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Na + transport across rumen epithelium of hay‐fed sheep is acutely stimulated by the peptide IGF‐1 in vitro
Author(s) -
Shen Zanming,
Martens Holger,
SchweigelRöntgen Monika
Publication year - 2012
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2011.061580
Subject(s) - rumen , amiloride , epithelium , medicine , hay , chemistry , butyrate , endocrinology , ussing chamber , biology , in vitro , sodium , biochemistry , zoology , fermentation , organic chemistry , genetics
An energy‐rich diet leads to enhanced ruminal Na + absorption, which is associated with elevated plasma insulin‐like growth factor 1 (IGF‐1) levels and an increased number of IGF‐1 receptors in rumen papillae. This study examined the in vitro effect of IGF‐1 on Na + transport across the rumen epithelium of hay‐fed sheep, in which the IGF‐1 concentration in plasma is lower than in concentrate‐fed animals. At concentrations ranging from 20 to 100 μg l −1 , serosal LR3‐IGF‐1, a recombinant analogue of IGF‐1, rapidly (within 30 min) stimulated the mucosal‐to‐serosal Na + flux ( J ms Na) and consequently the net Na + flux ( J net Na). Compared with controls, J net Na increased by about 60% ( P < 0.05) following the serosal application of LR3‐IGF‐1 (20 μg l −1 ). The IGF‐1‐induced increment of J ms Na and J net Na was inhibited by mucosal amiloride (1 mmol l −1 ). Neither IGF‐1 nor amiloride altered tissue conductance or the short‐circuit current of the isolated rumen epithelium. These data support the assumption that the stimulating effect of serosally applied IGF‐1 on Na + transport across the rumen epithelium is mediated by Na + –H + exchange (NHE). A further study was performed with cultured rumen epithelial cells and a fluorescent probe (BCECF) to estimate the rate of pH i recovery after acid loading. The pH i of isolated rumen epithelial cells was 6.43 ± 0.15 after butyrate loading and recovered by 0.26 ± 0.02 pH units (15 min) −1 . Application of LR3‐IGF‐1 (20 μg l −1 ) significantly increased the rate of pH i recovery to 0.33 ± 0.02 pH units (15 min) −1 . 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 rumen epithelium results from increased NHE activity. Insulin‐like growth factor 1 is thus important for the fast functional adaptation of ruminal Na + transport via NHE.

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