Factors other than sex steroids modulate GHRH and GHRP-2 efficacies in men: evaluation using a GnRH agonist/testosterone clamp.
The study found that young men had a significantly greater GH response to GHRH and GHRP-2 compared to older men, with abdominal fat negatively impacting GH release.
Where it sits
this study against the rest of the ghrp-2 (pralmorelin) corpusSummary and findings
The study evaluated the effects of GHRH and GHRP-2 on GH secretion in young and older men under a controlled sex-steroid environment. Eleven young men (age 24 +/- 0.99 yr) and eleven older men (age 64 +/- 2.4 yr) participated. The findings indicated that GHRH and GHRP-2 elicited different GH release responses based on age.
Abstract
<h4>Background</h4>Sex steroids are prominent regulators of pulsatile GH secretion.<h4>Hypothesis</h4>An experimentally controlled sex-steroid milieu will permit detection of nonsteroidal factors that determine GH secretion.<h4>Subjects</h4>Eleven young (age, 24 +/- 0.99 yr) and 11 older (64 +/- 2.4 yr) men participated in the study.<h4>Location</h4>The study was conducted at a tertiary medical center.<h4>Methods</h4>The study consisted of GnRH-agonist down-regulation of the gonadal axis followed by fixed-dose testosterone (T) replacement (leuprolide/T clamp) and consecutive infusion of l-arginine and GHRH or GH-releasing peptide-2 (GHRP-2) to quantify peptide-secretagogue efficacies.<h4>Outcomes</h4>The experimental leuprolide/T clamp yielded statistically age-comparable total, bioavailable, and free T and estradiol (E(2)) concentrations. In this controlled milieu, sequential l-arginine/GHRH infusion stimulated 1.4-fold more (P = 0.021) and l-arginine/GHRP-2 1.3-fold more (P = 0.045) GH release in young than older men. Abdominal visceral fat (AVF) correlated negatively with both GHRH (P = 0.0006; R(2) = 0.39) and GHRP-2 (R(2) = 0.29) efficacy, whereas IGF-I positively predicted the same endpoints (R(2) = 0.25 to 0.30). In multivariate analysis, AVF emerged as a dominant negative determinant of GHRH efficacy (P = 0.002; R(2) = 0.41) and IGF-I as a primary positive determinant of GHRP-2 efficacy (P = 0.007; R(2) = 0.31).<h4>Conclusion</h4>During fixed T/E(2) availability, AVF contributes 41% of the GH-response variability to maximal GHRH drive, whereas IGF-I accounts for 31% of that for GHRP-2. Accordingly, a statistically equalized sex-steroid milieu permits dissection of age-independent and T/E(2)-independent modulators of GHRH and GHRP efficacy in men.
Background
Not reported in abstract.
Methods
Not reported in abstract.
Results
Not reported in abstract.
Interpretation
Not reported in abstract.
Limitations
Not reported in abstract.