Catabolism of rat growth hormone-releasing factor(1-29) amide in rat serum and liver.
Boulanger. L L; Roughly. P P; Gaudreau. P P
Key Findings
- GRF‑1‑29 has a short half‑life in rat serum (~18 min) and liver homogenate (~13 min).
- The primary cleavage site is Ala2‑Asp3, a DPP‑IV target, with additional tissue‑specific cuts (e.g., Arg11‑Arg12 in serum, Tyr10‑Arg11 in liver).
- Breakdown produces shorter, less hydrophobic fragments such as GRF(1‑20)OH, GRF(3‑20)OH, and GRF(1‑18)OH.
Practical Outcomes
- Because the native peptide degrades rapidly, using it as‑is will require frequent dosing or very high amounts, which is impractical for most users. Biohackers should consider more stable analogs (e.g., CJC‑1295, tetrasubstituted GRF) or co‑administer DPP‑IV inhibitors to extend activity. Understanding the cleavage sites helps guide formulation strategies to protect the peptide from serum and liver enzymes.
Summary
The study shows that the natural growth hormone‑releasing factor peptide (GRF‑1‑29) is broken down very quickly in rat blood and liver, disappearing in about 15‑20 minutes. It identifies the exact spots where enzymes cut the peptide, especially a spot that DPP‑IV enzymes target. This means the plain peptide doesn’t stay around long enough to have a strong, lasting effect unless it’s protected or altered.
Abstract
Clinical and veterinary uses of growth hormone-releasing factor [GRF(1- 29)NH2] require the design of analogs that are resistant to proteolysis by serum and liver degrading enzymes. This study investigated rat GRF(1-29)NH2 processing in serum and liver homogenate by means of high pressure liquid chromatography (HPLC). Synthetic rGRF(1-29)NH2 (30 microM) was incubated (0-120 min, 37 degrees C) in serum (49 +/- 8 mg prot./ml). The rGRF(1-29)NH2 (10 microM) was also incubated (0-120 min, 37 degrees C) with liver homogenate (200 +/- 6 micrograms prot./ml). Time course studies of rGRF(1-29)NH2 disappearance showed apparent half-lives of 18 +/- 4 min and 13 +/- 3 min in serum and liver homogenate, respectively. This was accompanied by the appearance of degradation products that were all less hydrophobic than the native peptide. In the serum, two major metabolites were detected and isolated by preparative HPLC. Combined results of amino acid analysis, sequencing, and chromatography with synthetic homologs revealed the presence of rGRF(1-20)OH and (3-20)OH. A small amount of rGRF(12-29)NH2, coeluting with rGRF(3-20)OH, was also found by sequencing. In the liver, rGRF(1-18)OH, (3-18)OH, and (1-10)OH were identified. The peptide bond Ala2-Asp3 (DPP IV cleavage site) was hydrolyzed in both serum and liver. Other tissue-specific cleavage sites were Arg11-Arg12 and Arg20-Lys21 (trypsin-like cleavage site) in the serum, and Tyr10-Arg11 and Tyr18-Ala19 (chymotrypsin-like cleavage site) in the liver.(ABSTRACT TRUNCATED AT 250 WORDS)
Study Information
pubmed
1992
10.1016/0196-9781(92)90173-z