Growth hormone releasing factor infusion does not sustain elevated GH-levels in normal subjects.
To evaluate the dynamics of GH-secretion after infusion of growth hormone releasing factor, human pancreatic growth hormone releasing factor (hpGRF1-44) was infused over 2 and 5 h at a dosage of 100 micrograms hpGRF1-44/h into 11 healthy subjects. The infusion was started and terminated with a 50 micrograms hpGRF1-44 bolus injection. In 5 subjects 200 micrograms TRH was given 4 h after starting the infusion. In addition, 4 healthy subjects received 50 micrograms hpGRF1-44 bolus injection every 2 h. GRF, somatostatin, GH, Prl, and TSH were measured by radioimmunoassay. The initial 50 micrograms GRF bolus increased GH-levels in all 11 subjects with a maximum at 30 min (24.1 +/- 5.1 ng/ml +/- SE). However, though hpGRF1-44 was continuously infused and GFR-levels remained elevated, GH decreased to a minimum 270 min after start of infusion (2.6 +/- 0.6 ng/ml). The GH-response to the second bolus at the end of the infusion was lower compared to the first response (14.6 +/- 3.4 ng/ml after 2 h and 7.6 +/- 2.5 ng/ml after 5 h). TRH did not lead to a GH-increase during hpGRF1-44 infusion though Prl and TSH rose normally. The intermittent bolus injection of 50 micrograms hpGRF1-44 led to continuously decreasing GH-responses to the same GRF-dosage (I. bolus: 16.5 +/- 1.6 ng/ml; II. bolus: 4.2 +/- 0.8 ng/ml; III. bolus: 3.4 +/- 0.5 ng/ml). No change in somatostatin levels was observed. These findings show that GRF infusion or bolus injection in short intervals does not sustain elevated GH-levels.(ABSTRACT TRUNCATED AT 250 WORDS)
D000328:Adult; D005260:Female; D013006:Growth Hormone / Q000097:blood* / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D006801:Humans; D007263:Infusions, Parenteral; D008297:Male; D011388:Prolactin / Q000097:blood; D011863:Radioimmunoassay; D013972:Thyrotropin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D013997:Time Factors
D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D013972:Thyrotropin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone