IN-VITRO AND IN-VIVO EVIDENCE ON THE SITE OF NEUTRALIZATION OF EQUINECHORIONIC-GONADOTROPIN (ECG) BY AN ECG ANTISERUM

This study was designed to determine whether the major site of eCG neu tralization by an antiserum to the hormone is at the peripheral or ova rian level. Hamsters hypophysectomized at oestrus were injected s.c. w ith 25 iu eCG. Three days later, preovulatory follicles were dissected and cultured for 5 h and the medium was changed every hour. At the en d of the first hour of incubation, oestradiol and androstenedione accu mulation was high, with a sharp drop over the next 4 h, whereas proges terone concentrations did not change over the entire period. Addition of eCG antiserum to the incubated follicles did not affect steroidogen esis. Addition of 1.0 iu eCG in the second hour or every hour sustaine d oestradiol production at supraphysiological amounts. However, additi on of eCG plus eCG antiserum every hour eliminated the stimulatory eff ects of eCG on oestradiol production. In another experiment, hamsters injected with eCG were treated 3 days later by i.p. injection of eCG a ntiserum and groups of animals were killed over the next 8 h. Serum sa mples before and after injecting eCG antiserum were incubated overnigh t with a goat anti-rabbit immunoglobulin to separate free, unbound eCG from bound eCG. At time zero (before injecting the antiserum) free eC G was increased, but within I h after eCG antiserum there was an eight fold decrease of the hormone, and these concentrations were maintained over the next 7 h. The fall in unbound eCG in vivo coincided with the decay in serum oestradiol and androstenedione. These results obtained in vitro and in vivo demonstrate that the long biological half-life o f eCG is essential to replenish the supply provided to the ovary const antly to maintain steroidogenesis; eCG antiserum inactivates eCG in se rum but not by complexing with eCG at the receptor of the follicular c ell surface.