Permeability of the sheep placenta to unmetabolized polar non‐electrolytes.

Development of Accessory Cells in B‐Cell Compartments Is Retarted in B‐Cell‐Depleted Fetal Sheep

“…Although the final differentiation to a mature phenotype occurred in early postnatal life, the closer study of patterns of enzyme reactivity and the morphometric analysis of the size of lymph node primary follicles showed that FDCs underwent modification during the last third of gestation and it was concluded that stromal cells in primary follicles of fetal lymph nodes were continuously developing structures (Halleraker et al, 1994). As sheep are only exposed to exogenous nonself antigens after birth because of the protection provided by a syndesmochorial placenta (Brambell, 1970;Boyd et al, 1976), it follows that factors other than exogenous nonself antigens are responsible for this modification.…”

“…As sheep are only exposed to exogenous nonself antigens after birth because of the protection provided by a syndesmochorial placenta (Brambell, 1970;Boyd et al, 1976), it follows that factors other than exogenous nonself antigens are responsible for this modification.The interdependence of lymphoid-cell differentiation and stromal-cell development has been the subject of a number of studies. In man, rat and sheep, the early occurrence of FDCs was concomitant with B-cell aggregation and the appearance of primary follicles (Markgraf et al, 1982;Kroese et al, 1987;Halleraker et al, 1994 (Press et al, 1996) has allowed the investigation of the development of lymphoid and accessory-cell populations in a species shielded from exogenous antigen during gestation.…”

“…As sheep are only exposed to exogenous nonself antigens after birth because of the protection provided by a syndesmochorial placenta (Brambell, 1970;Boyd et al, 1976), it follows that factors other than exogenous nonself antigens are responsible for this modification.…”

Placental diffusing capacities at varied carbon monoxide tensions.

“…However, our measurements of urea transfer were not affected by increasing [HbCO] on the fetal side of the placenta (Table III). Urea permeability in the sheep placenta is membrane limited (26). While the pathways of transfer for urea may not be the same as those for CO (hydrophilic vs. lipid routes), these measurements argue against a severe disruption of placental membrane transport.…”

Extracellular volume and blood volume in chronically catheterized fetal sheep.

“…The remaining 75 % is probably accounted for by the smaller size of mannitol, allowing greater penetration of tissues (Law, 1982). As well, mannitol is small enough to cross the sheep placenta (Boyd, Haworth, Stacey & Ward, 1976;Basso, Fernandez, Althabe, Sabini, Piriz & Belitzky, 1977). However, since only small amounts of both inulin and mannitol were recovered in maternal urine in the 48 h after the experiment began, it is unlikely that placental transfer of mannitol contributed significantly to the higher mannitol volume of distribution during the experiment.…”