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Biomedical subjects

R G Richards

Publications and source records attributed to R G Richards.

70 records · Page 4Linked to original sources
PubMed1988

Comparison of virologic and serologic responses of lambs and calves infected with bluetongue virus serotype 10.

Four lambs and 3 calves, seronegative to bluetongue virus (BTV), were inoculated intravenously with a highly plaque-purified strain of BTV Serotype 10. A single calf and lamb served as controls and were inoculated with uninfected cell culture lysate. All BTV-inoculated lambs exhibited mild clinical manifestations of bluetongue, whereas infected calves were asymptomatic. Viremia persisted in BTV-infected lambs for 35-42 days, and for 42-56 days in BTV-infected calves. Neutralizing antibodies were first detected in sera collected at Day 14 post-inoculation (PI) from 2 BTV-infected calves and all 4 infected lambs, and at Day 28 PI in the remaining calf. The appearance of neutralizing antibody in serum did not coincide with clearance of virus from blood; BTV and specific neutralizing antibody coexisted in peripheral blood of infected lambs and calves for as long as 28 days. The sequential development, specificity and intensity of virus protein-specific humoral immune responses of lambs and calves were evaluated by immunoprecipitation of [35S]-labelled proteins in BTV-infected cell lysates by sera collected from inoculated animals at bi-weekly intervals PI. Sera from infected lambs and calves reacted most consistently with BTV structural proteins VP2 and VP7, and nonstructural protein NS2, and less consistently with structural protein VP5, and nonstructural protein NS1. Lambs developed humoral immune responses to individual BTV proteins more rapidly than calves, and one calf had especially weak virus protein-specific humoral immune responses; viremia persisted longer in this calf than any other animal in the study. The clearance of virus from the peripheral blood of BTV-infected lambs and calves is not caused simply by the production of virus-specific neutralizing antibody, however the intensity of humoral immune responses to individual BTV proteins might influence the duration of viremia in different animals.

Animals↗
PubMed1988

Bluetongue virus genome remains stable throughout prolonged infection of cattle.

Infection of three calves with a highly plaque-purified strain of bluetongue virus (BTV) resulted in prolonged infections, during which virus and neutralizing antibodies co-circulated in peripheral blood. Oligonucleotide fingerprint analyses of the original challenge virus and of the final virus isolate obtained from each calf demonstrated the BTV genome to remain stable throughout prolonged infection as no differences in fingerprint patterns were detected. Six neutralizing monoclonal antibodies (MAbs), and a polyclonal rabbit antiserum, were produced against the challenge virus. This panel of MAbs recognized at least two distinct neutralizing epitopes as demonstrated by immune precipitation. Neutralizing epitopes remained stable through the prolonged infections, as all MAbs and the polyclonal rabbit antiserum neutralized the challenge virus and the final calf isolates to equivalent titres. These results suggest that antigenic drift is not the mechanism by which BTV is able to persist in cattle in spite of a strong humoral immune response.

Animals↗
PubMed1987

Vitreous humor chemistry: the use of potassium concentration for the prediction of the postmortem interval.

Upon review of the literature, extensive disagreement was found as to the usefulness of vitreous humor potassium concentration as a predictor of the postmortem interval (PMI). A pilot study of 1427 cases was performed to address this problem. The requisite statistical analysis for the prediction of PMI is inverse prediction. The 95% inverse prediction interval was found to be approximately +/- 20 h. The linear regression equation for the data was y = 0.238 chi + 6.342, with a coefficient of determination (r2) of 0.374. This r2 value means that 62.6% of the variation of potassium is unaccounted for by the variation in PMI. Further studies are required to attribute this unaccounted variation to quantifiable factors. This would narrow the inverse prediction interval and enable vitreous potassium to be a useful aid in the prediction of PMI.

Adolescent↗
PubMed1986

Induction of 2',5'-oligoadenylate synthetase activity in peripheral blood mononuclear cells by gamma interferon.

Activity of the interferon-induced enzyme 2',5'-oligoadenylate (2-5A) synthetase was measured in peripheral blood mononuclear cells (PBMC) of 32 cancer patients treated with recombinant human gamma-interferon (rHGIF). Pretreatment activities varied widely but remained constant for each individual. The minimum dose of rHGIF that consistently stimulated activity was 12 MU/m2, although in some patients as little as 0.004 MU/m2 was stimulatory. Enzyme activity in responding patients increased threefold at 24 h after the initial infusion and remained elevated nearly twofold at 72 h independent of dose. This increase is less than that observed after infusions of alpha-interferon and parallels results observed in vitro. Pretreatment enzyme activity did not correlate with response. Twenty-minute infusions of a fixed dose were as effective as four- and 24-h infusions in raising enzyme levels. The level of activity achieved after the initial infusion could not be sustained with twice-weekly infusions. We conclude that rHGIF does induce 2-5A synthetase activity in PBMC but not to the levels induced by alpha-interferon. The observation that brief infusions of low doses can be maximally stimulatory in vivo suggests that the response of PBMC in vivo is being confounded by factors yet to be determined. Furthermore, it appears that the capacity of PBMC to maximally respond to rHGIF in vivo, with increases in enzyme activity, is transient.

2',5'-Oligoadenylate Synthetase↗
PubMed1986

Drug concentration-dependent DNA lesions are induced by the lipid-soluble antifolate, piritrexim (BW301U).

The lipid-soluble folate antagonist, 2,4-diamino-6-(2,5-dimethoxybenzyl)-5-methylpyrido[2,3-d]pyrimidin e (piritrexim; BW301U), induced misincorporation of dUMP in human B (SB)- and T (MOLT-4)-lymphoblastoid cells, and in human promyelocytic leukemia cells (HL-60). Analysis by alkaline sucrose gradients and alkaline elution indicated that 3H-DNA that had been labeled for 15 min distributed into progressively smaller DNA fragment sizes in a drug concentration-dependent manner from 0 microM to 50 microM piritrexim. This phenomenon was observed regardless of the labeled nucleotide precursor employed for detection of newly synthesized DNA [( 3H]deoxyuridine, [3H]deoxyadenosine, or [3H]deoxycytidine). In contrast, formaldehyde denaturation and sedimentation of DNA in neutral denaturing sucrose gradients released only 3-4% of the newly synthesized DNA as 3S-6S fragments (80-200 nucleotides), whereas the remaining population of newly synthesized DNA pelleted to the bottom of the tube. Failure to detect DNA fragmentation under neutral conditions to the extent observed under alkaline conditions indicated the presence of apurinic and apyrimidinic sites in DNA--lesions which would be expected in DNA undergoing excision-repair of misincorporated dUMP. Cytotoxicity resulting from dUMP misincorporation was consistent with the enhanced toxicity of piritrexim which was observed when HL-60 cells or MOLT-4 cells were exposed concurrently to exogenous deoxyuridine. Deoxyuridine-enhanced toxicity was demonstrated to be concentration dependent for both cell lines when piritrexim concentrations were marginally toxic. The cytotoxic effect of dUMP misincorporation was further substantiated by the observation that MOLT-4 cells treated with 0.5 microM piritrexim alone eventually developed resistance to the drug, whereas treatment with both piritrexim and 10 microM deoxyuridine prevented the selection of piritrexim-resistant cells.

B-Lymphocytes↗
PubMed1985

Misincorporation of deoxyuridine in human cells: consequences of antifolate exposure.

Treatment of B and T lymphoblastoid cell lines (SB and MOLT-4, respectively) and a promyelocytic leukemia cell line (HL-60) with the lipid soluble antifolate, 2,4-diamino-5-methyl-6-(2',5'-dimeth-oxybenzyl) -pyrido (2,4-d) pyrimidine (BW301U), led to drug dose-dependent inhibition of [3H]deoxyuridine (dU) incorporation into DNA as thymidine, and to misincorporation of [3H]dU as dUMP. After a 15 min preincubation with up to 50 microM BW301U and a further 15 min incubation after addition of [3H]dU, the number of alkaline labile apyrimidinic sites increased with increasing drug dose, as demonstrated by alkaline sucrose gradient analysis. Significantly, new replication of DNA was inhibited only approximately 50% by 50 microM BW301U when [3H]dU incorporation was greater than or equal to 97% inhibited. Additional preliminary findings suggest that newly replicated DNA containing misincorporated dUMP is rapidly degraded in vivo by extensive excision-repair processes.

B-Lymphocytes↗
PubMed1985

Digoxin-like immunoreactive substance in postmortem blood of infants and children.

A digoxin-like immunoreactive substance (DLIS) has been reported in the serum of infants not receiving digoxin. This study was undertaken to determine if DLIS is present in the postmortem blood and tissues of infants or children and whether the endogenous substance could interfere with forensic toxicological analysis in suspected overdose. Ninety blood specimens taken from the heart at autopsy of children or infants were screened for DLIS using commercial radioimmunoassay kits. The average age at death in these cases was 8.6 months, the median age was 2 months. DLIS equivalent to 0.25 to 2.0 ng/mL digoxin was found in one third of the cases. The incidence of positive findings was 5/6 stillborns, 10/45 Sudden Infant Death Syndrome (SIDS), 10/15 deaths as a result of infection, 4/7 homicides, 1/8 deaths caused by congenital defects, and 0/9 accidental deaths. The body distribution of DLIS was investigated and highest levels were found in the liver. Findings of DLIS in blood were correlated with renal failure, (elevated vitreous urea nitrogen), electrolyte imbalance, and liver trauma. Apparent concentrations were in the equivalent therapeutic range of digoxin and would not be confused with accidental or intentional overdose with digoxin.

Autopsy↗
PubMed1984

The occurrence and consequences of deoxyuridine in DNA.

Deoxyuridine can become resident in the DNA of prokaryotic and eukaryotic cells via two general mechanisms - deamination of cytosine to uracil, and nucleotide pool changes that lead to misincorporation of deoxyuridine in place of thymidine. In this paper we have examined the chemical basis of deamination reactions in DNA and discussed a possible mechanism for an increased rate of deamination by means of cross-strand protonation of cytosine by alkylated guanine. In addition, we have examined the genetic and drug-induced conditions that lead to dUMP misincorporation into DNA in place of thymidine and have presented experimental evidence indicating that the antifolate-induced lesion is a general drug-dose dependent lesion of human blood cells. Finally, the toxic and genetic impact of this lesion has been evaluated within the context of a review of the repair mechanisms elicited by dUMP in DNA.

Base Composition↗
PubMed1983

Sudden Infant Death Syndrome: a biochemical profile of postmortem vitreous humor.

Postmortem chemical analysis of vitreous humor from Sudden Infant Death Syndrome (SIDS) infants was done. The results were compared to a pediatric control group. The concentrations of potassium, calcium, phosphorus, glutamic oxaloacetic transaminase, glutamic pyruvate transaminase, creatinine phosphokinase, and lactate dehydrogenase were all significantly different from the pediatric control group. Thus it appears that SIDS infants are a different population from the pediatric control group.

Enzymes↗
PubMed1981

The use of brain digoxin concentrations to confirm blood digoxin concentrations.

Recent research suggests that the cardiotoxic as well as the neurotoxic effects of digitalis may be mediated by the central nervous system. Therefore brain regions implicated in the genesis of cardiac rhythm disorders were assayed for digoxin. An 125I-labeled radioimmunoassay was used to determine blood and tissue digoxin concentrations. Digoxin was found in the optic tract and optic chiasm in each of four persons who had been taking digoxin regularly. Digoxin is apparently concentrated from blood by the choroid plexus of the fourth ventricle but not by the choroid plexus of the lateral ventricle. However, digoxin was present in the area postrema and nucleus of the vagus only in the two digoxin overdose cases. Digoxin was not detected in any of the other brain regions analyzed. The presence of digoxin in the area postrema (the chemoreceptor trigger zone) and the nucleus of the vagus in the toxic but not in the therapeutic cases suggests a mechanism for the emesis and cardiac arrest brought about by digoxin toxicity in humans. The digoxin content of the medulla, especially the surface of the medulla under the obex, may be useful in confirmation of elevated blood digoxin concentrations.

Aged↗
PubMed1976

Death from intravenously administered narcotics: a study of 114 cases;.

A careful study of more than 100 fatal cases due to intravenously administered narcotics provides further evidence of the complexity involved in the certification of death. The wide range of blood morphine concentrations found in these cases indicates that tissue concentrations alone will not always provide the necessary information. High concentrations of morphine, the major metabolite of heroin, in blood and other tissues may be consistent with overdose. But in those cases involving very low concentrations at the time of death, other criteria must be considered.

Adolescent↗
PubMed1975

A simple, rapid method for measurement of acetate in tissue and serum.

A simple and rapid method is described for determining the free acetate concentration in liver and serum. After extraction, the acetate is converted to its benzyl ester by thermal degradation of its benzyldimethylphenylammonium salt in the vaporizer of a gas chromatography. Good quantitation is achieved in the range of 0.033-2.5 mumoles of acetate per gram of liver or per milliliter of serum.

Acetates↗