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Biomedical subjects

P D Walker

Publications and source records attributed to P D Walker.

At least 19 recordsLinked to original sources
PubMed1992

Bacterial vaccines: old and new, veterinary and medical.

Developments in veterinary and medical bacterial vaccines are outlined. In the former case, economic considerations are paramount, and cruder, less purified products of proven efficacy continue to be employed. For human use, however, safety and absence of side effects are increasingly demanded. Various examples of human and veterinary vaccines are discussed, and interaction between the two fields is illustrated by reference to the pig-bel disease in New Guinea and the possible aetiology of Sudden Infant Death Syndrome.

Adolescent↗
PubMed1992

Reactive oxygen metabolites in toxic acute renal failure.

We have examined the role of reactive oxygen metabolites (ROM) in gentamicin nephrotoxicity and in glycerol-induced acute renal failure, a model for myoglobinuric acute renal failure. Several agents which affect mitochondrial respiration have been shown to enhance the generation of hydrogen peroxide. Based on gentamicin's ability to alter mitochondrial respiration both in vitro and in vivo we postulated that gentamicin may enhance the generation of ROM by renal cortical mitochondria. Gentamicin, in a dose-dependent fashion, enhanced hydrogen peroxide production by rat renal cortical mitochondria as measured by the decrease in scopoletin fluorescence. At the highest concentration of gentamicin tested (4.0 mM), the rate of hydrogen peroxide generation was markedly increased from 0.17 +/- 0.02 to 6.21 +/- 0.67 nmol/mg/min. We next demonstrated that hydroxyl radical scavengers and an iron chelator provide a marked functional and histological protection in gentamicin-induced acute renal failure in rats. Hydroxyl radical scavengers and the iron chelator deferoxamine also protected renal function in glycerol-injected rats, a model for acute renal failure due to muscle injury. Although these data suggest that ROM may be important mediators of toxic renal injury, in vivo generation of ROM by kidney in normal and pathological states has not been previously examined. Aminotriazole (AT) irreversibly inactivates catalase only in the presence of hydrogen peroxide and previous studies have shown that AT-mediated inhibition of catalase in a sensitive measure of in vivo changes in the hydrogen peroxide generation. Using this method, we have demonstrated the in vivo generation of hydrogen peroxide under normal conditions and enhanced generation of hydrogen peroxide in rats treated with gentamicin or glycerol.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed1991

Role of glutathione in an animal model of myoglobinuric acute renal failure.

In a previous study we have shown a role for reactive oxygen metabolites in glycerol-induced acute renal failure, a well-established model for myoglobinuric acute renal failure. In the present study we examined the role of glutathione in this model of acute renal failure. Administration of 50% (vol/vol) glycerol at a dose of 10 ml/kg of body weight to rats intramuscularly resulted in significant renal failure associated with depletion of total kidney glutathione (GSH) from 2.6 +/- 0.1 mumol/g (mean +/- SEM control level) to 1.7 +/- 0.1 mumol/g after 6 hr (P less than 0.001). If GSH were important in glycerol-induced acute renal failure, one would anticipate that exogenously administered GSH should afford protection, while injury should be potentiated if endogenous GSH is depleted. We examined the effect of i.p. administration of L-buthionine-(S,R)-sulfoximine (BSO) at 2 mmol/kg (which results in depletion of kidney GSH) and the effect of increasing renal GSH by i.v. administration of reduced GSH (2 mmol/kg every 3 hr) on kidney function in glycerol-treated rats. Glycerol-injected rats treated with BSO showed significantly worse renal failure than did rats given glycerol alone, while administration of GSH resulted in significant amelioration of glycerol-induced acute renal failure [glycerol treatment alone, blood urea nitrogen (BUN) = 96 +/- 10 and creatinine = 2.5 +/- 0.4 mg/dl; BSO + glycerol treatment, BUN = 123 +/- 7 and creatinine = 3.5 +/- 0.1 mg/dl (n = 9, P less than 0.05); GSH + glycerol treatment, BUN = 78 +/- 10 and creatinine = 1.25 +/- 0.2 mg/dl (n = 8, P less than 0.05)]. In separate experiments 1,3-bis(chloroethyl)-1-nitrosourea (BCNU) [which interferes with the enzyme GSH reductase and prevents recycling of oxidized GSH (GSSG) into GSH] resulted in worsening of glycerol-induced acute renal failure similar to that produced by BSO. These functional differences between GSH-depleted and GSH-repleted rats were further substantiated by significant histological differences in tubular injury. Taken together, these results provide evidence for an important role of GSH in glycerol-induced acute renal failure.

Acute Kidney Injury↗
PubMed1991

Serotonin regulation of neostriatal tachykinins following neonatal 6-hydroxydopamine lesions.

In order to determine whether dopamine mediates the effects of serotonin on tachykinin biosynthesis in the neostriatum, serotonin neurotransmission was altered following depletion of dopamine. Neonatal rats received intracisternal injections of saline or the dopamine neurotoxin 6-hydroxydopamine (6HD). This lesion caused significant reductions in the neostriatum of substance P-like immunoreactivity as well as levels of mRNA coding for preprotachykinin (PPT; the prohormone precursor to tachykinins substance P, neurokinin A and related peptides). Two months later, rats were treated for 5-6 days with saline or the serotonin-uptake inhibitor, zimelidine. Zimelidine treatment of unlesioned animals significantly increased PPT mRNA levels in the neostriatum. However, zimelidine treatment failed to increase PPT mRNA content in 6HD-treated animals. By contrast, neostriatal substance P-like immunoreactivity was restored by zimelidine treatment of 6HD-lesioned animals. These results suggest that an intact nigrostriatal pathway may be required for serotonin neurotransmission to alter PPT mRNA levels in the neostriatum. However, neostriatal tachykinins may be regulated by direct serotonin innervation.

Animals↗
PubMed1991

Serotonin regulation of tachykinin biosynthesis in the rat neostriatum.

Serotonin (5-HT) neurotransmission was altered to determine its role in regulating the biosynthesis of tachykinins in the neostriatum (NS). Depletion of 5-HT with subchronic p-chlorophenylalanine (pCPA) treatment decreased preprotachykinin (PPT, the prohormone precursor to SP) mRNA levels in the NS. By contrast, raising extracellular 5-HT levels with zimelidine (a 5-HT uptake inhibitor) or clorgyline (a monoamine oxidase inhibitor) resulted in increased levels of PPT mRNA. To determine whether 5-HT receptors played a role in mediating the changes in PPT mRNA, animals were treated with the 5-HT2 agonist DOI. This drug significantly increased both PPT mRNA and SP-like immunoreactivity in the NS. These results together indicate that neostriatal tachykinin biosynthesis is sensitive to alterations in 5-HT neurotransmission.

Animals↗
PubMed1991

A comparison of substance P peptide and preprotachykinin mRNA levels during development of rat medullary raphe and neostriatum.

Substance P (SP) and the mRNA coding for its precursor peptide, preprotachykinin (PPT), were measured in medullary raphe nuclei (MRN) and neostriatum (NS) over development in order to determine (1) whether PPT mRNA levels correlate with peptide development, and (2) whether changes in PPT mRNA might help to account for the apparent decline in SP seen immunohistochemically in certain brain areas postnatally. Total RNA was quantified in dissected tissue pieces using the sensitive orcinol reaction. When MRN PPT mRNA levels measured by Northern blot analysis were adjusted to total RNA levels, PPT mRNA per MRN increased over development with a profile similar to that seen for SP peptide. Moreover, both peptide and mRNA levels exhibited a similar decline after postnatal day 15. Therefore, developmental regulation of SP biosynthesis in the MRN may, in part, explain previous evidence documenting a postnatal decline in SP there. In the NS, SP peptide and PPT mRNA increased with a similar profile from E18 through the first postnatal week. Thereafter, SP increased less rapidly than its mRNA, indicating incongruities in prohormone message and processed peptide in the NS.

Animals↗
PubMed1991

Hydrogen peroxide cytotoxicity in LLC-PK1 cells: a role for iron.

Reactive oxygen metabolites have been postulated to play an important role in both toxic and ischemic forms of acute renal tubular epithelial injury. In the present study, we examined the effect of enzymatically generated hydrogen peroxide on LLC-PK1 cells, a renal proximal tubule cell line. Exposure of LLC-PK1 cells to glucose and glucose oxidase (GO; which generates hydrogen peroxide) resulted in cytotoxicity (as measured by trypan blue exclusion) which was dose dependent and increased linearly over time to 81 +/- 5% at 180 minutes (8 +/- 1% at time 0; mean +/- SEM, N = 3 to 7). Catalase (which decomposes hydrogen peroxide) completely prevented the cytotoxicity, confirming that the toxicity was due to hydrogen peroxide production. To assess whether the hydrogen peroxide toxicity was a direct effect or mediated by other toxic oxygen metabolites, several scavengers of reactive oxygen metabolites and iron chelators were used. Superoxide dismutase (a scavenger of superoxide) had no effect. Deferoxamine (DFO), an iron chelator, provided marked protection (GO alone 45.9 +/- 4.4%; GO + DFO 13.0 +/- 2.0%; control 7.1 +/- 1.2%; N = 15 to 17, P less than 0.001). Pretreatment with DFO (1 hr, then 2 washes to remove DFO before GO addition) also markedly inhibited the cytotoxicity, suggesting that DFO's effect was due to iron chelation. Two other metal chelators (dihydroxybenzoic acid and 1,10-phenanthroline) also significantly decreased the GO-induced cytotoxicity. However, three of four hydroxyl radical scavengers used (mannitol, dimethyl sulfoxide, sodium benzoate) did not significantly decrease cell death. Only dimethylthiourea provided protection.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Receptor-mediated increase in cytosolic calcium in LLC-PK1 cells by platelet activating factor and thromboxane A2.

Several studies indicate an important role of platelet activating factor (PAF) and thromboxane A2 (TXA2) in glomerular pathophysiology. However, the potential role of PAF or TXA2 in renal tubular pathophysiology has received little attention, and the presence of functional receptors for these autacoids in renal tubular epithelium has not been previously studied. We examined the effects of PAF and the TXA2 analogue, ONO11113, on the cytosolic free calcium concentration [( Ca2+]i) in cultured LLC-PK1 cell line using a fluorescent probe, fura-2. In these cells, the addition of PAF or ONO11113 caused a significant increment in [Ca2+]i in a dose-dependent manner: both agonists (10(-7) M) increased [Ca2+]i from 148 +/- 16 to 288 +/- 39 nM and from 130 +/- 8 to 240 +/- 18 nM, with the values of EC50 for PAF and ONO11113 being 17 +/- 4 and 17 +/- 2 nM, respectively. These effects were both rapid and transient, returning to baseline in two minutes. The effect of PAF was selectively blocked by PAF receptor antagonist BN50730, but not by TXA2 receptor antagonist L657925. Similarly ONO11113 response was abolished by L657925, but not by BN50730. PAF- or ONO11113-challenged cells did not respond to a second addition of the same agent and showed heterologous desensitization to the other agonist. The initial peaks of [Ca2+]i as well as the sustained elevations in [Ca2+]i induced by PAF or ONO11113 were reduced following the chelation of extracellular Ca2+ by 10 mM ethylene glycol-bis(beta-aminomethyl ether)-N,N,N',N'-tetraacetic acid (EGTA).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Tryptophan hydroxylase inhibition increases preprotachykinin mRNA in developing and adult medullary raphe nuclei.

In order to study the regulation of co-localized monoamine and peptide neurotransmitters in the medullary raphe nuclei (MRN), we determined whether inhibition of serotonin (5-HT) synthesis affected levels of preprotachykinin (PPT; the prohormone precursor of substance P) mRNA in the MRN. Adult rats received p-chlorophenylalanine (pCPA), an irreversible inhibitor of tryptophan hydroxylase (TPH), via Alzet minipumps. TPH activity was inhibited by 70-80% for 3 weeks following pump implantation. During this period Northern mRNA analysis revealed that PPT mRNA levels in the MRN were increased 1.5-2-fold. The pCPA-induced increase was specific for PPT mRNA since no change was detected in mRNA coding for neuron-specific enolase (NSE; a constitutive neuronal protein) or 28 S ribosomal RNA. To determine whether fetal inhibition of 5-HT synthesis affected development of PPT mRNA in the MRN, pregnant rats were administered pCPA via Alzet minipump implanted on embryonic day 8. In pCPA-treated litters TPH activity was decreased by 60-70% from E16 to postnatal day 3 (P3), returning to control levels by P8. Northern mRNA analysis revealed that PPT mRNA levels increased 2.4-fold of control levels at P1. Infusion of pCPA for one week resulted in an earlier increase in PPT mRNA levels, suggesting that birth was not required to elicit the surge in PPT message. These results support the hypothesis that alterations in 5-HT metabolism have regulatory consequences for co-localized substance P formation in the MRN.

Animals↗
PubMed1990

Reactive oxygen metabolites in endotoxin-induced acute renal failure in rats.

Based on recent reports that reactive oxygen metabolites may play a role in endotoxin-induced injury in other tissues, we postulated that reactive oxygen metabolites may be important mediators of endotoxin-induced acute renal failure. Superoxide dismutase, a scavenger of superoxide, or catalase, which destroys hydrogen peroxide, did not protect against endotoxin-induced renal failure. Similarly, neither the hydroxyl radical scavenger dimethylthiourea nor the iron chelator deferoxamine (which presumably would act by preventing the generation of hydroxyl radical via the iron-catalyzed Haber-Weiss reaction) prevented the endotoxin-induced fall in renal function. In separate experiments, we found no increase in renal cortical lipid peroxidation (a marker of reactive oxygen metabolite-mediated tissue injury) in endotoxin-treated rats, providing further evidence against a role for reactive oxygen metabolites in endotoxin-induced renal injury. Finally, using the aminotriazole-induced inhibition of catalase (a measure of in vivo changes in the hydrogen peroxide generation) we found no evidence of enhanced hydrogen peroxide generation in the renal cortex in endotoxin-treated rats. Taken together, the data from these three separate experimental approaches suggest that reactive oxygen metabolites are not important mediators of endotoxin-induced acute renal failure.

Acute Kidney Injury↗
PubMed1989

Minimal connectivity between six month neostriatal transplants and the host substantia nigra.

The present study sought to determine if axonal connectivity is established between 6-month-old neostriatal transplants and the host substantia nigra. Cell suspensions of fetal neostriatum were transplanted into the adult rat neostriatum lesioned previously by kainic acid. Horseradish peroxidase injections into the ipsilateral ventral midbrain labelled the lesion site and the intact neostriatum extensively, but no appreciable anterograde or retrograde label was found within the graft. These results demonstrate a paucity of connectivity between neostriatal grafts and the host brain at a time when other investigators have described transplant-mediated recovery of function.

Animals↗
PubMed1988

Evidence suggesting a role for hydroxyl radical in puromycin aminonucleoside-induced proteinuria.

A single intravenous injection of puromycin aminonucleoside (PAN) results in marked proteinuria and glomerular morphological changes that are similar to minimal change disease in humans. We examined the effect of hydroxyl radical scavengers and an iron chelator on PAN-induced proteinuria. PAN in a dose of 5 mg/100 g body wt significantly increased urinary protein by day 5 (saline: 15 +/- 2, N = 24: PAN: 63 +/- 17, N = 23, P less than 0.001); the proteinuria rapidly increased thereafter, reaching 216 +/- 34, N = 23 by day 7. Concurrent administration of hydroxyl radical scavengers dimethylthiourea, (DMTU 500 mg/kg followed by 125 mg/kg i.p. twice a day) and sodium benzoate (BENZ, 150 mg/kg followed by 125 mg/kg i.p. twice a day) starting the evening before PAN injection markedly reduced proteinuria throughout the course of the study (urinary protein, mg/24 hours on day 7, mean +/- SEM: PAN: 229 +/- 45, N = 15; PAN + DMTU: 30 +/- 5, N = 18; PAN + BENZ: 80 +/- 18, N = 16. Because of the participation of iron in biological systems to generate hydroxyl radical, we also examined the effect of deferoxamine (DFO, 30 mg/day), an iron chelator, on the PAN-induced proteinuria. Concurrent administration of DFO was also protective. In a second series of experiments, DMTU and DFO (administered as described above and then for two additional days after the PAN) provided marked protection even when they were stopped prior to the onset of proteinuria. The protective effects of two hydroxyl radical scavengers and iron chelator implicate an important role for hydroxyl radical in PAN-induced nephrotic syndrome.

Animals↗
PubMed1988

Evidence suggesting a role for hydroxyl radical in glycerol-induced acute renal failure.

Reactive oxygen metabolites, in particular hydroxyl radical, have been shown to be important mediators of tissue injury in several models of acute renal failure. The aim of the present study was to examine the role of hydroxyl radical in glycerol-induced acute renal failure, a model for myoglobinuric renal injury. Rats injected with glycerol alone (8 mg/kg im following dehydration for 24 h) developed significant renal failure compared with dehydrated controls. Rats treated with glycerol and a hydroxyl radical scavenger, dimethylthiourea (DMTU), had significantly lower blood urea nitrogen (BUN) and creatinine. In contrast, urea, which is chemically similar to DMTU but is not a hydroxyl radical scavenger, provided no protection. In addition, DMTU prevented the glycerol-induced rise in renal cortical malondialdehyde content (a measure of lipid peroxidation that serves as a marker of free radical-mediated tissue injury). A second hydroxyl radical scavenger, sodium benzoate, had a similar protective effect on renal function (as measured by both BUN and creatinine). Because the generation of hydroxyl radical in biological systems requires the presence of a trace metal such as iron, we also examined the effect of the iron chelator, deferoxamine on glycerol-induced renal failure. Deferoxamine was also protective. The interventional agents were also associated with a marked reduction in histological evidence of renal damage. The protective effects of two hydroxyl radical scavengers as well as an iron chelator implicate a role for hydroxyl radical in glycerol-induced acute renal failure.

Acute Kidney Injury↗
PubMed1988

Evidence suggesting a role for hydroxyl radical in gentamicin-induced acute renal failure in rats.

The protective effect of hydroxyl radical scavengers and iron chelators has strongly implicated the hydroxyl radical in several models of tissue injury. Based on in vitro studies showing gentamicin-enhanced generation of reactive oxygen metabolites in renal cortical mitochondria, we examined the effect of hydroxyl radical scavengers and iron chelators in gentamicin-induced acute renal failure. Rats treated with gentamicin (G) alone (100 mg/kg, s.c. x 8 d) developed advanced renal failure (BUN 215 +/- 30 mg/dl) compared to saline-treated controls (BUN 16 +/- 1 mg/dl, P less than 0.001). In contrast, rats treated with gentamicin and either dimethylthiourea (DMTU, an hydroxyl radical scavenger, 125 mg/kg, i.p. twice a day) or deferoxamine (DFO, an iron chelator, 20 mg/day by osmotic pump) had significantly lower BUN (G + DMTU 48.8 +/- 8 mg/dl, P less than 0.001, n = 8; G + DFO 30 +/- 7 mg/dl, P less than 0.001, n = 8). In separate experiments, treatment with two other hydroxyl radical scavengers (dimethyl sulfoxide or sodium benzoate) and a second iron chelator (2,3,dihydroxybenzoic acid) had a similar protective effect on renal function (as measured by both BUN and creatinine). In addition, histological evidence of damage was markedly reduced by the interventional agents. Finally, concurrent treatment with DMTU prevented the gentamicin induced increase in renal cortical malondialdehyde content (G: 4.4 +/- 0.2 nmol/mg; G + DMTU: 3.1 +/- 0.2 nmol/mg, P less than 0.0001, n = 8) suggesting that the protective effect of DMTU was related to free radical mechanisms rather than to some other effect. Taken together, these data strongly support a role for hydroxyl radical or a similar oxidant in gentamicin-induced acute renal failure.

Acute Kidney Injury↗
PubMed1987

Minimal connectivity between neostriatal transplants and the host brain.

The present study sought to determine if axonal connectivity is established between neostriatal transplants and the host brain during the first two months of graft development. Cell suspensions of embryonic neostriatum were transplanted into the adult rat neostriatum lesioned previously by kainic acid. After 1-2 months, injections of horseradish peroxidase conjugated with wheat germ agglutinin (HRP) were made either within the graft, into adjacent host neostriatum or the host ventral midbrain. In animals with HRP injection sites restricted to the graft no retrograde or anterograde label was found in the host brain. However, both anterograde axon label and retrogradely labelled neurons were found in areas within the transplant but distal to the injection site. Neither ventral midbrain nor host neostriatal HRP injections resulted in any significant anterograde or retrograde label within the graft. These results demonstrate a lack of connectivity between neostriatal grafts and the host brain 1-2 months post-transplantation but an ability of grafted neurons to project to different locations within the transplant. Therefore, transplanted neostriatal neurons develop for the first two months in the absence of normal neostriatal afferent and efferent connections.

Animals↗