The placental and mammary transport of (14C) menaquinone-4 [vitamin K] in rats

The transfer of menaquinone-4 (vitamin K2(20)) to the fetus and milk was studied in pregnant and lactating rats, respectively, after oral administration (4 mg/kg) of [3'-14C]menaquinone-4. Intestinal absorption of menaquinone-4 was rapid and the highest level of radioactivity in each tissue except guts of fetal rats was observed at 4 h after dosing. The level in the fetal homogenate was low. At that time, the concentration of menaquinone-4 in the fetal liver was 84 ng/g, corresponding to 9% of the value found in the placenta. Therefore, we conclude that the transfer of menaquinone-4 to the developing rat fetus is restricted by the blood-placenta barrier, but that a sufficient amount of menaquinone-4 (more than the essential amount of vitamin K to ensure full carboxylation) can be transferred into the fetal liver. It was also observed that the radioactivity was transferred to milk after oral administration to lactating rats. Milk/blood concentration ratios at 6 and 24 h after dosing were 13.8 and 65.1, respectively. The elimination half-life of radioactivity in milk was about 17 h. Eighty-four percent of milk radioactivity was due to menaquinone-4. These results suggest that the prophylactic maternal oral administration of menaquinone-4 may be efficacious for a prophylaxis of neonatal and infantile vitamin K deficiency.