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Pralmorelin vs Other Growth Hormone Secretagogues: Receptor Selectivity and Clinical Use
The growth hormone secretagogue landscape includes dozens of peptides, but pralmorelin occupies a specific niche due to its receptor binding profile and duration of action. Sermorelin, for example, is a growth hormone-releasing hormone (GHRH) analog that acts
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- The growth hormone secretagogue landscape includes dozens of peptides, but pralmorelin occupies a specific niche due to its receptor binding profile and duration of action. Sermorelin, for example, is a growth hormone-releasing hormone (GHRH) analog that acts on GHRH receptors in the pituitary. A different receptor class entirely. Pralmorelin, by contrast, acts on ghrelin receptors, which are expressed not only in the pituitary but also in the hypothalamus, gastrointestinal tract, and adipose tissue. This broader receptor distribution explains why ghrelin receptor agonists like pralmorelin have been investigated for appetite stimulation and metabolic effects beyond GH release.
- Hexarelin and GHRP-2 are structurally similar to pralmorelin and also act as GHS-R1a agonists. The primary differences lie in potency, receptor selectivity, and secondary effects. Hexarelin, for instance, has been shown to produce cardiovascular effects. Including increased cardiac contractility. That are independent of GH release, likely due to GHS-R1a expression in cardiac tissue. Pralmorelin's cardiovascular activity is less pronounced, making it a more selective GH secretagogue in that regard.
- Clinical trials in the late 1990s and early 2000s explored pralmorelin for growth hormone deficiency in children and adults, cachexia in HIV and cancer patients, and age-related GH decline. A pivotal study published in Metabolism: Clinical and Experimental evaluated pralmorelin's ability to increase lean body mass and reduce fat mass in elderly men over a 16-week period. Results showed modest improvements in body composition. Approximately 1.5 kg increase in lean mass and 1.2 kg reduction in fat mass. But these changes were accompanied by transient increases in cortisol and prolactin, both of which are known side effects of ghrelin receptor activation.
- That cortisol spike is worth understanding. GHS-R1a activation not only stimulates GH release but also activates the hypothalamic-pituitary-adrenal (HPA) axis, leading to ACTH and cortisol secretion. In short-term use, this is unlikely to be clinically significant. In chronic, repeated administration, elevated cortisol could theoretically blunt some of the anabolic benefits of increased GH and IGF-1. This is why research protocols using pralmorelin typically involve intermittent dosing rather than continuous daily administration.