Study summary · research use only
d-Lys-GHRP-6 does not modify the endocrine response to acylated ghrelin or hexarelin in humans
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
In this human study of six normal volunteers, the authors tested whether D-Lys-GHRP-6 antagonizes the endocrine responses to acylated ghrelin and to hexarelin. Different doses of D-Lys-GHRP-6 (2.0 microg/kg as bolus or infusion, and a higher regimen) were given with or without acylated ghrelin or hexarelin (1.0 microg/kg), and GH, prolactin, ACTH, and cortisol were measured. They report that acylated ghrelin and hexarelin stimulated all four hormones (p<0.05), and that D-Lys-GHRP-6, whether as bolus or infusion, did not modify spontaneous or stimulated hormone secretion, nor the GH response to 0.25microg/kg acylated ghrelin. The authors question D-Lys-GHRP-6 as a GHS-R1a antagonist for human studies.
Abstract
Acylated ghrelin exerts numerous endocrine and non-endocrine activities via the GH Secretagogue receptor type 1a (GHS-R1a). D-Lys-GHRP-6 has been widely studied in vitro and in vivo in animal studies as GHS-R1a antagonist; its action in humans has, however, never been tested so far. Aim of our study was to verify the antagonistic action of D-Lys-GHRP-6 on the endocrine responses to acylated ghrelin and hexarelin, a peptidyl synthetic GHS, in humans. The effects of different doses of D-Lys-GHRP-6 (2.0microg/kg iv as bolus or 2.0microg/kg/h iv as infusion) on both spontaneous and acylated ghrelin- or hexarelin (1.0microg/kg iv as bolus) -stimulated GH, PRL, ACTH and cortisol levels were studied in six normal volunteers (age [mean+/-SEM]: 25.4+/-1.2yr; BMI: 22.3+/-1.0kg/m(2)). The effects of D-Lys-GHRP-6 (2.0microg/kg iv as bolus+4.0microg/kg/h iv) on the GH response to 0.25microg/kg iv as bolus acylated ghrelin was also studied. During saline, spontaneous ACTH and cortisol decrease was observed while non changes occurred in GH and PRL levels. Acylated ghrelin and hexarelin stimulated (p<0.05) GH, PRL, ACTH and cortisol secretions. D-Lys-GHRP-6 administered either as bolus or a continuous infusion did not modify both spontaneous and acylated ghrelin- or hexarelin-stimulated GH, PRL, ACTH and cortisol secretion. D-Lys-GHRP-6 did not modify even the GH response to 0.25microg/kg iv acylated ghrelin. In conclusion, D-Lys-GHRP-6 does not affect the neuroendocrine response to both ghrelin and hexarelin. These findings question D-Lys-GHRP-6 as an effective GHS-R1a antagonist for human studies.
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