Inhibition of recombinant human growth hormone-induced and prolactin-induced activation of neutrophils by octreotide.

Growth hormone, prolactin and somatostatin are polypeptide hormones of the neuroendocrine and peripheral nervous systems. In vitro, these have opposing effects on cells of the immune system. We compared the effects of these peptides on activation of neutrophils using a recombinant preparation of human growth hormone, human prolactin and octreotide, a long acting analog of somatostatin. In the absence of growth hormone, octreotide did not affect either neutrophil locomotion or respiratory burst. Octreotide, however, significantly antagonized growth hormone-induced activation of neutrophils for enhanced respiratory burst as well as growth hormone-induced inhibition of stimulated migration. As the effect of growth hormone on neutrophils is mediated by the prolactin receptor, its inhibition by octreotide was also tested using prolactin as priming agent. Data indicate comparable effects of octreotide on priming of neutrophils by prolactin. The effect of octreotide was dose-dependent and appeared to be selective, as activation of neutrophil respiration burst by gamma-interferon, and inhibition of stimulated migration by tumor necrosis factor-alpha were unaffected by octreotide. The present study suggests that octreotide may act on neutrophils directly by antagonizing growth hormone or prolactin at the cellular level.