Fasting Levels of Growth Hormone in Men and Women

Abstract

THE finding of a twenty-fold difference in fasting sera between adult females and males, as reported by Unger et al.¹, is intriguing. It may serve to explain the higher free fatty acid levels observed in both healthy and diabetic female subjects compared with males², for the effect of growth hormone both in vitro and in vivo on enhancing the lipolytic activity of adipose tissue is well known³. On the other hand, the possibility that at least part of this sex-difference may be attributed to the presence of prolactin must be considered. This might occur in either or both of the following ways : (1) the growth hormone antigen used contained some contaminating prolactin; (2) human, prolactin cross-reacts with anti-human growth hormone antisera. The biochemical similarity between these two polypeptides is well known⁴ and the in vivo similarity between them has also been noted⁵. The problem of immunological specificity is also open to some question, as recently discussed by Berson et al.⁶. Indeed, Hayashida⁷ has considered the evidence that human prolactin and growth hormone represent different activities of the same molecule. Greenwood⁸ has also reported that he has noted a cross-reacting substance in plasma throughout pregnancy, and also in placental extracts. This presumably is related to the placental lactogen of Josimovich, which has been shown to be immunologically similar to growth hormone⁹.