Immunoreactive human chorionic gonadotropin β core fragment in human pituitary

Summary

The human pituitary has been shown to produce small amounts of immunoreactive human chorionic gonadotropin (hCG) and its α- and ß- subunit (hCGα, hCGß). The aim of the present studies was to further examine the various hCG-related materials in the human pituitary, particularly to search for the existence of pituitary hCGß core fragment (hCGßcf) — like material. HCGßcf has been found in the urine of pregnant women, patients with trophoblastic tumors and also in postmenopausal women. Gel chromatography of pituitary extract on Superdex 200 showed three distinct peaks of hCG-related immunoreactivities, i.e. hCG, hCGß and hCGßcf, which were distinguishable from hLH and hLHß peaks. HCGßcf was recognized by a specific immunometric assay (crossreactivities with hCGß 0.016 %, hLHß 0.04 %), but unreactive in an hLH + hLHß assay. It was purified and displayed physical properties similar to those of hCGßcf derived from pregnancy urine. Apart from immunological differences between the small molecular weight forms or fragments of hCG and LH origin, reversed phase HPLC was able to physically discriminate between hCGßcf and hLHß fragment. The latter was much more abundant than the former in the pituitary extract. HCGßcf showed microhet-erogeneity related to its sialic acid content.

In conclusion, the present data indicate that immunoreactive hCGßcf is present in human pituitary extracts. The physical and immunological properties of pituitary hCGßcf are distinguishable from those of the more abundant hLHß and its fragment, and compare favorably with those of urinary hCGßcf of trophoblastic origin.

Key words

hCG - hCGß core fragment - hLHß core fragment - pituitary gland