Pharmacokinetics of human growth hormone releasing factor (hGRF-44 NH2) in normal men after intravenous administration of a large range of doses.

Three ranges of doses of growth hormone releasing factor (2.5-80 micrograms, 80-320 micrograms and 75-600 micrograms) were intravenously administered to healthy young volunteers in three double blind studies. Serum circulating GRF levels were determined by radioimmunoassay. Experimental concentration curves were fitted, using the extended least squares method, to a biexponential model for the structural model and power function for the variance model. The power variance model, compared to the constant variance model greatly reduced the coefficient of variation of the biexponential parameters. The power of the variance model was estimated to be 1.95. The distribution half-life was 6.6 min and the elimination half-life was 39.0 min (harmonic means). Total clearance was 0.12 +/- 0.01 microgram/l/min. No difference between these parameters was found for the various doses. GRF kinetics was linear established in the range 10 to 600 micrograms which means that elimination was not altered by the increased doses.