Study summary · research use only
Kinetics and disposition of hexarelin, a peptidic growth hormone secretagogue, in rats
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This pharmacokinetic study documented the disposition of hexarelin, a peptidyl GH secretagogue, in male Sprague-Dawley rats given a 5 microg/kg intravenous bolus or subcutaneous doses of 5, 10, and 50 microg/kg, with tritium-labelled hexarelin used to assess tissue distribution and excretion. The authors report an intravenous half-life of 75.9 minutes, systemic clearance of 7.6 ml/min/kg, and a steady-state volume of distribution of 744 ml/kg, with subcutaneous bioavailability of 64%. They report kinetics appeared first order up to 50 microg/kg, rapid subcutaneous absorption, and that biliary excretion was the primary elimination route, with total radioactivity in bile, urine, and feces corresponding to 60, 22, and 10% of the dose. High recovery of unchanged peptide in bile and urine was reported, indicating stability toward proteolytic enzymes.
Abstract
To document the disposition of hexarelin, a peptidyl growth hormone secretagogue, male Sprague-Dawley rats received a 5-microg/kg bolus i.v. dose or three single s.c. doses of 5, 10, and 50 microg/kg. To assess hexarelin tissue distribution and excretion, rats were given 1 microg/kg of [(3)H]hexarelin (9.4 Ci/mmol). Metabolism of [(3)H]hexarelin was assessed in bile duct-exteriorized rats given 50 microg/kg where radiolabeled hexarelin biliary and urinary excretion was quantified. After its i.v. injection, hexarelin displayed a half-life of 75.9 +/- 9.3 min, a systemic clearance of 7.6 +/- 0.7 ml/min/kg, and a volume of distribution at steady state of 744 +/- 81 ml/kg. After s.c. administration, the area under the curve (477-3826 pmol.min/ml) estimated with increasing doses confirmed the absence of hexarelin accumulation. Clearance/F (12-15 ml/min/kg) and volume of distribution/F (1208-1222 ml/kg) were dose independent. Hexarelin bioavailability given s.c. was 64%. The highest radioactivity levels were detected in the kidney, liver, and duodenum. The pattern of hexarelin excretion was similar after i.v. or s.c. administrations. Total radioactivity in bile, urine, and feces corresponded to 60, 22, and 10% of the dose, respectively. Of the radioactivity excreted in bile and urine, 90 and 71% was unchanged hexarelin, respectively. These results suggest that: 1) the kinetics of hexarelin appear to be first order up to 50 microg/kg; 2) hexarelin is rapidly absorbed after s.c. administration; 3) biliary excretion is the primary route of hexarelin elimination; and 4) the high recovery of unchanged peptide in bile and urine demonstrates hexarelin stability toward proteolytic enzymes.
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