| 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. |
