HETEROGENEITY OF CIRCULATING GROWTH-HORMONE

Human growth hormone (GH) represents a family of related proteins aris ing from two genes, alternative mRNA splicing, and several post-transl ational modifications. In addition, post-secretory events occur when G H enters the circulation. The full scale of GH heterogeneity is only b eginning to be appreciated, and new GH forms or related proteins may b e discovered in the future. GH measurements are affected by GH heterog eneity. Immunoassays are influenced by the mixture of GH variants, but are not sensitive to GH binding proteins (GHBPs). In contrast, radior eceptor assays are sensitive to both GH variant mixtures and to the hi gh affinity GHBP. It is hoped that in the future, these problems can b e minimized by rigorous characterization of existing antibodies with r espect to epitope recognition on various GH forms, and ultimately, by production of GH variant-specific antibodies that permit direct and in dividual assessment of the circulating members of the GH family.