In vivo activation of circulating monocytes by exogenous growth hormone in man.

Animal studies have shown that administration of growth hormone improves wound healing. Monocyte activation is a prerequisite for optimal repair of damage. In vitro, human recombinant growth hormone was shown to be a potent human monocyte chemoattractant. It induced random migration and chemotaxis at picomolar concentrations of recombinant human growth hormone; combinations of growth hormone with other chemoattractants deactivated the chemotactic response. Other functions of monocytes that are activated by growth hormone include release of superoxide anion and production of cytokines. In order to test activation of human monocytes by growth hormone in vivo, we investigated the effects of recombinant human growth hormone administration on monocyte migration in nine healthy young adults. After a single dose of recombinant human growth hormone (4 IU subcutaneously injected), random migration of circulating monocytes significantly increased, whereas chemotaxis of monocytes that was maximally stimulated with f-Meth-Leu-Phe decreased (p < .05). The alterations paralleled the concomitantly measured plasma levels of growth hormone. After recombinant human growth hormone administration, no changes were seen in plasma levels of proinflammatory cytokines. These in vivo data on monocyte migration are comparable to effects of growth hormone on monocyte migration in vitro and strongly suggest that recombinant human growth hormone can activate circulating monocytes in man.