Search PubMed⌕ Search

Biomedical subjects

R C Brown

Publications and source records attributed to R C Brown.

At least 127 records · Page 7Linked to original sources
PubMed1989

Fate and toxicity of temephos applied to an intertidal mangrove community.

The distribution, persistence, and toxicity of the mosquito larvicide temephos was monitored following aerial applications to an intertidal mangrove community in Lee County, Florida. The amount of temephos penetrating to the mangrove floor ranged from 15 to 70% of the amount entering the upper leaf canopy, with 50-60% of that applied remaining on the mangrove leaves. Rainfall caused an additional influx of temephos from the leaves to the mangrove floor. Residues were detected in intertidal water at 2 h, but not 4 h after application. However, temephos was observed to persist in simulated tidal pools and on mangrove leaves for up to 72 h and in oysters for up to 48 h after application. Marine organisms placed in cages at 3 test sites and a control site were monitored for toxic effects. Mortality among natural mosquito larvae was simultaneously monitored. Mysids (Mysidopsis bahia) exhibited a significant mortality at one site during 1 of 3 applications monitored; however, no correlation was observed between mortality and temephos concentration in water. No significant mortality was observed for the other organisms, which included: brown shrimp (Panaeus aztecus), grass shrimp (Palaemonetes pugio), juvenile snook (Centropomis undecimalis) and sheepshead minnow (Cyprinodon variegatus).

Animals↗
PubMed1989

Modification of fibrous Oregon erionite and its effects on in vitro activity.

A sample of erionite, a fibrous zeolite, was modified by milling to reduce the number and length of the fibres and by extraction with cyclohexane. The in vitro activities of this mineral were found to depend on the presence of long fibres. The erionite contained fewer of these fibres than the UICC asbestos samples but, unlike these materials, erionite can cause the transformation of C3H 10T1/2 cells. Erionite did not increase the activities of benzo[a]pyrene in this cell transformation assay. The cytotoxic activities of both asbestos and erionite have a similar dependence on the number of long fibres. Extraction with cyclohexane did not affect the activity of erionite.

Aluminum Silicates↗
PubMed1989

A twelve year follow-up of iodine deficiency in Bulape, Zaire.

In a defined population of Bulape, Zaire, the prevalence of simple goitre was 42.4 +/- 1.3%. Compared with studies in the same population done twelve years previously, the prevalence of simple goitre had increased by 13.9% (P less than 0.05). Urinary iodine determination remained approximately the same. We conclude that over the twelve year period, the prevalence of iodine deficiency has not improved in the Bulape population.

Adolescent↗
PubMed1989

Air filtration: protection against respirable dust.

The principal health hazard associated with airborne dust is attributable to particles with aerodynamic diameters of a few micrometers or less, and filtration is, in principle, a good way of obtaining protection against such small particles. The elements of filtration theory can be deduced from simple arguments, which illustrate that it is difficult to remove particles that are 1 or 2 microns in diameter from air by filtration using a filter made from ordinary textile fibres. Either much finer or electrically charged fibres must be used and, in general, the latter solution is preferable. A number of different electrically charged filter materials exist, examples of which are materials that are charged triboelectrically, by corona, or by induction. The mechanism of action of these materials is described, along with conditions necessary for their successful use.

Air Pollution↗
PubMed1989

Risk factors for mortality after primary combined valvular and coronary artery surgery.

Risk factors for death after combined valvular and coronary artery bypass graft surgery (CABG) were examined in 141 patients undergoing isolated mitral valve (MV) surgery and CABG (n = 47) or isolated aortic valve (AV) surgery and CABG (n = 94) between January 1, 1986, and January 1, 1988. Actuarial survival was 92% at 1 month and 79% at 1 year. The hazard function for death was highest immediately after operation, had a single phase of decline, and reached a low level only after about 4 months. Risk factors for death included older age at operation, preoperative hemodynamic instability, left main coronary artery disease, ischemic mitral valve disease, important tricuspid valve incompetence, and longer ischemic time. The adverse effect of hemodynamic instability at time of surgery was most pronounced in the elderly (age 70 years or more, 20% 30-day mortality). A favorable risk group includes patients under 70 years of age without left main stenosis, hemodynamic instability, or ischemic mitral valve disease; the 30-day mortality for this subset undergoing isolated valve surgery and CABG is less than 5%. A proper comparison of surgical therapy in differing patient subsets with combined valvular and coronary artery disease should include multivariate analysis in which nondichotomous variables are examined in a continuous manner rather than establishing arbitrary stratifications.

Actuarial Analysis↗
PubMed1989

Radiologic appearance of the upper cervical canal in women with a history of premature delivery. II. Relationship to clinical presentation and to tests of cervical compliance.

Two hundred twelve women with histories of spontaneous second-trimester abortions or early preterm births (less than 34 weeks) were evaluated with hysterography in the nonpregnant state. The canal:cannula (C:CN) ratio, a representation of the width of the upper cervical canal, was related to the clinical characterization of the early delivery. Narrow canals were associated with bleeding or premature rupture of the membranes (PROM) preceding preterm labor. Wide canals were found in association with the clinical diagnosis of cervical incompetence. Those patients in whom preterm labor occurred in the absence of preceding bleeding or PROM had intermediate values. The results of two tests of cervical compliance, Hegar dilator passage and catheter balloon traction, were concordant and varied with the C:CN ratio.

Abortion, Habitual↗
PubMed1988

Comparison of the performance and clinical utility of a carboxy-terminal assay and an intact assay for parathyroid hormone.

A comparison of the performance of a two-site immunochemiluminometric assay for intact parathyroid hormone with that of an in-house radioimmunoassay for carboxy terminal parathyroid hormone has been performed on samples from unselected patients being investigated for hypercalcaemia. The intact parathyroid hormone assay was found to be a simple and robust technique with a broad working assay range (CV less than 10% between 1.8-212 pmol/l) and a detection limit of 0.2 pmol/l. Clinically it is superior to the carboxy terminal assay in its ability to distinguish between patients with hyperparathyroidism from those with other causes of hypercalcaemia especially in the presence of impaired renal function.

Adult↗
PubMed1988

Comparison of poly- and monoclonal antibodies as labels in a two-site immunochemiluminometric assay for intact parathyroid hormone.

We have evaluated the potential of monoclonal antibodies in the development of a non-isotopic immunometric assay for intact human parathyroid hormone (PTH). The assay has been designed to utilise a chemiluminescent acridinium ester labelled anti-aminoterminal (anti-N) antibody and a solid-phase anti-carboxyterminal antibody in order to measure specifically the intact hormone. In this system the characteristics of the labelled antibody proved crucial to the performance of the assay. A low affinity monoclonal reagent yielded insufficient analytical sensitivity, while a higher affinity monoclonal reagent cross-reacted poorly with the intact molecule relative to the amino terminal PTH fragment to which it was raised. Neither antibody could therefore match the performance of an affinity-purified polyclonal anti-N PTH reagent. These results highlight the problems to be addressed in the selection of suitable reagents for immunometric assay development when specificity and sensitivity are crucial requirements.

Animals↗
PubMed1988

A rapid method of preparing hepatic parenchymal cells for studying drug metabolism.

Parenchymal cells were prepared from the livers of male Sprague-Dawley rats by collagenase perfusion and purified by a self-generating Percoll gradient. The method consisted of mixing 31% Percoll and 5 x 10(6) cells/ml, followed by centrifugation at 10,000 x g for 10 min. A self-generated gradient provided a rapid and efficient recovery of highly viable parenchymal cells. The parenchymal cells were determined to be very stable during incubation at 37 degrees C for at least 2 h. Cell integrity was evaluated by trypan blue dye exclusion, lactate dehydrogenase leakage, and membrane peroxidation. In addition, drug metabolism and conjugation were evaluated as markers of intracellular integrity. With increasing p-nitroanisole (pNA) concentration, the formation of p-nitrophenol (pNP) increased. The rate of sulfation was maximal at a pNA concentration of 0.25 mM and decreased greatly above 1.0 mM. Glucuronidation increased from 0.25 mM to a maximum rate of 2.0 mM pNA. Above 1.0 mM pNA, nonconjugated pNP increased proportionately to the decrease in sulfation. These results indicate that the cell integrity was maintained, and that these cells can be used as a model for studying drug metabolism.

Animals↗
PubMed1988

Anomalies in the assay of parathyroid hormone in normocalcaemic patients with renal stone disease.

A group of 22 normocalcaemic patients with renal stone disease were retrospectively studied using seven different immunoassays for parathyroid hormone (PTH). N-terminal immunoradiometric assays and an intact hormone immunochemiluminometric assay sometimes gave results which fell above the normal range. These results were at variance with values obtained in three region-specific radioimmunoassays and an immunoradiometric assay for the intact hormone. Since these atypical samples contained normal levels of biologically active PTH the elevated immunoassay results were not thought to relate to the normal circulating hormone but rather to interference in the immunometric assays. The interfering substance was thought to be a large molecule which could not be removed by charcoal and did not dilute out in parallel to the PTH standard curve.

Adolescent↗
PubMed1988

Secretion of intact PTH by dispersed human hyperparathyroid cells.

The rate of secretion of intact PTH by cells dispersed from adenomatous and hyperplastic human parathyroid tissue was measured using a two-site immunochemiluminometric assay specific for the intact peptide. Secretion rates were monitored following incubation in high and low-calcium media. The mean rate of secretion from hyperplastic cells was significantly greater (P less than 0.05) at low calcium and significantly more suppressible at high calcium (P less than 0.01) compared with adenomatous cells. These studies have demonstrated: (1) the calcium-dependent secretion of intact PTH, (2) that intact hormone release contributes to the non-suppressible component of secretion, and (3) differences in the secretory characteristics of adenomatous and hyperplastic parathyroid cells.

Adenoma↗
PubMed1988

Vitamin D3 metabolites in chronic renal failure and after renal transplantation.

Circulating vitamin D3 metabolites were measured in 31 adult patients with chronic renal failure and 31 adults between 3 and 30 months after renal transplantation. No subject excreted over 1 g urinary protein daily nor received vitamin D or its metabolites. There was a positive correlation between 1,25(OH)2D3 and GFR between 15 and 90 ml/min in both chronic renal failure (r = 0.60, P less than 0.001) and transplant subjects (r = 0.49, P less than 0.01) and between 1,25(OH)2D3 and 25(OH)D3 after transplant (r = 0.69, P less than 0.001), but not in chronic renal failure (r = 0.22, P = ns). There was a weak inverse correlation between 1,25(OH)2D3 and serum phosphate in chronic renal failure (r = 0.36, P less than 0.05) but not post transplant (r = 0.03, P = ns). Compared with 1,25(OH)2D3 concentrations in 16 normal subjects (mean +/- SEM: 39.5 +/- 1.9 pg/ml), chronic renal failure subjects with mild renal impairment (GFR 45-90 ml/min, mean: 61.5 +/- 3.3 ml/min, n = 17) had reduced 1,25(OH)2D3 (28.9 +/- 2.7 pg/ml, P less than 0.01). In transplant subjects with mild impairment (GFR 45-90 ml/min, mean: 61.4 +/- 3.7), 1,25(OH)2D3 was positively (r = 0.79, P less than 0.001) and iPTH inversely correlated (r = 0.51, P less than 0.05) with 25(OH)D3. In each of nine such subjects studied, seasonal variations in 1,25(OH)2D3 (P less than 0.001) and PTH (P less than 0.05, 1-tailed test), as well as in 25(OH)D3 and 24,25(OH)2D3, were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Nutrition surveillance by QUAC stick.

The QUAC stick method of nutrition assessment was used as an indicator of change in a nutrition surveillance system in Zaire. The method is quick, simple and can be done by primary school teachers. Results of QUAC stick measurements are reproducible and easy to report.

Anthropometry↗
PubMed1987

The effect of anti-tuberculosis chemotherapy on vitamin D and calcium metabolism.

Serum 25-hydroxycholecalciferol (25-(OH)D3), calcium and albumin have been measured in 27 patients undergoing treatment for pulmonary tuberculosis. Patient 25-(OH)D3 was significantly lower than controls pre-treatment. Throughout the period of treatment patient median 25-(OH)D3 remained below 10 ng/ml, significantly lower than levels in matched healthy controls. Patients' median serum levels varied between 35% and 66% of controls' values during treatment, but rapidly rose to equal control values once treatment had been stopped. Patients' serum calcium, corrected for albumin, remained virtually identical with control values throughout treatment. Clinicians should be aware that standard anti-tuberculosis chemotherapy may depress Vitamin D stores and that this may be important for patients who are already at risk from osteomalacia.

Adult↗