Quantitation of human chorionic gonadotrophin (hCG) by radioreceptor assay.

A sensitive radioreceptor assay was developed for pharmaceutical preparations of human chorionic gonadotrophin with the use of rat testicular membranes as receptor preparation and human 125I-chorionic gonadotrophin as tracer. The addition of unlabelled human chorionic gonadotrophin or luteinizing hormone inhibited the binding of 125I-chorionic gonadotrophin to the receptors in a concentration dependent way. Concentrations of human chorionic gonadotrophin between 30-300 mIU ml(-1) were normally used for a three-dose assay fulfilling pharmacopoeial statistical requirements for assay validity. The relative standard deviation for five assays was 7%. Estimates of potency of commercial preparations of human chorionic gonadotrophin obtained with the radioreceptor assay correlated well with corresponding estimates from in vivo assays. The proposed radioreceptor assay, however, provides a considerable saving in the number of animals required, requires less technical support, and is more precise than the in vivo method.