Plasma estrogen levels during pregnancy in the western spotted skunk

The present study was undertaken to obtain an estrogen profile throughout gestation in the western spotted skunk with special emphasis on relating changes in estrogen levels to blastocyst development. Blood samples were collected from 130 pregnant animals by cardiac puncture and plasma estrogen levels were determined by radioimmunoassay (RIA). Estrogen levels varied throughout the period of embryonic diapause, with mean levels ranging between 3 to 18 pg/ml. There was a tendency for estrogen levels to be less variable and somewhat lower during the 15 days immediately prior to blastocyst implantation than during the preceding period. Plasma estrogen levels in skunks with delayed implanting blastocysts (diameters of 1.1 mm or less) were significantly higher (P less than 0.05) than those in females with activating blastocysts (i.e., diameters of 1.2 mm or greater), again suggesting that estrogen levels were reduced during the period immediately preceding implantation. However, the exact physiological significance, if any, of this modest reduction in estrogen levels remains to be determined.