Growth hormone secretion dynamics in a patient with ectopic growth hormone-releasing factor production

A female patient with acromegaly, hypercalcemia, and Zollinger-Ellison syndrome was found to have a very high plasma concentration (average 2,300 pmol/liter; normal less than 50 pmol/liter) of growth hormone-releasing factor as measured by a radioimmunoassay to human pituitary growth hormone-releasing factor-1-44. The plasma concentration of growth hormone averaged 25 mIU/liter (normal less than 5 mIU/liter) and there was no rise following an intravenous 100 micrograms bolus of human pituitary growth hormone-releasing factor-1-44. Plasma growth hormone and growth hormone-releasing factor levels were unaffected by bromocriptine, insulin-induced hypoglycemia, and sleep. A long-acting somatostatin analogue lowered both the growth hormone-releasing factor and the growth hormone levels. Thyrotropin-releasing hormone stimulation and oral glucose tolerance tests produced significant increases in plasma growth hormone levels whereas the growth hormone-releasing factor level remained unchanged, suggesting that when normal somatotrophs are exposed to maximal growth hormone-releasing factor stimulation, thyrotropin-releasing hormone becomes a secretagogue of growth hormone from the pituitary. It is proposed that in the absence of a radioimmunoassay for growth hormone-releasing factor, a lack of growth hormone response to growth hormone-releasing factor in a patient with acromegaly is compatible with a source of ectopic growth hormone-releasing factor production.