New insights into growth hormone�s actions on the macrophage: Implications for non-growth related actions of growth hormone

Introduction Growth hormone, besides being essential for post-natal growth in mammals, affects the metabolism of fat, protein and carbohydrates. At cellular level, the pleiotropic actions of growth hormone are due to its interaction with growth hormone receptor, followed by activation of the janus kinase 2–signal transducers and activators of transcription signalling cascade. The effects of growth hormone have been most intensely investigated in tissues such as liver, bone, muscle and adipocytes, in which growth hormone receptor expression is abundant, and are thus considered canonical targets of growth hormone action. However, recent studies on biological effects and physiological relevance of growth hormone action in non-canonical targets such as blastocysts, cardiomyocytes, colonic epithelium, glomerular podocytes and macrophages argue the importance of non-growth-related functions of growth hormone. In this review, we discuss immunomodulatory and metabolic effects of growth hormone on the macrophages. This review also highlights the role of growth hormone on macrophage migration, alternative activation and paracrine effect on adipocyte differentiation. Conclusion As we expand our knowledge about the role of growth hormone on regulating the components of immune system and metabolism, it may be possible to exploit the new information to enhance host resistance to infection, improve sensitivity to insulin and prevent atherosclerosis in conditions such as acquired immunodeficiency syndrome, short bowel syndrome, Prader-Willi and lipodystrophy syndromes.