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Biomedical subjects

D H Alpers

Publications and source records attributed to D H Alpers.

At least 163 records · Page 9Linked to original sources
PubMed1982

Absorption and transport of cobalamin (vitamin B12).

This review apprises the reader of recent advances in cobalamin absorption and transport since 1970. This field has been of interest to gastroenterologists, hematologists, and biochemists as well as nutritionists. Clinical conditions leading to cobalamin deficiency present especially to the first two of these specialties. Many recent advances involve biochemical definition of the specific transport proteins themselves. Full understanding of the multiple clinical conditions associated with cobalamin deficiency requires some knowledge of these proteins. We do not discuss every paper in the field, especially the early literature (see 47, 61, 150). Despite rapid strides in understanding the mechanism of absorption and transport of cobalamin both in prokaryotic and eukaryotic cells, the complete sequence of events during cellular absorption at the plasma membrane level and events in the cells that mediate intracellular movement of cobalamin have not been elucidated completely. Here we emphasize the current state of knowledge about cobalamin absorption and transport in man and other mammalian systems, particularly the physiological role and biochemical nature of proteins involved (intrinsic factor, intrinsic factor-cobalamin receptor, transcobalamins).

Animals↗
PubMed1982

Hepatobiliary and pancreatic clearance of circulating pancreatic amylase.

The hepatobiliary and pancreatic uptake of pancreatic amylase was studied in the conscious rabbit. Four hours after intra-arterial injection of 125I-labeled porcine or rabbit pancreatic amylase, about 7% of the administered radioactive dose appeared in liver and bile, but less than 0.2% appeared in the pancreas and pancreatic juice. No amylolytic activity was detectable in bile, but a significant fraction of the acid-precipitable radioactive counts in bile comigrated with the injected amylase on gel autoradiography. Enzymatic activity appeared in bile after continuous intraarterial infusion of pancreatic amylase with excellent correlation between biliary and plasma amylase activities (r greater than or equal to 0.94). Only a small percentage (0.002%) of amylase delivered to liver, however, was excreted into bile. After intraduodenal instillation of radiolabeled pancreatic amylase or ribonuclease A, virtually none of the radioactivity appeared in the pancreas, and none in bile was acid precipitable. We conclude that a small but definite amount of the circulating pancreatic amylase is excreted intact into bile in the conscious rabbit. There is, however, no significant enterohepatic or enteropancreatic circulation of pancreatic enzymes.

Amylases↗
PubMed1982

Postnatal development of intestinal secretin in rats and guinea pigs.

The amounts and concentrations of secretin in extracts of rat and guinea pig small intestine were measured with a porcine secretin radioimmunoassay. Immunoactivity in the extracts comigrated with porcine secretin in sodium dodecyl sulfate acrylamide gel electrophoresis. In the small intestines of adult rats and newborn and adult guinea pigs, there was a marked proximal-to-distal gradient in secretin concentration; newborn rats exhibited approximately equal proximal and distal secretin concentrations. Concentrations were as follows: most proximal newborn or adult guinea pig segments, 80 ng/mg prot; most distal newborn or adult guinea pig segments, 2 ng/mg prot; most proximal adult rat segments, 50 ng/mg prot; most distal adult rat segments, 8 ng/mg prot; and newborn rat intestine, 11 ng/mg prot. In either rats or guinea pigs, the secretin concentration in the proximal small intestine fell between days 2 and 6 postpartum to levels 3- and 10-fold below their respective newborn values. It is consistent with the relatively mature state of the newborn guinea pig digestive tract that it displays the proximal-to-distal gradient of secretin that is characteristic of both adult guinea pigs and rats. In the proximal intestine of both species, intestinal growth outpaces the accumulation of secretin.

Aging↗
PubMed1982

Localization of immunoreactive alkaline phosphatase in the rat small intestine at the light microscopic level by immunocytochemistry.

Monospecific antibody to purified alkaline phosphatase hs been used to localize alkaline phosphatase in the rat small intestine at the light microscopic level. Pieces of duodenum, jejunum, and ileum were removed from 2-, 9-, 12-, 18-, 21-, 26-day-old and adult wistar rats. They were fixed in Bouin's fluid and examined for the presence of alkaline phosphatase by th immunoperoxidase method. Slides were graded blindly for the intensity of staining. The localization of alkaline phosphatase by the immunoperoxidase method extends previous histochemical observations in several ways. First, diffuse cytoplasmic staining is present particularly in the opical portion of the villus and crypt epithelium. Second, staining for alkaline phosphatase is present on the brush border and in the apical portion of the deep crypt cells throughout the duodenum, jejunum, and ileum at the various ages tested. Third, in the adult rat distal ileum there is more staining on the brush border of the deep crypt epithelial cells than on the villus absorptive cells. These observations are consistent with the presence of a non-brush border alkaline phosphatase in all intestinal cells and with fan enzymatically inactive form of alkaline phosphatase in the deep crypt epithelium.

Alkaline Phosphatase↗
PubMed1981

Independent biosynthesis of soluble and membrane-bound alkaline phosphatases in the suckling rat ileum.

Enzymically active intestinal alkaline phosphatase exists in both soluble and membrane-bound forms in the suckling rat. Antiserum prepared against purified soluble alkaline phosphatase (anti-AlP) was shown to be monospecific when assessed by Ouchterlony double-diffusion analysis and immunoelectrophoresis. The two forms of alkaline phosphatase were antigenically identical and possessed similar affinities for anti-AlP. To study the biosynthesis of the two forms, 14-day-old rats were injected intraperitoneally with [(3)H]leucine. The labelling kinetics of alkaline phosphatase, extracted from supernatant and brush-border membrane fractions with anti-AlP, was followed over 20h. Incorporation of [(3)H]leucine into membrane-bound alkaline phosphatase was rapid, reaching a plateau at 6h. The soluble enzyme showed slower incorporation of label and maximal radioactivity was not reached until 12h after labelling, a lag of 6h behind the membrane-bound enzyme. Soluble alkaline phosphatase could not have been a precursor of the membrane form, as there was no early peak of radioactivity in the soluble form. To determine if the soluble enzyme was irreversibly derived from the membrane enzyme, a newly developed technique of labelling brush-border membrane proteins in vivo by intraluminal injection of diazotized [(125)I]iodosulphanilic acid was used. The appearance of (125)I in soluble and membrane alkaline phosphatase was then monitored over a 7h period, encompassing the lag between maximal leucine labelling of the two forms. The results failed to show either a proportional transfer of radioactivity from membrane to soluble alkaline phosphatase or an absolute increase in radioactivity of the soluble form during degradation of brush-border alkaline phosphatase. Therefore there does not appear to be a serial precursor/product relationship between the soluble and membrane-bound forms of suckling-rat intestinal alkaline phosphatase.

Alkaline Phosphatase↗
PubMed1981

Interaction of receptor for intrinsic factor-cobalamin complex with synthetic and brush-border lipids.

The intestinal receptor for intrinsic factor-cobalamin complex integrates preferentially with cationic liposomes in such a way that its ligand binding sites are exposed to proteases and to antibody to the receptor. After integration the receptor could be solubilized from the liposomes by detergents and chaotropic salts. Kinetically, the brush-border and the liposome-bound receptor behaved similarly, and Triton X-100 had no effect either on Ka or Vmax, suggesting the absence of any effects of a lipid domain on ligand binding activity. However, acidic phospholipids caused inhibition when added to the receptor-ligand assay system in the absence of liposomes.

Animals↗
PubMed1981

Labelling of intestinal brush border membrane proteins in vivo using diazotised[125I]iodosulfanilic acid.

Membrane proteins of the intestinal brush border were labelled in vivo by intraluminal injection of diazotised [125I]iodosulfanilic acid, a highly polar molecule. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of brush border membranes labelled in this manner showed 20 protein bands, 11 of which contained significant radioactivity. The most heavily labelled proteins had molecular weights greater than 150000, indicating that they were the most exposed to the intestinal lumen. Little radioactivity was detected in proteins with molecular weights of less than 94000. The majority of these smaller proteins were likely to have been brush border core proteins. The evidence that diazotised [125I]iodosulfanilic acid bound primarily to brush border membrane proteins when administered in this way, was: (a) the specific activity of brush border proteins was up to 3-fold greater than that of total cell particulate proteins (pelleted by 27000 x g from mucosal homogenates); (b) principal peaks in the gel radioactivity profile of total cell particulate proteins corresponded to the most heavily labelled proteins of the isolated brush border membrane; and (c) brush border core proteins showed minimal radioactivity in vivo, but considerably higher radioactivity when brush border membranes were labelled in vitro. A small amount of label was absorbed across the intestinal mucosa. However, secondary labelling of brush border proteins by this absorbed label was minimal, since the specific activity of brush border proteins in jejunum adjacent to the labelled loop was only 0.22% of the level for those proteins in the labelled segment. Since this technique did not affect the cellular morphology, enzyme activity or biochemical integrity of the membrane, it should prove useful as a means of accurately studying in vivo turnover rates of brush border membrane proteins.

Animals↗
PubMed1981

Effect of intralumenal cation-exchange resin on excretion of ammonia in rat ileum.

Ammonia excretion was studied in rat ileal segments during perfusion of the animal through the saphenous vein. In the first 10 min during and after intravenous infusion of L-glutamine (116 mg/kg to double arterial glutamine concentration) average net change in lumenal ammonia was 13 +/- 8 (S.E.) nmole NH3/min/g ileum; average net change in ileal venous ammonia was 28 +/- 9 nmole NH3/min/g ileum; and average net change in total ammonia (lumen + ileal vein) was 41 +/- 13 compared to -5 +/- 10 nmole/min/g ileum for animals infused with saline P less than 0.025. These data suggest that ileal metabolism of arterial glutamine liberates ammonia to both ileal venous blood and intestinal lumen. When a cation-exchange resin which binds ammonia was infused intralumenally, average net change in lumenal ammonia in the first 10 min during and after intravenous infusion of 116 mg/kg L-glutamine was 415 +/- 156 nmole NH3/min/g ileum (p less than 0.01 compared to value during perfusion of Earle's solution alone). During the first 10 min during and after glutamine infusion net change in ileal venous plasma ammonia was -8 +/- 14 when resin was being perfused through the lumen compared to +28 +/- 9 nmole/min/g ileum during perfusion of Earle's solution alone without resin P less than 0.05. Thus resin in the small intestine can trap very large amounts of ammonia.

Ammonia↗
PubMed1980

Jejunoileal bypass. Late metabolic sequelae and weight gain.

Of 101 patients originally operated on, the status of 98 is known. Given the mortality and reanastomosis rates, the operation must be considered an absolute failure in 28 percent of the patients. Given the other complications that appear (or persist) late postoperatively, only 18 percent of the entire series of patients have had what can be considered a good result. We therefore conclude that intestinal bypass is not an appropriate operation for morbid obesity and that complete long-term follow-up is essential for all patients who undergo the operation, despite what might seem to be a smooth course in the 1st 2 years postoperatively.

Body Weight↗
PubMed1980

Turnover of intestinal brush-border proteins during postnatal development in rat.

Protein turnover in brush-border membranes of rats during postnatal development has been studied by the double isotope technique. Unlike adult animals where only large proteins (mol wt > 140,000) show relatively rapid turnover, most brush-border proteins in 12-day-old rats show high 3H-to-14C ratios of leucine incorporation, consistent with rapid turnover. Lysosomal proteases, including cathepsin B, are partly responsible for this rapid turnover. This conclusion is based on the following findings: 1) In vivo treatment of 12-day-old animals with leupeptin, an inhibitor of cathepsin B, alters relative turnover rates, enzyme activity, and content of many brush-border proteins. Activities of maltase and trehalase rise while lactase falls. 2) Cathepsin B activity falls rapidly in intestine after the animals are 16 days of age, at a time when luminal pancreatic proteases are rising. Moreover, cathepsin B activity shows less latency in distal intestine at 12 and 16 days than at later ages or in proximal intestine. It is suggested that during postnatal development lysosomal enzymes, e.g., cathepsin B, play an important role in the turnover of intestinal brush-border proteins.

Aging↗
PubMed1980

Effect of secreted Bacteroides proteases on human intestinal brush border hydrolases.

Selected bacteroides species secreted various amounts of protease and glycosidase into their growth medium. Bacteroides vulgatus, distasonis, and ovatus secreted the most (31-60% of total). The secreted protease was similar in action to the protease within the organism, in that it had a broad pH optimum of 6-9, a K(m app.) for casein of 0.1 muM, and was inhibited by benzamidine, phenylmethylsulfonyl fluoride, diisopropylfluorophosphate (DIFP), and by an elastase inhibitor, Ac(Ala)(3)AlaCH(2)Cl. Exposure of human brush border preparations to the secreted protease reduced maltase and sucrase activities; the reduction could be prevented by DIFP. In contrast, brush border alkaline phosphatase activity either did not change or increased after exposure to bacterial secretions. >90% inhibition of secreted glycosidase using EDTA and p-chloromercuribenzoic acid did not prevent the reduction of brush border maltase and sucrase activity, suggesting that glucosidases were not likely to be involved in the destruction of brush border enzymes. Moreover, the bacterial proteases caused only a small net release of active maltase or sucrase from the brush border. Most of the loss of activity was due to destruction of the enzyme. Proximal bowel fluid of three patients with overgrowth contained DIFP-inhibitable protease that destroyed sucrase in isolated brush borders. A Bacteroides species was isolated from each sample that secreted protease and destroyed brush border sucrase. We conclude that in bacterial overgrowth syndromes, brush border damage may occur from protease(s) secreted by Bacteroides.

Alkaline Phosphatase↗
PubMed1980

Dog intestinal mucosa contains two vitamin D-stimulating calcium binding proteins.

Dog intestinal mucosa has been found to contain more than one vitamin D-responsive calcium-binding protein (CaBP). Duodenal and upper jejunal mucosa contains a protein that has a mol wt of 19,000 and a Kd of 1.2 microM, and that increases in activity over twofold after administration of 1,25 (OH)2 vitamin D3. This protein could not be demonstrated in ileal tissue. In ileal mucosa all the calcium binding activity resides in fractions that elute from Sephadex G200 with a mol wt of about 57,000. Calcium-binding activity was demonstrated in gel electrophoresis corresponding to a protein with an Rf of about 0.5, unlike the small CaBP, which has an Rf of 1.0. The calcium-binding activity from the ileum was demonstrated to coincide with a protein band on acrylamide gel electrophoresis, and to be destroyed by pronase. This large CaBP responded to 1,25 (OH02 vitamin D3 by increasing activity by about 50%, and was inhibited similarly to the small protein by Sr, Ba, and Mg. Neither fresh tissue homogenates, nor explants cultured up to 20 hr showed any evidence of the small CaBP on disc gel acrylamide electrophoresis. The small CaBP could be demonstrated on gel electrophoresis only in tissue that was partially autolyzed or was treated with a 10% (milligrams per milligram) solution of trypsin. The small CaBP was relatively resistant to trypsin. It is suggested that the small CaBP may be derived at least in part from the large protein.

Animals↗