Effects of dietary protein and growth hormone-releasing peptide (GHRP-2) on plasma IGF-1 and IGFBPs in Holstein steers

H. G. Lee, Y. J. Choi, S. R. Lee, H. Kuwayama, H. Hidari, Seungkwon You

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Abstract

This study was conduct to determine the influence of dietary protein on the response of plasma insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding proteins (IGFBPs) to exogenous growth hormone releasing peptide-2 (GHRP-2 or KP 102) in Holstein steers. Eight 16-month-old Holstein steers were grouped by liveweight to two feeding treatments; high protein (HP; CP 1.38 kg/day and TDN 4.5 kg/day DM intake, n = 4) or low protein (LP; CP 0.66 kg/day and TDN 4.42 kg/day DM intake, n = 4). The experiment was a single reverse design whereby each group was injected twice daily with GHRP-2 (12.5 μg/kg body weight (BW)/day) or saline solution into the jugular vein for a 6-day period. Plasma IGF-1 in the HP group were higher than in the LP group (P < 0.05), but plasma 34 kDa IGFBP-2 was lower in the HP than the LP group (P < 0.05). The amplitude of the maximum growth hormone (GH) peaks responding to GHRP-2 injection were higher at day 1 than at day 6 of saline or GHRP-2 treatment in both LP and HP steers (P < 0.05). The area under the GH response curve for 180 min after the GHRP-2 injection was not significantly different between the LP and the HP groups at days 1 and 6. A response in plasma IGF-1 concentration to GHRP-2 treatment in the HP group was observed at day 1 (198.9 ± 18.1 ng/ml), day 2 (195.2 ± 21.1 ng/ml) and day 6 (201.3 ± 14.8 ng/ml) (P < 0.05). No increase in plasma IGF-1 was observed from GHRP-2 administration in the LP group. Although the response of plasma IGF-1 concentration to GHRP-2 administration was increased in the HP group (P < 0.05), there was no apparent effect of GHRP-2 treatment on plasma 38-43 kDa IGFBP-3 and 34 kDa IGFBP-2 at days 2 and 6 of treatment. In conclusion, it is proposed that the 34 kDa IGFBP-2 is sensitive to dietary protein level and may play an important role in the regulation of circulating IGF-1 in ruminant. In addition, increased plasma IGF-1 concentration observed in the HP group in response to the GHRP-2 treatment did not appear to affect plasma IGFBPs.

Original languageEnglish
Pages (from-to)134-146
Number of pages13
JournalDomestic Animal Endocrinology
Volume28
Issue number2
DOIs
Publication statusPublished - 2005 Feb 1

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Keywords

  • Dietary protein
  • GHRP-2
  • IGF-1
  • IGFBPs
  • Steer

ASJC Scopus subject areas

  • Animal Science and Zoology
  • veterinary(all)
  • Endocrinology

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