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P13 Absorption enhancement of hydrophilic compounds by racemic verapamil after rectal administration in rats
391 Up to 300 PM verapamil caused an increase in TEER, whereas from concentrations of 700 PM onwards an abrupt dose-dependent drop in TEER was observed which was fully reversible within 2 h after removal of the compound. A second treatment of verapamil gave a much larger effect on TEER than the first treatment. At these concentrations no cell death could be observed. At concentrations of 1 mM verapamil caused severe damage to the cell layers. At a concentration of 700 .uM, the transport of Flu was enhanced 13- and 26-fold after the first and the second verapamil treatment, while the transport of FD-4 was increased 4and 6-fold, respectively. TEER experiments with the R- and S-verapamil enantiomers point in the direction that no enantioselective mechanism is involved.
P13 Absorption enhancement of hydrophiiic compounds by racemic verapamil after rectal adminis~tjon in rats. A.B.J. Noach, M.C.M. Blom-Roosemalen, A.G. de Boer and D.D. Breimer, Leiden/Amsterdam Centerfor Drug Research, Division of Pharmacology, Center for Bio-Pharmaceutical Sciences, Leiden University,P. 0. Box 9503, 2300 RA Leiden, The Nether~an~ Absorption of hydrophilic compounds, like peptides, from the intestinal lumen into the blood is restricted to the paracellular transport route. This route is impeded by the tight junctions on the apical side of the cells. Among the factors which are involved in maintaining this barrier is calcium. In an earlier study we investigated the effect of the calcium channel blocking agent verapamil on the paracellular permeability of hydrophilic model compounds through epithelial Caco-2 cell monolayers. In the present study we verified in vivo the promising effect of verapamii, which was found in the vitro study. As a hydrophilic model compound FITC-labelled dextran (M, 4000) (FD-4) was used. Male Wistar rats ( 180-200 g) were cannulated in a carotid artery for blood sampling and a device was introduced in the rectum for the administration of FD-4 solution with and without verapamil. In order to study the kinetic profile of FD-4 a carotid artery (blood sampling) and a jugular vein canula (administration) were implanted. The kinetics of FD-4 after i.v. administration of 10 or 1 mg FD-4 could be described by a two-compartment model with a terminal half-life of approx. 36 min. Rectal administration was performed as a bolus dose (24 s) or as a rectal infusion (32 min) of 200 ~1 solution containing 10 mg FD-4. A concentration of 700 PM verapamil, as was used in the in vitro experiments, did not show any effect. At a concentration of 7 mM verapamil, a very slight enhancement of the FD-4 uptake could be seen after bolus administration. After rectal infusion the effect was larger although still small. A major problem with these experiments is that the variation in effect between animals is quite large. The data indicate that verapamil is in vivo not a very effective absorption enhancer.
P14 Gastrointestinal absorption and plasma clearance of vaeopressin anatogues in the rat. S. Lundin” and H.G. Folkessonb, Departments of “Clinical Pharmacolo~ and bAnimat Physiology, Lund University,Lund, Sweden The gastrointestinal absorption of a series of vasopressin anafogues with enhanced enzymatic stability was determined in chronically catheterized, conscious rats. The following peptides were used: [Mpa’, D-A$]-vasopressin (dDAVP), [Mpa’, Asn4, D-Arg8]-vasopressin (4-Asn-dDAVP), [Mpa’, Val“, D-Arg’]-vasopressin (4-Val-dDAVP), [ Mpa’, (CH,), Ala4, o-Arg*]-vasopressin (4-(CH-,), Ala-dDAVP), [ Mpa’, Tyr*(Et), D-Arg’j-vasopressin (2-Tyr(Et)-dDAVP). The peptides were administers by gavage and blood samples were taken for 3 h. In another series of experiments plasma clearance rates (Cl,) were determined using the constant infusion method. Plasma concentrations were measured by use of a cross-reacting dDAVP antiserum. The bioavailability of all peptides was below 0.1 I, ranging from 0.0 13 to 0.046%. The Cl, values were between 4.3 (2Tyr(Et)-dDAVP) and 14.7 ml kg-’ min-’ (CAsn-dDAVP). There was no apparent relationship between peptide hydrophilicity and either Cl, or bioavailability. It can be concluded that, in the rat, the bioavailability of dDAVP is lower than in other species. This could be attributed to a higher Cl, rather than a lower intestinal permeability. Therefore, the use of rat intestinal segments may prove to be a good model with which to predict intestinal permeability in man. Furthermore, it is obvious that small molecular changes, i.e., single amino acid substitutions or derivatizations, have profound effects on Cl, and consequently on peptide bioavailability. P15 The adjuvant effect of polyacryl starch microparticles with conjugated human serum albumin. L. Deglinga.’ and P. Stj~~kvistb.‘, aDepartment of Pharma~~tics, University of Uppsala, Box 580, S-751 23 Uppsala, Sweden: bDepartment of Pharmaceutical Biochemistry, Universityof Uppsala, Box 5 78, S- 75125 Uppsala,Sweden: ‘Division ofpharmacy, Medical Products Agency, Box 26, S-751 03 Uppsala, Sweden Background: New safer vaccines which consist of purified proteins and peptides are often weakly immunogenic. To be effective, these new vaccines require adjuvants, that act nonspecifically to increase the immune response to the specific antigen. Thus, there is a need for development of safe and effective adjuvants for human use that elicit both a humoral and cellular immune response. Adjuvans appear to function with different mechanisms. One mechanism is the creation of a depot at the site of injection which prolongs the release of antigen, e.g., mineral oil (Freund’s incomplete adjuvants, FIA). Another mechanism is targeting of antigen to cells of the immune system, i.e., macrophages, e.g., microparticular carrier systems f 1 ] _ Polyacryl starch microparticles is a drug carrier with a typical distribution to macrophages in the reticuloendothelial system (RES). Starch microparticles are not immunogenic themseives, and do not induce an immune response against entrapped homologous proteins [ 21. The microparticles can
P13 Absorption enhancement of hydrophiiic compounds by racemic verapamil after rectal adminis~tjon in rats. A.B.J. Noach, M.C.M. Blom-Roosemalen, A.G. de Boer and D.D. Breimer, Leiden/Amsterdam Centerfor Drug Research, Division of Pharmacology, Center for Bio-Pharmaceutical Sciences, Leiden University,P. 0. Box 9503, 2300 RA Leiden, The Nether~an~ Absorption of hydrophilic compounds, like peptides, from the intestinal lumen into the blood is restricted to the paracellular transport route. This route is impeded by the tight junctions on the apical side of the cells. Among the factors which are involved in maintaining this barrier is calcium. In an earlier study we investigated the effect of the calcium channel blocking agent verapamil on the paracellular permeability of hydrophilic model compounds through epithelial Caco-2 cell monolayers. In the present study we verified in vivo the promising effect of verapamii, which was found in the vitro study. As a hydrophilic model compound FITC-labelled dextran (M, 4000) (FD-4) was used. Male Wistar rats ( 180-200 g) were cannulated in a carotid artery for blood sampling and a device was introduced in the rectum for the administration of FD-4 solution with and without verapamil. In order to study the kinetic profile of FD-4 a carotid artery (blood sampling) and a jugular vein canula (administration) were implanted. The kinetics of FD-4 after i.v. administration of 10 or 1 mg FD-4 could be described by a two-compartment model with a terminal half-life of approx. 36 min. Rectal administration was performed as a bolus dose (24 s) or as a rectal infusion (32 min) of 200 ~1 solution containing 10 mg FD-4. A concentration of 700 PM verapamil, as was used in the in vitro experiments, did not show any effect. At a concentration of 7 mM verapamil, a very slight enhancement of the FD-4 uptake could be seen after bolus administration. After rectal infusion the effect was larger although still small. A major problem with these experiments is that the variation in effect between animals is quite large. The data indicate that verapamil is in vivo not a very effective absorption enhancer.
P14 Gastrointestinal absorption and plasma clearance of vaeopressin anatogues in the rat. S. Lundin” and H.G. Folkessonb, Departments of “Clinical Pharmacolo~ and bAnimat Physiology, Lund University,Lund, Sweden The gastrointestinal absorption of a series of vasopressin anafogues with enhanced enzymatic stability was determined in chronically catheterized, conscious rats. The following peptides were used: [Mpa’, D-A$]-vasopressin (dDAVP), [Mpa’, Asn4, D-Arg8]-vasopressin (4-Asn-dDAVP), [Mpa’, Val“, D-Arg’]-vasopressin (4-Val-dDAVP), [ Mpa’, (CH,), Ala4, o-Arg*]-vasopressin (4-(CH-,), Ala-dDAVP), [ Mpa’, Tyr*(Et), D-Arg’j-vasopressin (2-Tyr(Et)-dDAVP). The peptides were administers by gavage and blood samples were taken for 3 h. In another series of experiments plasma clearance rates (Cl,) were determined using the constant infusion method. Plasma concentrations were measured by use of a cross-reacting dDAVP antiserum. The bioavailability of all peptides was below 0.1 I, ranging from 0.0 13 to 0.046%. The Cl, values were between 4.3 (2Tyr(Et)-dDAVP) and 14.7 ml kg-’ min-’ (CAsn-dDAVP). There was no apparent relationship between peptide hydrophilicity and either Cl, or bioavailability. It can be concluded that, in the rat, the bioavailability of dDAVP is lower than in other species. This could be attributed to a higher Cl, rather than a lower intestinal permeability. Therefore, the use of rat intestinal segments may prove to be a good model with which to predict intestinal permeability in man. Furthermore, it is obvious that small molecular changes, i.e., single amino acid substitutions or derivatizations, have profound effects on Cl, and consequently on peptide bioavailability. P15 The adjuvant effect of polyacryl starch microparticles with conjugated human serum albumin. L. Deglinga.’ and P. Stj~~kvistb.‘, aDepartment of Pharma~~tics, University of Uppsala, Box 580, S-751 23 Uppsala, Sweden: bDepartment of Pharmaceutical Biochemistry, Universityof Uppsala, Box 5 78, S- 75125 Uppsala,Sweden: ‘Division ofpharmacy, Medical Products Agency, Box 26, S-751 03 Uppsala, Sweden Background: New safer vaccines which consist of purified proteins and peptides are often weakly immunogenic. To be effective, these new vaccines require adjuvants, that act nonspecifically to increase the immune response to the specific antigen. Thus, there is a need for development of safe and effective adjuvants for human use that elicit both a humoral and cellular immune response. Adjuvans appear to function with different mechanisms. One mechanism is the creation of a depot at the site of injection which prolongs the release of antigen, e.g., mineral oil (Freund’s incomplete adjuvants, FIA). Another mechanism is targeting of antigen to cells of the immune system, i.e., macrophages, e.g., microparticular carrier systems f 1 ] _ Polyacryl starch microparticles is a drug carrier with a typical distribution to macrophages in the reticuloendothelial system (RES). Starch microparticles are not immunogenic themseives, and do not induce an immune response against entrapped homologous proteins [ 21. The microparticles can