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Biomedical subjects

K Mason

Publications and source records attributed to K Mason.

At least 91 records · Page 5Linked to original sources
PubMed1983

Asymmetrical noise exposure and hearing loss among shingle sawyers.

Shingle sawyers are exposed to noise predominantly from the left side. This study examined the asymmetry in hearing loss among shingle sawyers and its possible relation to the difference in noise exposure to the two ears. The results suggest that the lateral difference in noise exposure in industry, even in the obvious case of a shingle sawyer, is small. The resulting asymmetrical noise-induced hearing loss is also relatively small. Therefore, significant asymmetry in hearing loss in this type of occupation should be viewed with caution. Special tests and medical examination should be undertaken to determine if there are other contributing factors.

Adult↗
PubMed1982

Specificity of amino acids as activators and substrates for phenylalanine hydroxylase.

Rat liver phenylalanine hydroxylase can be markedly activated by a variety of different procedures including those that lead to covalent modification of the enzyme, such as limited proteolysis by alpha-chymotrypsin and alkylation of sulfhydryl groups by N-ethylmaleimide, and those that lead to reversible changes, such as the interaction of the enzyme with lysolecithin and related compounds. These treatments not only lead to increased activity toward the normal substrate for the enzyme, phenylalanine, but they lead to even greater increases in activity toward normally poor substrates such as m-tyrosine. Activations of this type, therefore, in effect, appear to broaden the amino acid specificity of the enzyme. We have now found that the extent of the change in substrate specificity on activation of the enzyme is much greater than had been heretofore realized. Indeed, the lysolecithin-activated enzyme is able to act on nonaromatic amino acids such as methionine and norleucine, catalyzing their conversion to methionine sulfoxide and epsilon-hydroxynorleucine, respectively. These amino acids are also substrates for phenylalanine hydroxylase that has been activated by limited proteolysis with alpha-chymotrypsin and by reaction with N-ethylmaleimide. By contrast, the unactivated hydroxylase as little or no activity toward methionine and norleucine. Rat liver phenylalanine hydroxylase can also be activated by its substrate, phenylalanine. We have now found that the novel substrates, methionine and norleucine, are also able to activate the enzyme. On a molar basis, however, they are not as active as phenylalanine. A model that can account for the broadened substrate specificity of the activated enzyme is discussed.

Amino Acids↗
PubMed1981

Outbreak of aplastic crises in sickle cell anaemia associated with parvovirus-like agent.

Since 1952, 112 children with sickle cell anaemia (SCA) in Jamaica have had an aplastic crisis. Outbreaks occurred in 1956, 1960, 1065-67, 1971-73, and 1979-80. Most cases occurred in children under 10 years of age, and an aplastic crisis in a patient over the age of 15 years is rare. There were 38 cases in 1979-80 and stored serum specimens from 28 of these were available for virus studies. Evidence for infection with a parvovirus-like agent was found in 24 of these 28 cases. Viral antigen was detected in 2 patients, both of whom demonstrated seroconversion. Seroconversion during 1980 was detected in a further 7, increasing amounts of antibody during the convalescent period were found in 5, antibody was found in 2 of 4 patients from whom only an acute phase specimen was available and the remaining 10 were antibody positive in the only convalescent phase sample available for testing. Antibody was found in 4 of 94 controls with the SS genotype (in retrospect 2 of these may have had an aplastic crisis) and in 17% of 48 controls with a normal haemoglobin (AA) genotype. The results accord with the possibility that the parvovirus-like agent is the principal cause of aplastic crisis in SCA.

Adolescent↗
PubMed1981

Shooting, sensorineural hearing loss, and workers' compensation.

Pure-tone audiograms of 29,953 workers with histories of shooting and occupational noise exposure were analyzed. The analysis was based on the asymmetry of hearing loss. Results of this study show that shooting is related to asymmetrical hearing loss, suggesting that shooting may cause an additional amount of hearing loss other than that due to occupational noise exposure. Asymmetry was found to increase as the length of shooting history increased and was significant only at 2 kHz and above and most prominent at 4 kHz. Results also indicated that as long as compensable frequencies remain below 3 kHz the shooting effect is not likely to influence compensation for workers with histories of less than ten years of shooting.

Hearing Loss, Noise-Induced↗
PubMed1981

The development of haematological changes in homozygous sickle cell disease: a cohort study from birth to 6 years.

A cohort study of sickle cell disease from birth has allowed observations on the disease without the symptomatic selection inherent in previous series. The development of haematological indices from birth to 6 years in male and female infants with homozygous sickle cell (SS) disease is presented and compared with values in age and sex matched controls with a normal haemoglobin (AA) genotype previously presented elsewhere. In SS disease total haemoglobin levels fell rapidly from birth to a plateau at 3-6 months before falling again to 15 months after which no age related change occurred. Mean cell haemoglobin concentration fell from birth to lowest values at 15-18 months before increasing to reach the level present at birth by the age of 5 years. Red cell counts fell rapidly after birth to a plateau at 2 months, increased slightly to 6 months and then fell steadily throughout the remaining period of the study. The men cell volume and mean cell haemoglobin also fell rapidly after birth reaching the lowest values by 6 months and then increased progressively. Female patients showed significantly higher MCV from 4 to 8 months and significantly higher haemoglobin levels from 15 months to 4 1/2 years. Compared to AA controls, SS patients manifested significantly lower levels of haemoglobin from 2 weeks, and red cell counts from 1 month, and significantly higher levels of MCHC from 4 months to 3 years, MCV from 8 months to 5 years, and serum iron levels from 1 to 4 years. Children with SS disease were partially protected from iron deficiency in early childhood, perhaps by increased intestinal absorption of iron, and the associated increase in intracellular haemoglobin concentration might be disadvantageous during this high risk period.

Anemia, Sickle Cell↗
PubMed1981

Long-term effects of pulmonary damage in mice on lung weight, compliance, hydroxyproline content and formation of metastases.

The development of "metastatic" colonies of fibrosarcoma in the lungs of mice after IV injection of a single-cell suspension of tumour cells varied with time after irradiation or administration of bleomycin. Most notably, there was a late radiation-induced enhancement of colony-forming efficiency that coincided with an increase in lung weight and hydroxyproline content and a decrease in compliance. There was no radiation-induced enhancement of "spontaneous" metastases from a mammary carcinoma implanted in the thighs of the animal. The sequence of events after administration of bleomycin was similar to that after irradiation, but the duration of the treatment was different and the temporal relationship between enhanced colony-forming efficiency and changes in lung weight and hydroxyproline content was not as clear cut.

Animals↗
PubMed1980

Haematological indices in normal negro children: a Jamaican cohort from birth to five years.

Haematological indices, including total haemoglobin, mean cell haemoglobin concentration, red cell count, mean cell volume, mean cell haemoglobin, reticulocytes, and serum iron values, in a cohort of 243 randomly selected Negro children with normal haemoglobin genotype, followed from birth to 5 years, are reported. Total haemoglobin fell rapidly from high levels at birth to a plateau at 2-6 months; a secondary fall occurred after 6 months and a gradual increase after 18 months. The red cell count also fell rapidly, but increased after 2 months to a plateau and then slowly declined from age 1-5. Mean cell volume and mean cell haemoglobin fell continuously from birth to the lowest values at 15 months and then progressively increased to the age of 5 years. Serum iron levels were low at one year of age (mean 9.7 mumol/l) increasing slowly by age 4 and sharply by age 5. Mean cell haemoglobin concentration fell gradually to 1-1 1/2 years and then increased progressively to age 5. Values for Hb, MCHC, MCV, and MCH were consistently and often significantly lower in males before the age of 2 years, compatible with greater depletion of iron stores. Serum iron values were generally lower in males but there was no sex difference at one year when highly significant differences in Hb, MCHC, MCV, and MCH occurred. The cause of sex differences in early haematological development is currently unclear.

Anemia, Sickle Cell↗
PubMed1979

Biosynthesis of trans-4-hydroxy-L-proline by Streptomyces griseoviridus.

Radioisotopic experiments have revealed that free trans-4-hydroxy-L-proline is an intermediate synthesized from L-proline during formation of the peptide-bound cis-4-hydroxy-D-proline residue in the antibiotic, etamycin. This conclusion was based on the fact that 1) both radiolabeled L-proline and trans-4-hydroxy-L-proline are precursors of the bound D-imino acid as noted previously by Hook and Vining ((1973) J. Chem. Soc. Chem. Commun. 185-186; (1973) Can. J. Biochem. 51, 1630-1637), 2) the unlabeled trans isomer specifically inhibited the incorporation of radiolabel from proline into the antibiotic, 3) the 14C-hydroxyimino-acid was isolated from the intracellular pool and medium following incubations with L-[14C]proline during antibiotic biosynthesis and when etamycin synthesis was blocked by D-leucine. By means of chromatographic and enzymatic analyses, it was established that the free imino acid possesses the trans-L configuration.

Amino Acids↗
PubMed1979

Comparison of sickle cell-beta0 thalassaemia with homozygous sickle cell disease.

Clinical and haematological features in 41 patients with sickle cell-beta0 thalassaemia (Sbeta0 thalassemia) and in 123 age--sex matched controls with homozygous sickle cell (SS) disease were compared. Persistence of splenomegaly was more common and fetal loss less common in Sbeta0 thalassemia but other clinical features were similar in the two genotypes. Total haemoglobin, Hb A2, PCV, CCV, and red cell count were significantly higher and MCV, MCH, MCHC, and ISC counts significantly lower in Sbeta0 thalassaemia. Proportional reticulocyte counts were significantly lower in Sbeta0 thalassaemia but there was no difference in absolute reticulocyte counts. Persistence of splenomegaly and low ISC counts are compatible with decreased intravascular sickling which may result from the lower mean cell haemoglobin S concentration in Sbeta0 thalassaemia. If beneficial effects of a low MCHC can be confirmed then a carefully monitored trial of iron deficiency in SS disease may be a logical experimental procedure.

Adolescent↗
PubMed1979

Is a healthier person less susceptible to noise-induced hearing loss?

Several studies in the literature suggest that poor health is related to hearing loss. One hundred subjects claiming occupational hearing loss were chosen randomly for this study. Information was obtained on employment, noise exposure, medical history, family history, and use of cigarettes, alcohol, and medication. Physical examination audiometric tests, and biological tests were carried out. Computer analysis of the data with chi-square test did not show conclusively that noise-induced hearing loss is related to poor health, indicated by abnormal biological or physical findings, or both. There were, however, some indications that the presence of cardiovascular risk factors may influence hearing loss.

Analysis of Variance↗
PubMed1978

Enhancement of lung colony-forming efficiency by local thoracic irradiation: interpretation of labeled cell studies.

The dynamics of 125IUdR-labeled tumor cell retention in the lungs have been compared with the efficiency of lung colony formation over a wide range of inoculum sizes in normal mice and in mice pretreated with 1000 rads local thoracic irradiation (LTI). These studies indicate that the increase in lung colony yield after LTI cannot be ascribed to improved intravascular trapping or interstitial lodgement of tumor cells. Hypotheses purporting that active specific or nonspecific host defense might be impaired by LTI were reassessed but rejected in favor of the idea that radiation-induced alterations in the physiological mocroenvironment of the lungs improve an intrinsically poor survival capability of intravenously disseminated tumor cells.

Animals↗
PubMed1978

Dibutryl cyclic adenosine monophosphate: effect on radiosensitivity of tumors and normal tissues in mice.

The effect of dibutryl cyclic adenosine monophosphate (db-cAMP, 30 mg/kg), injected into mice before irradiation, on the radiation sensitivity of various tissues was investigated. Survival of proliferating hair follicles, small gut stem cells, fibrosarcoma (FSa) micrometastases in the lungs, and two different mammary carcinomas, as assayed by the TCD50 method, were studied. Intraperitoneal injection of db-cAMP before irradiation resulted in higher survival of hair follicles irradiated on the third day after plucking. Stem cells in the small gut showed increased survival if irradiated 4 hours after injection. There was no effect on the survival of FSa micrometastases by preinjection and the TCD50/120 days of the mammary carcinomas was not altered.

Animals↗
PubMed1978

Response of selected tumour cell populations separated from a fibrosarcoma following irradiation in situ with fast neutrons.

We have characterized selected populations of fibrosarcoma cells separated on density gradients of Renografin with respect to distribution in the cell cycle, clonogenic ability, and response to radiation. The latter two parameters have been observed to be related to the density of the cells, the denser populations being less clonogenic but more resistant to both low and high LET radiation. We have determined that these cells effectively repair potentially lethal damage if allowed to remain in situ following exposure to low LET radiation. This repair ability is not observed, however, following neutron irradiation. In addition, cells left in situ are relatively more sensitive to low doses of either low or high LET radiation. This difference in response is believed to be due to differences in the expression of damage by cells left in situ as compared to those assayed immediately. These data reflect the usefulness of cell separation methods in the study of solid tumour systems. Specifically, these methods reduce the heterogeneity found in the solid tumour by allowing for the isolation of subpopulations which then can be studied either individually or in relation to the entire tumour.

Animals↗
PubMed1977

Comparison of haematological features of the beta0 and beta+ thalassaemia traits in Jamaican Negroes.

Haematological characteristics have been compared in 29 subjects with heterozygous beta0 thalassaemia and in 33 subjects with heterozygous beta+ thalassaemia, identified by the type of sickle cell-beta thalassaemia among close relatives, in a Jamaican Negro population. Total haemoglobin, MCV and MCH were significantly lower in the beta0 type but the level of Hb A2 was not significantly different. Individual values for MCV, MCH and Hb A2 in the beta+ type occasionally overlapped those in the normal population casting doubt on the adequacy of these criteria in identifying all cases of heterozygous beta+ thalassaemia. The haematological differences are those which would be expected on theoretical grounds. The inability to confidently differentiate the two types of heterozygous beta thalassaemia has implications for genetic counselling. The inability to distinguish heterozygous beta+ thalassaemia from normals on any single haematological index suggests that surveys depending on estimations of Hb A2 or on MCV alone may have underestimated the prevalence of the beta+ thalassaemia gene.

Adolescent↗