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Biomedical subjects

K F Sewing

Publications and source records attributed to K F Sewing.

At least 127 records · Page 7Linked to original sources
PubMed1990

Single dose pharmacokinetics of ciclosporin and its main metabolites after oral ciclosporin as oily solution or capsule.

The commercially available oily solution of ciclosporin which has to be suspended before intake is disliked by some patients for bad taste and has a variable bioavailability. In this investigation the oral pharmacokinetics of ciclosporin and its main metabolites 1 and 17 of the oily solution (Sandimmun) and a soft gelatine capsule preparation of ciclosporin were compared in a crossover fashion in 10 kidney allograft recipients. The results demonstrate a bioequivalence of both formulations. In either case metabolite 17 had a significantly longer half-life than either ciclosporin or metabolite 1. At earlier time-points the concentration of ciclosporin could be best correlated with metabolite 1 and at later time-points with metabolite 17. Both metabolites were less correlated with each other in the late absorption phase of ciclosporin.

Adult↗
PubMed1989

Arachidonic acid metabolism in isolated gastric mucous and parietal cells.

Arachidonic acid metabolism was studied in isolated gastric mucous and parietal cells. During a 90 min incubation, mucous cells incorporated [1-14C]arachidonic acid (4.5 mumol/l) into triacylglycerols (500 pmol/mg protein), phosphatidylcholine (520), phosphatidylethanolamine (290) and phosphatidylinositol (100). 230 pmol/mg protein was recovered as 14CO2 and 130 pmol/mg protein in the form of unidentified water-soluble metabolites. The incorporation rates were linearly related with arachidonic acid concentration up to 10 mumol/l. Neither equimolar concentrations of oleic acid, palmitic acid and linoleic acid nor prostaglandin E2 (1 mumol/l) or indomethacin (10 mumol/l) affected incorporation. During prolonged incubation incorporated arachidonic acid was transferred from triacylglycerols and phosphatidylcholine to phosphatidylethanolamine. Upon subcellular fractionation most of the incorporated arachidonic acid was found in the microsomal fraction. Compared with mucous cells, parietal cells incorporated arachidonic acid less quickly into phospholipids, but utilized it more efficiently for energy metabolism. In conclusion gastric cells show a highly dynamic metabolism of arachidonic acid which is qualitatively similar but quantitatively different between cell types.

Animals↗
PubMed1989

Inhibition of acid formation in rabbit parietal cells by prostaglandins is mediated by the prostaglandin E2 receptor.

The affinities of seven natural and synthetic prostaglandins [PGE2; 16,16-dimethyl PGE2; iloprost (stable prostacyclin analogue); PGF2 alpha; PGD2; BW245c (stable PGD2 analogue); and U46619 (stable thromboxane analogue)] to the PGE2 binding site of rabbit gastric mucosa were determined by measuring [3H]PGE2 displacement from its high-affinity plasma membrane binding sites. In parallel, the potency of each prostaglandin in inhibiting acid generation in vitro was determined by measuring the inhibition of histamine-stimulated [14C]aminopyrine accumulation in rabbit parietal cells prepared by enzymatic dispersion and enriched by counterflow elutriation. All seven prostaglandins displaced [3H]PGE2 and inhibited histamine-stimulated [14C]aminopyrine accumulation in a concentration-dependent manner. For all tested prostaglandins, the IC50 values were in excellent agreement for both variables measured. It is concluded that (a) a PGE2 receptor is localized on the parietal cell and mediates inhibition of acid formation by all prostaglandins and (b) the different in vitro antisecretory potencies of prostaglandins can be attributed to their different affinities to this PGE2 receptor.

Aminopyrine↗
PubMed1989

Up-regulation of prostaglandin E2 binding and of prostanoid release in rabbits producing antibodies against prostaglandin E2.

German Giant rabbits successfully immunized against prostaglandin (PG) E2 as shown by a rise in antibody titers developed gastric mucosal lesions. Enzymatically dispersed gastric mucosal cells of these animals had a significantly enhanced production of PG E2 and PG I2 as measured by specific radioimmunoassays. This may be explained by an increased supply with endogenous arachidonic acid (as indicated by an enhanced phospholipase A2/LAT ratio) and by a higher activity of the subsequent PG forming enzymes (as indicated by a more effective stimulation of PG production by exogenous arachidonic acid). Gastric mucosal plasma membranes of immunized rabbits had significantly higher PG E2 binding capacity (108 +/- 9 fmol/mg protein) than those of nonimmunized rabbits (72 +/- 5 fmol/mg protein). The ligand affinity was not affected by immunization. Neither histamine-stimulated 14C-amino-pyrine uptake of isolated parietal cells as a marker for acid production nor its inhibition by PG E2 were influenced by receptor up-regulation. The increased eicosanoid release can be regarded as an endogenous defense mechanism against increased mucosal vulnerability caused by PG E2 scavenging. The potential role of PG E2 receptor up-regulation in support of this process remains to be established.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

Ca2+-dependent and -independent secretagogue action on gastric mucus secretion in rabbit mucosal explants.

The secretion of high-molecular weight glycoprotein was studied in rabbit antral and fundic explants in response to acetylcholine (ACh), the calcium ionophore A23187, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), forskolin, histamine, pentagastrin, and prostaglandin E2 (PGE2). Glycoprotein secretion was measured in pulse-chase experiments by incorporation of [14C]N-acetyl-D-glucosamine into explants and quantification of the secreted high-molecular weight-labeled glycoprotein. All tested agents except histamine and pentagastrin stimulated glycoprotein secretion in a concentration-dependent manner. The response to A23187 was abolished by removal of extracellular Ca2+ and greatly reduced by the calmodulin antagonist N-(6-amino-hexyl)-l-naphthalenesulfonamide (W7). The response to ACh was abolished by equimolar concentrations of atropine and by depletion of intracellular Ca2+ stores, an effect which was reversible on addition of Ca2+, and reduced by W7. The response to forskolin and PGE2 was not significantly affected by either extracellular or intracellular Ca2+ depletion. The combination of ACh with forskolin and A23187 with TPA had a synergistic effect on secretion. The absolute dependence of cholinergic stimulation on the presence of intracellular Ca2+ and the Ca2+-independent stimulatory effect of forskolin and PGE2 suggest that gastric mucus secretion can be elicited by at least two distinct pathways.

Acetylcholine↗
PubMed1989

Urinary excretion of ciclosporin and 17 of its metabolites in renal allograft recipients.

Renal elimination of the immunosuppressant ciclosporin is virtually unknown. Therefore, in 17 renal allograft recipients under steady-state conditions we studied the urinary excretion of ciclosporin and 17 of its metabolites in blood and 24-hour urine. Patients with liver dysfunction or treated with drugs potentially influencing the metabolism and elimination of ciclosporin were excluded from the study. Ciclosporin and its metabolites were measured by HPLC. Metabolite but not ciclosporin excretion was strongly correlated with creatinine clearance. Metabolites 18 and 26 (beta, epsilon-cyclic metabolite) were rarely found in blood but were excreted in considerable amounts in urine. Approximately 3% of the administered dose of ciclosporin per day undergoes renal elimination in unchanged form or as metabolites investigated. The data suggest glomerular filtration of ciclosporin metabolites, a difference in the rate of elimination between ciclosporin and the metabolites and some kind of metabolism or active transport mechanism for metabolites in the kidney.

Adolescent↗
PubMed1989

Incorporation of N-acetyl-[14C]D-glucosamine and [3H]L-leucine by isolated pig gastric mucosal cells.

Glycoprotein and protein production of isolated pig gastric mucosal cells were determined by the incorporation of N-acetyl-[14C]D-glucosamine ([14C]GlcNAc) and [3H]L-leucine ([3H]Leu) into acid-insoluble macromolecules (AIM). In four cell fractions (F1-F4), obtained by counterflow centrifugation, specific [14C]GlcNAc incorporation was greatest in the mucous cell-enriched F2. Tracer incorporation by F2 cells, proceeded linearly up to 20 h, was inhibited by cycloheximide or incubation at 0 degree C, and enhanced by PGE2 1 mumol/l. Gel chromatography of released AIM revealed that PGE2-stimulated [14C]GlcNAc incorporation was predominantly directed into high molecular weight (2 X 10(6) daltons) glycoproteins, whereas [3H]Leu incorporation was mainly related to proteins of albumin-like molecular weight. We conclude that incorporation of [14C]GlcNAc by enriched pig gastric mucous cells (F2), further analyzed by gel chromatography, is a suitable probe to study the production of high molecular weight gastric mucous glycoproteins in vitro.

Acetylglucosamine↗
PubMed1989

Interaction of rioprostil with the parietal cell prostaglandin E2 receptor.

The interaction of rioprostil with the porcine parietal cell prostaglandin (PG) E2 receptor and with uterine 3H-PGE2 binding sites was investigated. The in vitro antisecretory effect was measured by the inhibition of histamine stimulated 14C-aminopyrine uptake in isolated pig parietal cells. Rioprostil displaced 3H-PGE2 competitively from the porcine fundic PGE2 receptor and had 1/25 of the affinity (Kd = 8 X 10(-8) mol/l) of the natural ligand; it was, however, equipotent with the synthetic prostacyclin analogue, iloprost. Similar affinity ratios were found in uterine muscle. Rioprostil inhibits parietal cell acid production with an IC50 in the range of its gastric binding dissociation constant. It is concluded that rioprostil exerts its antisecretory effects via a parietal cell E-type receptor. The compound cannot discriminate between fundic and uterine 3H-PGE2 binding sites with as yet unknown functional implications.

Animals↗
PubMed1988

Omeprazole, SCH 28080 and doxepin differ in their characteristics to inhibit H+/K+-ATPase driven proton accumulation by parietal cell membrane vesicles.

The effects of omeprazole, SCH 28080 and doxepin were studied on H+/K+-ATPase mediated H+ accumulation in parietal cell membrane vesicles. Omeprazole had no effect on the initial rate of H+ accumulation and the initial steady state concentration of H+; an inhibition was found after the vesicles were acidified. This inhibition was counteracted by the SH reducing agent dithioerythritol. SCH 28080 inhibited the initial rate of H+ accumulation and the steady state H+ concentration. The inhibitory effect of SCH 28080 was counteracted by KCl. Doxepin (3-100 microM) reduced the initial steady state H+ concentration. Doxepin concentrations lower than 0.5 microM had no such effect but dissipated the proton gradient after the vesicles were fully acidified. This doxepin effect was partially counteracted by KCl and was also obtained in vesicles in which the pump reaction was stopped by EDTA. These data show that (i) omeprazole is an acid-activated compound which interferes with SH groups of the H+/K+-ATPase localized inside the vesicles; (ii) SCH 28080 interferes with the K+ site of the H+/K+-ATPase; and (iii) doxepin interacts by a K+ antagonistic activity at the H+/K+-ATPase site and in addition by intravesicular neutralization and/or a protonophoric mechanism with the process of H+ formation.

Adenosine Triphosphatases↗
PubMed1988

Studies on the mechanism of action of the omeprazole-derived cyclic sulphenamide.

The inhibitory effects of omeprazole and omeprazole-derived metabolites were studied on Escherichia coli glutaminase activity at pH 2.5 which might represent the conditions present at the target enzyme (K+/H+-ATPase) in the secretory membrane of the intact parietal cell. Omeprazole and the omeprazole-derived cyclic sulphenamide inhibited glutaminase at pH 2.5 with identical potency (IC50 36 microM). The substrate, glutamine as well as the mercaptane, dithiothreitol, protect the enzyme. Furthermore, dithioerythritol was found to reverse inhibition. This indicates that an SH-group localized in the substrate binding center of glutaminase is most likely involved in the reaction leading to enzyme inhibition. Glutaminase inhibition by both compounds was less pronounced at pH 5.0. Omeprazole radical, the metabolite generated from the cyclic sulphenamide at more neutral pH values, failed to affect the enzyme. These findings were in contrast with the properties of the omeprazole-derived cyclic sulphenamide and radical at the K+/H+-ATPase preparation. This enzyme was inhibited by both compounds at pH 7.5 with a high potency, and reversal experiments with dithiothreitol demonstrate that these agents interfere with SH-groups of the K+/H+-ATPase. From these data it is suggested that the cyclic sulphenamide and the radical interfere by different reaction pathways with enzymatic SH-groups.

Adenosine Triphosphatases↗
PubMed1988

Enrichment and characterization of specific [3H]PGE2 binding sites in the porcine gastric mucosa.

[3H]Prostaglandin E2 (PGE2) binding sites were 10-fold enriched from a porcine fundic mucosal homogenate by differential centrifugation and subsequent discontinuous sucrose gradient separation. PGE2 bound with an activation energy of 66 kJ/mol to a single class of sites with an affinity of 1.5 +/- 0.4 nM and a capacity of 274 +/- 76 fmol/mg protein. There was no indication for any cooperativity between the binding sites. Kinetic analysis revealed a kon of 3 x 10(5) M x s-1 at 30 degrees C and pH 5.5. Dissociation was biphasic with an initial rapid (koff = 10(-3) s-1) and a subsequent slower phase (koff = 4 X 10(-5) s-1), presumably reflecting the existence of two interchangeable forms of [3H]PGE2 binding sites. The rank order of affinity for other prostanoids (PGE2 greater than PGE1 greater than PGA2 greater than iloprost (PGI2 derivative) greater than PGF2 alpha greater than PGB2 greater than PGD2) is discussed against the background of the recently postulated E-type receptors in the stomach.

Animals↗
PubMed1988

Effects of endogenous and exogenous prostaglandins on glycoprotein synthesis and secretion in isolated rabbit gastric mucosa.

We studied gastric glycoprotein synthesis and secretion in organ culture before and during cyclooxygenase inhibition and replacement with exogenous prostaglandins (16,16-dimethyl prostaglandin E2 and prostaglandin F2 alpha). Isolated rabbit antral and fundic mucosal explants incorporated [14C]N-acetylglucosamine and [3H]leucine in a linear fashion and steadily secreted labeled proteins and glycoproteins during the 24-h incubation period. On sepharose 4B, greater than 90% of the secreted protein-bound [14C]N-acetylglucosamine was found in the high molecular weight peak. Incorporation of tracer was not influenced by cyclooxygenase inhibition with indomethacin or the addition of exogenous prostaglandins. Secretion of newly formed glycoprotein, however, was significantly inhibited by indomethacin and stimulated by both tested prostaglandins in a concentration-dependent manner. 16,16-Dimethyl prostaglandin E2 caused significant stimulation in concentrations that are well in the physiologic range for endogenous prostaglandin E2, whereas prostaglandin F2 alpha stimulated in 100 times higher concentrations. We conclude that in the isolated gastric mucosa both endogenous and exogenous prostaglandins stimulate mucus secretion. For prostaglandin E2, but not prostaglandin F2 alpha, a role in the physiologic regulation of gastric mucus secretion is probable.

Animals↗
PubMed1988

Interaction of antidepressants and neuroleptics with histamine stimulated parietal cell adenylate cyclase and H+ secretion.

The tricyclic antidepressants trimipramine and doxepin, and the neuroleptic agents trifluoperazine and haloperidol were tested for their effect on histamine H2-receptor-mediated adenylate cyclase activity and H+ secretion in guinea-pig parietal cells. All compounds inhibited histamine-stimulated adenylate cyclase and H+ secretion in a concentration-dependent manner. The antisecretory potency was 1-2 orders of magnitude higher than that for adenylate cyclase inhibition. All drugs caused a rightward shift in the concentration-response curves of histamine-induced adenylate cyclase activation with Schild-plot lines having a slope significantly different from unity. Histamine-stimulated H+ secretion was inhibited by the drugs in a noncompetitive fashion. These results demonstrate that antidepressants and neuroleptics interfere noncompetitively with the parietal cell histamine H2-receptor and that this receptor blocking activity is not related to the antisecretory activity of the drugs.

Adenylyl Cyclases↗
PubMed1988

Comparative pharmacology of histamine H2-receptor antagonists.

There was no significant difference between the concentration-dependent inhibitory effects produced by roxatidine acetate, roxatidine and ranitidine on adenylate cyclase derived from isolated and enriched guinea-pig parietal cells. All the compounds shifted the concentration-response curve of histamine to the right and transformation of this data to Schild-plots produced straight lines with slopes greater than 1 but not significantly different from each other. The pA2 values characterising the potencies were roxatidine acetate 6.85 +/- 0.86, roxatidine 7.14 +/- 0.04, and ranitidine 6.92 +/- 0.01. Histamine-stimulated acid production from isolated guinea-pig parietal cells, measured by the 14C-aminopyrine accumulation technique, was similarly affected by the 3 compounds. Schild-plot slopes of roxatidine acetate and ranitidine were not significantly different from unity and pA2 values were similar to those of the adenylate cyclase inhibition, roxatidine acetate 7.15 +/- 0.09, roxatidine 7.03 +/- 0.02, and ranitidine 6.83 +/- 0.10. In conclusion, roxatidine acetate and its major metabolite roxatidine behave like competitive antagonists with potencies similar to ranitidine on H2-receptors on the guinea-pig parietal cell.

Histamine H2 Antagonists↗
PubMed1988

Chemical and biologic differences between various H2-receptor antagonists.

After a brief historical review, the common chemical features of various H2-receptor antagonists are discussed, demonstrating that an imidazole, furan, thiazole, and the piperidinylmethylphenoxy moiety can serve as an aromatic nucleus of histamine H2-receptor antagonists. Furthermore, it is paradigmatically illustrated that the histamine H2-receptor antagonists in use or under clinical investigations inhibit, in a competitive and surmountable manner, parietal cell acid secretion and histamine H2-receptor-linked adenylate cyclase. Furthermore, toxicologic problems of unsurmountable and/or or long-acting histamine H2-receptor antagonists (tiotidine, loxtidine, and SK&F 93479) are discussed.

Animals↗