Abstract
Changes in relaxin concentrations in plasma throughout pregnancy and early lactation up to one month after parturition were characterized in 10 Japanese monkeys by a heterologous radioimmunoassay (RIA) based on the porcine RIA. Plasma levels of LH/monkey chorionic gonadotropin (mCG), estradiol-17β, progesterone and immunoreactive (ir-) inhibin were also monitored for the entire period. Relaxin levels in the plasma were low before conception. An accelerated rise in plasma relaxin levels was found during pregnancy. The first increase was noted during early pregnancy, with a peak (267.5 ± 50.5 pg/ml) at Day 31 ± 2.4 of pregnancy (Day 0= day of LH surge). The second increase was noted just before term with a peak (235.6 ± 37.5 pg/ml). After parturition, relaxin levels in the plasma abruptly declined but were maintained at approximately 100 ng/ml during early lactation. The first rise in plasma relaxin during pregnancy was in parallel with rises of mCG and progesterone, and the second rises was well correlated with those of plasma estradiol-17β ,progesterone and ir-inhibin. These results suggest that the major source of relaxin is corpus luteum and placenta during pregnancy in Japanese monkeys.
