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Biomedical subjects

J W Robinson

Publications and source records attributed to J W Robinson.

At least 55 records · Page 3Linked to original sources
PubMed1982

The simultaneous preparation of basolateral and brush-border membrane vesicles from guinea-pig intestinal epithelium, and the determination of the orientation of the basolateral vesicles.

A rapid method is described for the simultaneous preparation of both membranes of guinea-pig enterocytes, using simple differential centrifugation techniques. Basolateral membranes were purified on a Percoll gradient and the final yield of (Na+ + K+)-ATPase was 12.4% of the original activity with an enrichment factor of 12.6-fold. Purification of the brush-border fraction was achieved by a calcium-precipitation technique. The yield of alkaline phosphatase was 18.9% of the original activity with an enrichment of 17.5-fold. Both fractions could be obtained within 3 h of the original homogenization. The characteristics of the preparations were checked by negative-staining electron microscopy and by the determination of glucose uptake. The orientation of the basolateral vesicles was determined by measuring the Mg2+-ATPase and (Na+ + K+)-ATPase activities and the [3H]ouabain binding before and after treatment of the preparation with a mixture of deoxycholate and EDTA which transforms the vesicles into sheets. There was a 60% rise in (Na+ + K+)-ATPase activity and ouabain binding, but no change in Mg2+-ATPase activity. It was therefore concluded that 60% of the original preparation consisted of inside-out vesicles and 40% of membrane sheets.

Animals↗
PubMed1982

Ion fluxes and electrical characteristics of the short-circuited rat colon in vitro.

The unidirectional fluxes of sodium and chloride across stripped rat colon mucosa were measured and compared with the electrical characteristics of the tissue under voltage-clamped conditions. The relationship between the serosal-mucosal fluxes of the two ions and an imposed potential revealed that the serosal-mucosal flux of sodium was entirely paracellular, whereas there was also a transcellular component of the corresponding chloride flux. In the absence of sodium, the short-circuit current and net chloride flux were abolished; in the absence of chloride, the net sodium flux was reduced but not abolished, and the short-circuit current was unchanged. From an analysis of the effects of the inhibitors, amiloride, theophylline, acetazolamide, furosemide and piretanide, a plausible model was developed to explain the characteristics of these transports. It was proposed that both membranes possess Cl-/HCO-3 antiports, though their sensitivities to inhibitors were different. There is also a Na+/Cl- symport and an electrogenic sodium entry mechanism in the brushborder membrane.

Acetazolamide↗
PubMed1982

Structural and functional correlations in the hypertrophic mucosa of intestinal remnants following resection in rats.

Microdissection techniques were applied to determine the absolute increase in villus size and absorptive surface in the mucosa of rat intestinal remnants 3 weeks after 60% proximal resection. Adjacent tissues were used to evaluate the operational kinetic parameters describing the influx of L-phenylalanine and alpha-methyl-D-glucoside into intestinal rings. The villi of ileal remnants were enlarged significantly in all dimensions; the mean surface area of the villus was 2.5 times, and mucosal:serosal surface ratio 1.9 times larger than normal. The influx of phenylalanine and alpha-methyl-glucoside into the mucosa of ileal remnants was reduced, but the change could not be ascribed to an attenuation of one specific kinetic parameter. Using the microdissection data to transform the Vmax-values to a mucosal area basis, we could demonstrate that the Vmax for both substrates was smaller than normal. The results may derive from changes in the maturity of the cell population in intestinal remnants.

Animals↗
PubMed1982

Single-site uptake of neutral amino acids into guinea-pig intestinal rings.

1. A kinetic analysis of amino acid influx into guinea-pig small intestinal rings has been performed in an attempt to ascertain whether one or more transport sites for these substrates exists in the luminal membrane of the enterocyte. 2. No indirect correction for uptake into the extracellular space was applied, but it was assumed in the analysis that the total uptake included a diffusion term. This procedure was vindicated by the results obtained. 3. All analyses were performed by non-linear regression techniques. In many experiments, both substrate and inhibitor concentrations were varied within the same experiment, thus giving rise to three-dimensional diagrams describing transport processes. 4. All results pointed to the existence of a single transport agency shared by all amino acids tested. The kinetic constants, Km and Vmax, were independent of the concentration range used for their estimation; such behaviour would not be expected if several sites with different kinetic constants were available for transport. The value of KD, the constant describing the diffusive component of uptake, was the same when estimated from the uptake of an amino acid alone or when determined as the asymptote of the curve describing the inhibition of this uptake by an analogue. Finally, the Ki for an amino acid when used as an inhibitor was identical to its Km when used as substrate. This property was maintained even when the most disparate pair of amino acids, threonine and isoleucine, was examined.

Amino Acids↗
PubMed1982

Functional alterations in the dog colon mucosa following temporary ischaemia.

Segments of dog colon were subjected to 1 h of total ischaemia. In one experimental group, the colon was not touched before the trauma; in another, it was rinsed out before the intervention; while in a third, it was perfused with Krebs bicarbonate buffer during injury. In all groups, the mucosa after the trauma is the site of net movement of water, sodium and chloride towards the lumen, while glucose absorption is greatly reduced. The accumulation of amino acid and sugar in vitro by samples of ischaemic mucosa is reduced but not abolished. The capacity for organic solute transport in vitro is greater in samples removed after the perfusion than in specimens excised immediately after the end of the ischaemia. According to the test in vitro, the mucosa can be protected from the deleterious effects of the ischaemia by intraluminal perfusion during the ischaemia. Immediately after 1 h of ischaemia, slight alterations in the histological structure of some villi were observed under the light microscope in occasional animals, particularly when the colon was not rinsed out before the ischaemia.

Animals↗
PubMed1981

Intestinal obstruction in germ-free dogs.

Mechanical occlusions were created in the intestines of four germ-free dogs. At the time of the operation, a control loop of mid-intestine was perfused in vivo and then excised for examinations in vitro, which included the determination of the equilibrium uptake of phenylalanine and of beta-methyl-glucoside, the influx kinetics of phenylalanine and morphometric analysis of the mucosa by microdissection and stereological techniques. Seven days after establishment of the occlusion the abdomen was reopened, and loops above and below the occlusion were perfused, and then excised for the same tests in vitro. Unlike occluded loops of conventional dogs, the intestine of the germ-free animal above the occlusion does not secrete water and electrolytes into the lumen. Its transport properties in vitro do not differ from those of the control loop, and the morphometric analyses reveal only slight changes in villus structure. The loop below the obstruction undergoes marked atrophy, as has been observed in conventional dogs. The results suggest that the copious secretion that occurs above an intestinal obstruction in normal animals is due to the presence of an abundant bacterial population in the obstruction fluid.

Animals↗
PubMed1981

A systematic approach to the analysis of intestinal transport kinetics.

A statistical technique for the estimation and differentiation of the operational kinetic parameters for influx of solutes into intestinal rings incubated in vitro is presented. Influx data were fitted to an equation comprising the sum of saturable and diffusional components; the latter is assumed to include entry into the extracellular space, thus avoiding the necessity of indirect assessment with space markers. The estimations are made by non-linear regression analysis on a logarithmic scale. Comparison between data sets is carried out by performing a joint fit under the restriction of parameters common to the two sets. If an F-test reveals no significant loss of information, then the parameter(s) in question do not differ from one set to another. The method is illustrated by an experiment to determine which kinetic parameters for influx of beta-methyl-D-glucoside are altered when sodium is removed from the incubation medium. The results show that the Km is principally affected by this manoeuvre.

Animals↗
PubMed1980

The effect of cyclic AMP on dog renal function.

The infusion of dibutyryl-cyclic AMP into the dog renal artery in vivo leads to diuresis, natriuresis and glucosuria. Addition of the nucleotide to the incubation medium bathing dog renal cortex slices in vitro causes inhibition of p-amino-hippurate accumulation and stimulation of glycine and beta-methyl-glucoside transport. The results are interpreted in terms of the development of a blood-lumen flux of sodium and water in the renal proximal tubule, analogous to that seen in the intestine.

Animals↗
PubMed1980

[Ischemic disorders of the large intestinal wall. Ischemic colitis and rectitis secondary to intrinsic vascular disorders].

Ischaemic diseases of the large intestinal wall is a characteristic syndrome caused by vascular insufficiency of varying degrees. The ischaemia results from haemodynamic disturbances and often arises in spite of the patency of the vessels. The mucosa of the intestine is the tissue layer that is most vulnerable to ischaemia. Ischaemia of the colon occurs in the presence of a microbial flora that is often highly pathogenic, and hence the lesions rapidly become infected. For this reason the inflammatory features of the disease tend to conceal its vascular origin and ischaemic colitis has often been confused with other infectious, inflammatory, ulcero-haemorrhagic disorders of the large intestine. Although the syndrome may occur in any patient, it is much more common in elderly subjects with a history of arteriesclerosis and cardiac disease. Two main varieties can be identified, depending on the extent of the vascular insufficiency. In the first, the lesion may heal spontaneously or evolve towards fibrous strictures of the colonic wall; in the second, gangrenous necrosis of the colon or rectum may develope, the clinical picture of which has more in common with an "acute abdomen' than with ulcerative disease of the colon.

Colitis↗
PubMed1980

Source of net water and electrolyte loss following intestinal ischaemia.

Ischaemia of the dog intestine lasting 1 h causes desquamation of the epithelium at the villus tips and congestion in the villus capillaries. The crypt cells are relatively undamaged. These changes are associated with a loss of active transport of organic solutes, determined in vitro, a reduction in mucosal sucrase activity and an abolition of glucose absorption in vivo. A profuse net loss of water and electrolytes into the lumen in vivo develops. The net sodium loss is due primarily to an inhibition of the lumen-blood flux of this ion, the blood-lumen flux being relatively unchanged. In uraemic dogs, the loss of urea into the lumen is the same in control and ischaemic loops, testifying to the lack of change in the unidirectional water flow from blood to lumen. Perfusion of the dog intestine with 1% Triton X-100 leads to morphological changes that have certain similarities with those provoked by ischaemia. Damage was restricted to the villus tips, protection from further alterations apparently being provided by a mucus layer that forms on the mucosal surface; the crypt region remained unchanged. After 10 min exposure, organic solute transport in vitro and glucose absorption in vivo were both reduced by not abolished; sodium and water absorption in vivo were suppressed, but no net secretion occurred. To account for these observations, we have suggested that the normal crypt cell is a secretory element with respect to sodium and water. During maturation, its absorptive properties develop such that the mature enterocyte, possessing both absorptive and secretory mechanisms, is capable of net absorption of sodium. After destruction of the villus tips, net secretion continues in the crypts; if there are insufficient villus cells remaining to ensure reabsorption, a net secretory capacity is observed.

Animals↗
PubMed1980

Morphological and functional recovery of the canine gallbladder mucosa following two hours' ischemia.

Temporary interruption of the circulation to the canine gallbladder causes hemorrhagic necrosis of the mucosa and an abolition of active transport of glycine in vitro. The first signs of epithelial recovery following two hours' ischemia are seen in animals examined 7 days after the injury and are characterized by the appearance of a layer of cuboidal epithelial cells in which some mitotic figures are observed, accompanied by a decrease in the amount of necrosis and the presence of granulation tissue. At the same time, there is some slight resumption in glycine uptake. Two weeks after injury, the new epithelium covers a larger surface of the gallbladder wall but recovery is still incomplete. Four weeks after operation, structural and functional recovery has occurred in almost all the animals studied: the epithelium is columnar and does not differ greatly from that seen in the normal gallbladder. Mucosal folds are present although their morphological appearance is slightly altered in comparison with those of control specimens. The gallbladder wall is thickened by fibrosis. Measurements of active glycine transport in vitro confirm that the new epithelium functions normally.

Animals↗
PubMed1980

Structural and functional correlations in the atrophic mucosa of self-emptying blind loops of rat jejunum.

Marked atrophy of the mucosa develops in self-emptying blind loops of rat jejunum. The application of microdissection techniques revealed a 74% reduction in the mucosal surface area of the blind loops, 3 weeks after their creation. Kinetic studies of the influx of L-phenylalanine and beta-methyl-D-glucoside into rings of blind loops showed that the Km for both mechanisms was unchanged, but that there was a small reduction in the Vmax for both substrates, when expressed in terms of unit weight of incubated tissue; this attained 31% for phenylalanine and 12% for beta-methyl-glucoside. When the kinetic data were combined with the morphometric results, it could be shown that the Vmax for both substrates, when expressed per unit area of mucosal surface, was more than twice as large in the blind loop epithelium as in normal tissue. Such findings indicate either that the individual cells of the blind loop epithelium possess more transport sites than normal, or that there is a greater proportion of absorptive cells within the blind loop mucosa.

Animals↗