Variation in the thyrotropic activity of human chorionic gonadotropin in Chinese hamster ovary cells arises from differential expression of the human thyrotropin receptor and microheterogeneity of the hormone.

The nature of human chorionic gonadotrophin glycoforms in gestational thyrotoxicosis

“…There is no doubt that hCG has intrinsic thyroid stimulating activity in vitro (Tomer et al ., 1992; Yoshimura et al ., 1993; Kraiem et al ., 1994; Yoshimura et al ., 1994; Sakaguchi et al ., 1997). Thus, studies using FRTL‐5 rat thyroid cells (Hoermann et al ., 1991; Ballabio et al ., 1991; Pekary et al ., 1993), Chinese hamster ovarian cells (Hoermann et al ., 1995) and human thyroid follicles (Kraiem et al ., 1997) suggest that desialylation enhances the thyrotrophic activity of hCG, with the less acidic forms being more active than those of a more acidic pI. Moreover, there is evidence from studies performed in vitro that the more basic forms of hCG obtained from hydatiform moles (Yoshimura et al ., 1994) are more bioactive and that hCG glycoforms > pI 4·6 in serum from pregnant patients are associated with thyroid stimulating activity in vitro (Ballabio et al ., 1991).…”

Stimulation of thyroidal and extrathyroidal thyrotropin receptors

“…Does some regulation reside within the stimulator or is it the potency of the stimulator or is it the binding to distinct regions of the receptor? Our own data on stimulation of human TSH receptor by hCG show that variation in the cAMP response arises from the microheterogeneity of the hormone, and suggest a role of the microheterogeneity in fine tuning of the thyroid response (Hoermann et al, 1995).…”

“…Endocrinology &Diabetes tor with human chorionic gonadotropin (hCG). The direct proof of this hypothesis, however, could only be obtained after the successful cloning of human TSH receptor and expression of its encoding cDNA in cell lines lacking endogenous TSH receptor when hCG and its variant form asialo-hCG were shown to directly bind to the recombinant human TSH receptor (Hoermann et al, 1994(Hoermann et al, , 1995. These findings may explain the clinical observation of gestational hyperthyroidism, which has been reported to occur in a subclinical or overt form in up to 18% and 1-2%, respectively, of pregnant women.…”

Immunological and Biological Activity of Different Commercial Preparations of Human Chorionic Gonadotropin

“…In this study, CHO cells transfected with human TSH receptor were used. This method has been established since several years and proven to have high sensitivity for biological activity in various hCG molecules [6,7]. This cell system with hCG receptor has not been reported yet.…”