Na+ transport across rumen epithelium of hay-fed sheep is acutely stimulated by the peptide IGF-1 in vitro.
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.
Laboratory of Animal Physiology and Biochemistry, Nanjing Agricultural University, China.
Zanming
Z
Shen
Holger
H
Martens
Monika
M
Schweigel-Röntgen
D000821:Animal Feed; D000818:Animals; D002478:Cells, Cultured; D004040:Dietary Carbohydrates / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D009924:Organ Culture Techniques; D010446:Peptide Fragments / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D011897:Random Allocation; D011994:Recombinant Proteins / Q000494:pharmacology; D012417:Rumen / Q000166:cytology / Q000378:metabolism*; D012756:Sheep; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000819:agonists / Q000378:metabolism*; D013997:Time Factors
D004040:Dietary Carbohydrates; D010446:Peptide Fragments; D011994:Recombinant Proteins; D017923:Sodium-Hydrogen Exchangers; D007334:Insulin-Like Growth Factor I; D012964:Sodium