Human Brain and Pituitary Glands Possess Specific Receptors for GH Secretagogues

Background Growth hormone (GH) is a crucial peptide hormone that regulates growth, metabolism, and body composition. Its release is tightly controlled by the hypothalamus and pituitary gland. Synthetic GH secretagogues (GHS) are compounds designed to stimulate GH release, offering potential therapeutic benefits for conditions like GH deficiency or sarcopenia (age-related muscle loss). However, despite their known physiological effects, the precise molecular targets and anatomical distribution of specific GHS receptors within key human endocrine and neurological tissues, particularly the brain and pituitary gland, remained largely uncharacterized. This knowledge gap hindered a full understanding of their mechanism of action and optimal therapeutic development.

What They Found The study successfully identified specific, high-affinity binding sites for GH secretagogues in both the human pituitary gland and various brain regions. The most significant finding was the presence of a remarkably high density of specific GHS receptors within the anterior lobe of the pituitary gland, exhibiting a maximum binding capacity (Bmax) of 165 ± 15 fmol/mg protein and a dissociation constant (Kd) of 0.75 ± 0.1 nM, indicating very high affinity. Substantial specific binding was also observed in the hypothalamus, a key brain region for GH regulation, with a Bmax of 95 ± 10 fmol/mg protein and a Kd of 1.1 ± 0.2 nM. Furthermore, specific GHS binding was detected in other brain areas such as the hippocampus (Bmax 30 ± 5 fmol/mg protein) and brainstem, albeit at lower densities, suggesting broader neurological roles. Competition assays confirmed that unlabeled MK-0677 could displace 92% of the radioligand binding, demonstrating high specificity, while other unrelated peptides showed minimal displacement (<5%).