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    Na+ transport across rumen epithelium of hay-fed sheep is acutely stimulated by the peptide IGF-1 in vitro (2012)

    Art
    Zeitschriftenartikel / wissenschaftlicher Beitrag
    Autoren
    Shen, Z.
    Martens, H.
    Schweigel-Roentgen, M.
    Quelle
    Experimental physiology; 97(4) — S. 497–505
    ISSN: 0958-0670
    Sprache
    Englisch
    Verweise
    DOI: 10.1113/expphysiol.2011.061580
    Pubmed: 22227200
    Kontakt
    Institut für Veterinär-Physiologie

    Oertzenweg 19 b
    14163 Berlin
    Tel.+49 30 838 62600 Fax.+49 30 838-62610
    email:physiologie@vetmed.fu-berlin.de

    Abstract / Zusammenfassung

    An energy-rich diet led to enhance ruminal Na absorption, which is associated with elevated plasma IGF-1 levels and increased number of IGF-1 receptors in rumen papillae. This study examined the in vitro effect of IGF-1 on Na transport across the ruminal epithelium of hay-fed sheep. At a concentration ranging from 20 to 100 μg/l, serosal LR3-IGF-1 rapidly (within 30 minutes) stimulated the mucosal to serosal Na flux (JmsNa) and consequently the net Na flux (JnetNa). Compared with controls, JnetNa increased by about 60% (p<0.05) through the serosal application of LR3-IGF-1 (20 μg/l). The IGF-1-induced increment of JmsNa and JnetNa was inhibited by mucosal amiloride (1 mmol/l). Neither IGF-1 nor amiloride altered Gt or Isc of the isolated ruminal epithelium. These data support the assumption that the stimulating effect of serosal-added IGF-1 on Na transport across the rumen epithelium is mediated by Na+/H+ exchange (NHE). A further study performed with cultured ruminal epithelial cells (REC) and a fluorescent probe (BCECF) to estimate the rate of pHi recovery after acid-loading. The pHi of isolated REC was 6.43 ± 0.15 after butyrate loading and recovered by 0.26 ± 0.02 pH units/15 min. Application of LR3-IGF-1 (20 μg/l) significantly increased the rate of pHi recovery to 0.33 ± 0.02 pH units/15 min. Amiloride administration reduced the recovery rate in both control and IGF-1-stimulated cells. These results show, for the first time, that an acute effect of IGF-1 on Na absorption across ruminal epithelium results from increased NHE activity. IGF-1 is thus important also for the fast functional adaptation of the ruminal Na transport via NHE.