Context: Some indirect evidence suggests hypothalamic control of GH secretion in acromegaly.

Objective: To examine whether GH secretion in acromegaly is dependent on endogenous GHRH.

Patients and study design: We studied 8 patients with untreated acromegaly due to a GH producing pituitary tumor. All patients received an intravenous infusion of normal saline for 24 h and GHRH-antagonist (GHRH-ant) at 50 µg/kg/h for 7 days. GH was measured every 10 min for 24 h during the normal saline infusion and on the last day of the GHRH-ant infusion. A group of 9 different patients with untreated acromegaly served as the control group and underwent blood sampling for GH every 10 min for two 24 h periods to assess the day-to-day variability of GH secretion.

Setting: University referral center.

Main outcome measure: Twenty-four hour mean GH.

Results: In 6 out of 8 subjects treated with GHRH-ant, 24 h mean GH decreased by 5.8-30.0% during iv. GHRH-ant and in 3 subjects the change in the 24 h mean GH was greater than the upper limit of the 95% confidence interval of the spontaneous day-to-day variability of the mean GH in patients with acromegaly. Based on the binomial distribution, the probability of this magnitude of change to occur in 3/8 subjects by chance alone is 0.0008.

Conclusion: in some patients with acromegaly due to a pituitary adenoma, GH secretion is under partial control by endogenous GHRH.