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Biomedical subjects

M R White

Publications and source records attributed to M R White.

At least 91 records · Page 5Linked to original sources
PubMed1989

Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen.

Early Earth and early Mars were similar enough such that past geochemical and climatic conditions on Mars may have also been favorable for the origin of life. However, one of the most striking differences between the two planets was the low partial pressure of dinitrogen (pN2) on early Mars (18 mb). On Earth, nitrogen is a key biological element and in many ecosystems the low availability of fixed nitrogen compounds is the main factor limiting growth. Biological fixation of dinitrogen on Earth is a crucial source of fixed nitrogen. Could the low availability of dinitrogen in the primordial Martian atmosphere have prevented the existence, or evolution of Martian microbiota? Azotobacter vinelandii and Azomonas agilis were grown in nitrogen free synthetic medium under various partial pressures of dinitrogen ranging from 780-0 mb (total atmosphere=1 bar). Below 400 mb the biomass, cell number, and growth rate decreased with decreasing pN2. Both microorganisms were capable of growth at a pN2 as low as 5 mb, but no growth was observed at a pN2 < or = 1 mb. The data appear to indicate that biological nitrogen fixation could have occurred on primordial Mars (pN2=18 mb) making it possible for a biotic system to have played a role in the Martian nitrogen cycle. It is possible that nitrogen may have played a key role in the early evolution of life on Mars, and that later a lack of available nitrogen on that planet (currently, pN2=0.2 mb) may have been involved in its subsequent extinction.

Atmosphere↗
PubMed1989

Experimental visceral leishmaniasis in the opossum.

Adult wild-trapped opossums were infected with Leishmania donovani (Khartoum strain, WR 378) and evaluated as an animal model of visceral leishmaniasis. All infected opossums died within 32 days. Loss of body fat, hepatomegaly, and petechiae of skin and abdominal musculature were seen at necropsy. Microscopically, numerous amastigote-laden macrophages were seen in histologic sections of liver, spleen, and lymph nodes; fewer parasite-laden macrophages were in the bronchial-associated lymphoid tissues and renal glomeruli. Hematological findings included thrombocytopenia (terminal), neutropenia, and lymphopenia. Blood lymphocyte blastogenesis in response to concanavalin A and phytohemagglutinin was decreased markedly at day 24 post-infection (PI). Serum antibodies (1:40 dilution) to promastigotes of L. donovani were detected in five of eight infected opossums tested on days 10 and 24 PI. Total bilirubin concentrations and alanine aminotransferase and aspartate aminotransferase activities were increased after day 25 PI. Activated partial thromboplastin times and one-stage prothrombin times were prolonged before death. Concurrently, factors V, VIII, and XII activities were decreased.

Animals↗
PubMed1989

Chemotherapy of experimental visceral leishmaniasis in the opossum.

Visceral leishmaniasis is a severe chronic disease of people and animals. The disease is caused by several subspecies of a protozoal organism, Leishmania donovani. If not treated, visceral leishmaniasis is often fatal. The most commonly used chemotherapeutic agents to treat the disease are pentavalent antimonials, which can be toxic, must be administered by parenteral routes, and are sometimes ineffective. In this study, meglumine antimoniate, a pentavalent antimony, was compared with WR 6026, an 8-aminoquinoline derivative, as to antileishmanial efficacy. The results indicate that either of these 2 drugs are effective in the suppression of amastigotes in the liver and spleen of the opossum. Despite the marked parasite suppression in the liver and spleen of the infected opossums, the experimental disease was fatal in all of the infected opossums, regardless of the therapy.

Aminoquinolines↗
PubMed1989

A comparison of experimental visceral leishmaniasis in the opossum, armadillo and ferret.

Visceral leishmaniasis is a severe, chronic protozoal disease of humans and animals. Although chemotherapeutic agents are available for the treatment of this disease, problems such as drug toxicity, drug ineffectiveness and drug resistance of the parasite are responsible for treatment failures. To determine whether a drug is a potential antileishmanial agent, screening tests are performed using in vitro and in vivo models. Subsequently, a study using an appropriate animal model is performed to clearly determine the efficacy of a drug against Leishmania. Due to current public concerns regarding the use of companion animals in addition to the high costs of obtaining and maintaining these animals for research use, conventional animal models used in these chemotherapy studies, notably the dog and monkey, are becoming less acceptable. Therefore, new, less expensive and more accessible animal models are needed for the study of antileishmanial compounds. In this study, the armadillo, ferret and opossum were evaluated as possible new animal models for visceral leishmaniasis. The marked body weight loss, hepatomegaly, splenomegaly, large amastigote densities and the microscopic lesions observed in the infected opossums indicated that the opossum was more susceptible to visceral leishmaniasis than the armadillo or ferret.

Animals↗
PubMed1988

Desmin as a marker for canine botryoid rhabdomyosarcomas.

The intermediate filament desmin was present in three canine botryoid rhabdomyosarcomas. The use of desmin as a diagnostic tool may, as in these tumours in man, be of value in the classification of canine sarcomas where the origin of the tumour is not always apparent from routine histological sections.

Animals↗
PubMed1986

A nephrotic-like syndrome with an associated mesangio-proliferative glomerulopathy in a cow.

A 3-year-old Limousin cow was admitted to the University of Georgia Teaching Hospital with a history of chronic weight loss and diarrhea of more than 1 year's duration. Clinical laboratory findings included proteinuria and hypoproteinemia and were suggestive of a nephrotic-like syndrome. Necropsy findings included generalized edema of the visceral organs and diffuse red glistening foci on the capsular and cut surfaces of the cortex of both kidneys. Microscopically, the kidney had hypercellular and hypersegmented glomeruli, focal glomerulosclerosis, periglomerular fibrosis, and tubular nephrosis. The glomerular hypercellularity was confirmed by electron microscopy to be due to increased mesangial cells.

Animals↗
PubMed1984

A comparison of total white blood cell counts on the Technicon H6000 and Coulter Counter Model ZBI in an occupational health program.

White blood cell (WBC) counts obtained using a Technicon H6000 in a large occupational health program were compared with counts obtained on identical samples using a Coulter Counter Model ZBI. To assure quality control and to assess the comparability of results obtained on the two machines, a 25% systematic sample (N = 586) of analyses performed on the Technicon were performed independently and blindly on the Coulter Counter. The Pearson product-moment-correlation between WBC counts from the two machines was r = 0.94 (P less than or equal to 0.0001). The mean WBC count was 6,664 cells/mm3 for the Technicon and 6,790 cells/mm3 for the Coulter Counter. The estimated prevalence of leukopenia (WBC counts less than or equal to 4,500 cells/mm3) was 10.6% using the Technicon and 9.7% using the Coulter Counter. The results demonstrate that the two machines provide results that can be compared directly without corrections.

Humans↗
PubMed1981

Identity of two syndromes. Proteolytic, lipolytic, and amylolytic deficiency of the exocrine pancreas with congenital anomalies.

We describe further a patient previously reported to have "proteolytic and lipolytic deficiency of the exocrine pancreas." Features not previously reported include absent permanent teeth, hypoplastic alae nasi, scalp defect, normal thyroid function, and normal gonadotropins. Moreover, the normal amylase activity initially assumed to be of pancreatic origin proves to be of salivary origin. Thus the pancreatic deficiency is not only proteolytic and lipolytic but amylolytic as well. This disorder is identical with the "syndrome of congenital aplasia of the alae nasi, deafness, hypothyroidism, dwarfism, absent permanent teeth and malabsorption" subsequently reported by Johanson and Blizzard. The euthyroid status of this patient and that of another described in the literature suggest that hypothyroidism is probably not a major feature of this disorder. Our studies point to deficiency of the exocrine pancreas as the major cause of growth failure.

Amylases↗
PubMed1978

Inherited partial trisomy 8q (22 leads to qter).

We report clinical observations and cytogenetic studies of an inherited form of partial trisomy 8q. Although complete trisomy 8 has in recent years proven to be a clinically recognizable syndrome, partial trisomy 8q has been documented in only six individuals. Of these, five were familial and also partially trisomic for chromosome 22. There has been only one prior report of partial trisomy 8q without partial trisomy 22. Review of these cases provides support for the recent suggestion that the phenotype of trisomy 8 may be caused principally by trisomy of the distal segment of 8q.

Abnormalities, Multiple↗
PubMed1977

Benzocaine-induced methemoglobinemia.

Severe methemoglobinemia developed in a healthy 14-month-old infant following the topical application of a benzocaine-containing gel administered for the relief of the discomfort of teething. Congenital methemoglobinemia and hemoglobin M disease were excluded by appropriate laboratory studies. The patient is considered to have a normal methemoglobin-reducing capacity and her response to the drug is one that presumably could occur in any other child of comparable age on receiving an equivalent dose of benzocaine. Parents should be cautioned against the indiscriminate use of similar medications, particularly since the process for which these medications are administered is both benign and physiologic.

Administration, Topical↗
PubMed1976

Amylase polymorphism: studies of sera and duodenal aspirates in normal individuals and in cystic fibrosis.

Prior genetic studies of the human pancreatic amylase (Amy2) locus have been directed principally to the electrophoretic analysis of serum and urine, on the assumption that these fluids receive negligible contributions from the salivary (Amy 1) locus. In support of that assumption was the observation that the isozyme bands were lacking in patients with cystic fibrosis and in a postpancreatectomy patient. We have examined the sera of 97 patients having cystic fibrosis and find normal levels of serum amylase. On electrophoresis, three-quarters of the cystic fibrosis patients have a pattern (F-pattern) not observed in normal sera. The pattern is characterized by the absence of Pa 1. Comparative electrophoresis and mixing experiments indicate that the F-pattern is of salivary origin and is unmasked in cystic fibrosis by the absence of a pancreatic contribution. The normal serum pattern is considered to be an admixture of salivary and pancreatic amylase. On the assumption that duodenal fluids might more closely reflect the pancreatic (Amy 2) locus, electrophoretic studies were performed on 148 normal individuals and 37 individuals with cystic fibrosis. Electrophoretic phenotypes in duodenal aspirates are more complex than previously reported in studies of urine and serum; presumably because of the higher concentrations of amylase in the aspirates. Comparative electrophoresis and mixing experiments indicate that the phenotypes observed in duodenal aspirates also reflect admixture of pancreatic and salivary amylase. This recognition of pancreatic and salivary admixture in sera fortunately does not alter our prior understanding of the genetics of the Amy 2 polymorphism. The extensive studies which led to the delineation of the Amy 2 polymorphism were essentially based on the presence or absence of a variant band which proves now to be outside the zone of admixture.

Amylases↗
PubMed1975

Further identification of a D/E translocation.

An infant previously reported to have psychomotor retardation and multiple congenital anomalies including hypotonia, failure to thrive, peculiar facies, low-set ears, micrognathia, and cryptorchidism in association with monosomy due to a D/E (13-15/17-18) translocation has been reexamined. Further cytogenetic studies, using fluorescent techniques, indicate the translocation involves chromosomes 15 and 17. Only two other patients with partial monosomy due to grossly similar D/E translocations have been reported. On reexamination, the translocation in one has recently been found to involve chromosomes 15 and 18 and that in the other has not been further defined.

Abnormalities, Multiple↗
PubMed1975

Double aneuploidy. Turner-Down syndrome.

Double aneuploidy involving Down and Turner syndromes is a rare occurrence. Of the six patients reported to have combined Down and Turner syndromes, four fundamentally different forms of chromosome mosaicism have been noted and all have been mosaic with respect to monosomy X. Reported here is the first example of a Turner-Down patient in whom there is no X mosaicism. The different forms of the double aneuploidy cannot be explained by any single combination of nondisjunctional errors. The clinical findings in these patients and the several mechanisms of nondisjunctional error that may account for the observed forms of aneuploidy are reviewed and discussed.

Aneuploidy↗