Corticosteroids and progesterone in amniotic fluid and maternal plasma of the rat and their relation to parturition.
The concentration of total and free corticosteroids, total progesterone and corticosteroid binding activity were determined in the amniotic fluid of rats on each of the 5 days before birth. The levels of total and free corticosteroids were low 4 days before birth but increased to peak levels (15.8 +/- 2.9 micrograms/100 ml and 6.4 +/- 1.1 micrograms/100 ml, respectively) 1 day prior to birth. These increases in the concentration of corticosteroids in amniotic fluid coincided with changes in the level of free corticosteroids but not total corticosteroids in foetal plasma. The level of corticosteroid binding activity increased from 0.9 +/- 0.15 micrograms corticosterone bound/100 ml 4 days before birth to peak at 13.3 +/- 0.8 micrograms corticosterone bound/100 ml 2 days prior to birth. Preliminary investigations suggest that the binding activity is due to a corticosteroid binding globulin-like protein. The concentration of progesterone in amniotic fluid was low compared to that found in maternal plasma and they were not significantly correlated. The concentration of total and free corticosteroids in maternal plasma did not change significantly (P > 0.05) during the 4 days preceding birth and did not correlate with levels of total and free corticosteroids in amniotic fluid. However, there was a significant negative correlation (P < 0.01) between the declining level of progesterone in maternal plasma and increasing levels of total and free corticosteroids in amniotic fluid.
D000305:Adrenal Cortex Hormones / Q000378:metabolism*; D000653:Amniotic Fluid / Q000378:metabolism*; D000818:Animals; D003345:Corticosterone / Q000378:metabolism; D005260:Female; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism*; D051381:Rats; D011987:Receptors, Steroid / Q000378:metabolism
D000305:Adrenal Cortex Hormones; D011987:Receptors, Steroid; C024357:corticosterone receptor; D011374:Progesterone; D003345:Corticosterone