The development and characterization of a homologous radioimmunoassay for mouse placental lactogen.

A highly specific and sensitive homologous radioimmunoassay (RIA) has been developed for mouse placental lactogen(mPL). Mouse pregnancy serum and placental extracts showed parallel dilution-response curves, and no significant cross-reaction was seen with either mouse growth hormone or mouse prolactin. The sensitivity of the assay ranged from 0.5 to 1.0 ng/ml, and the intra- and inter-assay coefficients of variation were 5 and 11%, respectively. By RIA, mPL levels were detectable on day 9 of pregnancy (1 ng/ml) and increased until day 14 (100-150 ng/ml) in both C3H and BALB/c strains. On days 14-18 of pregnancy, mPL levels were maintained (95-125 ng/ml) in C3H mice, while they continued to increase (greater than 250 ng/ml) in BALB/c mice. In both strains, a midpregnancy peak in prolactin-like activity was detected by a radioreceptor assay but not by the mPL RIA.