Growth hormone-releasing peptide-2 infusion synchronizes growth hormone, thyrotrophin and prolactin release in prolonged critical illness

Objective: During prolonged critical illness, nocturnal pulsatile secretion of GH, TSH and prolactin (PRL) is uniformly reduced but remains responsive to the continuous infusion of GH secretagogues and TRH. Whether such (pert inent) secretagogues would synchronize pituitary secretion of GH, TSH and/o r PRL is not known. Design and methods: We explored temporal coupling among GH, TSH and PRL rel ease by calculating cross-correlation among GH, TSH and PRL serum concentra tion profiles in 86 time series obtained from prolonged critically ill pati ents by nocturnal blood sampling every 20 min for 9 h during 21-h infusions of either placebo (n = 22), GHRH (1 mu g/kg/h; n = 10), GH-releasing pepti de-2 (GHRP-2; 1 mu g/kg/h; n = 28), TRH (1 mu g/kg/h; n = 8) or combination s of these agonists (n = 18). Results: The normal synchrony among GH, TSH and PRL was absent during place bo delivery. Infusion of GHRP-2, but not GHRH or TRH, markedly synchronized serum profiles of GH, TSH and PRL (all P less than or equal to 0.007). Aft er addition of GHRH and TRH to the infusion of GHRP-2, only the synchrony b etween GH and PRL was maintained (P=0.003 for GHRH+GHRP-2 and P=0.006 for T RH + GHRH + GHRP-2), and was more marked than with GHRP-2 infusion alone (P = 0.0006 by ANOVA). Conclusions: The nocturnal GH, TSH and PRL secretory patterns during prolon ged critical illness are herewith further characterized to include loss of synchrony among GH, TSH and PRL release, The synchronizing effect of an exo genous GHRP-2 drive, but not of GHRH or TRH, suggests that the presumed end ogenous GHRP-like ligand may participate in the orchestration of coordinate d anterior pituitary hormone release.