Gonadotrophin and progesterone concentrations in placentae of grey seals (Halichoerus grypus)

Abstract

Chorionic gonadotrophin (CG) measured by bioassay and progesterone by immunoassay were present in the placentae of grey seals (Halichoerus grypus) from about 20 days after implantation until parturition. During this period a small and significant decrease in the concentration and a large increase in the total amount of placental CG occurred. The biological activity of seal placental CG was neutralized with an anti-hCG serum. There was a correlation between fetal length and the total amount of progesterone in the placenta. The corpus luteum persisted throughout pregnancy and there was a significant correlation (P less than 0.001) between CL diameter and the weight of the ipsilateral ovary. Hypertrophy of fetal testes and ovaries was observed and adult gonad size was reached at about the time of parturition. We suggest that placental CG is the hormone responsible for the precocious enlargement of fetal gonads in grey seals.

Immunohistochemical Localization of Steroidogenic Enzymes and Prolactin Receptors in the Corpus Luteum and Placenta of Spotted Seals (<i>Phoca largha</i>) during Late Pregnancy

“…Earlier researchers reported secretory activities in the placentae of several seal species [10][11][12] and presumed placental production of progesterone [3]. However, our previous [13] and present studies support placental production of estrogen rather than progesterone.…”

“…However, our previous [13] and present studies support placental production of estrogen rather than progesterone. On the other hand, placental production of chorionic gonadotropin has been reported [11,12]. The secretory activities in syncytiotrophoblasts of placentae in the seal species described by Harrison and Young [10] are therefore presumably derived from the secretion of estrogen and/or chorionic gonadotropin.…”

“…The presence of estrogen synthesized in luteal cells and the placenta during pregnancy may contribute to the synthesis or availability of intracellular progesterone receptors [5], whereas placental chorionic gonadotropin is believed to be essential for the maintenance of pregnant corpus luteum [25]. The placental chorionic gonadotropin of the grey seal (Halichoerus grypus) possesses biological activity similar to that of human chorionic gonadotropin (hCG), which has LH-like activity [11,12]. In the dog and mink, luteinizing hormone (LH) and prolactin are necessary for maintenance of the corpus luteum during post-implantation gestation.…”

Immunohistochemical Localization of Steroidogenic Enzymes in the Corpus Luteum and the Placenta of the Ribbon Seal(Phoca fasciata) and Steller Sea Lion.

“…Boyd [2] assumed that the placentae of grey seals (Halichoerus grypus) are capable of synthesizing progesterone in late pregnancy, based on the data of Hobson and Boyd [11]. However, they assayed concentrations of progesterone con- tained in the homogenized placentae, thus they were unable to detect the source of the progesterone with their methods.…”

Postpartum Dynamics of Reproductive Hormones in Gray and Hooded Seals

“…These results are consistent with those measured in most other mammals, where levels of estradiol 178 and progesterone are high during gestation to support fetal growth and preparation of the mammary gland (Forsyth and Hayden 1977). Both hormones then fall immediately following parturition (Challis et al 1971), as the expelled fetal-placental unit is a primary source (Hobson and Boyd 1984). This was most clearly demonstrated in the one female sampled nearest to parturition on 0 dpp.…”