The effect of fetal movement on the development of the hip joint was examined by restraining the leg movement using exo utero operation in rat fetuses. At embryonic day (E) 16.5, when the hip joint cavity starts to form, one side of the hind limb was sutured onto the embryonic membrane. After exo utero development to E18.5, the hip joint of the operated side was compared morphologically with those of the unoperated side, sham‐operated and unoperated in utero controls. The largest diameter of the femoral head (FH) and the gross morphology of the joint cavity of the operated side was not different from those of controls. By light microscopy (LM), the surface of the control E18.5 FH and acetabulum was smooth and covered by thin scale‐shaped cells which were partially pyknotic, and oval‐shaped cells underneath were rather regularly arranged in a thickness of a few cells. By transmission electron microscopy (TEM), scale‐shaped cells covered the FH surface incompletely, and the spaces in‐between were filled with the intercellular matrix. Oval‐shaped cells underneath had well developed rough endoplasmic reticulums. By scanning electron microscopy (SEM), mounds and grooves on the FH surface were evident at E17.0 but became unclear at E18.5. Subsurface collagen fibers formed a coarse meshwork at E17.0 but formed bundles at E18.5. On the operated side, by LM, the surface of the FH and acetabulum was irregular and lined by spindle‐shaped cells, whereas the underlying mesenchymal cells also showed an irregular cell shape and arrangement. By TEM, collagen fibrils in intercellular spaces were dense but did not generally form bundles. By SEM, the FH surface was rugged with banks and subsurface collagen fibers did not form bundles but remained as a dense meshwork. These results suggest that the fetal hind limb movement influences development of the surface structure of the FH and acetabulum and that this system may be useful to study prenatal etiology of the congenital dislocation of the hip.

We compared the structures of the femoral head (FH) of neonates between normal and operated legs with restrained fetal movement using an exo utero technique. At embryonic day (E) 16.5, one hind limb was sutured onto the embryonic membrane and the fetuses were allowed to develop exo utero until the term (E22.5). There was no significant difference in the largest diameter of the FH between the non-operated and operated side FH in the operated neonates and the FH of the non-operated neonates. By scanning electron microscopy, roughness and collagen fiber bundles, which were detected on the surface of the operated side FH at E18.5, disappeared at E22.5. However, the operated side FH was deformed and the surface cell arrangement was more irregular than that of the controls at E22.5 by light microscopy. These results suggest that the abnormality of cell arrangement caused by the restraint of fetal movement may induce the deformity and irregularity of the FH surface, although this operation may not disturb the basic cellular activities such as cell proliferation as well as the secretion of cartilage ma-trix and collagen fibers. To further investigate the recovery process in the operated newborns after releasing the restraint, we bred them artificially for a considerable period after birth. The operated side FH surface of the neonate bred for 45 hours was smoother than that at E22.5 and similar to that of the non-operated side FH. This result suggests that the proper movement of the extremities after birth may recover the deformity caused by restrained fetal joint movement.

Mouse embryos on embryonic day (E)13 or 14 were treated with ACTH1-24 by exo utero microinjection and the adrenal was examined after 16 and 32 h. Light microscopic morphometry showed that the ACTH treatment increased cell size and decreased cell density of the adrenocortical cells. Bromodeoxyuridine-labeling index did not alter significantly after the ACTH treatment. By immunohistochemistry, both number of cells expressing 11beta-hydroxylase and the staining intensity increased in the ACTH-treated glands compared to controls whereas expression of aldosterone synthase was detectable in neither the treated nor control groups. Ultrastructurally, the adrenocytes of the inner cortical zone of the ACTH-treated glands were characterized by strikingly increased content of the smooth endoplasmic reticulum, increased mitochondria with more vesicular cristae, lipid droplets with a much higher electron density along with the distribution altered from that in controls. All of the significant differences between the ACTH-treated and control glands occurred at 16 h but not at the 32 h interval. The present results indicated that the mouse fetal adrenocytes are already sensitive to ACTH during early period (E13 and 14) of their functional differentiation. In vivo acute treatment of ACTH stimulates cell-size, increase of fetal adrenocytes but not proliferation, and may directly or indirectly regulate multiple steps of the steroidogenic process of the fetal mouse adrenal.

No abstract