Steroidogenic enzyme expression in porcine conceptuses during and after elongation.

The following studies were performed to investigate levels of expression of steroidogenic enzymes in porcine conceptuses between days 12 and 21 postmating and to correlate these findings with estrogen levels in conceptus tissues. In the first experiment, levels of steroidogenic enzymes in individual day 12 blastocysts were examined by Western immunoblot analyses. In a second experiment, Northern blot, slot blot, and Western immunoblot analyses for 17 alpha-hydroxylase cytochrome P450 (P450(17) alpha) were performed on conceptus tissue pooled for each uterine horn of sows on days 12, 14, 16, and 21 postmating. On day 12, P450(17) alpha) protein was detectable in 6-mm blastocysts, with highest levels apparent in 10- to 15-mm (tubular) blastocysts. Filamentous blastocysts appeared to have less P450(17) alpha) protein than did littermate tubular blastocysts. Side-chain cleavage cytochrome P450 (P450scc) and aromatase cytochrome P450 (P450arom) followed a pattern similar to that of P450(17) alpha. 3 beta-Hydroxysteroid dehydrogenase was undetectable by Western analysis in blastocysts at the stages examined, but was detectable in placenta from fetuses at later stages of gestation. In pooled tissue, P450(17) alpha) protein and mRNA were greater in day 12 conceptuses than in conceptuses from all other days. However, transition from the tubular to the filamentous form on day 12 postmating was associated with a dramatic decline in the level of P450(17) alpha) mRNA. The conceptus 17 beta-estradiol concentration was highly correlated with immunoreactive P450(17) alpha) protein and hybridizable P450(17) alpha) mRNA over days 12, 14, 16, and 21 postmating. These data suggest that the decrease in blastocyst estrogen secretion occurring after the time of elongation in porcine conceptuses may be due to a decrease in P450(17) alpha expression.