The warfarin embryopathy: a rat model showing maxillonasal hypoplasia and other skeletal disturbances.

Sprague-Dawley rats were given daily subcutaneous doses of sodium warfarin (100 mg/kg) and vitamin K1 (10 mg/kg) for up to 12 weeks, starting on the day after birth. This dosing regimen creates an extrahepatic vitamin K deficiency while preserving the vitamin K-dependent processes of the liver. Control rats received either vitamin K1 only or were untreated. All rats survived without any signs of hemorrhage. The warfarin-treated rats developed a marked maxillonasal hypoplasia associated with a 11-13% reduction in the length of the nasal bones compared with controls. The length of the posterior part of the skull was not significantly different from controls. In the warfarin-treated rats, the septal cartilage of the nasal septum showed large areas of calcification, not present in controls, and abnormal calcium bridges in the epiphyseal cartilages of the vertebrae and long bones. The ectopic calcification in the septal cartilage may have been the cause of the reduced longitudinal growth of the nasal septum and the associated maxillonasal hypoplasia. It is proposed that (1) the facial features of the human warfarin embryopathy are caused by reduced growth of the embryonic nasal septum, and (2) the septal growth retardation occurs because the warfarin-induced extrahepatic vitamin K deficiency prevents the normal formation of the vitamin K-dependent matrix gla protein in the embryo.