M. Roumi et al., RADIOIMMUNOASSAY FOR HEXARELIN, A PEPTIDIC GROWTH-HORMONE SECRETAGOGUE, AND ITS PHARMACOKINETIC STUDIES, Peptides, 16(7), 1995, pp. 1301-1306
A radioimmunoassay (RIA) method for hexarelin, a peptidic growth hormo
ne secretagogue, has been developed and applied to pharmacokinetic stu
dies in dogs following an IV dose of 1 mu g/kg, and three SC doses of
1, 10, and 100 mu g/kg. The sensitivity of the assay was determined to
be 1.34 fmol/assay. Cross-reactivity of the antiserum with nine hexar
elin analogues was less than 1% upon modification of positions 3, 4, o
r 5 of the peptide. No apparent cross-reaction with endogenous hexarel
in metabolites were observed. Intra- and interassay coefficients of va
riation were less than 3% and 4%, respectively. Intravenous bolus phar
macokinetics of hexarelin displayed a high terminal half-life of 120 m
in, a fractional plasma clearance of 4.28 ml/min/kg, and a volume of d
istribution at steady state of 387.7 ml/kg. Following SC administratio
n of hexarelin, despite the increase in dose administered, both cleara
nce (3.93-5.17 ml/min/kg) and volume of distribution (316-544 ml/kg) p
arameters remained constant over the dose range studied.