The pituitary gland is capable of responding to two successive doses of growth hormone releasing hormone (GHRH)

We have studied the serum growth hormone (GH) response to two consecutive doses of growth hormone releasing hormone (GHRH) (50, 100, 200 micrograms) given 1, 2 or 3 h apart in seven adult males. The serum GH profile was analysed by deconvulution incorporating a variable half-life for GH. All three doses of GHRH stimulated maximal GH secretion: 50 micrograms, 146.0 mU/min (SEM 24.0); 100 micrograms, 128.1 mU/min (SEM 14.3); 200 micrograms, 134.1 mU/min (SEM 20.5) (one-way ANOVA, P = NS). The magnitude of the second secretory burst after the second dose of GHRH was less than that induced by the first injection of GHRH, particularly when doses of 200 micrograms were used. Factors influencing the response to the second dose were the GH secretory status at the point that the stimulus was applied and the time interval between administration of the first and second doses. These studies demonstrate that the pituitary gland is capable of responding to two consecutive doses of GHRH although the second response is always less than the first. The data demonstrate the importance of using methods of assessing GH secretion and not relying simply on measured serum GH concentration values.