Corticosterone levels during midgestation in the maternal plasma and fetus of cleft palate-sensitive and -resistant mice.

Corticosterone levels in the maternal plasma and fetal extracts during days 11--15 of gestation were measured by RIA in cleft palate-sensitive A/J and -resistant C57BL/6J mice. In both strains, the maternal plasma corticosterone increased from 10 micrograms/100 ml in nonpregnant animals to 100 microgram/100 ml between days 12--13. In A/J mice, the corticosterone level declined to 60 micrograms/100 ml by day 15, whereas in C57BL/6J mice, the corticosterone concentration remained elevated during this period. In contrast, fetal corticosterone levels in both strains remained unchanged between days 11-13 (0.5--1.0 ng/embryo) and increased on days 14 and 15 to 4--7 ng/embryo. The absence of significant differences in the concentration of maternal or fetal corticosterone between A/J and C57BL/6J mice suggests that the in vivo strain differences in the glucocorticoid susceptibility to cleft palate production are not related to any intrinsic differences in the endogenous levels of corticosterone between these two strains during midgestation.