Distribution, Metabolism, and Excretion of Human Chorionic Gonadotropin and Its Subunits in Man

Abstract

It has been well established that the serum and urine of pregnant women contain several molecules immunologically related to, but smaller than the human chorionic gonadotropin (hCG) molecule. A number of laboratories have reported that the most abundant of these hCG-related molecules is one which behaves on gel chromatography and in radioimmunoassays for the hCG alpha-subunit (hCGα) very much like the authentic hCGα subunit (Franchimont and Reuter, 1972; Hagen and McNeilly, 1975; Vaitukaitis et al., 1976; Good et al., 1977). Also, some workers have produced evidence to suggest that a moiety with properties like those of the hCG betasubunit (hCGß) can be found in the serum and urine of pregnancy (Franchimont and Reuter, 1972; Good et al., 1977). The presence of free hCG subunits, or molecules with similar immunological and physicochemical characteristics, in normal pregnancy raises questions concerning the origin of these hCG-related peptides. It is not known whether they are degradation products of secreted hCH, or whether they are secreted themselves, or whether they are degradation products of other hCG-related peptides. We have been exploring the distribution, metabolism, and excretion of hCG and its subunits in normal human subjects with the aim of establishing the fundamental kinetic characteristics of these molecules, and with the aim of assessing the extent to which the degradation of secreted hCG accounts for the presence of hCG-related peptides in the biological fluids of pregnancy. In this chapter, we will attempt to summarize recent findings on the kinetics of metabolism of hCG and its subunits and to present some information concerning their disposal and degradation pathways.