Low-dose growth hormone-releasing hormone tests: a dose-response study.

We have evaluated parameters of the serum growth hormone (GH) concentration response to saline and 1-, 10- and 100-micrograms intravenous bolus doses of amide analogue of GH-releasing hormone (GHRH (1-29)NH2) given in random order to 10 adult male volunteers of median body weight 68 (60-90)kg. Compared with saline, both 10- and 100-micrograms GHRH(1-29)NH2 doses (but not 1 microgram) resulted in significant peak GH responses (means and 95% confidence intervals: 24.03 (11.22-51.29) vs 26.09 (16.40-41.50) mU/l, respectively). Although the average rate of serum GH rise was similar after both 10 micrograms (2.05 (1.13-2.97) mU.l-1.min-1) and 100 micrograms of GHRH(1-29)NH2 (1.52 (0.69-2.35) mU.l-1.min-1; ANOVA F = 0.93, p = 0.35), the average rate of serum GH decline after peak GH was slower after the higher dose (10 micrograms vs 100 micrograms: 0.65 (0.40-0.90) vs 0.37 (0.23-0.50) mU.l-1.min-1; ANOVA F = 5.14, p = 0.04), suggesting continued GH secretion. Increasing GHRH(1-29)NH2 doses delayed the time to peak GH (1 microgram: 7.00 (3.50-10.52) min; 10 micrograms: 15.80 (13.62-17.98) min; 100 micrograms: 24.80 (18.40-31.12) min) and serum GH levels were still elevated significantly 2 h after injection of 100 micrograms GHRH(1-29)NH2 compared with other doses (saline: 0.98 (0.48-2.04) mU/l; 1 microgram: 0.68 (0.48-0.93) mU/l; 10 micrograms: 1.07 (0.56-2.04) mU/l; 100 micrograms: 5.01 (2.34-10.86) mU/l; ANOVA F = 11.10, p < 0.001). In a second study we tested five adult male volunteers with lower doses (0.5-10 micrograms) of GHRH(1-29)NH2.(ABSTRACT TRUNCATED AT 250 WORDS)