A MODEL IN COMPARATIVE TERATOGENESIS .2. RESPONSE TO 5-FLUORO-2-DEOXYCYTIDINE AT SUCCESSIVE STAGES IN ORGANOGENSIS OF MICE OF STRAINS C57BL/6JHANFFM AND C57BL/10JFFM-+LD

Ten mg/kg 5‐fluoro‐2‐deoxycytidine (FCdR) was given intraperitoneally to pregnant mice of the inbred C57BL/6JHanFfm and C57BL/10JFfm‐ + ld strains once at successive stages of organogenesis. Near‐term fetuses were analyzed for gross and skeletal malformations. The following observations were made. (1) The critical period for eye defects occurred at stages IV–X with a maximum response at stages VIII:18 for C57BL/10− + ld and IX for C57BL/6. Females were more often affected than males, and right eyes more often than left. (2) The critical period for the vertebral column was at stages VI–XII with maximum response at stages IX–XI for vertebral bodies and neural arches and IX for ribs. (3) Limb primordia reacted at stages VIII:18–XII, with two peaks of maximum response at stages IX and XI. (4) Skull primordia reacted at stages VI–IX with no clear peak of maximum response. The types of malformations were described. They were found to be nonspecific for FCdR. Strain differences regarding times of maximum response were explained by the different rates of intrauterine development. Concerning the sporadic malformations seen in controls and at a higher rate and severity in the experimental series, it was concluded that FCdR changed the threshold for these genetically determined defects. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company