Vitamin K distribution in rat tissues: dietary phylloquinone is a source of tissue menaquinone-4

Abstract

The present study was undertaken to determine whether there is selective tissue distribution of vitamin K in the rat and whether this distribution mirrors the distribution of tissue vitamin K metabolism. The effects of feeding a vitamin K-free diet followed by resupplementation with phylloquinone (K1) were studied. K1was recovered in all tissues. In K1-supplemented rats, most tissues accumulated K1relative to plasma K1with the highest levels in liver, heart, bone, and cartilaginous tissue (sternum). Low K1levels were found in the brain. In the K1-free rats, relatively high K1levels were still found in heart, pancreas, bone and sternum. Surprisingly, menaquinone-4 (MK-4) was detected in all tissues, with low levels in plasma and liver, and much higher levels in pancreas, salivary gland and sternum. MK-4 levels exceeded K1levels in brain, pancreas, salivary gland and sternum. Supplementation with K1, orally and by intravenous infusion, caused MK-4 levels to rise. Some accumulation of K1and MK-4 in the mitochondrial fraction was found for kidney, pancreas and salivary gland. In the liver the higher menaquinones (MK-6–9) accumulated in the mitochondria. The results indicate that: (1) there is selective tissue distribution of K1and MK-4, (2) dietary K1is a source of MK-4. The results also suggest there may be an as yet unrecognized physiological function for vitamin K (MK-4).