title: Exogenous 20K growth hormone (GH) suppresses endogenous 22K GH secretion in normal men.
abstract: The physiological and pharmacological functions of the 20-kDa human GH (20K-hGH) isoform are unknown. We conducted a pharmacokinetic study of recombinant 20K-hGH in human subjects (Phase I clinical trial). Placebo or 20K-hGH was administered sc to normal men (20-31 yr of age, n = 6-8 per group) at 2100 h. Serum 20K- and 22K-hGH levels were monitored every 30 min for 24 h by specific enzyme-linked immunosorbent assays. Serum free fatty acid, insulin-like growth factor I, insulin, and glucose levels were measured for 24 h. In the placebo group, the secretion profiles of endogenous 20K- and 22K-hGH were pulsatile and similar to each other. The proportion of 20K- to 22K-hGH was fairly constant. In the 20K-hGH-treated groups, serum 20K-hGH levels increased in a dose-dependent manner over the dose range of 0.01-0.1 mg/kg. Maximum serum 20K-hGH levels were reached at 3-4 h and decreased with half-lives of 2-3 h. Marked suppression of endogenous 22K-hGH secretion was observed in a time-dependent manner. Serum free fatty acid and insulin-like growth factor I levels were significantly elevated (P < 0.01) at 4, 8, and 12 h and at 8, 12, and 24 h after 20K-hGH administration, respectively. Serum insulin and glucose levels did not change significantly within 24 h. These results suggested that: 1) regulation of 20K-hGH secretion is physiologically the same as that of 22K-hGH; 2) the pharmacokinetics after sc injection of 20K-hGH are comparable with those of 22K-hGH; 3) 20K-hGH regulates hGH secretion through "GH-induced negative feedback mechanisms"; and 4) administration of 20K-hGH is expected to exert GH actions (growth-promoting activity and lipolytic activity). Monitoring of serum 20K- and 22K-hGH levels may be useful in evaluating the effects of administered GH isoforms on their own release from the pituitary.
authors.affiliation: Institute of Biological Science, Mitsui Pharmaceuticals, Inc., Chiba, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: T
authors.initials: T
authors.lastname: Kamioka
authors.forename: M
authors.initials: M
authors.lastname: Hosaka
authors.forename: K
authors.initials: K
authors.lastname: Mabuchi
authors.forename: A
authors.initials: A
authors.lastname: Mizuchi
authors.forename: Y
authors.initials: Y
authors.lastname: Shimazaki
authors.forename: M
authors.initials: M
authors.lastname: Tsunoo
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
mesh_terms: D000328:Adult; D004797:Enzyme-Linked Immunosorbent Assay; D005230:Fatty Acids, Nonesterified / Q000097:blood; D019382:Human Growth Hormone / Q000037:antagonists & inhibitors* / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D007279:Injections, Subcutaneous; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008297:Male; D010446:Peptide Fragments / Q000037:antagonists & inhibitors* / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology; D012016:Reference Values
chemical_list: D005230:Fatty Acids, Nonesterified; D010446:Peptide Fragments; D011994:Recombinant Proteins; C404802:human growth hormone 22K; C039519:somatotropin 20K; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I