Secretagogue Desensitisation

Desensitisation is what happens when a growth hormone secretagogue is given often enough that each administration releases less than the one before. Three mechanisms operate at once and are often confused. At the receptor, sustained GHS-R1a occupancy drives phosphorylation, beta-arrestin recruitment and internalisation, reducing available receptors. At the pituitary, the readily releasable pool of stored hormone is finite and takes time to replenish. Above both, rising IGF-1 raises somatostatin tone and restrains the somatotroph directly.

The pattern is dose- and interval-dependent rather than absolute. Continuous infusion of a GHS-R1a agonist attenuates the response within hours to days, while intermittent administration spaced to let somatostatin tone fall and stores refill preserves much more of it. GHRH-receptor agonists are less prone to this than ghrelin-receptor agonists, and the two given together partly rescue a response that either alone has blunted. The same principle runs through endocrinology: continuous GnRH agonist exposure suppresses gonadotropins, pulsatile delivery stimulates them.

The consequence for interpretation is that acute studies overstate sustained effect. A single-dose growth hormone peak in healthy volunteers is a pharmacodynamic observation with a short shelf life, and extrapolating it to weeks of use assumes exactly what desensitisation denies. Anything claimed about chronic exposure needs chronic data.

The error encountered most often is inferring from a fading subjective response that the compound is still working at the original intensity, or the reverse, that escalating exposure restores it. More frequent stimulation of a desensitising receptor generally deepens the attenuation. Vendor material citing single-dose peak growth hormone concentrations as though they described ongoing use makes precisely this substitution.