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Biomedical subjects

K R Smith

Publications and source records attributed to K R Smith.

At least 109 records · Page 6Linked to original sources
PubMed1991

Remarriage patterns among recent widows and widowers.

Remarriage is one of the most important determinants of physical and economic well-being among the widowed. The goal of this study is to estimate how hazard rates for remarriage vary among widows and widowers on the basis of both observable and unobservable characteristics. The remarriage estimates rely on nationally representative samples of widows and widowers from the Panel Study of Income Dynamics. Continuous-time hazard rate regressions indicate strong age and duration dependence effects for middle-aged widows and widowers and for older widowers. Among middle-aged widows, blacks and those with dependent children in the home have lower rates of remarriage. For middle-aged widowers, living in urbanized areas limits the prospects of remarriage. For older widowers, education and, to some extent, economic status appear to have positive effects on the remarriage rates. Overall, age and time since widowhood have the strongest and most consistent effects on remarriage rates for different widowed groups.

Age Factors↗
PubMed1991

The effect of a stiff spinal implant on the bone-mineral content of the lumbar spine in dogs.

The response of canine lumbar vertebral bone to the application of a stiff transpedicular screw-plate implant from the third to the fifth lumbar vertebra, without arthrodesis, was investigated. Five groups of six dogs each were studied: dogs that had not had an operation (control group); dogs that had had a sham operation, with survival periods of three and six months; and dogs that had received an implant, with survival periods of three and six months. The results were the same in specimens from the control group and the group that had had a sham operation. In the groups that had received an implant, dual-photon absorptiometry revealed an insignificant decrease in bone-mineral content at the bypassed fourth lumbar segment (17 per cent at three months and 12 per cent at six months). When the data for the three and six-month intervals were pooled, the mean decrease in bone-mineral content of 14 per cent was significant. Histomorphic study yielded similar results; the mean decrease in bone-mineral content for the pooled three and six-month specimens was significant (16 per cent). Losses were similar for the ventral and dorsal columns. Histomorphometric analysis also showed a significant (13 per cent) loss of bone-mineral content at the adjacent caudad (sixth lumbar) vertebra for the pooled three and six-month groups. The results of the methods of analysis of loss of bone-mineral content correlated strongly. Under these experimental conditions, a stiff spinal implant caused loss of bone-mineral content of the bypassed vertebral segment, although the loss was less than anticipated and did not increase between three and six months.

Absorptiometry, Photon↗
PubMed1991

Asymptomatic versus symptomatic herniated thoracic discs: their frequency and characteristics as detected by computed tomography after myelography.

We retrospectively reviewed the myelograms of 433 patients and identified those who had no symptoms or signs referable to the thoracic cord, roots, or nerves. By post-myelography computed tomographic scan criteria, our frequency of asymptomatic thoracic herniated discs (ATHDs) was calculated. Post-myelography computed tomographic scans of 68 ATHDs were analyzed. Their imaging characteristics were compared with our own series of 5 symptomatic thoracic herniated discs and symptomatic thoracic herniated discs in the literature. We were unable to identify any imaging features that could reliably classify a disc as an ATHD or a symptomatic thoracic herniated disc. Our results call into question the propriety of prophylactic surgery for ATHDs, even when the lesions are radiographically impressive.

Adult↗
PubMed1990

Effects of dietary acidification and potassium depletion on acid-base balance, mineral metabolism and renal function in adult cats.

Effects of dietary potassium restriction, with or without dietary acidification, on acid-base balance, mineral metabolism and renal function were evaluated in 12 adult cats. Six cats were fed a potassium-restricted diet (0.2% potassium) for 8 wk, and six cats were fed the same potassium-restricted diet plus a dietary acidifier (0.8% NH4Cl) for 8 wk. Both groups of cats were then fed the same diet supplemented with potassium gluconate (0.7% dietary potassium) for an additional 4 wk. Renal function was evaluated before treatment and again at 8 and 12 wk. Serum potassium concentration declined in all cats by wk 1 and was also lower in NH4Cl-treated cats at 2, 3, 6 and 8 wk than in control cats. Metabolic acidosis developed in both groups of cats. Dietary balance studies indicated negative potassium balance in NH4Cl-treated cats. Glomerular filtration rate declined significantly in NH4Cl-treated cats after 8 wk but was unchanged in control cats. From the results of this study, we conclude that adding a dietary acidifier to a potassium-restricted diet worsens hypokalemia, possibly by affecting gastrointestinal potassium handling, and induces severe metabolic acidosis and renal dysfunction in adult cats.

Acidosis, Renal Tubular↗
PubMed1990

Comparison of cilofungin and amphotericin B for therapy of murine candidiasis.

We compared the efficacies of cilofungin and amphotericin B treatment in a murine model of disseminated candidiasis. Three different dosages of each drug plus controls were evaluated. Statistically improved survival was noted only among mice treated with 1 mg of amphotericin B per kg of body weight (P less than 0.05). While all amphotericin B regimens and the two lower-dosage cilofungin regimens significantly reduced yeast cell counts in kidneys compared with the controls, the amphotericin B-treated mice had a significantly higher percentage of sterile kidneys following therapy compared with those treated with cilofungin (P = 0.0001).

Amphotericin B↗
PubMed1990

Indoor air pollution in developing countries.

Of the four principal categories of indoor pollution (combustion products, chemicals, radon and biologicals), research in developing countries has focused on combustion-generated pollutants, and principally those from solid-fuel-fired cooking and heating stoves. Such stoves are used in more than half the world's households and have been shown in many locations to produce high indoor concentrations of particulates, carbon monoxide and other combustion-related pollutants. Although the proportion of all such household stoves that are used in poorly ventilated situations is uncertain, the total population exposed to excessive concentrations is potentially high, probably several hundred million. A number of studies were carried out in the 1980s to discover the health effects of such stove exposures. The majority of such studies were done in South Asia in homes burning biomass fuels or in China with coal-burning homes, although a sprinkling of studies examining biomass-burning have been done in Oceania, Latin America and Africa. Of the health effects that might be expected from such exposures, little, if any, work seems to have been done on low birthweight and eye problems, although there are anecdotal accounts making the connection. Decreased lung function has been noted in Nepali women reporting more time spent near the stove as it has for Chinese women using coal stoves as compared to those using gas stoves. Respiratory distress symptoms have been associated with use of smoky fuels in West India, Ladakh and in several Chinese studies among different age groups, some with large population samples. Acute respiratory infection in children, one of the chief causes of infant and childhood mortality, has been associated with Nepali household-smoke exposures. Studies of chronic disease endpoints are difficult because of the need to construct exposure histories over long periods. Nevertheless, chronic obstructive lung disease has been associated with the daily time spent near the stove for Nepali women and found to be elevated among coal-stove users compared to gas-stove users in Shanghai. In contrast to early reports, there seems to be little or no risk of nasopharyngeal cancer from cookstove smoke. Several studies in China, however, have found smoke to be a strong risk factor for lung cancer among non-smoking women. In addition, severe fluorosis has been observed in several parts of China where coal fluoride levels are high.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants↗
PubMed1989

Identification and purification of a protein that stimulates the helicase activity of the Escherichia coli Rep protein.

A polypeptide (Mr = 15,000) has been purified from Escherichia coli cell extracts that significantly stimulates the duplex DNA unwinding reaction catalyzed by E. coli Rep protein. The Rep helicase unwinding reaction was stimulated by as much as 20-fold, upon addition of the stimulatory protein, using either a 71-base pair or a 343-base pair partial duplex DNA molecule as a substrate. The purified Rep helicase stimulatory protein (RHSP) had no intrinsic helicase activity or ATP hydrolysis activity and did not stimulate the single-stranded DNA-dependent ATP hydrolysis reaction catalyzed by Rep protein. It is likely that RHSP stimulates the Rep helicase unwinding reaction by stoichiometric binding to single-stranded DNA. However, a specific interaction between Rep protein and RHSP cannot be ruled out, since RHSP did not stimulate the duplex DNA unwinding reactions catalyzed by E. coli helicase I or the recently discovered 75-kDa helicase. RHSP did stimulate the duplex DNA unwinding reaction catalyzed by E. coli helicase II. The identification and subsequent purification of RHSP from cell extracts demonstrates the feasibility of using direct helicase assays to purify stimulatory proteins.

Adenosine Triphosphatases↗
PubMed1989

Permeability and mechanism of albumin, cationized albumin, and glycosylated albumin transcellular transport across monolayers of cultured bovine brain capillary endothelial cells.

We have measured the permeability and binding characteristics of bovine serum albumin (BSA), cationized BSA (cBSA), and glycosylated BSA (gBSA) to primary cultures of bovine brain capillary endothelial cells (BBCEC). These endothelial cells serve as an in vitro model to study the binding, uptake, and transcellular transport of small and large molecule flux across the blood-brain barrier. The rate of [3H]BSA flux across the cultured BBCEC monolayers grown onto polycarbonate membranes (5-microns pore size) was linear with increasing BSA concentration and the flux could be inhibited by temperature reduction to 0-4 degrees C. The maximal binding of [3H]BSA was 0.04 fmol/mg total cell protein and could not be inhibited by nonradiolabeled BSA. The binding of cBSA and gBSA was rapid and could be inhibited by nonradiolabeled cBSA or gBSA, respectively. The maximal amount bound was 1.8 fmol/mg total cell protein for cBSA and 17.4 fmol/mg total cell protein for gBSA. The dissociation constants (Kd's) were 27 +/- 13 and 3.7 +/- 1.1 nM for cBSA and gBSA, respectively. The flux rates of cBSA and gBSA across the endothelial cell monolayers were linear with respect to concentration and they were approximately seven times greater than those observed for BSA. Each of the proteins appeared on the antiluminal side of the endothelial cell monolayers primarily (90%) as intact protein as determined by trichloroacetic acid (TCA) precipitations and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE). The results for BSA are similar to those observed for lucifer yellow, a fluid-phase endocytic marker.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗
PubMed1989

The effect of chronic dietary acidification using ammonium chloride on acid-base and mineral metabolism in the adult cat.

Adult cats with normal renal function were fed a nutritionally balanced, vitamin A-replete, experimental dry diet with or without ammonium chloride (NH4Cl) for 6 mo to study the effects of chronic dietary acidification on acid-base parameters and the metabolism of selected minerals. Dietary balance studies were performed monthly. Blood and urine samples were collected monthly to evaluate acid-base parameters, plasma parathyroid hormone (PTH) and 1.25-dihydroxycholecalciferol levels. Ammonium chloride-treated cats had significantly lower blood and urinary pH, and lower blood bicarbonate concentrations. Treated cats also had higher blood ionized calcium concentrations, hypercalciuria and lower intestinal calcium absorption relative to baseline (prior to feeding the experimental diet) and to control cats. This resulted in the development of lower calcium balance in the first several months. PTH levels were unaffected by dietary acidification; however, 1.25-dihydroxycholecalciferol levels were significantly decreased in treated cats. Treated cats had negative potassium balance during 5 mo of dietary acidification. Magnesium, sodium, and phosphorus balances were lower, but positive, in treated cats compared to control cats. Cats consuming the NH4Cl-supplemented diet had increased chloride balance. Thus, chronic dietary acidification with 1.5% NH4Cl produced chronic metabolic acidosis and lower or negative, calcium and potassium balance.

Acid-Base Equilibrium↗
PubMed1988

Characterization of specific receptors for atrial natriuretic factor on cultured bovine brain capillary endothelial cells.

A specific receptor for rat atrial natriuretic factor (rANF) was identified on primary cultures of bovine brain capillary endothelial cells (BBCEC's). Cultured BBCEC's have been developed in our laboratory as an in vitro model of the blood-brain barrier. The binding of [125I]-rANF was rapid, reversible, saturable and unaffected by the presence of hormonal peptides such as insulin, vasopressin and angiotensin II. Scatchard analysis of competitive binding studies indicated the presence of a single class of binding sites for rANF with a dissociation constant of 400 pM and maximal binding capacity of 52 fmol/mg total cell protein. Binding of [125I]-rANF was inhibited to varying degrees by atriopeptins I-III with atriopeptin III being the most potent and atriopeptin I being the least potent. BBCEC's also rapidly internalized [125I]-rANF (100% after 60 min at 37 degrees C) by a temperature-dependent process.

Animals↗
PubMed1988

Molecular analysis of the gene encoding alpha-lytic protease: evidence for a preproenzyme.

A 1.7-kb EcoRI fragment containing the structural gene for alpha-lytic protease has been cloned from Lysobacter enzymogenes 495 chromosomal DNA: the first example of a gene cloned from this organism. The protein sequence deduced from the nucleotide sequence encoding this serine protease matches the published amino acid sequence [Olson et al., Nature 228 (1970) 438-442] precisely. Sequence analysis and S1 mapping indicate that, like subtilisin [e.g., Wells et al., Nucleic Acids Res. 11 (1983) 7911-7925] alpha-lytic protease is synthesized as a pre-pro protein (41 kDa) that is subsequently processed to its mature extracellular form (20 kDa). This first finding of a large N-terminal protease precursor in a Gram-negative bacterial protease strengthens the hypothesis that large precursors may be a general property of extracellular bacterial proteases, and suggests that the N- or C-terminal location of the precursor segment may be significant.

Amino Acid Sequence↗
PubMed1988

Physical activity, diet, and risk of colon cancer in Utah.

A population-based case-control study was used to assess the relations of physical activity and diet to the development of colon cancer in Utah. Data were obtained for a reference period of two years prior to interview for controls (204 females and 180 males) and two years prior to the date of diagnosis for cases (119 females and 110 males). Both leisure time and occupational activities were ascertained by level of intensity and were converted to calories expended per week for analysis. Dietary data were obtained from a quantitative food frequency questionnaire. Physical activity and dietary data were divided into quartiles based upon the distribution in the study population for analyses. Total physical activity was protective against the development of colon cancer for both males (odds ratio (OR) = 0.70) and females (OR = 0.48) when high and low quartiles of activity were compared. Intense physical activity was the component of activity that had the greatest protective effect for males (OR = 0.27); a similar relation was seen for females (OR = 0.55). The observed relation between physical activity and colon cancer was not confounded by dietary intake of calories, fat, or protein, nor was the diet and colon cancer relation confounded by physical activity (odds ratios for calories, protein, and fat in males were 2.40, 2.57, and 2.18, respectively). Assessment of the interrelations among physical activity, diet, and colon cancer suggests that physical activity modifies colon cancer risk associated with diet.

Adult↗
PubMed1988

Diabetes in Utah among adults: interaction between diabetes and other risk factors for microvascular and macrovascular complications.

From a telephone survey of the health status of a random sample of the general population of Utah, we identified 255 people with adult onset diabetes. We compared them to 622 non-diabetic controls, matched for age, sex, and urban/rural country of residence. We examined diabetes as a risk factor for heart diseases, stroke, and blindness and its interaction with other known risk factors. Diabetes interacted with smoking history so as to increase the risk of stroke, heart disease, and blindness. Diabetes also interacted with hypertension in their effect on the prevalence of blindness and, to a small extent, heart disease. Among the diabetics, duration of diabetes was associated with macrovascular and microvascular complications developing after the diagnosis of diabetes. Those with longer duration of disease showed an increase in risk for microvascular (kidney disease, blindness) and macrovascular (heart disease, stroke, amputations) complications. Although the estimates were imprecise, the effect of duration on macrovascular complications was greater among diabetics with a history of hypertension; the effect on microvascular complications was greater among smokers. The findings are compared to previous studies and the utility of diabetes prevalence data is discussed.

Adult↗
PubMed1987

Cortical generators of the CI component of the pattern-onset visual evoked potential.

Thirteen-channel visual evoked potentials (VEPs) to pattern-onset were recorded with stimuli restricted to individual octants of the peripheral field, to halves and to quadrants of the fovea. The voltage of the CI component was measured in each channel to define its topography for each stimulated sector. The potential fields so obtained were then analysed to find the orientation and location of a dipole that would produce a corresponding pattern of voltages at the scalp. The locations of the computed dipoles are consistent with the hypothesis that CI is generated in striate cortex. The computed locations and orientations are not compatible with alternative arrangements of sources in extrastriate cortex. A significant problem remains. If CI is indeed generated by the striate cortex then the orientation of the dipoles excited by stimulation of the peripheral field indicates that the cortex is surface negative. This leads to the prediction that foveal stimuli will elicit a CI which is negative at posterior electrodes. The experiments reported here confirm that CI is positive with such stimuli, and its source is calculated as a horizontal dipole with its positive pole oriented posterolaterally. Two possible explanations are considered for the reversed polarity of foveal CI: (a) that macropotentials associated with stimulation of the fovea are opposite in polarity from those associated with stimulation of the peripheral field; (b) that the foveal area of the retinotopic map extends into the lateral calcarine fissure with the effect that much of it faces in the reverse direction from the cortex at the pole.

Adolescent↗