Radioimmunoassay of Human Plasma Thyrotropin.

Many pituitary hormones possess partial or complete immunological species specificity. Earlier reports suggested that thyrotropin (TSH) did not have such specificity since the biological activity of human pituitary or plasma TSH could be neutralized by antisera to bovine TSH in doses similar to that which blocked the biological activity of bovine TSH (2, 3). However, recent studies have shown that much smaller doses of antisera to bovine or human TSH were able to neutralize the biological activity of homologous TSH preparations than the activity of the other hormone (4, 5). Furthermore, in studies using both human and bovine TSH and antisera to each, Arquilla, Catz, and Finn (6) found no immunological crossreactivity in vitro using hemagglutination and hemagglutination-inhibition techniques. More recently data were presented that antisera to highly purified human and bovine TSH reacted in vitro and, in separate experiments, blocked the biological effect in vivo only of the homologous antigen (7). Thus, considerable immunological species specificity of TSH now seems well established. Previous attempts to measure endogenous plasma TSH in man by immunoassay utilizing the hemagglutination-inhibition technique were unsuccessful due to the presence of nonspecific inhibitory substances in plasma and to the use of anti-bovine TSH sera (8, 9). A radioimmuno-