The kinetics of disappearance of endogenous mouse placental lactogen-II in intact and hypophysectomized pregnant mice.

The kinetics of disappearance of endogenous mouse placental lactogen-II (mPL-II) were determined in day 12 and day 16 pregnant Swiss Webster mice and in day 16 pregnant mice that had been hypophysectomized (hypox) on day 12. Blood samples from anesthetized animals were taken at different time intervals after bilateral hysterectomy and the maternal serum mPL-II concentration was measured by homologous radioimmunoassay (RIA). Disappearance curves of mPL-II for day 12 and day 16 pregnant mice were resolved into two exponential components: a rapid phase of disappearance, followed by a slow phase. Although the serum mPL-II concentration was higher on day 16 of pregnancy than on day 12, the alpha rate constant for the fast component of the disappearance curve for day 12 pregnant mice (0.054 +/- 0.005 ml/s) was similar to the value observed for day 16 animals (0.052 +/- 0.005 ml/s). The half-life of the fast component of the disappearance curve for day 12 and day 16 pregnant mice was 13.3 +/- 0.9 s and 14.8 +/- 1.5 s, respectively. The slow component of the disappearance curves for day 12 and day 16 pregnant mice had a beta rate constant of 0.00088 +/- 0.00017 ml/s and 0.00083 +/- 0.00009 ml/s, respectively. The half-life of the slow phase of the disappearance curves for day 12 pregnant mice was 1216.4 +/- 376.0 s, while the slow phase of day 16 disappearance curves displayed a half-life of 954.4 +/- 102.7 s.(ABSTRACT TRUNCATED AT 250 WORDS)