Human pancreatic growth hormone-releasing factor (hpGRF): dose-response of GRF- and GH-levels.

Synthetic human pancreatic growth hormone-releasing factor (hpGRF1-44) was given as an i.v. bolus to 8 healthy volunteers in 5 different dosages. Blood was collected before and up to 120 min after GRF-injection. Four subjects received only placebo, five received 3.3 micrograms, three 12.5 micrograms, four 50 micrograms, 5 received 100 micrograms, and three 200 micrograms hpGRF1-44. No serious side effects were recorded after hpGRF1-44. All dosages with the exception of the 3.3 micrograms-dosage lead to a clearcut and significant increase of GH-levels with a maximum occurring 15 to 30 minutes after hpGRF1-44. A dose-response-relationship between the injected GRF-dosage and growth hormone levels was only found from 3.3 to 50 micrograms hpGRF1-44. The administration of 100 or 200 micrograms hpGRF1-44 did not lead to a further increase of GH-levels compared to the 50-micrograms-dose. This was in contrast to the clearcut dose dependency of hpGRF1-44-levels measured by a specific radioimmunoassay over the whole dose range with a maximum occurring 5 minutes after the injection. The mean halftime of disappearance for the 200-micrograms-dose of hp-GRF1-44 was 7.6 +/- 1.7 minutes (+/- SE). We conclude that there is a marked heterogeneity of the GH-response to hpGRF1-44 in healthy volunteers though a dose-response-relationship over the range from 3.3 to 50 micrograms hpGRF i.v. could be established. The dose-response-dependency of hpGRF1-44-levels up to the 200-micrograms-dose indicates that the maximal GH-response is reached when 50 micrograms hpGRF1-44 are administered.(ABSTRACT TRUNCATED AT 250 WORDS)