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Biomedical subjects

B J Miller

Publications and source records attributed to B J Miller.

At least 37 records · Page 2Linked to original sources
PubMed1998

Educational benefits and cost savings from an interactive multimedia "best practice".

BACKGROUND: Developing and deploying "clinical practice guidelines" and "best practices" is a major strategic goal of our organization. We developed and evaluated a novel way of educating our colleagues on the office management of shoulder pain, using an interactive multimedia computer program to allow rapid access to user-selected audiovisual educational materials through a simple point and click interface. METHODS: Pre- and post-testing of 30 practicing primary care providers was conducted to assess ability to evaluate and manage patients who present with shoulder pain, and a post-use survey was administered to assess clinician acceptance and confidence, ability to use as a just-in-time tool, and changes in utilization of medical resources. RESULTS: Pre- and post-testing demonstrated that clinicians used this tool to improve their scores in a wide variety of clinical areas including history, physical examination, diagnosis, and management of conditions causing painful shoulder above their scores using textbooks and other traditional educational materials alone. The post-use survey showed outstanding acceptance by clinicians and their reported increased confidence as well as the potential for their increased abilities to translate into significant cost savings through more focused use of radiographic studies, orthopedic consultations, and physical therapy treatments. CONCLUSIONS: It was concluded that "The Multimedia Reference for Office Management of Shoulder Pain" is an effective and valuable learning resource for practicing clinicians, and demonstrates the potential to use an interactive multimedia tool to augment clinical skills and promote cost effective management of patients with this common clinical problem.

Attitude to Computers↗
PubMed1997

The coupling of cyclic GMP and photopolarization of Pelvetia zygotes.

Unidirectional blue light directs the rhizoid-thallus axis in the apolar zygotes of Fucus and Pelvetia. Here, it is shown that blue light (but not red light) increased cyclic GMP levels of Pelvetia zygotes by about a factor of 2. When the increase in cyclic GMP was blocked by a guanylyl cyclase inhibitor, photopolarization was also blocked. Bathing the cells in a permeant cyclic GMP analog, which should tend to collapse intracellular cyclic GMP gradients, reduced the degree of photopolarization. Growing the cells in the dark in a gradient of the analog caused the rhizoids to tend to form on the low concentration side. It appears that the stimulation of the blue light photoreceptors on the side nearer the light activates guanylyl cyclase and results in a transcytoplasmic cyclic GMP gradient that is necessary for polarization.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Alterations in hepatic p53 gene methylation patterns during tumor progression with folate/methyl deficiency in the rat.

Chronic dietary methyl deficiency in F344 rats was used as an in vivo mammalian model in which to evaluate the gene-specific alterations in DNA methylation patterns during multistage hepatocarcinogenesis. Using bisulfite mapping, the site-specific methylation profile within exons 6-7 of the 53 gene was determined in control liver, preneoplastic nodules (after 36 weeks of folate/methyl deficiency) and in hepatocellular carcinoma (after 54 weeks of deficiency). A progressive loss of methyl groups was observed at most CpG sites on both coding and non-coding strands during the first 36 weeks of folate/methyl deficiency, with the greatest loss occurring on the coding strand. When the same sequence was evaluated in tumor DNA after 54 weeks of deficiency, the majority of cytosines were unexpectedly found to have become remethylated. CpG sites that had previously lost methyl groups on both strands during preneoplasia as well as CpG sites that had been constitutively non-methylated, had undergone de novo methylation in tumor DNA. Maintenance methyltransferase and de novo methyltransferase activity in nuclear extracts were assessed using hemimethylated and non-methylated DNA substrates, respectively. In tumor, de novo methyltransferase capacity was increased approximately 4-fold relative to control or preneoplastic liver and associated with a relative increase in both p53 and genome-wide methylation density. In the preneoplastic nodules, the level p53 mRNA was increased and associated with hypomethylation in the coding region of the gene, whereas in tumor tissue, p53 mRNA was decreased and associated with relative hypermethylation. Taken together, these results provide additional insights into the dysregulation and instability in DNA methylation that accompanies the transition to tumor.

Animals↗
PubMed1997

Characterization of cellular response to silicone implants in rats: implications for foreign-body carcinogenesis.

Foreign-body (FB) carcinogenesis is a classic model of multistage tumour development in rodents. Previous studies have demonstrated that the physical characteristics of the implant, and not the chemical composition, are the critical determinants of tumour development. The recent controversy over silicone breast implants has raised questions regarding the potential carcinogenicity of lifetime tissue exposure to silicone products. The present study was designed to determine whether the inflammatory and fibrotic reactions associated with silicone implants are due to a non-specific foreign-body reaction or whether these responses reflect the unique chemical composition of silicone. F344 rats were implanted subcutaneously with one of three biomaterials: silicone elastomer (Group 1); impermeable cellulose acetate filters (Group 2, positive control); or porous cellulose acetate filters (Group 3, negative control). The silicone and cellulose implants of Groups 1 and 2 have been previously shown to induce fibrosarcomas in rodents, whereas the porous cellulose acetate implants of Group 3 have been shown to be non-carcinogenic. One week and two months after implantation, the pericapsular tissues were evaluated using histopathological and in situ immunohistochemical analyses. Endpoints included expression of leucocyte antigens CD4 (T helper/inducer), CD8 (T suppressor/cytotoxic) and CD11 b/c (macrophage), proliferating cell nuclear antigen (PCNA) as an indicator of proliferation, and in situ end-labelling (ISEL) of 3'OH DNA strand breaks as an indicator of DNA damage and apoptosis. The results indicated that the acute and chronic cellular responses to silicone (Group 1) were not different from impermeable cellulose filters (Group 2) of identical size and shape, suggesting that these responses were not unique to silicone. The inflammatory response to the carcinogenic cellulose and silicone implants (Groups 1 and 2) was attenuated and associated with the formation of a thick fibrotic capsule. In contrast, the porous cellulose filters (Group 3) induced a markedly different cellular response in which the inflammatory reaction was more extensive, prolonged and associated with minimal fibrosis. Within the fibrotic capsule surrounding the tumorigenic implants, but not the non-tumorigenic implants, cell proliferation and apoptotic cell death were increased and associated with persistent DNA strand breaks. Taken together, the results suggest that the micrometre-scale surface morphology of the implant determines the nature of the subsequent cellular response which may predispose to tumour development. Further, these studies serve to emphasize the critical importance of appropriate physical controls in studies designed to evaluate carcinogenic or autoimmune manifestations associated with silicone implants in order to rule out the contribution of the chronic foreign-body reaction.

Acute Disease↗
PubMed1997

Presence and consequence of uracil in preneoplastic DNA from folate/methyl-deficient rats.

Uracil can arise in DNA by misincorporation of dUTP into nascent DNA and/or by cytosine deamination in established DNA. Based on recent findings, both pathways appear to be promoted in the methyl-deficient model of hepatocarcinogenesis. A chronic increase in the ratio dUTP:dTTP with folate/methyl deficiency can result in a futile cycle of excision and reiterative uracil misincorporation leading to premutagenic apyrimidinic (AP) sites, DNA strand breaks, DNA fragmentation and apoptotic cell death. The progressive accumulation of unmethylated cytosines with chronic methyl deficiency will increase the potential for cytosine deamination to uracil and further stress uracil mismatch repair mechanisms. Uracil is removed by a highly specific uracil-DNA glycosylase (UDG) leaving an AP site that is subsequently repaired by sequential action of AP endonuclease, 5'-phosphodiesterase, a DNA polymerase and DNA ligase. Since the DNA polymerases cannot distinguish between dUTP and dTTP, an increase in dUTP:dTTP ratio will promote uracil misincorporation during both DNA replication and repair synthesis. The misincorporation of uracil for thymine (5-methyluracil) may constitute a genetically significant form of DNA hypomethylation distinct from cytosine hypomethylation. In the present study a significant increase in the level of uracil in liver DNA as early as 3 weeks after initiation of folate/methyl deficiency was accompanied by parallel increases in DNA strand breaks, AP sites and increased levels of AP endonuclease mRNA. In addition, uracil was also detected within the p53 gene sequence using UDG PCR techniques. Increased levels of uracil in DNA implies that the capacity for uracil base excision repair is exceeded with chronic folate/methyl deficiency. It is possible that enzyme-induced extrahelical bases, AP sites and DNA strand breaks interact to negatively affect the stability of the DNA helix and stress the structural limits of permissible uracil base excision repair activity. Thus substitution of uracil for thymine induces repair-related premutagenic lesions and a novel form of DNA hypomethylation that may relate to tumor promotion in the methyl-deficient model of hepatocarcinogenesis.

Animals↗
PubMed1997

Apoptosis and proliferation under conditions of deoxynucleotide pool imbalance in liver of folate/methyl deficient rats.

Weanling male F344 rats were fed either a semi-purified diet low in methionine and lacking in choline and folic acid (folate/methyl deficient) or a supplemented control diet for periods of 2, 5, 7 days, 3 weeks, and 9 weeks. Two days after initiating the folate/methyl deficient diet in weanling F344 rats, the incidence of apoptotic bodies, identified by in situ end-labeling of 3'-OH DNA strand breaks, was significantly increased in liver sections from the deficient rats. Apoptotic cell death was confirmed biochemically by an increase in nuclear Ca2+/Mg2+-dependent endonuclease activity that paralleled the increase in apoptotic bodies over the 9-week feeding period. There was no morphologic evidence of necrotic foci or necrosis-associated inflammatory response over the 9-week period. Confirming that cell turnover is chronically elevated in this model, the increase in apoptotic rate was accompanied by a sustained increase in the mitotic index (MI). The DNA repair-associated enzyme, poly(ADPribose) polymerase (PARP), was similarly elevated and was associated with significant decreases in the substrate for ADPribose polymer synthesis, nicotinamide adenine dinucleotide (NAD). Because folate metabolites are essential for de novo purine and thymidine biosynthesis, prolonged deficiency in folic acid can induce an imbalance in the deoxynucleotide precursors for DNA replication/repair and negatively affect the fidelity of DNA synthesis. Using an HPLC method, hepatic deoxyuridine triphosphate (dUTP) levels were increased at 3 and 9 weeks after initiation of the deficient diet and levels of thymidine triphosphate (dTTP) were reduced. An increase in dUTP/ dTTP ratio is consistent with a block in folate-dependent de novo thymidylate biosynthesis and may predispose to uracil misincorporation and DNA repair-related DNA strand breaks.

Animals↗
PubMed1997

Chemoprevention of spontaneous tumorigenesis in nullizygous p53-deficient mice by dehydroepiandrosterone and its analog 16alpha-fluoro-5-androsten-17-one.

Transgenic mice with both alleles of the p53 tumor suppressor gene product 'knocked out' by gene targeting are susceptible to early development of tumors, chiefly lymphomas and sarcomas. Compared with the control group, administration of dehydroepiandrosterone (DHEA) at 0.3% of the diet to male p53-deficient mice extended their lifespan by delaying death due to neoplasms (from 105 to 166 days on study, P = 0.002), primarily by suppressing lymphoblastic lymphoma (from 45 to 6% of neoplastic deaths, P = 0.010). Treatment with a synthetic DHEA analog, 16alpha-fluoro-5-androsten-17-one (compound 8354), at 0.15% of the diet also increased lifespan, to 140 days for mice that developed tumors (P = 0.037). The effects of these steroids on lifespan and tumor development did not appear to be strongly related to inhibition of food consumption and weight gain, in that a group pair-fed with control diet to the reduced food consumption of the DHEA-treated group developed and died of the same types of neoplasms at the same rate as the controls fed ad libitum. The chemopreventive effect of these steroids has been proposed to be due to suppression of DNA synthesis by inhibition of glucose 6-phosphate dehydrogenase, the rate-limiting enzyme of the pentose phosphate pathway. Although DHEA and its analog are strong non-competitive inhibitors of this enzyme in vitro, treatment with DHEA did not deplete cellular nucleotide pools in the liver, as would have been predicted. The chemopreventive effect of DHEA in this model may be due to steroid-induced thymic atrophy and suppression of T cell lymphoma, permitting these mice to survive long enough to develop tumors with longer latency.

Androstenes↗
PubMed1997

Dietary nucleotides: effects on cell proliferation following partial hepatectomy in rats fed NIH-31, AIN-76A, or folate/methyl-deficient diets.

The requirement of a number of tissues for dietary nucleotides could explain some of the differences observed in animals fed natural ingredient diets vs. those fed purified diets lacking a source of dietary nucleotides. Lack of dietary nucleotides is exacerbated in animals fed folate- or methyl-deficient semipurified diets, in which both salvage and folate-dependent de novo synthetic pathways are diminished. We examined hepatocyte proliferation following partial hepatectomy in weanling male Fischer-344 rats fed natural ingredient NIH-31 diet, nucleotide-free purified AIN-76A diet or a basal diet similar to AIN-76A but deficient in the methyl donors folate, choline and methionine. Additional groups were fed AIN-76A or folate/methyl-deficient diets supplemented with 0.25% yeast RNA. Compared with NIH-31, AIN-76A increased dUMP/dTTP ratios, reduced the mitotic index (MI) and increased the ratio of proliferating cell index (PCI) to mitotic cells, an indication that hepatocytes were delayed in S-phase. Addition of yeast RNA to AIN-76A reversed (by approximately 50%) the effects of AIN-76A on dUMP/dTTP and cell proliferation. A folate/methyl-deficient diet also produced an increased dUMP/dTTP ratio and markedly reduced the MI, increasing the PCI/MI, which suggested even further delay of cells in S-phase. Addition of yeast RNA to the folate/methyl-deficient diet was effective in significantly reversing the effects of folate/methyl deficiency.

Animal Feed↗
PubMed1997

Where the sun never shines: anorectal melanoma.

BACKGROUND: Melanoma occurring in the anorectal region is recognized to be an uncommon tumour with a poor prognosis. Queensland has the highest incidence rate of cutaneous melanoma in the world. The purpose of the present study was to determine if the very high incidence of cutaneous melanoma in Queensland has any bearing on the incidence of anorectal melanoma, and to compare this with published studies from other parts of the world. An assessment of the authors' results in the treatment of anorectal melanoma was made by a review of patients presenting during the last decade throughout Queensland. METHODS: All cases of melanoma occurring in Queensland are accumulated in the Melanoma Register, administered by the Queensland Melanoma Project, and data from this were used to derive the results in the present study. Queensland population data were provided by the Australian Bureau of Statistics. RESULTS: During the study period 1985-95 in Queensland there were 21,391 cases of cutaneous melanoma which occurred in an average population, during that time, of 2.89 million. During the same time there were nine cases of anorectal melanoma, giving a relative incidence therefore of 0.04%. This contrasts with published relative incidences of 0.2% for white people in North America, 11% for Southwestern Native Americans, and 14.2% for Northern Pakistan (P < 0.0001). However, the population-based incidence rates of anorectal melanoma for Queensland, United States white people, Southwestern Native Americans and Northern Pakistan are not significantly different from each other. All patients in the present series presented with large tumours, and none survived beyond 25 months despite standard surgical and adjuvant therapy. CONCLUSIONS: The protection against cutaneous melanoma afforded by skin pigmentation is not apparent in the anal area. Anorectal melanoma is no more or less frequent in Queensland, even with the very high incidence rate of cutaneous melanoma. Sun exposure appears to be neither protective nor a risk factor. The outcome of therapy for this condition remains disappointing in the authors' experience.

Adult↗
PubMed1996

Laparoscopic versus open appendectomy: prospective randomized trial.

A prospective randomized trial comparing laparoscopic appendectomy with open appendectomy in patients with a diagnosis of acute appendicitis was conducted between October 1992 and April 1994. Of the 158 patients randomized, 7 patients were excluded because of protocol violations (conversion to laparotomy in 4, appendix not removed in 3). The 151 patients randomized to either a laparoscopic (n = 79) or an open appendectomy (n = 72) showed no difference in sex, age, American Society of Anesthesiology (ASA) rating, or previous abdominal surgery. The histologic classification of normal, catarrhal, inflamed, suppurative, and gangrenous appendicitis was not different between the two groups. Conversion from laparoscopic to open appendectomy was necessary in seven patients (9%) who had advanced forms of appendiceal inflammation. When compared to open appendectomy the laparoscopic group had a longer median operating time (63 minutes versus 40 minutes), fewer wound infections (2% versus 11%), less requirement for narcotic analgesia, and an earlier return to normal activity (median 7 days versus 14 days). There was no difference in morbidity, and both groups had a median time to discharge of 3 days. Laparoscopic appendectomy is as safe as open appendectomy; and despite the longer operating time, the advantages such as fewer wound infections and earlier return to normal activity make it a worthwhile alternative for patients with a clinical diagnosis of acute appendicitis.

Adolescent↗
PubMed1996

Colorectal injury: where do we stand with repair?

BACKGROUND: The chief danger of colonic injury is sepsis resulting from faecal spill. Primary repair is now well established in the USA, particularly injuries, in up to 81% of patients. However, in Australia, highly destructive blunt trauma forms a larger proportion of injuries, and the purpose of this study was to determine if there are any contrasts in the management of these patients. METHOD: A retrospective survey was undertaken over the past 20 years of all of the patients with full-thickness colorectal injuries presenting at the three major hospitals which receive multi-trauma patients in Brisbane. RESULTS: Of 112 patients 114 sustained full-thickness colorectal injuries. Forty patients had penetrating injuries, 41 had blunt injuries and 33 had iatrogenic injuries. Primary repair or resection and anastomosis was performed in 39% of patients with colonic injuries and the leak rate was 8%. Exteriorized repairs had a 67% leak rate. A colostomy was used in 58% of patients. The mortality for penetrating injuries was zero. The mortality for blunt colonic injuries was 17% and for iatrogenic injuries was 7%, but for blunt rectal injuries was 50%. The overall mortality was 10%. Colostomy closure had a 20% morbidity but no mortality. CONCLUSIONS: In the absence of shock, associated injuries, or gross faecal soiling primary repair or resection with anastomosis may be considered. For blunt injury, colostomy is still usually indicated, often with resection. For iatrogenic injury, when seen early, primary repair can be performed. We do not recommend exteriorized repair. Extraperitoneal rectal injuries require proximal colostomy and distal washout, with drainage where appropriate. Blunt devitalizing injury is relatively more common in Australia than in the USA, and therefore there is less indication here for primary repair. Colostomy remains an important consideration in operative management.

Anastomosis, Surgical↗
PubMed1996

Conjunctival mycobacteriosis in two emus (Dromaius novaehollandiae).

Avian tuberculosis was diagnosed in two young adult female commercial emus (Dromaius novaehollandiae) with granulomatous conjunctivitis. Histologically, the granulomas appeared typical of avian tuberculosis. Caseonecrotic cores were surrounded by a broad ring of palisading epithelioid macrophages and multinucleate giant cells with a moderate admixture of heterophils, lymphocytes, and plasma cells. One conjunctival granuloma had multifocal mineralization. At necropsy, granulomas were also found in visceral organs of both birds. Acid-fast bacilli were demonstrated in all lesions using Ziehl-Neelsen or Fite's stains. Culture confirmed the bacilli to be Mycobacterium avium (complex).

Animals↗
PubMed1995

Breaks in genomic DNA and within the p53 gene are associated with hypomethylation in livers of folate/methyl-deficient rats.

Male weanling Fischer 344 rats were fed either a semipurified diet deficient in the methyl donors methionine, choline, and folic acid or a supplemented control diet for a period of 9 weeks. At intervals of 2, 5, and 7 days, 3 weeks, and 9 weeks after initiation of the respective diets, the relative level of DNA strand breaks and the degree of cytosine methylation were quantified in high molecular weight DNA and also within the p53 gene in liver samples from these rats. Genome-wide strand break accumulation was associated with progressive genomic hypomethylation and increased DNA methyltransferase activity. With the use of quantitative PCR as a gene-specific DNA strand break assay, unique DNA strand breaks were detected in exon 5 but not in exons 6-8 of the p53 gene, and were accompanied by significant p53 gene hypomethylation. DNA hypomethylation has been shown to alter the conformation and stability of the chromatin structure, rendering affected regions more accessible to DNA-damaging agents. To determine whether methylation status alters the sensitivity of DNA to strand breakage, DNA in isolated nuclei was methylated in vitro and exposed to endogenous calcium/magnesium-dependent endonuclease activated under defined conditions. The incidence of enzyme-induced DNA strand breaks was decreased significantly with increased DNA methylation. In nuclei isolated from livers of methyl-deficient rats, the hypomethylated DNA was found to be more sensitive to enzyme- and oxidant-induced DNA strand break induction. Taken together, these results provide evidence that DNA strand breaks are induced in high molecular weight DNA and also within the p53 gene in liver tissue from methyl-deficient rats. The increased incidence of these strand breaks in DNA from methyl-deficient rats may be related to alterations in chromatin accessibility associated with DNA hypomethylation.

Animals↗
PubMed1995

Detection of autoantibodies to SS-A/Ro by indirect immunofluorescence using a transfected and overexpressed human 60 kD Ro autoantigen in HEp-2 cells.

The objective of the study was to determine the sensitivity and specificity of an indirect immunofluorescence (IIF) assay using transfected HEp-2 cells to detect anti-SS-A/Ro autoantibodies in human sera. Seventy-three sera having SS-A/Ro autoantibodies as determined by double immunodiffusion (ID) and immunoblotting (IB) were tested by IIF on a HEp-2 cell substrate that had been transfected with a full-length cDNA encoding a human 60 kD SS-A/Ro autoantigen. Controls included 30 normal human sera and 50 sera with a variety of other antinuclear antibodies. Prototype human and rabbit sera directed against the 60 kD SS-A/Ro antigen produced intense speckled nuclear and nucleolar staining of transfected cells. Sixty-nine of 73 (95%) SS-A/Ro positive sera also produced this characteristic staining pattern. The endpoint autoantibody titers on transfected cells was fivefold greater than on untransfected cells. The 30 normal human sera and the 50 sera with other antinuclear antibodies did not produce this characteristic staining. Six of 32 (19%) unselected sera that were sent for autoantibody testing had reactivity with transfectants by IIF. Four of the six sera were confirmed to have anti-SS-A/Ro antibodies by ID and 5/6 by IB. By contrast, only three of these sera were scored as having a staining pattern compatible with SS-A/Ro antibodies by IIF on standard HEp-2 substrates. We conclude that SS-A/Ro autoantibodies can be detected by an IIF assay using a HEp-2 cell substrate transfected with a SS-A/Ro cDNA. This new substrate detects SS-A/Ro antibodies that were not identified on standard HEp-2 substrates and by other immunoassays.

Autoantibodies↗
PubMed1994

In vitro folate deficiency induces deoxynucleotide pool imbalance, apoptosis, and mutagenesis in Chinese hamster ovary cells.

The genetic and epigenetic effects of nutritional folate deficiency were studied in two Chinese hamster ovary (CHO) cell lines. The CHO-AA8 cell line (hemizygous at the aprt locus) and CHO-UV5 (DNA repair-deficient mutant of AA8) were cultured in Ham's F-12 medium or in custom-prepared Ham's F-12 medium lacking folic acid, thymidine, and hypoxanthine. Cells cultured acutely in the folate deficient medium exhibited initial growth arrest, followed by massive cell death and DNA fragmentation into nucleosomal multimers characteristic of apoptosis. Although prolonged culture in the folate deficient medium was cytostatic and lethal to the majority cells, minor subpopulations in both cell lines failed to initiate cell death, exhibited phenotypic abnormalities, and adapted a selective growth advantage under marginal folate conditions. These "resistant" clones exhibited major alterations in deoxynucleotide pools associated with an increase in mutant frequency at the aprt locus as detected by resistance to cytotoxicity in 8-azaadenosine. The mutation frequency in the DNA repair-deficient CHO-UV5 cells was approximately 100-fold greater than that in the parental AA8 clones, underscoring the importance of DNA repair under conditions of folate deficiency and nucleotide pool imbalance. The enhanced mutation frequency in the DNA repair-competent folate-deficient CHO-AA8 cells suggests that DNA repair activity is less effective under folate-deficient conditions. These results add to the accumulating clinical and experimental evidence relating chronic folate deficiency to genomic instability and carcinogenesis.

Animals↗
PubMed1993

A simplified HPLC method for simultaneously quantifying ribonucleotides and deoxyribonucleotides in cell extracts or frozen tissues.

Agents and conditions that induce alterations in deoxyribonucleotide pools can have important regulatory effects on the rate of DNA synthesis as well as cell cycle progression. A simplified procedure for the separation of both ribonucleoside triphosphates (NTP) and deoxyribonucleoside triphosphates (dNTP) is presented which utilizes reversed phase high-performance liquid chromatography coupled with diode array detection. The simultaneous resolution of NTP and dNTP peaks within the same cell extract effectively eliminates the need for post-extraction steps such as periodate oxidation and/or boronate affinity chromatography previously used to degrade or isolate co-eluting NTP from dNTP. The resolution of two nucleotides, dGTP and ADP, was found empirically to vary with the efficiency of the C18 column. High efficiency columns (> 90,000 plates/m) provided good separation; however, less efficient columns resulted in co-elution of dGTP and ADP. These co-eluting nucleotides can be accurately quantified, if necessary, using diode array technology and a mathematical expression which incorporates molar peak coefficients and peak areas obtained by monitoring at dual wave-lengths. Tissue samples or single cell suspensions were extracted with trichloroacetic acid and the neutralized extract was injected directly into the column without prior lyophilization. The per cent recovery of standards was > or = 99% and replicate extractions within or between samples were highly reproducible (SD < 5%). The single step method described minimizes potential losses associated with post-extraction manipulation and provides the capability to examine alterations in nucleotide precursor-product metabolism under various physiological and pharmacological conditions.

Adenosine Diphosphate↗