Involvement of intracellular Ca2+ during growth hormone-induced priming of human neutrophils

Growth hormone (GH) primes and augments O2- production in neutrophils. The exact signaling of the priming pathway by GH has not been demonstrated. In this study, we investigated intracellular signaling of priming by recombinant human growth hormone (rGH) in human neutrophils. A low concentration of rGH (10-100 ng/ml) significantly enhanced the O2- production from neutrophils triggered with N-formyl-1-methionyl-1-leucyl-1-phenylalanine in a dose-dependent manner. Recombinant GH directly increased the fluorescence intensity of intracellular Ca2+ labeled with fluo 3-AM in neutrophils. The change of fluorescence intensity of cytosolic Ca2+ was dependent on the rGH concentration. The peak level of fluorescence intensity was observed at 3 to 5 min after treatment with rGH. The priming effect of rGH on O2- production via Ca2+ was abrogated by Ca2+ channel blockers such as dentrolene and verapamil. Furthermore, preincubation with genistein, a tyrosine kinase inhibitor, blocked the rGH-induced increases in Ca2+ and O2- production. This finding suggests that GH can act through the increase of intracellular Ca2+ as a priming agent to activate neutrophils for an enhanced respiratory burst.