Abstract

In 1941, Gellhorn and colleagues reported experiments in which modest reductions of blood sugar were induced in hypophysectomized/adrenodemedullated (HA) rats by intraperitoneal injection of human blood. Based on the effects of intraperitoneal injections of known amounts of Lilly insulin on blood sugar in HA rats, Gellhorn estimated that the "insulin" content of normal human blood (collected two and a half hours "after luncheon") was 200uU/ml (Gellhorn, Feldman, and Allen 1941). However, discrepancies between measurements of plasma insulin concentration by in vitro bioassays, which began in earnest in the late 1940s and early 1950s, and, beginning in 1960, by radioimmunoassay (RIA), intimated that insulin was not ..