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Biomedical subjects

J Stevens

Publications and source records attributed to J Stevens.

At least 253 records · Page 14Linked to original sources
PubMed1990

Technique for identifying cutting artefacts in sections of undecalcified bone biopsy specimens.

Areas of fragmentation found in trabecular and cortical bone of iliac crest biopsy specimens have been described as bone quality defects and were thought to be the major factor responsible for femoral neck fractures. These appearances have also been regarded as cutting artefacts and to resolve this difference of opinion consecutive sections cut at right angles to each other in biopsy specimens from 15 patients with femoral neck fractures were compared. Sections were assessed by four independent observers; agreement by at least three was required before an area was accepted as a bone quality defect. In all, 270 were identified. Of the 161 found in sections cut parallel to the cortices, there were only 20 (12%) in coincident areas in consecutive sections. This study shows conclusively that areas of fragmentation previously described as bone quality defects are not artefacts which may be created or excluded depending on the plane of section.

Aged↗
PubMed1990

Determination of peptidyl dipeptidase activity in 24 bacterial species.

Of 24 bacterial species examined for lisinopril refractive peptidyl dipeptidase activity, only 8 contained activity. Activity in Pseudomonas maltophilia was more than fourfold higher than that of any other species. Pseudomonas maltophilia may be unique among bacteria in possessing high peptidyl dipeptidase activity that is both EDTA inhibitable and lisinopril resistant.

Animals↗
PubMed1989

Two NF1 translocations map within a 600-kilobase segment of 17q11.2.

Balanced translocations, each involving chromosome 17q11.2, have been described in two patients with von Recklinghausen neurofibromatosis (NF1). To better localize the end points of these translocation events, and the NF1 gene (NF1) itself, human cosmids were isolated and mapped in the immediate vicinity of NF1. One cosmid probe, c11-1F10, demonstrated that both translocation breakpoints, and presumably NF1, are contained within a 600-kilobase Nru I fragment.

Animals↗
PubMed1989

Influence of body habitus and race on bone mineral density of the midradius, hip, and spine in aging women.

Osteoporosis and fractures of the hip are less common in black women and in obese white women than in nonobese white women. To determine the effects of race, age, and body weight on bone mineral density (BMD), BMD of the lumbar spine, trochanter, and femoral neck were determined by dual-photon absorptiometry in 131 nonobese white women and 34 nonobese black women, all of whom were within 30% of their ideal body weight, and in 24 obese white women and 27 obese black women, all of whom weighed more than 30% of their ideal body weight and were in the same age range as the nonobese women. All of them were 51 years of age or older, and most of them were postmenopausal. BMD of the midradius was measured by single-photon absorptiometry. Whereas body weight was significantly higher in the black as compared to the white women, the ages of the two groups were not different from each other. BMD declined with age and increased with body weight in both the black and white women at each of the four sites measured. After adjusting for age and weight by covariate analyses, black women had greater BMDs than white women at the midradius, lumbar spine, and femoral neck (p less than 0.001), but not at the trochanter (p = 0.18). The increases in BMD observed in the obese and black women in the present study are consistent with the previous findings that osteoporosis and fractures of the hip are less common in black and in obese white women than in nonobese white women.

Aged↗
PubMed1989

A peptidyl dipeptidase-4 from Pseudomonas maltophilia: purification and properties.

A peptidyl dipeptidase-4 (bacterial PDP-4) was purified to near homogeneity from a supernatant of Pseudomonas maltophilia extracellular medium. Bacterial PDP-4 is a single-polypeptide-chain enzyme, 82 kDa, with an alkaline isoelectric point. Peptides susceptible to hydrolysis by bacterial PDP-4 include angiotensin 1, bradykinin, enkephalins, atriopeptin 2, and smaller synthetic peptides. N-acylated tripeptides are hydrolyzed, but free tripeptides are not. A free carboxy terminus is required for hydrolysis. Peptides with ultimate and penultimate Pro residues are not hydrolyzed. The enzyme does not require an anion for activity. Bacterial PDP-4 was inhibited by EDTA and the dipeptide Phe-Arg. Thiorphan was an inhibitor only at levels well above those required for inhibition of neutral metalloendopeptidase (NEP), an enzyme for which thiorphan is specific. A second NEP and thermolysin inhibitor, phosphoramidon, did not inhibit bacterial PDP-4. The potent angiotensin-converting enzyme inhibitor lisinopril was not inhibitory. Bacterial PDP-4 is distinguished from a similar enzyme from Escherichia coli, which is not susceptible to EDTA inhibition, and one from Corynebacterium equi, which hydrolyzes free tripeptides. These data indicate that the bacterial PDP-4 catalytic site is unlike those of other enzymes that function either wholly or in part as peptidyl dipeptidases.

Chromatography↗
PubMed1989

The influence of liposomal encapsulation on sodium cromoglycate pharmacokinetics in man.

The pharmacokinetics of pulmonary-administered sodium cromoglycate (SCG) has been studied in five healthy volunteers. SCG, 20 mg, was inhaled as a solution and encapsulated in dipalmitoyl phosphatidylcholine/cholesterol (1:1) liposomes. Liposomal SCG produced detectable drug levels in plasma from four volunteers taken 24 and 25 hr after inhalation. Inhaled SCG solution, although producing peak plasma levels more than sevenfold greater than liposomal drug, was not detectable in 24-hr samples from any volunteer. The decline in plasma levels following inhalation of liposomal SCG (reflecting the absorption phase) was best described by a biexponential equation. The two absorption rate constants differed by more than an order of magnitude. The rapid absorption phase was probably due to free or surface-adsorbed SCG in the liposomal formulation, since the absorption rate constant for this phase did not differ significantly from the absorption rate constant for SCG in solution. The phase of slow drug absorption may then be attributed to absorption of drug released from vesicles. The data indicate that encapsulation of SCG prior to pulmonary administration prolonged drug retention within the lungs and altered its pharmacokinetics.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Teratological evaluations of atrazine technical, a triazine herbicide, in rats and rabbits.

Atrazine technical was evaluated for its embryotoxic, fetotoxic, and teratogenic potential in both rats and rabbits. The compound was orally administered at doses of 0, 10, 70, or 700 mg/kg.d to groups of rats on gestational d 6-15, while rabbits were administered doses of 0, 1, 5, or 75 mg/kg.d on gestational d 7-19. Maternal toxicity was observed at doses greater than or equal to 70 mg/kg.d in rats and at doses greater than or equal to 5 mg/kg.d in rabbits. Minor fetal effects, concurrent with maternal toxicity, were observed in rats at doses greater than or equal to 70 mg/kg.d. Among rabbits, fetal effects concurrent with severe maternal toxicity were only observed at the 75 mg/kg.d dose level. There were no adverse maternal or fetal effects in either rats or rabbits at the low dose levels. These findings indicated that pregnant rabbits were more sensitive than pregnant rats to the effects produced by atrazine technical and the compound was not teratogenic at maternally toxic dose levels in either species.

Abnormalities, Drug-Induced↗
PubMed1988

Bone mass and dementia in hip fracture patients from areas with different aluminium concentrations in water supplies.

The relationship between bone mass and dementia in elderly hip fracture patients from areas with different aluminium concentrations in water supplies has been investigated, to determine whether a high concentration of aluminium in the drinking water and the negative calcium balance of age-related osteoporosis together predispose to senile dementia. Mental test scores were recorded on admission to hospital, and Singh indices of radiographs taken at that time assessed blind by a single trained observer. No significant difference in either mental test score (chi 2 = 1.253, df = 2, P = 0.53) or Singh index (chi 2 = 1.039, df = 5, P = 0.96) was found between patients resident in high versus low water aluminum areas. No correlation was detectable between mental test score and Singh index (chi 2 = 0.95, df = 1, P = 0.33).

Aged↗