CARBONIC-ANHYDRASE ACTIVITY IN DIFFERENT PLACENTA TYPES - A COMPARATIVE-STUDY OF PIG, HORSE, COW, MINK, RAT, AND HUMAN

The placenta has multiple functions, being the organ which provides ox ygen and nutrients to the developing conceptus. In the placenta, the e nzyme carbonic anhydrase (CA) may provide ions for exchange with Na+, K+ and Cl- in transepithelial movement of ions and fluid, as well as f acilitating carbon dioxide diffusion. It can also be active in interme diary metabolism, such as gluconeogenesis, urea, and fatty acid synthe sis. Placental material from pig, horse, cow, mink, rat, and human was therefore investigated, representing placenta types with variations i n shape, internal architecture, and nature of the interhemal barrier. After glutaraldehyde fixation, sections were stained by a histochemica l CA-method demonstrating all active isozymes. The most striking featu re in common was a positive reaction in the maternal capillaries, when present, as in pig, horse, cow, and mink. In the maternal epithelium, the activation of CA was only observed in the pig, which also exhibit ed the strongest activity at the maternal interface, which reacted mod erately in rat, weakly in horse, and was not visible in cow and human. The trophoblast was positive in pig and rat, whereas it was negative in horse, cow, human, and mink placentae except for few scattered trop hoblast cells in pig, horse, and cow, which showed very intense activi ty. In the fetal capillaries, a positive reactivity was only observed in mink and human. The utilization of CA in placental transfer and met abolism is thus highest in the pig, rat, and mink, compared with horse , cow, and human. It can therefore be concluded that the activation an d localization of CA in the placental interhemal barrier varies consid erably among species. (C) 1997 Wiley-Liss, Inc.