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Biomedical subjects

S L Johnson

Publications and source records attributed to S L Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1986

Nurse practitioner and physician assistant satellite health centers. The pending demise of an organizational form?

A national cohort of 44 rural satellite health centers originally staffed by nurse practitioners (NPs) and physician assistants (PAs) was studied in 1975 and resurveyed in 1979 and in 1984 to examine the viability of this type of health-care delivery organization during a period of significant growth in the nation's physician supply. Twelve of these practices had ceased to function, although eight have been replaced by physician practices. Of the remaining 32, 14 have physicians on their staffs and 18 remain staffed only by NPs and PAs. Those centers staffed by physicians experience greater patient utilization, charge more for office visits, have larger budgets, and generate more of their budgets from fees for services and therefore appear to be more organizationally stable than centers staffed only by NPs and PAs. Although broader studies are needed for substantiation, these findings suggest that the period when NP/PA-staffed satellite health centers were important organizations for delivering care to previously underserved rural communities may be ending.

Community Health Centers↗
PubMed1985

Inhibitors of Na+/H+ exchange block stimulus-provoked arachidonic acid release in human platelets. Selective effects on platelet activation by epinephrine, ADP, and lower concentrations of thrombin.

We have observed previously that removal of extraplatelet Na+ blocks platelet secretion of dense granule contents in response to epinephrine, ADP, and 0.004 unit/ml thrombin, all agents which must mobilize arachidonic acid for its subsequent conversion to cyclooxygenase products in order to elicit platelet secretion. The present studies demonstrate that removal of extraplatelet Na+ blocks arachidonic acid mobilization in response to epinephrine, ADP, and 0.004 unit/ml thrombin without altering arachidonic acid conversion to thromboxane A2. The data also provide several lines of evidence which suggest that the blockade of arachidonic acid release due to removal of extraplatelet Na+ is a manifestation of blockade of Na+/H+ exchange system. 1) There is a concentration-dependent effect of extraplatelet Na+ (EC50 congruent to 55 mM) on [3H]arachidonic acid release such that mobilization is observed when [Na+]o greater than [Na+]i. 2) Increasing extraplatelet [H+] (i.e. decreasing extraplatelet pH from pH 7.35 to 6.8) causes a concentration-dependent decline in stimulus-provoked [3H]arachidonic acid release. 3) Ethylisopropylamiloride and other potent 5-amino analogs of amiloride block [3H]arachidonic acid release with a potency that parallels their effects on Na+/H+ exchange in other cellular systems. None of the above manipulations alter primary aggregation induced by epinephrine, ADP, or 0.004 unit/ml thrombin, indicating that stimulus-receptor binding, subsequent exposure of fibrinogen receptors, and fibrinogen-mediated platelet-platelet cross-linking are not significantly inhibited by [3H]arachidonic acid release in response to greater than 0.1 unit/ml thrombin, a stimulus that can elicit platelet secretion in the absence of products of the cyclooxygenase pathway. Therefore, Na+/H+ exchange may selectively modulate arachidonic acid mobilization in response to the so-called "weak agonists," agonists that require this mobilization to effect vigorous platelet aggregation and dense granule secretion.

Adenosine Diphosphate↗
PubMed1985

Gastrointestinal absorption as a function of age: xylose absorption in healthy adults.

Xylose oral absorption was examined in 24 healthy male subjects ranging in age from 32 to 85 years. Absorption was evaluated from xylose plasma concentration-time data after administration of a 25 gm po or a 5 gm iv dose. There was no relationship between various estimates of the rate of absorption and age. The absolute oral bioavailability or the extent of xylose absorption showed no relationship to age in our population. In contrast with previous suggestions, xylose absorption does not decline with age. General statements of decreased gastrointestinal absorption efficiency as a function of age may not be correct.

Administration, Oral↗
PubMed1984

Quantitation of xylose from plasma and urine by capillary column gas chromatography.

A specific and sensitive assay for quantitation of xylose from plasma and urine has been developed. Following a clean-up procedure, plasma (0.1 ml) or urine (0.2 ml) samples are concentrated and undergo two sequential derivatization steps. A methyloxime derivative is formed initially, followed by trimethylsilylation of all hydroxyl groups. The derivatized samples are quantitated by capillary column gas chromatography using flame ionization detection. Xylose and the internal standard (2-deoxy-D-ribose) have retention times of 6.5 and 5.2 min, respectively. Other monosaccharides (e.g. ribose, arabinose) do not interfere with the assay. Standard curves are linear and reproducible over a concentration range of 10-200 mg/l for plasma and 100-2000 mg/l for urine. The within-day and day-to-day percentage coefficients of variation were less than 5 and 9%, respectively, for plasma and urine.

Arabinose↗
PubMed1984

Correlates of weight loss and its maintenance over two years of follow-up among middle-aged men.

This paper analyzes demographic, social, psychological, and behavioral correlates of weight loss and maintenance in a group of 89 middle-aged men. Measures were collected before and after a 15-week intervention program and at 3-month and 1-year follow-up evaluations. Associations were examined through 2 years of follow-up observation. Principal findings were (a) a strong inverse relationship between prior participation in an organized weight control program and both short- and long-term weight loss; (b) a positive association between efficacy expectations and weight loss; (c) a positive association between attendance at treatment sessions and weight loss; (d) an inverse relationship between spouse attendance and weight loss; and (e) positive associations between weight loss and perceived social support, reported improvement in eating behavior, reported improvement in exercise behavior, and affirmative response to relapse episodes following treatment.

Body Weight↗
PubMed1984

Behavioral treatment of obesity with monetary contracting: two-year follow-up.

Reported is a 2-year follow-up of a behavioral weight reduction program for men using monetary contracts of varying size and group versus individual contingencies. Although initial weight losses were large, in the absence of an effective maintenance program weight losses at two years were modest, similar to those obtained with less effective initial weight loss procedures. Group contracts were significantly more effective in producing long term loss than individual contracts. Reported behaviors associated with weight loss at 2 years are presented.

Behavior Therapy↗
PubMed1984

Calorie requirements in weight loss: an estimate based on self-reported food intake in middle-aged men.

Twenty-eight men participating in a weight reduction program self-recorded foods eaten and calorie consumption for a 15-week period. These food records were examined to estimate calorie needs during weight loss as a function of age, entry weight, height and physical activity level. Only entry weight was significantly associated with calorie need. A predictive equation for calorie need is offered for setting individual calorie intake goals for patient-assessed calorie intake.

Body Weight↗
PubMed1984

Effect of bacterial secondary infection in an animal model of trachoma.

In trachoma the interaction between chronic chlamydial and acute bacterial conjuntivitis has been suggested as important in determining the severity of disease and, therefore, blindness. We investigated the effect of acute conjunctival infection with each of three common human pathogens, Haemophilus influenzae, Haemophilus aegyptius , and Streptococcus pneumoniae, in a model of trachoma established in cynomolgus monkeys. Although acute conjunctivitis developed, animals with trachoma were not more susceptible to infection than other monkeys, nor did they develop more severe disease as a result of the bacterial conjunctivitis. The failure of bacterial conjunctivitis to exacerbate the experimental trachoma indicates that, in this model at least, chronically maintained chlamydial infection alone is sufficient to produce the changes characteristic of trachoma.

Animals↗
PubMed1984

Detection of experimental Chlamydia trachomatis eye infection in conjunctival smears and in tissue culture by use of fluorescein-conjugated monoclonal antibody.

The immunofluorescent staining of conjunctival cytology smears with an antichlamydial monoclonal antibody is a new method for the detection of chlamydial eye infection. Using a monkey model of chlamydial eye infection, we compared the monoclonal antibody staining cytology with the established methods of Giemsa-stained cytology and chlamydial culture with cycloheximide-treated McCoy cells. Compared with either culture or monoclonal antibody-stained cytology, Giemsa cytology had a low sensitivity (30 and 24%, respectively) but was highly specific (100% in each case). Compared with culture, monoclonal antibody-stained cytology was highly sensitive (94%) but appeared to lack specificity (70%). However, examination of the changes in identification rates with time suggested that monoclonal antibody-stained cytology may be even more sensitive than culture and detect lower levels of infection. This study showed that monoclonal antibody-stained cytology of conjunctival smears might be a rapid, efficient, and inexpensive method of diagnosing ocular chlamydial infection.

Animals↗
PubMed1984

Low-sodium, high-potassium diet: feasibility and acceptability in a normotensive population.

Sixty-nine normotensive volunteers participated in an eight-week study to test the feasibility and acceptability of two low-sodium (less than 70 mEq), high-potassium (greater than 100 mEq) diets. The diet groups differed only in the use of KCl salt substitute. Both dietary groups were able to reduce sodium and increase potassium intake compared to the control group. Urine sodium excretion decreased in the diet groups but no change was observed in potassium. Potassium chloride salt substitute was not used as recommended, suggesting its unacceptability.

Adult↗
PubMed1983

Reversed-phase thin layer chromatography of some common sterols.

The chromatographic mobilities of 17 sterols and squalene on reversed-phase thin layer plates with four nonaqueous solvent systems is described. A degree of separation adequate to identify several of the sterols was obtained. It was possible to separate the pairs: cholestanol, epicholestanol; coprostanol, epicoprostanol; 5 beta-cholestan-3 alpha and 3 beta-ol and lanosterol, dihydrolanosterol.

Chromatography, Thin Layer↗
PubMed1983

In vitro and in vivo evaluations of the antibiotic efrotomycin.

Experiments were conducted to determine the potential of the antibiotic efrotomycin as a growth permittant for poultry and to further elucidate the mode of action of antimicrobial agents for that purpose. Efrotomycin as the semipurified antibiotic and as fermentation solids demonstrated excellent activity against Clostridium perfringens at .1 to .2 ppm based on suppression of gas production in an anaerobic tube test. Supplementing a soybean protein and sucrose-based diet with levels of 2.2, 11, and 55 ppm of the antibiotic, from the two sources each with two different purities, improved weight gain of chicks an average of 23% and improved feed efficiency an average of 13% at the higher levels (all P less than .01). Computed indexes for each antibiotic treatment, which represent the combined effects of both weight gain and feed efficiency, showed that a maximum response was generally obtained at the 11 ppm level and that the antibiotic as fermentation solids was slightly more active than the semipurified material. Supplementing the soybean protein and sucrose-based diet with levels of 1.1, 5.5, 16.5, and 55 ppm of efrotomycin reduced the numbers of C. perfringens organisms in ileal contents of chicks (all P less than .01). The effects were dose-related. Control chicks in this experiment averaged greater than 7.7 log10 of C. perfringens counts per gram of contents. The results of these experiments show that efrotomycin has excellent growth-permittant activity and the activity correlates with the antibacterial activity against C. perfringens.

Animals↗
PubMed1983

Effects of diet and bacitracin on growth, feed efficiency, and populations of Clostridium perfringens in the intestine of broiler chicks.

Experiments were conducted to demonstrate the activity of bacitracin as a growth permittant for poultry and to further elucidate the mode of action of antimicrobial agents for that purpose. Supplementing a soybean protein and sucrose-based diet with 2.2, 11, and 55 ppm of bacitracin resulted in significant improvements in weight gain and feed efficiency of chicks fed the higher levels. In a second experiment, graded levels of bacitracin from 1.1 to 55 ppm were fed. A regression analysis of the index scores, the combined effects of both weight gain and feed efficiency, on the log of the significant dose levels of 5.5 to 27.5 ppm gave a linear response line with r = .996. Based on the equation, the ineffective level of the antibiotic was determined to be 4 ppm and the maximum effective level 31 ppm. Supplementing the soybean protein and sucrose-based diet with levels of 5.5, 16.5, and 55 ppm of bacitracin reduced the numbers of Clostridium perfringens organisms in ileal contents of chicks (all P less than .05). Chicks fed a level of 1.1 ppm, a level that did not give a growth response, had numbers of the organism present that were not significantly different from controls. Supplementing a soybean meal and corn-based diet with a level of 55 ppm of bacitracin did not significantly affect weight gain, feed efficiency, or numbers of C. perfringens in the ileum of chicks.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Effects of diet, bacitracin, and body weight restrictions on the intestine of broiler chicks.

Six experiments were conducted to evaluate the effects of diet, bacitracin, and body weight restrictions on the intestine of the broiler chick. Bacitracin, at levels of 11 and 55 ppm, significantly increased body weight, significantly reduced small intestine weight, but had no significant effect on liver weight of chicks fed a soybean protein and sucrose-based diet. The greatest effects were observed in the ileum where weight, moisture, length per unit of body weight, and dry matter per unit of length were all significantly reduced. The least effects were observed in the duodenum where weight and length per unit of body weight were significantly reduced and dry matter per unit of length was significantly increased. Intestinal weight, as a percent of body weight, was not significantly affected when body weight was suppressed with a high level of nicarbazin added to a practical diet, but it was significantly reduced when bacitracin was added to the semipurified diet and chicks were restricted in food intake to 70% of controls. A level of 55 ppm of bacitracin added to the practical diet had no significant effect on body weight, intestinal weight, or liver weight. As discussed, the observed changes in the intestine, due to bacitracin, are probably indirect and most likely reflect the action of the antibiotic on the intestinal microflora.

Animals↗
PubMed1983

Effect of the antibiotic thiopeptin on Clostridium perfringens and growth and feed efficiency of broiler chicks.

Experiments were conducted to determine the potential of the antibiotic thiopeptin as a growth permittant for poultry. Thiopeptin as the semipurified antibiotic and as fermentation solids demonstrated activity against Clostridium perfringens at .03 ppm based on suppression of gas production in an anaerobic tube test. Supplementing a soybean protein and sucrose-based diet with levels of 2.2, 11, and 55 ppm of thiopeptin from each of the two sources resulted in significant improvements in weight gain and feed efficiency of chicks fed the higher levels. Computed indexes for each antibiotic treatment showed that the antibiotic as fermentation solids was slightly more active than the semipurified material at the lower levels. Supplementing the soybean protein and sucrose-based diet with 1.1, 5.5, 16.5, and 55 ppm thiopeptin reduced significantly (P less than .01) the numbers of C. perfringens organisms in ileal contents of chicks. Chicks fed 5.5, 16.5, and 55 ppm thiopeptin also had significantly fewer C. perfringens organisms in the intestine than those fed 1.1 ppm. A discussion is presented of the biological responses of thiopeptin relative to the antibiotics efrotomycin and bacitracin.

Animals↗
PubMed1983

An animal model of trachoma: IV. The failure of local immunosuppression to reveal inapparent infection.

Repeated inoculation with live chlamydia trachomatis is necessary to develop a model of trachoma in monkeys. However, it is not possible to reisolate chlamydia from the monkey's eye after the first 1 or 2 months of weekly reinoculation. The effect of subconjunctival steroid injections in monkeys that had received weekly inoculations with live chlamydia is reported. Despite a profound suppression of local inflammation, steroid treatment did not produce a reactivation of identifiable chlamydial infection as determined by repeated chlamydial cultures and cytologic examinations.

Adrenal Cortex Hormones↗
PubMed1982

An animal model of trachoma II. The importance of repeated reinfection.

An animal model of chronic cicatrizing trachoma has been produced by repeated ocular inoculation with Chlamydia trachomatis serotype E, a genitally transmitted strain. We have now produced a chronic follicular conjunctivitis on cynomolgus monkeys by repeated inoculation with C. trachomatis serotype A, which has been isolated from an area of endemic trachoma. This disease was similar in all respects to that which followed infection with the serotype E strain. Cynomolgus monkeys inoculated with a single dose of serotype E of C. trachomatis strain developed an acute, self-limited follicular conjunctivitis, which was intense for 4 weeks and then slowly subsided. The organism could be reisolated only during the first 4 weeks after inoculation. On reinoculation at 15 and 30 weeks after the initial infections, these animals demonstrated only a mild and transitory clinical response, and the agent could be recovered for only up to 14 days after inoculation. In contrast, repeated weekly reinoculation with either serotype led to a chronic progressive clinical response in these animals, although after the first 6 weeks the agent was isolated only occasionally. This chronic disease was shown not to be due to hypersensitivity to the egg yolk components in which the organism was grown. These data suggest that the serotype of the chlamydial organism may not be as important in determining the clinical course of disease as is the frequency or persistence of exposure to the chlamydial agent. Although a single inoculum produced an acute follicular conjunctivitis, repeated inoculation is needed to produce the chronic disease characteristic of trachoma in this animal model.

Animals↗