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Biomedical subjects

D Leon

Publications and source records attributed to D Leon.

30 records · Page 2Linked to original sources
PubMed1992

Partial purification and immobilization of ribonuclease T2.

A simple procedure, consisting of water extraction, heat treatment at pH 2.0, negative adsorption on DEAE-cellulose at pH 4.9, and concanavalin A-Sepharose chromatography, was developed for the partial purification of ribonuclease (RNase) T2 from taka-diastase powder with an overall yield of 5.5%. The partially purified enzyme when coupled to aminoethyl Bio-Gel P-60, retained 12-16% of the activity of the soluble enzyme. Temperature stability studies on RNase T2 bound to matrices, activated with increasing concentrations of glutaraldehyde, and the influence of lysine modification on the activity of the soluble enzyme revealed that the low activity observed for the gel-bound enzyme is probably due to the masking of the active site of the enzyme as a result of the involvement of lysine residues, situated near the active site, during coupling. Immobilization did not affect the pH and temperature optima of RNase T2. On repeated use, the bound enzyme retained approximately 55% of its initial activity after six cycles. These results are discussed, taking into consideration the factors affecting immobilized enzymes.

Adsorption↗
PubMed1991

Mortality of employed men and women.

This paper presents mortality data for a 1% sample of men and women in England and Wales who were employed at the time of the 1971 Census of Population. It provides background information on the "healthy worker effect" by age, social class (as determined by occupation), cause of death, and length of follow-up. As expected, relative mortality of those employed at census rose with subsequent follow-up. This effect was strongly age-related, apparently as a consequence of the development (and increasing predominance) of chronic diseases with age. This suggests a unified explanation for some of the variation described in the literature. Statistical modelling of the relationship between mortality and length of follow-up confirmed that the healthy worker effect did not entirely disappear as follow-up progressed in this study. We examined social background as an explanation for this persistently low mortality, but found no evidence to suggest that it was an important factor.

Adult↗
PubMed1991

Socioeconomic differentials in cancer among men.

The relationship between cancer and socioeconomic position is examined for men using data from three sources--the Whitehall Study of London civil servants, the OPCS Longitudinal Study and the Registrar General's Decennial Supplement. Mortality from, or registration for, malignant neoplasms was higher overall in lower socioeconomic groups. There was considerable variation in the strength, and to a lesser extent direction, of the association of specific cancer sites and socioeconomic position within each of the studies. However, between the studies the relationships between socioeconomic position and the particular cancers were very similar. The similarity in results, taken in conjunction with the differences in design and methods of the three studies, makes it very unlikely that these consistent associations are due to artefacts. The heterogeneity in relationships between specific cancer sites and socioeconomic position suggests that no single factor--such as differences in general susceptibility or differences in smoking behaviour--can account for these associations. However socioeconomic differentials displayed by a particular malignancy do offer clues to its aetiology, and provide an indication of the scope that exists for reducing the burden of cancer within a population.

Humans↗
PubMed1983

Citric acid airway constriction in dogs with hyperreactive airways.

To understand the mechanisms underlying the bronchoconstrictor response to 10% citric acid administered for 5 min in Basenji-Greyhound (BG) dogs, we evaluated the protection afforded by atropine (0.2 and 0.4 mg/kg iv) and by aerosols of isoproterenol (1 mg/ml) and cromolyn sodium (20 mg/ml). In untreated dogs, citric acid increased pulmonary resistance by 4.6- to 11.5-fold and decreased dynamic compliance (Cdyn) to 45-55% of the control response. Isoproterenol and cromolyn sodium significantly reduced the response, whereas atropine did not. Moreover we have demonstrated in the arterial plasma of these dogs a slow-reacting substance (SRS) after, but not before, citric acid challenge. This SRS exhibits both pharmacologic properties and chemical characteristics similar to leukotrienes. We conclude that mediators of immediate-type hypersensitivity rather than reflex mechanisms play a dominant role in the production of airway constriction during citric acid (5-min) challenge in BG dogs.

Airway Resistance↗
PubMed1983

Pulmonary uptake of mannitol as an index of changes in lung epithelial permeability.

To develop a simple, inexpensive, and nontoxic test for changes in bronchial permeability we have employed a specific gas chromatographic assay to measure the uptake of mannitol from the lung after administration of an intratracheal aqueous bolus (8 ml of 5% solution). We have tested the ability of our method to detect the known increase in lung epithelial permeability elicited by challenge of previously sensitized animals with aerosols of Ascaris suum antigen. In Ascaris-sensitive Basenji-Greyhound dogs, antigen challenge significantly increased the rate of appearance and peak plasma level of mannitol after administration of the intratracheal bolus. Peak plasma mannitol levels averaged 25 +/- 3 (SE) micrograms/ml in dogs challenged with Ascaris antigen aerosols, and 14 +/- 2 micrograms/ml in the same animals in separate control experiments employing saline aerosols. The method presented could be readily applied to animal and human studies as a simple, inexpensive, and nontoxic indicator of lung epithelial permeability.

Aerosols↗