Effect of Oral Glucose Administration on Plasma Growth Hormone-Releasing Hormone (GHRH)-Like Immunoreactivity Levels in Normal Subjects and Patients with Idiopathic GH Deficiency: Evidence that GHRH Is Released Not Only from the Hypothalamus but Also from Extrahypothalamic Tissue

Using a specific and sensitive RIA for GH-releasing hormone (GHRH), we examined the effect of oral administration of 75 g glucose on peripheral plasma GHRH-like immunoreactivity (GHRH-LI) in normal subjects (n = 12) and patients with idiopathic GH deficiency (IGHD) (n = 6). The normal subjects had two peaks of plasma GHRH-LI after oral glucose administration. The initial peak GHRH-LI levels occurred 30–150 min after glucose ingestion and corresponded to an increase in blood glucose. The increment in plasma GHRH-LI levels 30 min after glucose ingestion [7.4 ± 2.4 (±sem) pg/ml] was significantly higher (P < 0.05) than that during a control study. Second peaks in plasma GHRH-LI occurred 3.5–6 h after glucose ingestion, and the mean increment 5 h after glucose ingestion was 9.4 ± 2.4 pg/ml. This second rise of plasma GHRH-LI coincided with a significant increase in plasma GH after reactive hypoglycemia. This second GHRH-LI peak and the rise of plasma GH after hypoglycemia were absent in patients with IGHD, wh...