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Biomedical subjects

B Davis

Publications and source records attributed to B Davis.

At least 253 records · Page 14Linked to original sources
PubMed1979

Effect of terbutaline on movement of Cl- and Na+ across the trachea of the dog in vitro.

The epithelium of canine trachea maintains a transepithelial potential difference (lumen negative relative to submucosa) by active transport of Cl- toward the lumen and of Na+ away from the lumen. This study examined the effects of terbutaline (a beta-adrenergic agonist) on short-circuit current, potential difference, electrical conductance, and fluxes of 36Cl and 24Na measured across pieces of canine trachea mounted in Ussing-type chambers. In short-circuited tissues, 10(-5) M terbutaline increased unidirectional Cl- flux toward the lumen from 4.78 +/- 1.12 (mean +/- SEM) to 6.28 +/- 1.06 muEq/cm2.h. The other measured fluxes did not change significantly. Increases in unidirectional Cl- flux toward the lumen were related to terbutaline concentration (range, 10(-7) to 10(-5) M); 10(-6) M propranolol prevented or decreased these effects. These studies suggest that terbutaline acts via beta-adrenergic receptors to increase active transport of Cl- toward the lumen.

Animals↗
PubMed1979

The effect of beta-glucuronidase and chitinase on the cell wall of Aspergillus niger and Aspergillus fumigatus.

The effects of beta-glucuronidase and chitinase have been tested on the hydrolysis of the cell walls of the economically important fungi, Aspergillus niger and Aspergillus fumigatus. The extent of wall hydrolysis was measured by assaying for total reducing sugars, N-acetyl sugars and protoplast production. Maximum reducing sugar release was attained after 40 min incubation, both with beta-glucuronidase supplemented with chitinase and beta-glucuronidase alone, whereas N-acetyl sugar release reached a maximum at 80 min incubation. beta-Glucuronidase was effective in releasing protoplasts from both species of Aspergillus. This release was enhanced by adding chitinase to the incubation medium at 0 and 20 min, but with addition at 60, 80 and 100 min increase in protoplast yield was much reduced. The results of re-incubation experiments with chitinase suggest that this enzyme may in some way be inhibited during the later stages of incubation. Pronase used in combination with beta-glucuronidase slightly enhanced protoplast release.

Aspergillus fumigatus↗
PubMed1978

Regulation of Na+ and Cl- transport and mucous gland secretion in airway epithelium.

Ussing's short-circuit technique was applied to canine airway epithelium in vitrol and a net flux of Cl- towards the airway lumen was demonstrated, with a smaller net flux of Na+ in the opposite direction. Furosemide decreased and acetylcholine, terbutaline, and histamine increased net ion transport towards the airway lumen. Associated changes in water content in the airway lumen could affect mucociliary clearance, and therefore inhibition of ion transport may play a role in disease states. To study secretions from submucosal glands in vivo, two techniques were used to identify the duct openings in the exposed canine tracheal epithelium. (a) The exposed mucosal surface was coated with powdered tantalum; accumulated secretions produced elevations under which the duct openings were located. (b) A vital dye (0.1% Neutral red) was placed on the exposed mucosal surface; the dye stained the duct openings. With these techniques, the innervation of the submucosal glands and the autonomic regulation of their secretions were studied. Micropuncture techniques were used to sample the secretions from the glands and ducts.

Acetylcholine↗
PubMed1978

Diuretic effect of a combined preparation of frusemide and slow-release potassium chloride.

An open randomized crossover study was carried out in 10 healthy volunteers to compare the diuretic effect of a single tablet combining 40 mg frusemide and a slow-release formulation of 600 mg potassium chloride with that of the two agents given in separate tablets. The results showed that both treatments had a similar effect on urinary volume and on sodium and potassium excretion, but the hourly urinary volumes during the first 6 hours suggested that the diuretic action of the combined formulation occurred slightly earlier after administration.

Adult↗
PubMed1978

Prolonged negative feedback suppression after estradiol administration: proposed mechanism of eugonadal secondary amenorrhea.

The finding of normal gonadotropin and estradiol levels in eugonadal women with secondary amenorrhea suggests a disordered feedback relationship of the hypothalamic-pituitary-ovarian axis. To identify possible defects in negative and positive feedback, we compared the effects of five daily injections of 17 beta-estradiol (E2) in 13 normal women and 11 eugonadal patients with absent cyclic menses. The suppression phase of negative feedback was normal, as LH and FSH were similarly lowered in both groups on day 3. Continued LH (P less than 0.01) and FSH (P less than 0.02) inhibition on day 10 of the protocol, 5 days after the last E2 injection, indicated a defect in the recovery phase of negative feedback in the 11 amenorrheic women. In the 4 patients studied gonadotropin suppression persisted for 3 weeks, E2 did not blunt pituitary responsiveness to GnRH in the amenorrheic women, suggesting a central nervous system site for prolonged gonadotropin inhibition. Nine normal but only 2 amenorrheic women X2 = 4.15; P less than 0.05) exhibited a positive feedback increase in LH on days 4-6. We propose that a defect in the recovery phase of negative feedback to E2 rather than absent positive feedback may be the dominant physiological abnormality which causes secondary amenorrhea by preventing early follicular phase gonadotropin increments and follicular maturation.

Adult↗
PubMed1977

Interaction patterns between psychiatric aides and patients.

The present study investigated the manner in which psychiatric aides used their time when not involved in staff meetings or off-ward activities. Aides' behaviors on two shifts were observed during times they had the greatest likelihood of interacting with patients. It was found that aides were most likely to be observed in the Nursing Station on both shifts. Aides typically had a specific purpose for interacting with patients when they were on the wards. It was concluded that increased structuring of patient-aide interactions was necessary along with more stringent guidelines regarding the use of the Nursing Station.

Employee Performance Appraisal↗
PubMed1977

An in vitro system for studying insulin release: effects of glucose and glucose-6-phosphate.

1. Investigation of the ionic requirements of the in vitro insulin release system, which consists of cod islet plasma membrane and rabbit islet granules incubated at pH 6.5, showed that the presence of Ca(2+) was obligatory for the system to operate.2. Glucose-initiated insulin release was as effective in the presence of beta-gamma-methylene ATP, as it was in the presence of ATP. This analogue of ATP is a substrate neither for adenylate cyclase nor for any known animal membrane proteases. The effect of ATP on glucose mediated release is allosteric.3. Glucose (16 mM)-initiated insulin release was slower than that induced by glucose-6-phosphate (4 mM); 150 and 120 sec, respectively.4. The lag found with glucose-mediated insulin release was dependent upon glucose concentration. The lower the glucose concentration, the longer the lag. With 1 mM glucose the lag extended to 30 min.5. Once insulin release was initiated, the rate and amount of insulin release was independent of the glucose concentration.6. Pre-incubation of membranes with Ca(2+), glucose and ATP prior to the addition of granules, abolished the extended lag that had been obtained with 1 mM glucose. Events in the plasma membrane are the major contributor to the generation of the extended lag.7. The glucose analogue 5'thio-D-glucose, although not able to release insulin, was shown to compete with glucose for the glucoreceptor. By increasing the ratio of analogue to glucose the lag time increased. Thus, the lag time is dependent upon the ;effective' external glucose concentration.8. The max. amount of insulin released by 4 ng of membrane in the presence of glucose (16 mM) was 300 ng. The fact that membranes became refractory to glucose after this max. amount of insulin was released showed that recycling of release sites was not taking place in vitro and that granule: granule interactions were not occurring.9. The 120 sec lag before glucose-6-phosphate-initiated release was independent of glucose-6-phosphate concentration. The rate of insulin release with glucose-6-phosphate was concentration dependent.10. Glucose-6-phosphate did not cause further insulin release from a membrane that had released the max. amount of insulin it was capable of in the presence of glucose. The addition of tolbutamide (10 mM) to such a membrane did cause insulin release. This suggests that glucose and glucose-6-phosphate share a final common pathway.11. Adrenaline and somatostatin did not inhibit glucose-mediated insulin release.

Adenosine Triphosphate↗
PubMed1977

Effect of histamine on electrical and ion transport properties of tracheal epithelium.

Previously we showed that the active transport of Cl-toward and Na+ away from the tracheal lumen creates an electrical potential difference (lumen negative) across the canine tracheal epithelium in vitro. The present study examined the effect of histamine on the electrical properties and ion transport of the canine tracheal epithelium in vitro. In six pairs of membranes, under short-circuit conditions, histamine (10(-4) M) significantly increased the net flux toward the lumen of Cl- from 1.7 +- 0.5 SE to 2.4 +- 0.6 microneq/cm2-h and Na+ from -0.4 +- 0.3 to 0.2 +- 0.3 microneq/cm2-h. The response to histamine was inhibited by diphenhydramine (10(-6) M), an H1-receptor antagonist, but not by burimamide (10(-4) M), an H2-receptor antagonist. These results are consistent with the hypothesis that an H1-type receptor mediates the increase of ion flux toward the lumen due to histamine. Increased ion flux toward the lumen may mediate water secretion into the airway lumen and have important effects on the physical properties of the liquid through which the respiratory cilia beat.

Animals↗
PubMed1976

New fibreglass casting system in orthopaedic practice.

The composition, manufacture and application of a new fibreglass casting system for use in orthopaedic practice are described. The performance of the first 51 fibreglass casts used in routine fracture work is reviewed. The advantages (the cast is waterprof, extremely light and strong) and the disadvantages (an ultraviolet light source is required to cure the cast and the fiberglass tape is rather expensive) are evaluated.

Adolescent↗
PubMed1976

Nonketotic diabetes mellitus: insulin deficiency or insulin resistance?

Ninety-five nonobese, nonketotic subjects were divided into five groups (one normal and four with varying degrees of glucose intolerance) according to their plasma glucose responses during an oral glucose tolerance test. These five groups were then compared on the basis of their insulin response during the oral glucose tolerance test and on the ability of exogenously infused insulin to limit hyperglycemia during a continuous infusion of glucose and insulin, while endogenous insulin was inhibited by the infusion of epinephrine and propranolol. The mean plasma insulin response of patients with either borderline abnormalities of glucose tolerance or chemical diabetes was equal to or greater than that of normal subjects at all points during the glucose tolerance test. Thus, the glucose tolerance of these two patient groups cannot be attributed to lack of insulin. On the other hand, the mean insulin response of patients with moderate fasting hyperglycemia (plasma glucose of 110 to 150 mg/100 ml) was somewhat attenuated, and patients with severe fasting hyperglycemia (plasma glucose greater than 150 mg/100 ml) had unequivocal insulin deficiency. In contrast, all four patient groups with abnormal carbohydrate metabolism were more resistant than normal subjects to the action of insulin. These results indicate that there is a very complex relationship between insulin deficiency and insulin resistance in patients currently classified as having nonketotic diabetes. Patients with either borderline abnormal glucose tolerance or chemical diabetes are more resistant to insulin than normal subjects, and are not insulin deficient. In these patients it seems reasonable to assume that their glucose intolerance is a direct function of their insulin resistance. Patients with severe fasting hyperglycemia are suffering from both insulin deficiency and insulin resistance, and the relationship between these two variables in the genesis of hyperglycemia in these subjects remains obscure. It seems apparent from these studies that nonketotic diabetes mellitus can no longer be considered to be a simple function of insulin lack, and that in order to understand this syndrome we will need to increase our knowledge of the relationship between insulin deficiency and insulin resistance in these patients.

Adult↗
PubMed1976

An in Vitro system for studying insulin release caused by secretory granules-plasma membrane interaction: definition of the system.

1. An in vitro system is described in which insulin beta-granule-plasma membrane interaction can be studied. 2. The system shows an absolute requirement for physiological amounts of Ca2+ (2 muM) in order for insulin release to proceed. 3. ATP (5 muM) is abot to augment the Ca2+ effect. 4. Glucose (17 mM) alone does not cause insulin release but in the presence of Ca2+ is as effective as ATP. 5. When glucose, ATP and Ca2+ are added together a positive cooperative effect is produced with over 85% of the total insulin, added in the form of beta-granules, being released into the medium in 10 min. 6. The system responds to tolbutamide, in the presence of Ca2+ and ATP, by releasing insulin. 7. Diazoxide, a potent insulin inhibitor in vivo, demonstrates a similar activity in vitro. 8. Various control experiments utilizing alternative membranes, granules, nucleotides, sugars and phosphorylated intermediates of metabolism have all reinforced the specificity of the release mechanisms. 9. These results demonstrate that the in vitro system mimics responses found in the intact organism and can be utilized to dissect the mechanisms associated with exocytosis of insulin granules. 10. Preliminary experiments utilizing adrenaline granules-adrenal plasma membranes and pituitary granules-pituitary plasma membranes suggest that the in vitro system can be extended to all granule secreting processes.

Adenosine Triphosphate↗