GROWTH HORMONE RESPONSIVENESS TO HUMAN PANCREATIC GROWTH HORMONE RELEASING FACTOR IN ACROMEGALY: MODULATORY EFFECTS OF BASAL HORMONE LEVELS AND OF CONCOMITANT SOMATOSTATIN ADMINISTRATION

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Abstract
Human pancreatic growth hormone releasing factor 1-44 (hpGRF), 100 .mu.g was administered as an i.v. bolus injection to 11 patients with acromegaly. The mean serum growth hormone (GH) levels rose (P < 0.001) from 54 .+-. 20 ng/ml-215 .+-. 126 ng/ml (.+-. SEM [standard error of mean]) 20 min after the injection. Although the maximum response of GH levels was highly variable it correlated positively with the individual GH levels (P < 0.01, Rs = +0.80). Thus the higher the GH levels, the greater the responsiveness to hpGRF. Administration of somatostatin (SRIF), 300 .mu.g/h, lowered basal GH levels from 76 .+-. 38 ng/ml-13 .+-. 5 ng/ml (P < 0.01) after 1 h, hpGRF administration during concominant SRIF infusion also led to highly variable growth hormone responses. The maximum GH responses again correlated positively with the GH level before hpGRF after 1 h of SRIF administration (P < 0.05, Rs = +0.79). GH responses to hpGRF were completely blocked by SRIF in 3 out of 4 patients whose GH levels decreased to normal levels during SRIF infusion. Thus the pituitary in acromegaly apparently is normally responsive to both SRIF and hpGRF but at a higher setting of basal GH levels.