Growth Hormone Pulsatility and its Impact on Growth and Metabolism in Humans

Abstract

Classical endocrinology was based on the quantitative features of hor-mone secretion, i.e., its deficiency or excess. Recent studies have shown that qualita-tive features of hormone delivery to the target cells may have an independent effect on tissue responses. Whether growth hormone (GH) may share a similar mecha-nism, through its continuous or pulsatile release, is a burgeoning field of recent endocrine research. This chapter provides an overview of the different regulators of GH signaling and the impact of these signals upon GH pulsatility, concentrating primarily on human studies, outlining the roles of total GH output, GH pulses, and interpulse levels in determining generation of IGF-1 (i.e., growth) and metabolic effects (primarily, lipolysis) in health and disease. These data suggest that it is not only the gross quantity of GH output, but also the pattern of presentation of GH to the peripheral tissues that plays an important role in determining its biological prop-erties. The understanding of the kinetic properties of GH secretion and their poten-tial impact on growth and metabolism may alter our understanding of GH physiology and action, and potentially devise novel and superior strategies to optimize the effects of exogenously administered GH tailored to a specific therapeutic goal.