Biomedical subjects
C A Edwards
Publications and source records attributed to C A Edwards.
Viscosity of food gums determined in vitro related to their hypoglycemic actions.
Experiments were carried out in vitro and in normal human subjects to evaluate alternative food-grade viscous polysaccharides as agents for reducing postprandial hyperglycemia and to assess the relationship between the in vitro and in vivo performance of the polysaccharides. A 1:1 mixture of xanthan and locust bean gum (X/LBG) had the greatest viscosity at equivalent concentrations and shear rates and was more effective than guar gum, xanthan, or locust-bean gum at inhibiting glucose movement in vitro. It was not, however, more efficient in lowering postprandial blood glucose and plasma insulin in human subjects when incorporated in a drink containing 50 g glucose. When the different gums were acidified and reneutralized to mimic conditions in the gut, there was a better correlation between viscosity and blood glucose and plasma insulin levels. This effect may explain why X/LBG was no more effective than the other gums in reducing postprandial hyperglycemia in man.
Mechanisms of association of Candida albicans with intestinal mucosa.
The association of Candida albicans with gastrointestinal (GI) mucosal surfaces was studied in vitro and in vivo. The caecal mucosal surfaces from antibiotic-treated and untreated control mice challenged orally with C. albicans revealed that large numbers of C. albicans were associated with the intestinal epithelium of antibiotic-treated mice but not with that of the control mice that possessed an indigenous wall-associated bacterial flora. Moreover, Candida cells only penetrated deep into the mucosa of animals in which the ecology of the intestinal microflora had been disrupted. In mice given antibiotics, C. albicans was associated with the mucosa of all areas of the GI tract; the caecal mucosa had the most associated Candida, whereas the stomach and small intestine had very few associated yeasts. Further examination of caecal mucosa from antibiotic-treated mice showed that C. albicans associated with the mucosa by at least five distinct mechanisms. These included: adhesion to epithelium, adhesion to mucus, co-adhesion to adherent fungi, co-adhesion to adherent bacteria, and entrapment in the mucous gel overlying the epithelium. The cell-surface hydrophobicity of C. albicans also was examined and found not to play a role in Candida adhesion to intestinal mucosa. The predominant association mechanisms appeared to be entrapment in the mucous gel, and adhesion to mucus and the epithelium. The ecological and pathological significance of co-adhesion by C. albicans to attached organisms is unclear but it may be important in the initiation of mucosal lesions.
The effect of two alpha 2-adrenoreceptor agonists and an antagonist on gastric emptying and mouth to caecum transit time in humans.
Experiments were performed to investigate the effect of two alpha 2-adrenoreceptor agonists, clonidine and lidamidine, and a specific alpha 2-adrenoreceptor antagonist, idazoxan, on gastric emptying and mouth to caecum transit time (MCTT) of a radiolabelled meal in 27 healthy male subjects. Lidamidine (20 mg p.o.) and clonidine (0.3 mg p.o.), given alone had no significant effect on gastric emptying or MCTT suggesting that the anti-diarrhoeal action of clonidine and lidamidine are unlikely to be explained by a slowing of small intestinal transit. Idazoxan (20 mg p.o.) reversed the effect of clonidine in 10 subjects, who showed a delay in MCTT after taking clonidine, but did not alter MCTT under basal conditions. These results suggest that although the sympathetic nervous system can influence upper gastrointestinal motility by an action on alpha 2-adrenoreceptors, this action does not exert a tonic influence on upper gastrointestinal motility under basal conditions.
Effect of oral administration of melatonin on GH responses to GRF 1-44 in normal subjects.
In order to investigate the role of melatonin on the neuroregulation of GH secretion, eight healthy male volunteers each underwent four separate tests in random order separated by at least 1 week. Following oral administration of melatonin (500 mg at -60 min and at -30 min) plasma GH levels were higher than after placebo at 45 min (mean +/- SEM 2.9 +/- 0.8 vs 0.9 +/- 0.4 ng/ml, P less than 0.01) and 60 min (mean +/- SEM 2.9 +/- 0.4 vs 0.8 +/- 0.1 ng/ml, P less than 0.05). Likewise, after prior administration of melatonin, GH responses to GRF 1-44 (1 micrograms/kg i.v. at 0 min) were greater than placebo plus GRF at 15 min (mean +/- SEM 22.4 +/- 6.1 ng/ml vs 11.3 +/- 2.3 ng/ml, P less than 0.05), 45 min (mean +/- SEM 26.2 +/- 5.3 ng/ml vs 13.3 +/- 2.5 ng/ml, P less than 0.01) and 60 min (mean +/- SEM, 24.7 +/- 7.4 ng/ml vs 11.1 +/- 2.5 ng/ml, P less than 0.05). In contrast we did not observe any effect of either 10(-9)M, 10(-7)M melatonin on in-vitro basal GH release and GH responses to 10(-8)M GRF by rat anterior pituitary cells in monolayer culture. These data suggest that melatonin plays a facilitatory role in the neuroregulation of GH secretion, probably by acting at the hypothalamic level.
Additive effects of growth hormone releasing factor and insulin hypoglycaemia on growth hormone release in man.
We have measured GH and PRL changes following separate and combined administration of insulin and GH releasing factor (GRF) in six normal males. Peak GH responses to separate administration of insulin and GRF were comparable (71.4 +/- 10.2 vs 70.1 +/- 27.7 mU/l; mean +/- SEM). However, the peak GH response following combined administration was significantly higher (120.8 +/- 29.7, P less than 0.05) as was the total GH released as calculated by measuring the area under the curve (P less than 0.05). In contrast the PRL response to hypoglycaemia was not altered by the combined administration of insulin and GRF. This effect was not due to any direct action of hypoglycaemia or insulin at pituitary level since basal and 10(-8) M GRF stimulated GH release from rat anterior pituitary cells in vitro was not influenced by varying glucose and insulin levels. Our findings support the hypothesis that GRF and insulin-induced hypoglycaemia release GH via different pathways which are, at least in part, additive.
Tri(n-butyl) phosphate/detergent treatment of licensed therapeutic and experimental blood derivatives.
Incubation of an AHF concentrate with 0.3% tri(n-butyl)phosphate (TNBP) and 0.2% sodium cholate was shown to inactivate at least 10,000 infectious doses of lipid-enveloped viruses, including hepatitis B and non-A, non-B viruses and HTLV-III [Prince et al., Lancet i, pp. 706-710, 1986]. The use of TNBP/detergent combinations for virus sterilization was evaluated further to determine its effect on the structure and function of a wide variety of blood proteins. Vesicular stomatitis and Sindbis viruses were used as markers of virus inactivation. TNBP/detergent treatment did not significantly alter the function of AHF, factor VII, factor IX, factor X, fibrinogen, factor XIII, fibronectin, anti-HBsAg and anti-HA in normal serum globulin, haptoglobin, tumor necrosis factor, alpha-interferon, and both native and chemically polymerized stroma-free hemoglobin. As compared with partially purified derivatives, the extent of virus sterilization of plasma and component cryoprecipitate with 0.3% TNBP and 0.2% sodium cholate at ambient temperature could be improved by raising the TNBP concentration and temperature. Virus sterilization by TNBP/detergent mixtures appears to be generally applicable to blood protein derivatives.
Effect of cisapride on the gastrointestinal transit of a solid meal in normal human subjects.
The effect of cisapride, a new gastrointestinal prokinetic agent, on the transit of a standard meal through the stomach, small intestine and colon was studied in 10 normal subjects. Cisapride had no significant effect on gastric emptying but decreased mouth to caecum transit time (p less than 0.01). Stool weight and frequency were not significantly increased but the time for the first appearance of stool markers and the arrival of 20% and 50% of stool markers was decreased after cisapride (p less than 0.05).
Effect of lidamidine, a proposed alpha 2-adrenoreceptor agonist, on salt and water transport in human jejunum.
The effects of a new antidiarrheal agent, lidamidine (10 mg per os) and an identical placebo on jejunal fluid and electrolyte transport in vivo were investigated in five normal volunteers during steady-state perfusion of a 25-cm length of jejunum with a plasma-like solution. Studies were carried out under basal conditions and during secretion stimulated by incorporation of prostaglandin E2 (5 X 10(-6) M) in the infusate. Lidamidine had no significant effect on jejunal fluid transport under basal conditions but reduced secretion induced by prostaglandin E2 (P less than 0.05).
Resolution and reconstitution of the iron-sulfur protein of the cytochrome bc1 segment of the mitochondrial respiratory chain.
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The degradation of guar gum by a faecal incubation system.
1. Homogenized and diluted faeces (50 g/l) from one human source were incubated with the complex plant polysaccharide, guar gum, to investigate the degradation of viscous polysaccharides by intestinal bacteria. 2. Incubation of the faecal homogenate with guar gum produced a rapid decrease in viscosity and in pH, accompanied by the release of hydrogen. 3. No changes in viscosity or pH were observed and there was no production of H2 gas when guar gum was incubated with autoclaved faecal homogenate (20 min, 1.03 x 10(5) Pa). 4. A bacteria-free filtrate of faeces was prepared by centrifuging the faecal homogenate (2400 g for 100 min) followed by filtration through a Seitz filter and then a millipore filter (size 0.45 micron). Incubating this with guar gum produced a slow decrease in viscosity, but no significant change in pH and no generation of H2. 5. Our results show that guar gum can be fermented by human colonic bacteria and suggest the possibility of predigestion by extracellular free enzymes.
Growth control of cultured rat calvarium cells by platelet-derived growth factor.
Platelet-derived growth factor (PDGF), which is released during the "clotting cascade", has a mitogenic effect on a variety of mesenchymal cells including those of the periosteum. Cell culture provides a method of studying these effects. In the present study, PDGF was studied for its ability to stimulate quiescent calvarium periosteal cells to enter G1, indicated by new protein synthesis. After addition of platelet poor plasma, these cells later entered S phase, indicated by uptake of 3H-thymidine. Three hours after PDGF stimulation, there were quantitative increases of at least 18 protein bands as compared to cells left in serum starvation medium. Two of these new protein bands (31K and 45K) required transcription. These data suggest that PDGF in extravasated blood may stimulate appositional bone formation beneath intact periosteum at the site of injury.
Simultaneous measurement of gastric emptying, small bowel residence and colonic filling of a solid meal by the use of the gamma camera.
A method for determining the profiles of gastric emptying, small intestinal residence, and colonic filling of a solid test meal, labelled with 250 microCi 99mTechnetium sulphur colloid has been evaluated in nine healthy volunteers and six patients with a disturbance in bowel habit. Mean small bowel transit time was determined by deconvolving the rate of colonic filling with the rate of gastric emptying. In normal subjects, the stomach appeared to empty exponentially with a half time of 1.2 +/- 0.3 hours (mean +/- SD). Food reached the colon by 2.8 +/- 1.5 hours. The mean small bowel transit time was 4.0 +/- 1.4 hours. In most normal subjects, the colon appeared to fill in a linear fashion with approximately 16% food residues entering every hour, and the profile of colonic filling in normal subjects was similar to the profile of ileal emptying observed after feeding a similar radiolabelled solid meal to 14 patients equipped with terminal ileostomies. There was a highly significant correlation between the onset of breath hydrogen excretion and the appearance of radioactivity over the caecum (r = 0.88, p less than 0.01), though in one third of subjects the increase in caecal radioactivity preceded the rise in breath hydrogen concentration by more than 20 minutes. There was also a highly significant correlation between the mean transit time and values for colonic filling but not values for gastric emptying. Patients with irritable bowel syndrome who had diarrhoea tended towards short small bowel transit and early colonic filling, whereas patients who have constipation tended towards long small bowel transit and delayed colonic filling. This method offers a novel means of assessing small bowel transit time, small bowel residence and the profile of colonic filling in man.
Effect of clindamycin on the ability of a continuous culture of colonic bacteria to ferment carbohydrate.
A continuous culture model of the proximal colon was used to study the effect of clindamycin on the ability of colonic bacteria to ferment carbohydrate. Six steady state anaerobic cultures of human faeces, in a medium simulating ileostomy effluent, were treated with 26 micrograms/ml clindamycin. They were paired with six untreated cultures, run under identical conditions. Clindamycin treatment eliminated the anaerobic bacteria, significantly decreased osmolality and the output of volatile fatty acids, particularly propionic acid and increased the residual carbohydrate concentration. Doubling the amount of carbohydrate in the medium increased osmolality and the production of volatile fatty acid, though the response of clindamycin treated cultures was less than that of untreated cultures. Attempts to introduce Clostridium difficile into three pairs of cultures were successful in only two cultures after administration with clindamycin and when a heavy inoculum (10(6)-10(9) organisms) had been used.
Hidradenitis suppurativa: evidence for an endocrine abnormality.
Women patients with premenstrual exacerbation of hidradenitis suppurativa have been studied to determine if an endocrine abnormality can be detected. A functional disorder of the hypothalamopituitary axis was found in 13 patients with hidradenitis when compared with 9 controls. In response to a combined thyrotrophin releasing hormone and gonadotrophin releasing hormone test, the prolactin and TSH responses were significantly greater in the hidradenitis patients than the controls. No significant differences were found in the mean basal levels of oestrogen, progesterone, testosterone, dehydroepiandrosterone sulphate, T3 and T4. These results may reflect a disturbance of feedback signals from peripheral hormones, rather than a primary dysfunction of the control of specific anterior pituitary cells.
Metabolism of mixed human colonic bacteria in a continuous culture mimicking the human cecal contents.
The purpose of this study was to develop an in vitro model of the proximal colon that would permit investigation of the function of colonic bacteria. Five continuous cultures of fecal bacteria were maintained anaerobically in steady state for at least 21 days in a medium simulating ileostomy effluent. The pH was maintained at 6 by the controlled infusion of sodium bicarbonate. Fresh medium (13 ml) was pumped into the culture for 2 min every hour and excess culture was simultaneously removed. The redox potential of all cultures remained below -300 mV, whereas the osmolality was maintained hypertonic compared with the original inoculum or medium. The cultures readily produced volatile fatty acids at a rate of 30.4 +/- 3.6 mmol/day (mean +/- SEM). Acetic acid (10-19 mmol/day) and propionic acid (5-30 mmol/day) were produced in the largest amounts, whereas butyric acid was produced only in small amounts or not at all. Ammonia was produced in each culture in amounts that varied from day to day and between cultures. The osmolality and volatile fatty acid production increased when the carbohydrate input was doubled and decreased when the cultures were deprived of carbohydrate. Thus it is possible to maintain actively fermenting viable cultures in vitro for prolonged periods; such cultures respond to changing conditions and may be useful in investigating the metabolic function of the colon.
The effects of pH on colonic bacteria grown in continuous culture.
A model of the proximal colon was used to investigate the effects of pH on fermentation by colonic bacteria in vitro. Twelve continuous anaerobic cultures of human faecal bacteria were maintained at constant pH in a medium simulating ileostomy effluent. Five cultures were maintained at pH 7, five at pH 6, and two at pH 5. The pH of each of three further cultures was altered after they had reached steady state, either from 7 to 6 and then to 5, or from 5 to 6 to 7. Both experimental designs showed that the pH exerted an important effect on bacterial metabolism without causing major changes in bacterial populations. Osmolality was lower in cultures run at a low pH. Total volatile fatty acid concentration was decreased at pH 5, and the production of propionic acid rather than acetic acid was favoured at pH 6. Changing the pH had no significant influence on the production of ammonia in these systems.
Prediction of response to endocrine therapy in pronounced cyclical mastalgia using dynamic tests of prolactin release.
Many of the endocrine agents currently used to treat symptomatic benign breast disease modify the action or secretion of prolactin. We have compared the responses to hormonal therapy with dynamic assessment of prolactin control in 29 patients with cyclical mastalgia and in 7 patients with non-cyclical mastalgia. The tests of prolactin release used were direct stimulation by TRH or dopaminergic blockade by domperidone. These were carried out before treatment in the mastalgic patients and also in 22 age-matched asymptomatic controls. The response to treatment was assessed using a special pain chart and visual linear analogue scale. Patients with cyclical mastalgia could be divided into two groups: those in whom the peak prolactin release was exaggerated (greater than 4000 mU/l) and those in whom the prolactin release was less marked and similar to control subjects and patients with non-cyclical mastalgia. Patients in the cyclical mastalgia group with a high peak prolactin release responded to hormonal treatment significantly more frequently (90%) than those with a normal prolactin release (50%). Basal prolactin levels did not correlate with the response to treatment. In the non-cyclical mastalgia group, no patient had peak prolactin release greater than 4000 mU/l and none responded to therapy. This study indicates that dynamic tests of prolactin release in cyclical mastalgia may be useful in predicting the subsequent satisfactory response to endocrine therapy if a high peak prolactin release is induced.