Plasma estradiol and progesterone after hypophysectomy and substitution with pituitary in female sea lampreys (Petromyzon marinus).

This study investigated plasma steroid concentrations 1 week after total hypophysectomy in adult female sea lampreys. Plasma estradiol significantly decreased (to 1.19 +/- 0.17 SE ng/ml) following hypophysectomy and was elevated (to 1.91 +/- 0.11 ng/ml) to a value similar to controls by a single injection of two pituitary equivalents in adult female sea lampreys in the stage of final maturation. Plasma progesterone also significantly decreased (to 69 +/- 10 pg/ml) following hypophysectomy and was elevated (to 183 +/- 71 pg/ml) to a value not different from uninjected controls by a single injection of two pituitary equivalents in females. Injection of two pituitary equivalents did not affect plasma estradiol in intact lampreys but surprisingly decreased plasma progesterone (to 67 +/- 14 pg/ml) compared to saline-injected intact lampreys (318 +/- 142 pg/ml). The decrease in estradiol and progesterone after hypophysectomy and their normalization after injection of pituitaries support the concept that the secretion of estradiol and progesterone is stimulated by gonadotropin or other pituitary hormones.