Secretory profile of immunoreactive growth hormone-releasing hormone (IR-GHRH) during sleep in man and its clinical value.

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.