Radioimmunoassay of Human Plasma Thyrotropin*

Abstract

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 neu-tralized 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 prepa-rations 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 cross-reactivity in vitro using hemagglutination and he-magglutination-inhibition techniques. More re-cently 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 speci-ficity of TSH now seems well established. Previous attempts to measure endogenous plasma TSH in man by immunoassay utilizing the hemagglutination-inhibition technique were un-successful due to the presence of nonspecific in-hibitory substances in plasma and to the use of anti-bovine TSH sera (8, 9). A radioimmuno-* Submitted for publication February 5, 1965; accepted