To clarify the role of growth hormone-releasing hormone (GHRH) in the regulation of
the episodic growth hormone (GH) secretion which is known to occur constantly in the
initial slow wave stage of nocturnal sleep in man, we studied the relation between
the secretions of plasma immunoreactive(IR)-GHRH and GH while recording electroencephalograms.
In subjects who showed a normal sleep pattern, the plasma IR-GHRH level increased
3- to 4-fold just before the surge of plasma GH, suggesting that GH release in the
initial slow wave stage of sleep is mainly mediated by GHRH. However, when there was
an apparent GH surge just before the onset of sleep, the magnitude of the GH response
associated with the initial slow wave stage tended to be blunted, even when sufficient
IR-GHRH was released. We also observed no appreciable fluctuations of plasma IR-GHRH
during nocturnal sleep in a patient diagnosed as having GH-deficient dwarfism, suggesting
the primary lesion was on the hypothalamus level, not the pituitary, in such a patient.
In a case of multiple endocrine neoplasia (MEN) type I with an ectopic GHRH-producing
pancreatic tumor, no remarkable elevation of plasma IR-GHRH was detected in the initial
slow wave stage of nocturnal sleep. We conclude that the present study is significant
not only in demonstrating the physiology of GHRH release, but also in establishing
a safe, reliable and practical test for routine clinical use to investigate intrinsic
ability to release GHRH and the primary lesions in patients with disorders of GH secretion.
Key words
Plasma GHRH in humans - GHRH and GH secretion during sleep - GHRH in idiopathic pituitary
dwarfism - GHRH-Producing tumor
