabeled pulse was of ascorbic or dehydroascorbic acid. The rat demonstrated little or no carrier involvement, with ascorbic acid crossing into ocular humors at rates very close to those of L-glucose, which is similar in size and is considered to cross the barriers studied via passive diffusion. Saturation studies with unlabeled glucose and glucose inhibitor drugs phloretin (10(-3) M) and phloridzin (10(-1)) had no apparent effect on ocular entry rates. Dehydroascorbic acid movement was also found to be passive.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

Facilitated glucose transport across the retinal pigment epithelium of the bullfrog (Rana catesbeiana).

Transport studies of glucose analogs [3H] 3-O-methyl-D-glucose (mD-glu) and L-[14C]glucose (L-glu) across the isolated retinal pigment epithelium (RPE) of the bullfrog was undertaken to determine whether the glucose transport mechanism was dependent upon the postulated ion-transport scheme and/or whether glucose transport is insulin-mediated. In addition, metabolic inhibitors were tested to explore the energy requirements of glucose transport across the RPE. Flux studies of mD-glu and L-glu performed with mounted RPE tissues, with short circuit current (SCC) and potential difference (PD) monitored via automatic voltage clamp apparatus, indicate that transport is clearly stereospecific with D-glucose being transported at least 13 times faster than L-glucose. The system was found to be saturable with a Km of about 24 mM glucose and Vmax of 1400 nmol cm-2 hr-1. Unidirectional Michaelis-Menten constants indicate that the RPE glucose carrier is accessible for transport from either the choroid or retinal side and a bidirectional facilitated diffusion mechanism is suggested. Insulin had no effect on either ion transport (SCC) or glucose transport (passive or facilitated). Both aerobic and anaerobic energy inhibitors decreased ion transport to less than 25% of control, but had little effect, if any, on glucose transport across the isolated RPE. Sodium iodoacetate decreased ion transport by 90% of control, but a much slower decrease in facilitated glucose transport of 22% of control suggests that carrier energy requirements, if any, are not direct or immediate. Osmotic studies performed with sucrose and glucose suggest that elevations in osmolarity increase passive glucose movement and decrease facilitated glucose-transport rates. Glucose was found to be much more detrimental to glucose transport than sucrose, suggesting that at high concentrations molecular glucose decreases facilitated transport and increases passive glucose movement by a mechanism other than can be accounted for by osmotic considerations. A model for RPE glucose transport, consistent with current data, is proposed which translocates D-glucose, via an alternating conformational change of the glucose carrier. This carrier does not require a direct supply of metabolic energy, nor a functioning ion-transport mechanism. At a given moment, a single binding site for D-glucose is postulated to be available on either side of the RPE membrane for glucose translocation, although binding site affinity for glucose could differ on each side.

3-O-Methylglucose↗

PubMed1985

In vivo effects of snake venoms on passive and facilitated glucose transport across blood-ocular and blood-CSF barriers of the rat.

The transport of (3H)-3-0-methyl-D-glucose (mD-glu) and (14C)-L-glucose (L-glu) across blood-ocular and blood-CNS barriers was studied in rats with previously introduced (i.v.) lethal doses of lyophilized venom from one of three venomous snakes; mojave rattlesnake, Crotalus scutulatus; cottonmouth mocassin, Agkistrodon piscivorus; yellow cobra, Naja nivea. Transport rate constants calculated for mD-glu are taken as an indication of carrier-mediated transport, whereas L-glu constants are considered a measure of passive barrier permeability. C. scutulatus venom increased L-glu transport (+121%) across the blood-vitreous barrier. A passive increase in blood-vitreous permeability was also observed with mD-glu. This venom also increased passive L-glu entry rate into CSF (+160%). A. piscivorus venom also increased passive L-glucose entry into vitreous. However, whereas rattlesnake venom had little effect on blood-aqueous transport, cottonmouth venom may have also decreased carrier transport across this barrier. In addition, mD-glu transport from blood into CSF is decreased, suggesting a loss of carrier function across this barrier. N. nivea venom decreased the transport of both L-glu and mD-glu across the blood-aqueous, blood-vitreous and blood-CSF barriers, suggesting a possible decrease in cerebral blood flow as causative. There is also a possible increase in passive transport across the vitreous barriers, which may be in part countered by the decreased blood flow. Transport from aqueous into lens and cornea remained unchanged by the three venoms tested. It is suggested that components of rattlesnake and cottonmouth venoms alter transport barrier properties, with the blood-vitreous barrier being most susceptible to damage, whereas cobra venom likely decreases the supply of blood-borne substances to brain and ocular fluids and tissues by decreasing cerebral blood supply.

3-O-Methylglucose↗

PubMed1976

Personal sampler for nitrogen dioxide.

A new type of personal sampler for gases in air, originally reported from this laboratory, has been adapted to measurement of NO2. The sampler depends on the transfer of NO2 by diffusion to a triethanolamine coated collector at the sealed end of a tube; the open end of the tube is exposed to the test environment. The devices are accurate, light, simple to use and have very good shelf life before and after sampling.

Air Pollutants↗

PubMed1975

Effects of changes in serum osmolarity on bulk flow of fluid into cerebral ventricles and on brain water content.

The effects of changes in serum osmolarity on the rate and osmolarity of bulk flow of fluid into the cerebral ventricles and on cortical white and grey matter water content were studied in cats. Bulk flow rates and osmolarities were measured during ventriculocisternal perfusion both before and after intravenous infusion of glucose solutions. Infusions of glucose in concentrations greater than 6% decreased fluid bulk flow rate and its osmolarity. Glucose in concentrations less than 6 percent increased fluid bulk flow rate and decreased its osmolarity. Bulk flow rate and serum osmolarity were found to be linearly related with a coefficient of osmotic flow of minus 0.835 mul/min per mOsm/l. At the extremes of induced serum osmolarities, (290 and 360 mOsm/l) bulk flow rate was either increased by 120 percent or completely inhibited. Effluent osmolarity also increased proportionately to serum osmolarity (0.338 mOsm/l per mOsm/l). When compared to controls, cortical grey and white matter water content increased by 1.9 percent and 2.9 percent, respectively, when the infused glucose concentration was 2.5 percent or less, and decreased by 1.8 percent and 2.9 percent when the concentration was 10 percent or more. The results of these experiments suggest that the increased bulk flow comes from the brain, rather then directly from the blood.

Animals↗