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Biomedical subjects

B Stanton

Publications and source records attributed to B Stanton.

At least 73 records · Page 4Linked to original sources
PubMed1989

Ultrastructure of Amphiuma distal nephron: evidence for cellular heterogeneity.

To obtain more information on the ultrastructure of the distal nephron of the salamander, Amphiuma, we conducted freeze-fracture electron microscopy and morphometric experiments. In the early distal tubule, the organization of the tight junction is variable, containing from one to two strands in the proximal region and four strands in distal regions. The length density of the tight junction in this segment varies from greater than 60 m/cm2 of apical membrane surface to less than 10/cm2 of apical membrane surface. These observations agree with a previous study demonstrating that the junction of this segment exhibits considerable axial heterogeneity. The junctions of the late distal tubule and collecting tubule are more complex. In the late distal tubule, the tight junction is composed of 6-8 strands, whereas the tight junction of the collecting tubule is composed of 8-12 strands. The collecting tubule contains principal cells and two types of intercalated cells: alpha and beta. The alpha-cells contain a high density of rod-shaped particles in the apical plasma membrane and in membranes of apical cytoplasmic vesicles. The beta-cells contain rod-shaped particles only in the basolateral membrane. In principal cells, we observed a novel organization of intramembranous particles within the apical plasma membrane. A model describing the relationship of the two types of intramembranous particles within the membrane is presented. This study demonstrates that the amphibian and mammalian distal nephron share many morphological characteristics including cellular and axial heterogeneity.

Animals↗
PubMed1989

Tibial torsion. Normal values in children.

In-toeing and out-toeing are common foot problems, and frequently are caused by torsional abnormalities of the tibia. Malleolar position, and thus tibial torsion, was measured in 281 children, 1 1/2 to 6 years of age, with a Tractograph, and normal values for the different age groups were determined. The authors discuss the clinical significance of torsional abnormalities of the tibia regarding gait.

Anthropometry↗
PubMed1989

Parasitic, bacterial and viral pathogens isolated from diarrhoeal and routine stool specimens of urban Bangladeshi children.

Few data exist in Bangladesh on longitudinal, community-based studies of bacterial or parasitic pathogens identified in routine and diarrhoeal stools of urban dwelling children. We undertook the following study on 343 children of age less than 6 years who resided in one of 51 slum settings in Dhaka, Bangladesh, between October 1984 and February 1986. Specimens from diarrhoeal episodes and from routine stools obtained at 3-monthly intervals were examined for parasites, rotavirus and pathogenic bacteria. Parasites were isolated from 509 (51%) of the 1006 routine stools and from 95 (42%) of the 225 diarrhoeal stools. Isolation rates steadily increased with age. Ascaris lumbricoides and Trichuris trichiura accounted for approximately 80% of all parasitic isolates in routine and diarrhoeal stools. Giardia lamblia was isolated from 11% diarrhoeal stools. Entamoeba histolytica was an uncommon isolate (less than 1%). Bacterial pathogens were identified in 55 (24%) of the diarrhoeal stools but were identified in only 164 (16%) of the 1028 routine stools examined (P less than 0.01). Toxigenic Escherichia coli, Shigellae and Campylobacter were the most frequent isolates from diarrhoeal and routine specimens. This pathogen profile appears to be more in keeping with that from urban settings in other developing countries than from rural Bangladesh, suggesting that extrapolations from rural-based data should not be made for urban settings.

Age Factors↗
PubMed1989

Chronic diarrhoea: a methodologic basis for its apparent heterogeneity.

The etiologic and epidemiologic patterns of chronic diarrhoea vary extensively between studies. While undoubtedly some of this heterogeneity reflects the complexity of the disease entity, inconsistencies in methodology between studies may result in some of the variation. To illustrate this problem we examined 44 papers on chronic diarrhoea for comparability of the age range of subjects under study and for the use of standardized definitions of 'chronic' and 'diarrhoea'. There was wide variation in the age ranges examined, extending from two weeks to 91 years. No definition or description of 'diarrhoea' was provided in 13 (30%) studies while 'chronic' remained undefined or undescribed in 11 (25%) papers. Among the 14 (32%) studies providing a definition of 'diarrhoea', four different sets of criteria were used and among the 22 (50%) papers defining 'chronic', eight different definitions were employed.

Adolescent↗
PubMed1988

Morphological heterogeneity of the rabbit collecting duct.

The localization of carbonic anhydrase by histochemistry, of Na-K-ATPase by immunocytochemistry and of rod-shaped intramembranous particles by freeze-fracture electron microscopy, was determined in the collecting duct of rabbits. In the cortical collecting duct (CCD), rod-shaped particles, which are abundant in intercalated cells were observed in both the apical and basolateral membrane of all intercalated cells examined. In the outer stripe of the outer medullary collecting duct (OMCDo) a high density of rod-shaped particles was found only in the apical membrane of intercalated cells. All cells of the inner stripe of the outer medullary collecting duct (OMCDi) had rod-shaped particles in the apical membrane but not in the basolateral membrane. As the collecting duct entered the inner medulla the density of rod-shaped particles decreased until they were virtually absent in the terminal segment. Na-K-ATPase, localized to the basolateral membrane, was more abundant in principal cells than in intercalated cells in the CCD. In the OMCDo, staining was equal in principal and intercalated cells. All cells of the OMCDi and the inner medullary collecting duct (IMCD) stained for Na-K-ATPase. Carbonic anhydrase in the CCD was localized to the cell membranes and cytoplasm of intercalated cells. Principal cells did not stain for carbonic anhydrase. A similar pattern was seen in the OMCDo. In the outer region of the OMCDi most cells did not stain for carbonic anhydrase, whereas in the inner region the apical and lateral membranes of all cells stained for carbonic anhydrase. Weak cytoplasmic staining was occasionally seen. A similar pattern was seen in the initial half of the IMCD, while the terminal half of the IMCD did not stain. In this study, the localization of enzymes and rod-shaped intramembranous particles associated with Na+, K+, and H+ transport shows both segmental and cellular heterogeneity, and correlates with the known transport properties of tubule segments. The distribution of these enzymes and rod-shaped intramembranous particles is different in rabbits and rats, and may explain some of the functional differences between homologous segments in these species.

Animals↗
PubMed1988

Cross-protection by B subunit-whole cell cholera vaccine against diarrhea associated with heat-labile toxin-producing enterotoxigenic Escherichia coli: results of a large-scale field trial.

The B subunit (BS) of cholera toxin and that of the heat-labile enterotoxin (LT) of enterotoxigenic Escherichia coli (ETEC) are antigenically similar. We therefore assessed whether a combined cholera toxin BS/whole-cell (BS-WC) oral vaccine against cholera conferred cross-protection against LT-producing ETEC (LT-ETEC) diarrhea in a randomized, double-blind field trial among rural Bangladeshi children and women. The 24,770 persons who ingested two or more doses of BS-WC vaccine were compared with 24,842 controls who took two or more doses of killed whole-cell (WC) oral cholera vaccine. Sixty-seven percent fewer episodes of LT-ETEC diarrhea were noted in the BS-WC group than in the WC group during short-term (three-month) follow-up (P less than .01), but no reduction was evident during the ensuing nine months. Short-term protection was particularly notable against LT-ETEC diarrhea causing life-threatening dehydration (protective efficacy, 86%; P less than .05).

Adolescent↗
PubMed1987

Comparability of results obtained by two-week home maintained diarrhoeal calendar with two-week diarrhoeal recall.

Many community based studies of diarrhoea in the developing world employ face-to-face interviews to obtain diarrhoeal histories. An alternative recording device that preserved the accuracy but avoided the expense and time commitment of the interview would be extremely valuable. To evaluate the comparability of episodes of diarrhoea obtained from a home-maintained two-week calendar with those histories given in response to a two-week health recall interview in a largely uneducated population, we studied approximately 1500 families for six months in Dhaka, Bangladesh. The diarrhoea records obtained for children by the two methods were highly comparable (Kappa value 0.83). The comparability was not impaired either by lack of maternal education nor by increased numbers of children in the household. We conclude that the two-week home maintained diarrhoea calendar offers comparable results with the two-week recall and in certain situations could be a useful substitute.

Bangladesh↗
PubMed1987

Electroneutral H+ secretion in distal tubule of Amphiuma.

This study examines the cellular mechanisms of acid secretion by the in vitro perfused late distal tubule of Amphiuma kidney. Acidification of tubule fluid occurred against an electrochemical gradient of 16 mV; thus H+ secretion was active. Amiloride (1 mM) or a reduction of sodium in the perfusion fluid (from 83.7 to 7.7 mM) partially reduced acidification. Amiloride, in the presence of low sodium, completely inhibited acidification. Furthermore, acetazolamide and ouabain in the bath solution (0.1 mM) also inhibited acidification. Conductive properties of the epithelium and of individual cell membranes were determined by means of cable analysis of the tubule and intracellular voltage recordings. The transepithelial voltage and resistance averaged -0.4 +/- 0.4 mV, lumen negative, and 7,147 +/- 845 omega X cm, respectively. Two functionally different cell types were identified by intracellular microelectrodes. Type I cells had a basolateral membrane voltage (Vbl) of -67.7 mV. As determined by ion substitution experiments, the basolateral membrane was conductive to K+ and Cl-. This cell also had a 4-acetamido-4'-isothiocyanostilbene-2-2'-disulfonic acid (SITS)-sensitive Na+-dependent HCO3- exit pathway in the basolateral membrane. Type II cells had a Vbl of -76.1 mV (P less than 0.05 vs. type I) and the basolateral membrane was conductive to K+ and Cl- but not to HCO3-. HCO3- movement across the basolateral membrane in this cell may occur by electroneutral Cl- -HCO3- exchange. The apical cell membrane of both cell types did not contain measurable ionic conductances, as evidenced by a high value of apical membrane fractional resistance (0.98 +/- 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1987

Localization of alpha 2-adrenoceptor-mediated increase in renal Na+, K+, and water excretion.

Free-flow micropuncture and clearance studies were conducted in male Sprague-Dawley rats to investigate the effects of alpha 2-adrenoceptor stimulation on Na+, K+, and water transport along the nephron. Intravenous infusion of the selective alpha 2-adrenoceptor agonist B-HT 933 at 1 mg X kg-1 X h-1 increased urinary flow rate from 16.2 +/- 3.6 to 84.8 +/- 11.9 microliter/min, fractional excretion of Na+ from 1.36 +/- 0.31 to 3.57 +/- 0.52%, and fractional excretion of K+ from 26.9 +/- 3.0 to 42.3 +/- 2.2%, The diuresis, saluresis, and kaliuresis were not the result of increases in glomerular filtration rate or mean arterial blood pressure. Urine osmolality decreased from 1,126 +/- 177 to 325 +/- 33 mosmol/kg water and in 8 of the 11 animals studied B-HT 933 decreased urine osmolality to hyposmotic levels, suggesting a possible interaction between the alpha 2-adrenoceptor agonist and vasopressin. The alpha 2-adrenoceptor antagonist yohimbine (0.25/mg bolus, iv) inhibited the diuresis, saliuresis, and kaliuresis. In micropuncture studies, B-HT 933 was without effect on single-nephron glomerular filtration rate or on Na+, K+, and water transport along the superficial proximal tubule, loop of Henle, or distal tubule. Thus stimulation of alpha 2-adrenoceptors increases Na+, K+, and water excretion by inhibiting tubule reabsorption of these substances at nephron sites beyond the superficial distal tubule, most likely by the collecting tubule.

Animals↗
PubMed1987

The collecting tubule of Amphiuma. I. Electrophysiological characterization.

Single collecting tubules of Amphiuma kidneys were perfused in vitro to characterize their electrophysiological properties. The lumen-negative potential (-24 mV) was abolished by amiloride in the lumen and by ouabain in the bath. Ion substitution experiments in the lumen demonstrated the presence of a large sodium conductance in the apical cell membrane, but no evidence was obtained for a significant potassium or chloride conductance. Ion substitutions in the bath solution and the depolarizing effect of barium on the basolateral membrane potential demonstrated the presence of a large potassium conductance in the basolateral cell membrane. Measurements of dilution potentials in amiloride-treated tubules revealed a modest cation selectivity of the paracellular pathway. These results support a cell model in which sodium reabsorption occurs by electrodiffusion across the apical cell membrane and active transport across the basolateral cell membrane. The absence of a detectable potassium conductance in the apical cell membrane suggests that secretion of this ion cannot take place by diffusion from cell to lumen.

Algorithms↗
PubMed1987

The collecting tubule of Amphiuma. II. Effects of potassium adaptation.

Electrophysiological and transport properties were studied in isolated and perfused Amphiuma collecting tubules from two groups of animals, one exposed to a high sodium (NA), the other to a high potassium (KA) environment (both conditions known to modulate blood aldosterone levels). The transepithelial lumen-negative potential was significantly larger (-38 +/- 5 mV) in tubules from KA animals than from NA animals (-15 +/- 3 mV). In addition, we observed an increase in the apical amiloride-sensitive sodium conductance and stimulation of the transepithelial sodium current. Although no measurable potassium conductance was found in the apical cell membrane in either group, a potassium selectivity of the paracellular transport pathway was observed in the KA animals. Net potassium secretion was demonstrated in KA tubules (helium-glow photometry and [3H]inulin analysis). Potassium secretion was abolished by luminal amiloride but imposition of a bath-to-lumen potassium gradient induced potassium secretion. We conclude that in contrast to the mammalian cortical collecting tubule in which potassium secretion is largely transcellular, potassium secretion in the Amphiuma collecting tubule is by diffusion through the paracellular pathway.

Adaptation, Physiological↗
PubMed1987

Independent effects of aldosterone and potassium on induction of potassium adaptation in rat kidney.

We examined the independent effects of a high potassium diet and increased aldosterone levels on the development of renal potassium adaptation. This condition is defined by the increased ability of the kidneys to excrete an acute infusion of potassium. Rats were adrenalectomized (ADX) and received aldosterone at basal levels (0.5 microgram/100 g X d) or at high levels (2.0 micrograms/100 g X d) for 10 d. In each experimental group, animals received either a control diet or a high potassium diet. In ADX animals with basal aldosterone levels, a high potassium intake increased but did not completely restore the ability to excrete potassium and induced proliferation of the basolateral membrane of principal cells in the collecting tubule (i.e., morphologic adaptation). In contrast, increased aldosterone did not induce functional adaptation. Elevated aldosterone and dietary potassium intake were required to produce functional potassium adaptation indistinguishable from that in potassium-loaded, adrenal-intact animals.

Adaptation, Physiological↗
PubMed1987

Scabies in urban Bangladesh.

As a part of a larger project on hygiene education and diarrhoeal diseases we followed 766 children less than 6 years of age from October 1984 to September 1985 in Dhaka, Bangladesh. The aims were to estimate the annual risk of infestation with scabies in children, to describe its involvement of other family members, and to determine some of the familial and individual risk factors for apparent infestation by scabies. During this period 589 (77%) children appeared to have been infected with scabies, and 125 (16%) children were infested for more than 6 months. Of the factors examined, direct and indirect indicators of decreased wealth and incorrect hygiene practices correlated with higher rates of apparent infestation, although scabies rates remained high at all socioeconomic levels.

Bangladesh↗
PubMed1986

Breast feeding as a determinant of severity in shigellosis. Evidence for protection throughout the first three years of life in Bangladeshi children.

Little is known about the effect of breast feeding upon the severity of illness due to specific diarrheal pathogens. Using a systematically sampled and evaluated population of children aged less than 3 years, who attended a diarrheal disease hospital in Bangladesh, the authors performed a case-control study that assessed whether breast feeding reduces the severity of illness in shigellosis. From 540 children presenting with shigellosis between 1980-1982, they created a group of cases (n = 53) with severe illness and controls (n = 487) with non-severe illness. Overall, the odds ratio relating breast feeding to the severity of shigellosis (0.49, p = 0.01) suggested a substantial mitigating effect of breast feeding upon clinical severity. The high degree of protection against severe shigellosis was evident for breast-fed children up to 35 months of age, as well as for children at high risk for death because of severe malnutrition or measles. Because shigellosis continues to account for substantial morbidity and mortality in children in developing countries, the results support prolonged breast feeding in these settings.

Bangladesh↗
PubMed1986

Follow-up of children discharged from hospital after treatment for diarrhoea in urban Bangladesh.

To determine the subsequent mortality of urban children in Bangladesh after an episode of diarrhoea we visited 74 children aged 2 to 5 years in their homes four months after they had received treatment for diarrhoea at the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B). Parents and health workers were questioned about their perceptions of the nutritional status of the children at this time. Although 43% of the children were severely malnourished and 28% were moderately malnourished at the time of presentation to ICDDR,B only two deaths (3%) had occurred in the cohort during follow-up. No deaths were noted for the severely malnourished two year old group, which contrasts with the high post-discharge mortality (33%) in similarly malnourished two year old Bangladeshi children living in rural areas (p = 0.004) at the time of follow-up parents were significantly (p = 0.02) less likely than health workers to recognize malnutrition in the children. We suggest that there may be substantial rural-urban differences in the survival of children after receiving treatment for diarrhoea. Further, we note that parental under-recognition of malnutrition may impede the nutritional rehabilitation that is necessary to avert much of the morbidity and mortality that ensues after an episode of diarrhoea.

Bangladesh↗
PubMed1985

Effects of adrenalectomy and chronic adrenal corticosteroid replacement on potassium transport in rat kidney.

Clearance experiments were carried out in pair-fed rats to examine the long-term effects of adrenalectomy and selective adrenal corticosteroid replacement in physiological amounts on renal potassium transport. To this end, clearance studies were conducted in rats that were sham operated, or adrenalectomized (ADX). ADX animals were given either vehicle, aldosterone (0.5 microgram/100 g body wt per day), dexamethasone (1.2 micrograms/100 g body wt per day), or aldosterone and dexamethasone, by osmotic minipump for 7-9 d whereupon clearance experiments were conducted. After chronic hormone treatment, during basal conditions when only Ringers solution was infused, all groups excreted similar amounts of potassium. However, in all ADX animals without mineralocorticoid replacement, the maintenance of urinary potassium excretion at control levels was associated with hyperkalemia, increased urine flow, and natriuresis; all are factors known to stimulate urinary potassium excretion. During acute potassium infusion, the increase in urinary potassium excretion was less in ADX rats than in controls. This functional deficiency in potassium excretion was partially corrected by dexamethasone and was uniformly associated with a significant increase in urine flow. Aldosterone replacement or aldosterone and dexamethasone given together chronically, sharply increased potassium excretion but did not restore excretion to control levels. Only acute aldosterone infusion (0.2 microgram/100 g body wt bolus plus 0.2 microgram/100 g body wt per hour), superimposed upon chronic aldosterone and dexamethasone treatment, fully restored potassium excretion to control levels. This aldosterone induced enhancement of potassium excretion, both chronic and acute, was not associated with hyperkalemia, and increased urine flow or natriuresis. Thus, physiological levels of both classes of adrenal corticosteroids stimulate renal potassium excretion albeit by different mechanisms. Mineralocorticoids stimulate tubular potassium excretion directly, whereas glucocorticoids augment excretion indirectly by increasing fluid and sodium delivery along the distal nephron.

Adrenal Cortex Hormones↗