Defective hormone secretion of CYP11A1 null embryos. A, Diagrams of the Cyp11a1 alleles showing the insertion of the neo gene or of the loxP site in the first exon in E1-Neo and E1-loxP, respectively. B, Western blot analysis of E18.5 adrenal CYP11A1 from the wild-type (WT) (+/+), heterozygous (+/−), or homozygous (−/−) Cyp11a1 mutant mice. C, Plasma levels of pregnenolone (P5) at E18.5 measured by RIA are shown as mean ± sem [*, P = 0.002 vs. control littermates; WT, n = 5; knockout (KO), n = 4]. D, Tissue levels of corticosterone (CORT.) in E18.5 adrenal measure by RIA are shown as mean ± sem (*, P = 0.03 vs. control littermates; WT, n = 4; KO, n = 5). E, Plasma levels of corticosterone at E18.5 (WT, n = 15; KO, n = 10) and E19 (WT, n = 11; KO, n = 10) measured by RIA are shown as mean ± sem (*, P = 0.001; #, P = 0.02). F, Transmission electron micrographs of mitochondria in adrenocortical cells at E17.5.