Structure and Steroidogenesis of the Placenta in the Antarctic Minke Whale (<i>Balaenoptera bonaerensis</i>)

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  • SASAKI Motoki
    Laboratory of Veterinary Anatomy, Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan United Graduate School of Veterinary Medicine, Gifu University, Gifu 501-1193, Japan
  • AMANO Yoko
    Laboratory of Veterinary Anatomy, Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan
  • HAYAKAWA Daisuke
    Laboratory of Veterinary Anatomy, Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan United Graduate School of Veterinary Medicine, Gifu University, Gifu 501-1193, Japan
  • TSUBOTA Toshio
    Laboratory of Wildlife Biology and Medicine, Department of Environmental Veterinary Science, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido 060-0818, Japan
  • ISHIKAWA Hajime
    Institute of Cetacean Research, Tokyo 104-0055, Japan
  • MOGOE Toshihiro
    Institute of Cetacean Research, Tokyo 104-0055, Japan
  • OHSUMI Seiji
    Institute of Cetacean Research, Tokyo 104-0055, Japan
  • TETSUKA Masafumi
    Department of Life Science and Agriculture, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan
  • MIYAMOTO Akio
    Department of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan
  • FUKUI Yutaka
    Department of Life Science and Agriculture, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan
  • BUDIPITOJO Teguh
    Faculty of Veterinary Medicine, Gadjah Mada University, Yogyakarta 55281, Indonesia
  • KITAMURA Nobuo
    Laboratory of Veterinary Anatomy, Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan United Graduate School of Veterinary Medicine, Gifu University, Gifu 501-1193, Japan

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  • Structure and Steroidogenesis of the Placenta in the Antarctic Minke Whale (Balaenoptera bonaerensis)

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Abstract

There are few reports describing the structure and function of the whale placenta with the advance of pregnancy. In this study, therefore, the placenta and nonpregnant uterus of the Antarctic minke whale were observed morphologically and immunohistochemically. Placentas and nonpregnant uteri were collected from the 15th, 16th and 18th Japanese Whale Research Programme with Special Permit in the Antarctic (JARPA) and 1st JARPA II organized by the Institute of Cetacean Research in Tokyo, Japan. In the macro- and microscopic observations, the placenta of the Antarctic minke whale was a diffuse and epitheliochorial placenta. The chorion was interdigitated to the endometrium by primary, secondary and tertiary villi, which contained no specialized trophoblast cells such as binucleate cells, and the interdigitation became complicated with the progress of gestation. Furthermore, fetal and maternal blood vessels indented deeply into the trophoblast cells and endometrial epithelium respectively with fetal growth. The minke whale placenta showed a fold-like shape as opposed to a finger-like shape. In both nonpregnant and pregnant uteri, many uterine glands were distributed. The uterine glands in the superficial layer of the pregnant endometrium had a wide lumen and large epithelial cells as compared with those in the deep layer. On the other hand, in the nonpregnant endometrium, the uterine glands had a narrower lumen and smaller epithelial cells than in the pregnant endometrium. In immunohistochemical detection, immunoreactivity for P450scc was detected in most trophoblast cells, but not in nonpregnant uteri, suggesting that trophoblast epithelial cells synthesized and secreted the sex steroid hormones and/or their precursors to maintain the pregnancy in the Antarctic minke whale.

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