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

• Published in: Domestic animal endocrinology 2005-02, Vol.28 (2), p.134-146
• Main Authors: Lee, H.G., Choi, Y.J., Lee, S.R., Kuwayama, H., Hidari, H., You, S.K.
• Format: Article
• Language: English
• Subjects: Animals; Blood Urea Nitrogen; Blotting, Western - veterinary; Cattle - blood; Dietary protein; Dietary Proteins - pharmacology; GHRP-2; IGF-1; IGFBPs; Insulin-Like Growth Factor Binding Protein 2 - blood; Insulin-Like Growth Factor Binding Protein 3 - blood; Insulin-Like Growth Factor Binding Protein 4 - blood; Insulin-Like Growth Factor I - metabolism; Male; Oligopeptides - pharmacology; Radioimmunoassay - veterinary; Steer
• ISSN: 0739-7240; 1879-0054
• DOI: 10.1016/j.domaniend.2004.07.001

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.