A Growth Hormone Binding Factor in the Serum of Pregnant Mice

Abstract

Using a radioreceptor assay (RRA) an apparent growth hormone-like activity (GH-LA) was first detected in the serum of Swiss Webster mice at mid-pregnancy with peak concentrations appearing one to two days before parturition. Hysterectomy at day 17 of pregnancy was followed by a transient increase in apparent GH-LA. In the RRA, displacement of human [125I]iodoGH from the receptor by serial dilutions of serum from pregnant mice paralleled that of purified human GH standards. After gel filtration of a sample of pregnant serum on a Sephadex G-100 column the apparent GHLA determined by RRA was found in fractions with a relative elution volume (Ve/Vo) of 1.2. Moreover, when a sample of serum from pregnant mice and human [125I]iodoGH were separated on a similar column, more than 75% of the labeled hormone also eluted with a relative elution volume (Ve/Vo) of 1.2 rather than 2.0 which was found when human [l25I]iodoGH alone or with serum from nonpregnant mice was fractionated on the same column. In these fraction...