EFFECT OF HYDROCORTISONE ON THE GROWTH-HORMONE RESPONSE TO GROWTH HORMONE-RELEASING HORMONE IN ACROMEGALY

Our recent data show that acute and sustained hypercortisolism decreas es circulating growth hormone (GH) levels in acromegaly with respect t o saline infusion. It has been hypothesized that in acromegalic patien ts, as well as in normal subjects, short-term increases in serum corti sol levels may be able to cause an enhancement of hypothalamic somatos tatin secretion, which in turn may be responsible for the glucocortico id mediated GH inhibition. The aim of our study was to investigate the acute effects of an intravenous infusion of hydrocortisone on the GH response to growth hormone-releasing hormone (GHRH) in acromegaly. We studied 6 adult patients with active acromegaly (3 M, 3 F; mean age 60 .5 +/- 4.1 years; mean body mass index 27.1 +/- 0.6 kg/ m(2)). All the patients underwent: (1) a bolus intravenous injection of 100 mg hydro cortisone succinate in 2 ml saline, at time -60 followed by a 120-min intravenous infusion of 250 mg hydrocortisone succinate in 250 ml sali ne, from -60 to 60 min; (2) a bolus intravenous injection of human GHR H 129NH(2) 100 mu g in 1 ml saline, 60 min after initiation of a 2-hou r hydrocortisone infusion; (3) a bolus intravenous GHRH injection 60 m in after initiation of a 2-hour saline infusion. In all of the acromeg alic patients during hydrocortisone succinate infusion, GH values clea rly decreased with respect to basal levels (mean nadir 47 +/- 8.6%, p < 0.05 with respect to basal levels). After GHRH injection and saline infusion all the patients showed a significant increase in GH levels ( mean peak 231.5 +/- 52.8%, p < 0.05). After hydrocortisone + GHRH admi nistration, all 6 patients showed absolute GH values not significantly different with respect to hydrocortisone alone and GH peaks after GHR H were significantly lower with respect to saline + GHRH (mean GH peak levels 118.8 +/- 12.9 vs. 231.5 +/- 52.8%, p < 0.05). We conclude tha t acute administration of pharmacological doses of glucocorticoids is able to decrease the GH response to GHRH in patients with acromegaly p robably through an enhancement of endogenous somatostatin tone.