Effect of o,p'-DDD and Similar Compounds on Thyroxine Binding Globulin

Abstract
O,p'-DDD has been observed to lower the serum protein bound iodine (PBI). Measurement of the binding capacity of thyroid binding globulin (TBG) by cellulose acetate electrophoresis demonstrated that the PBI lowering effect is probably due to competitive binding to this protein by o,p'-DDD, a diphenyl compound. Chemical similarities between o,p'-DDD and diphenylhydantoin, which also competes with thyroxine (T4) for TBG binding sites, are discussed. The effect of other compounds structurally similar to o,p'-DDD on T4 binding by TBG is noted.