GHRH

GHRH is the hypothalamus's accelerator pedal for growth hormone. It is a peptide that travels through the portal system to the anterior pituitary, where it tells the growth-hormone-making cells (somatotrophs) to manufacture and release their hormone.

GHRH works as one half of a push-pull pair. While GHRH presses the pituitary to release growth hormone, somatostatin from the hypothalamus does the opposite, restraining its release. The balance between these two opposing signals shapes the rising-and-falling pattern of growth hormone in the blood across the day.

Growth hormone is released mostly in pulses, with the biggest surge during deep sleep at night — a rhythm driven largely by alternating GHRH and somatostatin tone. This pulsatile pattern is important for normal growth in children and for tissue maintenance in adults.

Clinically, GHRH can be given as a stimulation test to probe whether the pituitary is capable of releasing growth hormone. Rarely, tumors elsewhere in the body secrete GHRH ectopically, overdriving the pituitary and producing acromegaly.