Effects of dietary protein and growth hormone-releasing peptide (GHRP-2) on plasma IGF-1 and IGFBPs in Holstein steers.
Lee. H G HG; Choi. Y J YJ; Lee. S R SR; Kuwayama. H H; Hidari. H H; You. S K SK
Key Findings
- High dietary protein increased baseline plasma IGF‑1 and lowered IGFBP‑2 levels in steers.
- GHRP‑2 raised IGF‑1 only in the high‑protein group; low‑protein steers showed no IGF‑1 increase.
- The acute GH response to GHRP‑2 was strongest on day 1 and faded by day 6, regardless of protein level.
- GHRP‑2 did not affect the larger IGFBP‑3 or the 34 kDa IGFBP‑2 during the later days of treatment.
Practical Outcomes
- If you plan to use GHRP‑2 for boosting IGF‑1, pairing it with a protein‑rich diet may be important for effectiveness, at least based on animal data. However, because the study was done in cattle, the results may not directly translate to humans, so proceed cautiously and consider protein intake as a potential factor when evaluating GHRP‑2 outcomes.
Summary
In a study on dairy cows, giving a high‑protein diet made the animals' baseline IGF‑1 levels higher and allowed the growth‑hormone‑releasing peptide GHRP‑2 to raise IGF‑1 even more. Low‑protein cows did not show this IGF‑1 boost from GHRP‑2. The peptide didn’t change the main IGF‑binding proteins, but a smaller binding protein (IGFBP‑2) was lower when protein intake was high.
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 microg/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.
Study Information
pubmed
2005
10.1016/j.domaniend.2004.07.001