The pathway
GHRH from the hypothalamus stimulates the pituitary to release growth hormone. Growth hormone acts on tissues directly and stimulates hepatic IGF-1 production. IGF-1 mediates many of the downstream effects and feeds back to suppress GH release. Somatostatin provides opposing inhibitory control.
Why the point of intervention matters
Supplying growth hormone directly bypasses hypothalamic and pituitary control, so feedback no longer regulates the amount present. Acting upstream with a GHRH analogue works through the pituitary, so the pulsatile pattern and feedback remain in place.
These are different interventions with different profiles, which is why GHRH analogues and recombinant growth hormone are studied as distinct approaches rather than as substitutes.
Pulsatility
Growth hormone is released in pulses rather than continuously, and several downstream responses depend on that pattern. Any intervention that flattens it changes more than the total amount present.
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