Effect of Dexamethasone on Growth Hormone (GH) Response to Growth Hormone Releasing Hormone in Acromegaly*

Abstract

The effect of dexamethasone on the GH responseto GH-releasing hormone (GHRH) was studied in vivoin six patients with acromegaly as well as in vitro in monolayercultures of GH-secreting pituitary tumor cells obtained fromthree of these patients. Oral administration of 9 mg/day dexamethasonefor 2 days decreased plasma GH responses to ivinjection of 100 μg GHRH-(1−44 amide) in all six patients. Bloodglucose levels were significantly increased, while plasma somatomedin-C levels were significantly decreased by this regimen ofdexamethasone treatment. On the other hand, 2-day pretreatmentwith 50 nM dexamethasone of monolayer cultures of pituitaryadenoma cells potentiated GH release basally and/or inresponse to 100 pM to 1 nM GHRH in vitro. These resultsindicate that the potentiating action of 2-day treatment ofdexamethasone in vitro is overwhelmed in vivo by some extrapituitaryaction, probably on the central nervous system, ofglucocorticoids in patients with acromegaly.