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Biomedical subjects

W H Church

Publications and source records attributed to W H Church.

15 recordsLinked to original sources
PubMed1996

Changes in uric acid during acute infusion of MPP+, 6-OHDA, and FeCl3. A microdialysis study in the substantia nigra of the guinea pig.

Extracellular uric acid levels were measured in the substantia nigra of guinea pigs via microdialysis/liquid chromatography with electrochemical detection (LCED) during infusion (60 min) of N-methyl-4-phenylpyridinium (MPP+), 6-hydroxydopamine (6-OHDA), or iron (III) chloride (FeCl3). Striatal and substantia nigra (SN) tissues were analyzed for uric acid (UA) and dopamine (DA) 3 h postinfusion. MPP+ infusion resulted in an increase in extracellular UA of 222 +/- 6%. The ipsilateral/contralateral ratio of nigral UA tissue levels was significantly increased over vehicle controls. Infusion of 6-OHDA produced an increase of 362 +/- 44% in extracellular UA. No significant changes were seen in UA tissue levels in either the striatum or the SN. Infusion of FeCl3 produced a significant decrease in extracellular nigral UA levels to 21.5 +/- 0.7% of preinfusion levels. The ipsilateral/contralateral ratio of nigral UA tissue levels increased by 38%, whereas the striatal ratio value decreased to 62% of the vehicle control levels. No changes in DA tissue levels were observed in any of the brain regions in the experimental groups. These results indicate that infusion of neurotoxins known to affect dopaminergic cells generates an acute change in UA levels within the nigrostriatal system of guinea pigs.

1-Methyl-4-phenylpyridinium↗
PubMed1994

Uric acid is reduced in the substantia nigra in Parkinson's disease: effect on dopamine oxidation.

Postmortem caudate and substantia nigra tissue samples from human parkinsonian patients (PD) and age-matched controls (NC) were analyzed for uric acid (UA), dopamine (DA), and ascorbic acid (AA) by HPLC/UV/ED. Uric acid and DA levels were significantly lower in the substantia nigra of PD by 54% and 85%, respectively. In the caudate, DA levels were significantly lower while UA levels were nonsignificantly reduced (0.10 < p < 0.05). Ascorbic acid levels were not significantly different from the controls in either brain region. Conditions favorable for oxidative stress were evaluated by measuring the oxidation of DA in individual brain homogenates. The rate constant for DA oxidation in control caudate was 0.34 x 10(-2) min-1 and in parkinsonian caudate was 4.20 x 10(-2) min-1. In control and parkinsonian substantia nigra DA oxidation rate constants were 2.82 x 10(-2) min-1 and 4.57 x 10(-2) min-1, respectively. Addition of UA or catalase to parkinsonian homogenate decreased the rate of DA oxidation, while addition of uricase to control homogenate increased the rate of DA oxidation. The data support the hypothesis that UA is decreased in nigrostriatal dopamine neurons in parkinsonian patients which contributes to an environment susceptible to oxidative stress, particularly through dopamine oxidation reactions.

Aged↗
PubMed1994

Thermal degradation of injectable epinephrine.

The degradation of epinephrine in USP injectable cartridges was investigated under different heating conditions. Epinephrine (EPI) and EPI sulfonic acid (EPI-SA) levels in 1:10,000 (0.1 mg/mL) EPI injectable solutions subjected to either cyclical (65 degrees C for 8 hr/d for 4 to 12 weeks) or constant (65 degrees C for 7 days) heating were determined using high-pressure liquid chromatography with diode array and electrochemical detection. Constant (169 total hours of heat exposure) heating resulted in complete degradation of both compounds and dark brown discoloration of the solution. Cyclical heating (672 total hours of heat exposure) resulted in a 31% reduction in EPI concentration and a 225% increase in EPI-SA concentration with no discoloration of the solution. In laboratory-prepared solutions, the degradation of EPI and the formation of EPI-SA was found to be dependent on sodium metabisulfite concentration and the duration of cyclical heating. These results indicate that the thermal stability of EPI and the formation of EPI-SA depends on the method of heat exposure and the amount of bisulfite present in the solution.

Chromatography, High Pressure Liquid↗
PubMed1994

Environmental temperature variations cause degradations in epinephrine concentration and biological activity.

This study determined the biological consequence of temperature induced epinephrine degradation. Two different epinephrine preparations (1:1,000 and 1:10,000) were exposed to either cold (5 degrees C) or hot (70 degrees C) temperature. The exposure occurred for 8-hour periods each day in 4-, 8-, and 12-week intervals. Samples and identical controls were then chemically evaluated using high-pressure liquid chromatography (HPLC), and biological activity of samples showing chemical degradation was assessed in conscious rats. Epinephrine (1:10,000) underwent a significant degradation and a loss of concentration of the parent compound after 8 weeks of heat treatment. By 12 weeks, 64% of the epinephrine was degraded. A smaller (30%) but significant loss of cardiovascular potency was determined by blood pressure and heart rate responses in conscious rats. The degradation of epinephrine (1:1,000) was not statistically significant even after 12 weeks of heat exposure. No change was noted from control in either epinephrine concentration when exposed to cold temperatures. In conclusion, epinephrine (1:10,000) deteriorates in the presence of elevated temperature and should be protected from high temperatures when carried by EMS providers. The degradation products may possess biological activity.

Animals↗
PubMed1993

Iron(III) chloride injection increases nigral uric acid in guinea-pig.

The present study was carried out to determine if iron chloride (FeCl3) injections into the substantia nigra of guinea-pigs produced changes in nigro-striatal uric acid levels. Two-weeks following unilateral injection of FeCl3 (185 nmol Fe3+), ipsilateral uric acid levels were increased 176% over contralateral levels in the substantia nigra. No effect on striatal uric acid levels was observed. Iron chloride injection produced a 74% depletion of dopamine levels in the ipsilateral striatum. Ipsilateral/contralateral ratios were significantly decreased for striatal dopamine and significantly increased for nigral uric acid when compared with saline-injected controls. The results of this work indicate that FeCl3 injections into the substantia nigra of guinea-pigs produce a significant, localized increase in tissue uric acid levels two weeks after treatment.

Animals↗
PubMed1989

The effect of argon laser trabeculoplasty upon the normal human trabecular meshwork.

The effect of argon laser trabeculoplasty (ALT) upon the normal human trabecular meshwork, as determined by scanning and transmission electron microscopy is reported. The lower nasal and temporal quadrants of an eye received ALT 5 and 1 day, respectively, prior to enucleation. Laser impact sites were identified as focal disruptions of trabeculae, together with connective tissue and cellular debris. Surviving trabecular endothelial cells near the laser lesions exhibited signs of phagocytic and migratory activity. Exogenous macrophages also contributed to the clearance of debris. Activated trabecular cells were observed leaving the meshwork by migrating over the corneal endothelium. By 5 days post-ALT increased amounts of trabeculae lacked an endothelial covering. More activated trabecular cells but fewer macrophages were noted. A laser lesion sited close to Schwalbe's line induced, within 5 days, a local corneal endothelial wave front to advance towards it, thus reflecting many late failed ALT specimens that we have seen.

Humans↗
PubMed1989

The visual evoked potential in acute primary angle closure glaucoma.

Visual evoked potentials (VEPs) were elicited from 29 patients who had experienced a previous attack of acute primary angle closure glaucoma. The VEPs were shown to be abnormal in at least one of the measures (latency, amplitude, contrast threshold, or slope) in 72.4% of affected eyes, whereas only 41.4% indicated obvious optic nerve damage. It is notable that 48.1% of fellow eyes with no (known) history of acute pressure rise also showed some form of VEP abnormality. The possible pathophysiological mechanisms operating in both affected and fellow eyes are discussed. It is concluded that, despite the presence of possible artefactual influences, the results probably reflect the presence of primary angle closure glaucoma.

Adult↗
PubMed1987

Extracellular dopamine in rat striatum following uptake inhibition by cocaine, nomifensine and benztropine.

A microdialysis/smallbore chromatographic system was used to monitor changes in extracellular dopamine concentration in the striatum of the rat following administration of drugs that block catecholamine uptake. Analysis of 0.5 microliter of dialysate every 5 min showed dose-dependent elevations in extracellular dopamine following systemic administration of nomifensine (1 and 10 mg/kg), benztropine (5 and 25 mg/kg) and cocaine (3, 10 and 30 mg/kg). The order of potency in vivo was nomifensine greater than cocaine greater than benztropine. The short sampling interval allows accurate temporal profiles following pharmacological manipulations to be acquired.

Animals↗
PubMed1987

Detecting behaviorally relevant changes in extracellular dopamine with microdialysis.

A method is described for monitoring extracellular levels of striatal dopamine in the rat during behavior. The extracellular fluid is sampled using a microdialysis probe modified for use in behaving animals. Dopamine concentration in the perfusate is determined every 5 min using an automated smallbore chromatographic system with electrochemical detection. The system is capable of detecting behaviorally related changes of 5 nM, in extracellular dopamine.

Animals↗
PubMed1987

Cryptococcal choroidoretinitis and immunodeficiency.

A 30 year old man with Hodgkin's disease, clinically in remission, presented with blurred vision in one eye due to a choroiditis. He developed headaches 10 days after commencing oral steroids and was subsequently found to have cryptococcal meningitis. The meningitis and choroiditis resolved on antifungal medication. This is the first case of cryptococcal choroiditis recorded in the United Kingdom.

Adult↗
PubMed1986

Striatal dopamine activity and unilateral barpressing in rats.

A micro-punch tissue assay was used to measure changes in dopamine content at twenty-six sites within the striatum of rats trained to barpress exclusively with one forepaw for food pellets. Analysis of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), was carried out using HPLC with electrochemical detection. The barpress group had a significantly higher DOPAC/DA ratio in both the contralateral and ipsilateral hemispheres when compared to feeding and homecage controls. The DOPAC/DA ratio is considered to be a measure of dopaminergic neuronal activity, thus suggesting a bilateral activation of the neostriatal dopaminergic afferents as a result of the motor performance. Topographical analysis within the barpress group revealed an anterior-posterior, medial-lateral gradient of dopaminergic activity with the posterior and lateral sites showing the greatest increases over the controls. The results of this experiment indicate that localized changes in neuronal activity can be monitored with the micro-punch assay-HPLC/EC technique and that voluntary motor behavior produces an activation of the striatal dopamine system.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1985

Dopamine depletion in a striatal subregion disrupts performance of a skilled motor task in the rat.

Unilateral 6-hydroxydopamine injections into the lateral neostriatum disrupted the ability of rats to retrieve small food pellets with the contralateral forepaw. Similar injections into the medial striatum did not interfere with performance accuracy. Dopamine assays indicated that of the 5 striatal subregions analyzed, the lateral striatum at the level of the anterior commissure was most directly related to the behavioral deficit. The behavioral results are interpreted as providing evidence in support of a sensory role for the lateral striatal dopamine system.

Animals↗