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Mechanism of action of somatostatin on the dog small intestine
270 MECHANISM OF ACTION OF SOMATOSTATIN ON THE DOG SMALL INTESTINE. Vergara P*, Woskowska Z, Cipris S, Fox-Threlkeld JET, Daniel EE. Div of Physiol and Pharmacol, McMaster University, Hamilton (Ontario), L8N 3Z5 Canada. The main objective was to determine if somatostatin causes excitation fn vivo by turning-off VIP and/or nitric oxide (NO) release. Dogs were anesthetized and a segment of the small intestine isolated ex-vivo and its vein and artery cannulated. Segments were perfused with Krebs solution and the venous effluent collected for VlP RIA. A pair of strain-gauges were placed to record circular muscle motility. Somatostatin (10-9-10 -7 M) induced a dose-dependent motility increase concomitant with a dose-dependent decrease of VIP output (p<0.001). The decrease of VIP output lasted longer than motility increase. A new infusion of somatostatin when VIP output was still decreased caused a similar motility response (30.81±9.64 and 28.21±7.8, mean±SEM). VIP infusion (2-10 -9 and 10 -7 M) simultaneously to somatostatin infusion only reduced the somatostatin response at the jejunum but not at the ileum. NG-nitro-L-arginine-methyl-esther (L-NAME) (3"104 M) caused a 48±14 % (n=9) reduction of somatostatin response. TTX (1.5 * 10 -6 M) significantly reduced somatostatin response (from 32.41±6.66 to 5.22±1.83, p<0.01). In conclusion, somatostatin produces an excitatory action on circular muscle of the small intestine inhibiting both tonic VlP and NO outputs. A direct action of somatostatin on smooth muscle can not be rejected either. •Present address: Dept of Cell Biol and Physiol, Universidad Aut6noma de Barcelona, 08193 Bellaterra, Spain. Personal financial support: DGCYT (Spain).
DISTRIBUTION OF INSULIN-LIKE IMMUNOREACTIVITY IN TWO SPECIES OF AMPHIOXUS P.D. Verhaert l, D.F. Steiner2, S.J. Chan2, B. Langvad-Hansen3, G.N. Hansen3, A.J. De Loof 1, lZoological Institute, University of Leuven, Naamsestraat 59, B-3000 Leuven, Belgium, 2Department of Biochemistry and Molecular Biology and The Howard Hughes Medical Institute, The Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637, USA and Jlnstitutes of Medical Microbiology and Cell Biology & Anatomy, University of Copenhagen, DK-2100 Copenhagen, Denmark Recently the primary structure of an insulin-like peptide and its cDNA have been characterized from a primitive chordate, the Californian lancelet, Branchiostoma californienselll. The results indicate that a relatively large amount of this material is present in this species, but the cells which are expressing the insulin-like peptide (a hybrid between insulin and IGF) were not identified. Previous accounts on the distribution of insulin-like compounds in amphioxus have concentrated on the gut of the European lancelet, Branchiostoma lanceolatum le.g. 2-3], where only minor amounts of material were found to be present (great variations in insulin-immunoreactivity were reported between individual animals, with the majority of the examined specimens even completely lacking insulin-immunoreactivity). The objectives of this study were to investigate whether the discrepancy between both results are simply due to species-differences (i.e., B. lanceolatum having actually much less insulin than B. californiense), and whether lancelet tissues other than the gut may contain insulin-like molecules. We have employed insulin antiserum GP-V (raised, in guinea pig, to bovine insulin) in an immunohistochemical approach, to screen serial sections of entire animals of both species for the presence of insulin-like substances. Our results confirm the above reports 12-31, that, in both cephalochordate species, paraneurone-type cells in selected parts of the gut indeed exhibit insulin-immunoreactivity (all specimens studied by us displayed constant and similar quantities of immunoreactive material). Moreover, it was observed that particularly in the major (cephalic) part of the amphioxus central nervous system ("brain"), a cluster of dorsally located large perikarya yielded consistent immunopositivity of moderate intensity to our insulin antiserum. This suggests an alternative neuronal site of storage/ synthesis of protochordate insulin-like molecules, which may be relevant from a phylogenetic consideration: it supports the current view that the original source of insulin, and perhaps other regulatory peptides, which are found in present-day vertebrates, may well have been the nervous system of early ancestral (pre-vertebrate) organismst4l. A closer study on the localization of insulin-like material(s) in amphioxus tissues, by use of an extended panel of various insulin antisera and monoclonal antibodies, is in progress. Literature cited: [1] Chan S.L et al., 1990 Proc Natl Acad Sci USA 87:9319-9323 [2] Rgineek¢M., 1981 Cell Tissue Res 219:445-456 13] Van NoordenS., PearseA.G.E. (1976) In: GrilloT.A.I. et al. (eds.) "The Evolutionof the PancreaticIslets': 163-178 [4] Duve H., Thorpe A., 1988 Nature 331:483-484
DISTRIBUTION OF INSULIN-LIKE IMMUNOREACTIVITY IN TWO SPECIES OF AMPHIOXUS P.D. Verhaert l, D.F. Steiner2, S.J. Chan2, B. Langvad-Hansen3, G.N. Hansen3, A.J. De Loof 1, lZoological Institute, University of Leuven, Naamsestraat 59, B-3000 Leuven, Belgium, 2Department of Biochemistry and Molecular Biology and The Howard Hughes Medical Institute, The Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637, USA and Jlnstitutes of Medical Microbiology and Cell Biology & Anatomy, University of Copenhagen, DK-2100 Copenhagen, Denmark Recently the primary structure of an insulin-like peptide and its cDNA have been characterized from a primitive chordate, the Californian lancelet, Branchiostoma californienselll. The results indicate that a relatively large amount of this material is present in this species, but the cells which are expressing the insulin-like peptide (a hybrid between insulin and IGF) were not identified. Previous accounts on the distribution of insulin-like compounds in amphioxus have concentrated on the gut of the European lancelet, Branchiostoma lanceolatum le.g. 2-3], where only minor amounts of material were found to be present (great variations in insulin-immunoreactivity were reported between individual animals, with the majority of the examined specimens even completely lacking insulin-immunoreactivity). The objectives of this study were to investigate whether the discrepancy between both results are simply due to species-differences (i.e., B. lanceolatum having actually much less insulin than B. californiense), and whether lancelet tissues other than the gut may contain insulin-like molecules. We have employed insulin antiserum GP-V (raised, in guinea pig, to bovine insulin) in an immunohistochemical approach, to screen serial sections of entire animals of both species for the presence of insulin-like substances. Our results confirm the above reports 12-31, that, in both cephalochordate species, paraneurone-type cells in selected parts of the gut indeed exhibit insulin-immunoreactivity (all specimens studied by us displayed constant and similar quantities of immunoreactive material). Moreover, it was observed that particularly in the major (cephalic) part of the amphioxus central nervous system ("brain"), a cluster of dorsally located large perikarya yielded consistent immunopositivity of moderate intensity to our insulin antiserum. This suggests an alternative neuronal site of storage/ synthesis of protochordate insulin-like molecules, which may be relevant from a phylogenetic consideration: it supports the current view that the original source of insulin, and perhaps other regulatory peptides, which are found in present-day vertebrates, may well have been the nervous system of early ancestral (pre-vertebrate) organismst4l. A closer study on the localization of insulin-like material(s) in amphioxus tissues, by use of an extended panel of various insulin antisera and monoclonal antibodies, is in progress. Literature cited: [1] Chan S.L et al., 1990 Proc Natl Acad Sci USA 87:9319-9323 [2] Rgineek¢M., 1981 Cell Tissue Res 219:445-456 13] Van NoordenS., PearseA.G.E. (1976) In: GrilloT.A.I. et al. (eds.) "The Evolutionof the PancreaticIslets': 163-178 [4] Duve H., Thorpe A., 1988 Nature 331:483-484