The accumulated evidence in the literature since 1930 reveals that pituitary extracts rich in “growth hormone” exert powerful diabetogenic effects. It has not been possible thus far to separate these two activities as belonging to two distinct molecular species. However, an analysis on broad biological principles makes it most probable that two hormonal entities compose the so-called growth hormone fraction. The somatotrophic component (STH) would be expected to exert the following actions: (1) promote protein synthesis (together with insulin); (2) cause orderly proliferation of epiphyseal cartilage; (3) lead to increased insulin liberation from B cells. The total effect would consist of growth in bodily length and enhanced protein synthesis. The diabetogenic component (here called adipokinetic .AK) would play its role in: (1) liberating fatty acids from adipose tissue, thus shifting cellular metabolism to the utilization of fat, whenever there develops a relative scarcity of carbohydrate. This shift would inhibit glucose use and lead to insulin resistance, ketone production, etc.
This analysis is presented in order to stimulate experimental approaches for testing the validity of either the “one” or “two” factor hypothesis of the pituitary growth hormone fraction. Available experimental evidence is not adequate nor sufficiently convincing for unequivocal decision.