Multiple Forms of Growth Hormone

Abstract

Increasingly, variant forms of growth hormone are being found, but an understanding of their significance has not kept pace with the ability to detect them. One of the problems is that the variants occur in much lower concentrations than the major form, thus making preparation of quantities for biologic testing a difficult task. In addition, availability of human pituitary glands for such studies was limited until recently, when clinical treatment with pituitary-derived growth hormone was discontinued and the glands became available for research projects concerned with identification of new substances. The low concentration of many of the forms raises a frequently asked question: can these forms have physiologic relevance when they occur in such small amounts compared to the major form? What is usually overlooked here is the fact that the major form occurs in an enormous quantity compared to the other pituitary hormones. A comparison of human pituitary hormones will illustrate this point. There are between 5000 and 7000 yg of the major form of human growth hormone (hGH) in a pituitary gland. If the concentration of a variant of hGH is 1% or this (50 to 70 yg), its concentration would be similar to that of FSH; a 3% concentration would equal the amount of prolactin in a gland.