The Gestational Pattern of Estradiol, Testosterone and Progesterone Secretion in Selected Strains of Mice

Peripheral levels of estradiol, testosterone and progesterone were characterized during pregnancy in strains of mice which differ in prenatal survival following genetic selection. Strain variation in the secretory pattern of these hormones was minimal during the period that requires pituitary support of luteal function. In every line examined, a midpregnancy increase in circulating testosterone occurred, followed by a second increase in testosterone late in gestation. Estradiol levels also increased during the latter half of pregnancy, except in a line selected for rapid growth. In general, progesterone levels increased from midpregnancy until shortly before parturition. Dramatic strain differences in hormone levels and their secretory pattern during the second half of pregnancy suggest that placental-ovarian function has changed in response to selection more than has pituitary control over ovarian steroidogenesis.