Growth hormone-releasing factor analogue (hGRF1-29NH2): immunoreactive-GRF plasma levels after intravenous and subcutaneous administration.
A homologous radioimmunoassay (RIA) system for human growth hormone-releasing factor 1-29NH2 (hGRF 1-29-NH2) was developed and applied to the measurement of immunoreactive (IR) concentrations of the peptide in anaesthetized rats to determine some of its pharmaco-kinetics after i.v. and s.c. administration. Analysis of the biphasic disappearance curve of IR-hGRF-1-29NH2 from plasma after i.v. injection (10 micrograms) gave values for the half-lives of the initial distribution phase (alpha) and for the elimination phase (beta) of 1.9 +/- 0.2 min and 10.4 +/- 0.2 min respectively. There was rapid uptake of the peptide from the site of s.c. injection but comparison of areas under the plasma IR-hGRF1-29NH2/time curves showed that the estimated total amount in the circulation after s.c. injection was only 4% of that obtained after i.v. administration. A large degree of degradation of the peptide is indicated either at the site of injection or during transfer to plasma; this susceptibility to rapid breakdown is reflected in the short half-life of the peptide in the circulation. Therefore the measurement of the above parameters is a prerequisite when assessing potency of GRF analogues in-vivo and when implementing suitable dosage regimens for clinical purposes.
Rafferty
B
B
Poole
S
S
Clarke
R
R
Schulster
D
D
D000818:Animals; D005260:Female; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000097:blood*; D007275:Injections, Intravenous; D007279:Injections, Subcutaneous; D008657:Metabolic Clearance Rate; D010446:Peptide Fragments / Q000008:administration & dosage / Q000097:blood*; D011863:Radioimmunoassay / Q000379:methods; D051381:Rats; D011919:Rats, Inbred Strains; D017337:Sermorelin
D010446:Peptide Fragments; D017337:Sermorelin; D013007:Growth Hormone-Releasing Hormone