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H M Said

Publications and source records attributed to H M Said.

At least 91 records · Page 5Linked to original sources
PubMed1988

Biotin transport in the human intestine: site of maximum transport and effect of pH.

Previous studies from our laboratory have characterized the transport process of biotin across the brush border membrane and the basolateral membrane of the human intestine. In this study we further characterized biotin transport in the human intestine by examining the vitamin's transport process in different areas of the small intestine (duodenum, jejunum, and ileum) and the effect of pH on the transport process using a brush border membrane vesicle technique. In all areas examined, the transport of biotin as a function of concentration was saturable in the presence of a Na+ gradient (out greater than in) but was linear and lower in the presence of a choline gradient (out greater than in). Transport of biotin by the Na+-dependent process (i.e., the carrier-mediated process) was found to be higher in the duodenum than the jejunum, which was in turn higher than that in the ileum. This decrease in biotin transport distally was found to be due to a decrease in the Vmax of the transport process of the vitamin with no changes in the apparent Km. This indicates that the number (i.e., the density) of transport carriers for biotin decreases distally. In the presence of a Na+ gradient (out greater than in), decreasing incubation buffer pH from 8.0 to 5.5 (intravesicular pH was 7.4) was found to cause an increase in biotin transport. This increase was found to be due to the acidic buffer pH (i.e., not due to the pH gradient imposed across the membrane) and occurred through an increase in the transport of the vitamin by the nonmediated process. These results demonstrate that the proximal part of the small intestine is the site of maximum transport of biotin in humans. Furthermore, variation in incubation medium pH affects biotin transport through changes in the substrate transport by the nonmediated process.

Biological Transport, Active↗
PubMed1988

Ontogenesis of the intestinal transport of biotin in the rat.

Developmental aspects of the intestinal transport of biotin were examined in suckling (16 day old) and weanling (24 day old) rats using the everted sac technique. The results were compared with those of adult rats previously reported by us using the same intestinal preparation. Transport of biotin was linear for 20 min of incubation in all age groups. Transport of biotin was significantly (p less than 0.05) lower in the jejunum than the ileum of suckling rats but was not significantly different in the jejunum and the ileum of weanling rats. In adult rats, biotin transport was significantly (p less than 0.01) higher in the jejunum than the ileum. In all age groups, transport of biotin in the jejunum was saturable at low concentrations (less than 10 microM) but linear at high concentrations. The apparent Km and Vmax of the saturable process showed a progressive increase from suckling to weanling to adult rats (apparent Km of 0.63, 2.49, and 3.37 microM; Vmax of 18.3, 44.7, and 124.4 pmol/g.min, respectively). On the other hand, the rate of transport by the nonsaturable process showed a progressive decrease with maturation (143.8, 111.6, and 87.5 pmol/g.min for suckling, weanling, and adult rats, respectively). Transport of biotin in suckling and weanling rats was similar to that of adult rats in that it was Na+-, energy-, and temperature-dependent and inhibited by structural analogues. These results demonstrate that biotin transport undergoes clear maturational changes. These changes include a decrease in the affinity and an increase in the activity (and/or the numbers) of the transport carrier, a decrease in the rate of transport by the nonsaturable process, and a change in the preferential site of transport.

Animals↗
PubMed1988

Folate transport in ileal brush border-membrane vesicles following extensive resection of proximal and middle small intestine in the rat.

Uptake of folic acid (PteGlu) was examined in remnant ileum of rats after resection of 65% of the small intestine with the brush border-membrane vesicle technique. The results were compared to that of sham-operated rats. In both rat groups transport of PteGlu was linear for approximately 40 s of incubation and was similar in the presence of a Na+ and a K+ gradient (out greater than in). In resected rats transport of PteGlu was inhibited by the structural analogues 5-methyltetrahydrofolate (5-CH3H4PteGlu) and methotrexate (MTX), by sulfasalazine, and by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) and was saturable as a function of concentration (apparent Kt = 18.3 microM). In the ileum of sham-operated rats, on the other hand, transport of PteGlu was not affected by 5-CH3H4PteGlu, MTX, sulfasalazine, or DIDS and was linear with concentration. These results suggest that the PteGlu transport system is induced in remnant ileum of the rat after extensive intestinal resection.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Intestinal uptake of retinol in suckling rats: characteristics and ontogeny.

Uptake of retinol in the developing intestine of suckling rats (14-15 day old) and its maturation in adult rats (90 day old) was examined using intestinal everted sacs. Uptake of retinol (0.06 microM) in the jejunum of suckling and adult rats was linear for 5 min incubation and occurred at a rate of 31.20 and 6.98 pmol/g tissue/min, respectively. In both age groups, uptake of retinol (0.06 microM) was significantly higher (p less than 0.01) in the jejunum than the ileum. Uptake of retinol was significantly higher (p less than 0.01) in suckling rats as compared to adult rats both in the jejunum and the ileum. In both suckling and adult rats, the uptake of retinol in the jejunum was 1) saturable with a Vmax value of 19.78 and 6.24 nmol/g tissue/5 min and an apparent Km value of 16.20 and 8.19 microM, respectively, 2) not affected by metabolic inhibitors, and 3) partially temperature dependent (Q10 = 2.51 and 1.92, respectively). The structural analogues retinal (50 microM) and retinoic acid (50 microM) did not affect the uptake of [3H] retinol (0.06 microM) whereas unlabeled retinol (50 microM) caused significant (p less than 0.01) inhibition. No difference in retinol metabolism by intestinal tissue was observed in the two age groups. These results demonstrate that retinol uptake in suckling rats is similar to that of adult rats in being a passive carrier-mediated process. The results also suggest that a decrease in the number and/or activity and an increase in the affinity of the uptake system of retinol occurs with maturation.

Animals↗
PubMed1987

A carrier-mediated transport for folate in basolateral membrane vesicles of rat small intestine.

The mechanism of exit of folate from the enterocyte, i.e. transport across the basolateral membrane, is not known. In this study we examined, using basolateral membrane vesicles, the transport of folic acid across the basolateral membrane of rat intestine. Uptake of folic acid by these vesicles represents transport of the substrate into the intravesicular compartment and not binding to the membrane surface. The rate of folic acid transport was linear for the first 1 min of incubation but decreased thereafter, reaching equilibrium after 5 min of incubation. The transport of folic acid was: (1) saturable as a function of concentration with an apparent Km of 0.6 +/- 0.17 microM and Vmax. of 1.01 +/- 0.11 pmol/30 s per mg of protein; (2) inhibited in a competitive manner by the structural analogues 5-methyltetrahydrofolate and methotrexate (Ki = 2 and 1.4 microM, respectively); (4) electroneutral; (5) Na+-independent; (6) sensitive to the effect of the anion exchange inhibitor 4,4'-di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS). These data indicate the existence of a carrier-mediated transport system for folic acid in rat intestinal basolateral membrane and demonstrate that the transport process is electroneutral, Na+-independent and sensitive to the effect of anion exchange inhibition.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1987

The microfibrillar proteins of human hair: separation by high-performance liquid chromatography and isolation of some proteins enriched in glycine and tyrosine.

The microfibrillar proteins of human hair have been studied by reversed-phase high-performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A chromatographic procedure which isolates the microfibrillar proteins from other hair-matrix proteins and separates them into collectable fractions has been introduced. These fibrous proteins fall into two major subgroups which are resolved into six components. The same procedure has also resulted in the identification and simultaneous separation of a group of proteins rich in glycine and tyrosine never before detected in human hair. Comparative electrophoretic studies of the crude microfibrillar proteins reveal five bands with apparent molecular weights of 47,000, 50,000, 53,000, 57,000, and 62,000. The relationship between the electrophoretic bands and the chromatographic fractions is now under investigation.

Amino Acids↗
PubMed1987

The enterohepatic circulation of methotrexate in vivo: inhibition by bile salt.

We examined the enterohepatic circulation of methotrexate (MTX) in the rat in vivo and determined the effect of the unconjugated bile salt, cholate, on the process. MTX (70 mg/kg body weight) was administered i. v. and the bile salt (1 mM) was delivered through intestinal perfusion. In the control group 38.43% +/- 4% of the administered dose of MTX appeared in bile 2 h after administration of the drug. In the bile salt-treated group 21.4% +/- 3.7% of the administered doses of MTX appeared in bile, which was significantly lower (P less than 0.01) than the proportion in the control group. The liver content of MTX was depressed by 23% in the bile salt-treated group compared with the control group. This study demonstrates, in vivo, the important role that the enterohepatic circulation plays in exposing the small intestine to toxic levels of MTX and shows that the unconjugated bile salt, cholate, inhibits the process.

Animals↗
PubMed1987

Aging-associated increase in intestinal permeability to polyethylene glycol 900.

Effect of aging on the intestinal permeability to medium size [3H]polyethylene glycol (PEG 900) was examined in vivo by gavage and in vitro in intestinal everted sacs of rats ranging in age from 5 to 102 weeks. Rats were gavaged with PEG 900 solution and urinary recovery of PEG 900 was measured for 6 hr in order to assess its absorption. Young rats, 5-15 weeks of age, absorbed 1-1.3% of administered PEG 900. In contrast, rats 35-102 weeks of age absorbed 1.8-2.4% of administered PEG 900 (P less than 0.05 vs younger animals). The increased absorption of PEG 900 with aging is due to changes in intestinal permeability since the total uptake (serosal appearance + tissue uptake) of PEG 900 by jejunum, ileum, and colonic everted sacs was significantly higher (P less than 0.05) in older rats (100 weeks) than young rats (9 1/2 weeks), while urinary excretion of PEG 900 following intravenous injection was the same in the two age groups. These studies indicate that aging rats have diminished capacity to exclude larger size molecules from penetrating the intestinal mucosa. The diminished barrier functions of the small intestine with aging may allow antigenic or mutagenic compounds to reach the systemic circulation.

Aging↗
PubMed1987

A carrier-mediated system for transport of biotin in rat intestine in vitro.

Transport of biotin was examined in rat intestine using the everted sac technique. Transport of 0.1 microM biotin was linear with time for at least 30 min of incubation and occurred at a rate of 3.7 pmol X g initial tissue wet wt-1 X min-1. Transport of biotin was higher in the jejunum than the ileum and was minimum in the colon (85 +/- 6, 36 +/- 6, and 2.8 +/- 0.6 pmol X g initial tissue wet wt-1 X 25 min-1, respectively). In the jejunum, transport of biotin was saturable at low concentrations (Kt = 3.73, microM, Vmax = 3.11 nmol X g initial tissue wet wt-1 X 25 min-1) but linear at higher concentrations (greater than 10 microM). The transport of low concentrations of biotin was inhibited by structural analogues (desthiobiotin, biotin methyl ester, diaminobiotin, and biocytin), Na+ dependent, energy dependent, temperature dependent, and proceeded against a concentration gradient in the serosal compartment. No metabolic alteration occurs to the biotin molecule during transport. This study demonstrates that biotin transport in rat intestine occurs by a carrier-mediated process at low concentrations and by simple diffusion at high concentrations. Furthermore, the carrier-mediated process is Na+, energy, and temperature dependent.

Animals↗
PubMed1987

Folate transport by human intestinal brush-border membrane vesicles.

Transport of folic acid (Pte-Glu) across the brush-border membrane of human intestine was studied using brush-border membrane vesicle (BBMV) technique. The transport of Pte-Glu was higher in BBMV prepared from the jejunum than those prepared from the ileum (0.70 +/- 0.05 and 0.14 +/- 0.02 pmol X mg protein-1 X 10 s-1, respectively). The transport of Pte-Glu appeared to be carrier mediated and was pH dependent and increased with decreasing incubation buffer pH; saturable (Kt = 1.69 microM, Vmax = 4.72 pmol X mg protein-1 X 10 s-1); inhibited in a competitive manner by the structural analogues 5-methyltetrahydrofolate, methotrexate, and 5-formyltetrahydrofolate (Ki = 2.2, 1.4 and 1.4 microM, respectively); not affected by inducing a relatively positive or negative intravesicular compartment; independent of Na+ gradient; and inhibited by 4,4'-diisothiocyanatostlibene-2,2'-disulfonic acid (DIDS), an anion exchange inhibitor. The increase in Pte-Glu transport on decreasing incubation buffer pH appeared to be in part mediated through a direct effect of acidic pH on the transport carrier and in part through the pH gradient imposed by activating Pte-Glu-:OH- exchange and/or Pte-Glu-:H+ co-transport mechanisms. The important role of an acidic extravesicular environment in Pte-Glu transport is consistent with a role for the intestinal surface acid microclimate in folate transport. These results demonstrate that Pte-Glu transport in human BBMV occurs by a carrier-mediated system that is similar to that described for rat and rabbit intestinal BBMV.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1987

A carrier-mediated, Na+ gradient-dependent transport for biotin in human intestinal brush-border membrane vesicles.

Transport of biotin across human intestinal brush-border membrane (BBM) was examined using brush-border membrane vesicle (BBMV) technique. Uptake of biotin by BBMV is mostly the result of transport of the substrate into an active intravesicular space with little binding to membrane surfaces. The transport of biotin was carrier mediated and was 1) Na+ (but not K+) gradient dependent with a distinct "over-shoot" phenomenon, 2) saturable as a function of concentration in the presence of a Na+ (but not a K+) gradient with an apparent Km and Vmax for the Na+ gradient-dependent system of 5.26 microM and 13.47 pmol.mg protein-1.20 s-1, respectively, and 3) inhibited by structural analogues and related compounds. Unlike the electrogenic transport of D-glucose, transport of the anionic biotin in the presence of a Na+ gradient (out greater than in) was not affected by imposing a relatively positive intravesicular electrical potential, suggesting that biotin transport is most likely an electroneutral process. These results demonstrate the existence of a carrier-mediated system for biotin transport in human BBM and show that the transport process is Na+ gradient dependent and electrically silent. It is suggested that biotin transport across the BBM is driven by a Na+ gradient most probably through a biotin-Na+ cotransport system.

Biological Transport↗
PubMed1987

Developmental maturation of D-glucose active transport system in rat intestine.

Developmental changes in the D-glucose-active transport system were examined in jejunum of rats of different age groups (3, 5, 7, 11, 13, 17, 25 and 90 days old) using the intestinal sheet technique. Transport of D-glucose by the active system was determined by subtracting the passive component, as determined by uptake of L-3H-glucose from the total uptake. The transport rate of 0.1 and 1 mM D-glucose in 13- and 90-day-old rats was linear with time for 12 min of incubation, but decreased thereafter. Kinetic parameters of the active transport system of D-glucose were determined by examining the transport of D-glucose after 12 min of incubation as a function of concentration. Vmax of the active transport system was highest in 3-day-old rats and decreased with age reaching the adult value by day 7 after birth. Kt of the active transport system was the same in 3- 5- and 7-day-old rats, but increased progressively with age reaching the adult value by day 25 after birth. These data demonstrate that transport of D-glucose by the active system is highest during the early days of life, but decreases thereafter. It also suggests that this enhancement is most probably due to greater activity and/or number, and affinity of the transporting carriers of D-glucose.

Aging↗
PubMed1987

Effect of small bowel resection on the intestinal surface acid microclimate in the rat.

The effect of extensive (65%) proximal and middle small bowel resection on the intestinal surface acid microclimate (ISAM) of the remaining ileum in the rat was examined and the results were compared to those of sham-operated rats. ISAM pH measurements were performed in vivo using a pH microelectrode; incubation was performed in Krebs-Ringer phosphate buffer (pH 7.40 +/- 0.02). In the resected rats, ISAM pH of 6.03 +/- 0.07 and 7.22 +/- 0.03 were recorded in the proximal and distal part of the remaining ileum, respectively. In the sham-operated rats, ISAM pH of 6.04 +/- 0.07, 6.98 +/- 0.03 and 7.28 +/- 0.02 were recorded in the proximal jejunum and in the proximal and distal part of the corresponding ileal segment. ISAM pH was significantly lower (p less than 0.01) in the proximal part of the remaining ileum of the resected rats as compared to the corresponding part in the sham-operated rats but was similar in distal ileum. In fact, the ISAM pH of the proximal part of the remaining ileum of resected rats was as acidic as that of the jejunum of the sham-operated rats. These results clearly demonstrate that adaptation in the ISAM occurs in the remaining ileum following extensive resection of proximal and middle small intestine.

Animals↗
PubMed1987

Intestinal glucose transport in suckling rats fed artificial milk with and without added epidermal growth factor.

Epidermal growth factor (EGF), a potent mitogen present in milk, is postulated to play an important physiologic role in the ontogeny of the intestine. An artificial rat milk, free of EGF, was developed and fed to newborn rats in an effort to evaluate the physiologic role of EGF on intestinal glucose transport. Comparisons were made between mother-fed (group 1) and artificially fed pups (group 2). Group 1 was divided into two subgroups to received either the EGF vehicle (group 1-A) or twice daily subcutaneous injections (0.1 micrograms/g body weight/day) of EGF (group 1-B). Group 2 was divided into four subgroups: formula without EGF (group 2-A), formula with 62 ng/ml of EGF (group 2-B), formula with 200 ng/ml EGF (group 2-C), and formula without EGF but added anti-EGF IgG (40 ng/ml) plus subcutaneous injections of 1 micrograms anti-EGF twice daily (group 2-D). Treatment regimens were initiated on day 3 and assays performed on day 11 of life. Glucose transport was measured using gut "sheet" preparations in all but group 2-C, which utilized brush border membrane preparations. Group 1-B showed a significant (p less than 0.03) increase in gut length (47.5 +/- 1.2 versus 42 +/- 0.9 cm) and an increase (p less than 0.03) in both Vmax (10.2 +/- 0.5 versus 7.2 +/- 0.3 nM/mg tissue) and Km (2.74 +/- 0.49 versus 1.20 +/- 0.19 mM) compared to group 1-A.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Studies on the intestinal surface acid microclimate: developmental aspects.

The existence and general characteristics of the intestinal surface acid microclimate (ISAM) in the developing intestine of suckling and weanling rats were examined. ISAM pH measurements were performed in vitro using a sensitive glass pH-microelectrode. The results showed that the ISAM does exist in both suckling and weanling rat intestine. In both suckling and weanling rats, ISAM pH was significantly (p less than 0.01) lower in the jejunum than in the ileum, an observation similar to that previously reported in the small intestine of adult rats. In the colon, however, ISAM pH of suckling rats was significantly (p less than 0.01) lower than that of weanling and adult rats. Studies on the relationship between jejunal ISAM pH of weanling rats and incubation buffer pH showed that the two are not in equilibrium. Jejunal ISAM pH of weanling rats was significantly inhibited by: 1) the mucolytic agent N-acetyl-L-cysteine, 2) stirring of the incubation medium, 3) Na+ removal, 4) glucose removal (or substitution by the unmetabolizable galactose), and 5) metabolic inhibitors (iodoacetate and dinitrophenol). These results demonstrate the existence of the ISAM in the developing intestine of suckling and weanling rats and shows the dependence of the ISAM on Na+, metabolizable substrate(s) and normal intracellular metabolism. Furthermore, surface mucus appears to play a role in maintaining the ISAM, most probably through retaining the H+ at the intestinal surface.

Acid-Base Equilibrium↗
PubMed1987

Persistently low blood retinol levels during and after parenteral feeding of very low birth weight infants: examination of losses into intravenous administration sets and a method of prevention by addition to a lipid emulsion.

Very low birth weight infants have little storage of hepatic retinol and are, therefore, highly dependent upon an exogenous supply. The recent association between low serum retinol level and bronchopulmonary dysplasia and the persistently low serum levels of retinol during total parenteral nutrition prompted a prospective study to evaluate serial changes in serum retinol levels during 1 month of total parenteral nutrition (retinol dose 455 micrograms/d) and again during 1 month of total enteral feeding (retinol dose 200 to 300 micrograms/d) in the same infants. Infants were divided into two groups. Group 1 consisted of infants weighing less than 1,000 g (n = 24) and group 2 consisted of infants weighing 1,000 to 1,500 g (n = 17). Although initial mean levels of retinol were similar in both groups (14.8 +/- 0.9 and 13.5 +/- 0.7 micrograms/dL), there was wide variation between infants. In group 1 infants, there was a significant (P less than .01) decline in retinol level by the second week of life (to 9.2 +/- 1 micrograms/dL), which persisted during total parenteral nutrition, but increased to 13.4 +/- 2 after 1 week of enteral feeding. This level was maintained throughout enteral feeding. In group 2 infants, there was no significant change in serum retinol level throughout the study. During total parenteral nutrition, several infants had retinol levels below 10 micrograms/dL, a level associated with signs of retinol deficiency in older children. Because losses of retinol are known to occur in smaller volume total parenteral nutrition solutions, it was speculated that losses of retinol in our patients were due to retinol losses in the total parenteral nutrition delivery system.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug Stability↗