To clarify how vitamin K2 prevents bone loss in vivo, it was given to ovariectomized 20-week-old rats for 2 weeks. Bone mineral density (BMD) in the whole femur and in 7 specific portions (F1 to F7 from the proximal to the distal end) was determined by dual-energy X-ray absorptiometry, and histomorphometry was also performed in proximal tibial metaphysis. Ovariectomy (OVX) resulted in significant decreases in the BMD in the whole femur and the F1, F2, F6 and F7 portions. Histomorphometrical analysis of the tibia showed that the bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th) and trabecular number (Tb.N) were decreased, while trabecular separation (Tb.Sp) and osteoclast number/bone surface (Oc.N/BS) were increased by OVX. The parameters for bone formation were not changed by OVX. These data indicate that the bone loss within 2 weeks is due to the enhancement of bone resorption. Vitamin K2 at 50 mg/kg inhibited the decrease in the BMD of the whole femur together with the F6 and F7 portions. Vitamin K2 also inhibited the decrease in Tb.N and the increases in Tb.Sp, Oc.N/BS and osteoclast surface/bone surface (Oc.S/BS) caused by OVX. These results suggest that vitamin K2 prevents bone loss through the inhibition of bone resorption and osteoclast formation in vivo.

No abstract

ABSTRACT-The effects of menatetrenone (2-methyl-3-tetraprenyl-1,4-naphthoquinone, MK-4) on cal cium balance were studied in male Sprague-Dawley rats. Experiment 1: Rats in metabolic cages that were fed a vitamin K-deficient diet and injected daily with latamoxef (100 mg/kg, i.p.) were either treated or untreated with MK-4 for 7 days. Daily food intake, urine volume and feces weight were determined, and calcium concentration in these samples was measured. Calcium balance was calculated as the difference between calcium intake and urinary and fecal calcium excretion. Cumulative calcium balance in the vitamin K-deficient group treated with latamoxef was lower than that in normal rats; this balance was significantly improved by MK-4 (1 and 10 mg/kg, s.c.) administered for 7 days. Experiment 2: Rats were fed a vitamin K-deficient diet containing 4.6°1o sodium chloride for 6 weeks. MK-4 was administered as a dietary supple ment. Forty-eight-hour calcium balance, determined once a week, was significantly reduced compared with that of normal rats after 3 and 5 weeks; the balance was restored dose-dependently by MK-4 administration (1 and 10 mg/kg). Experiment 3: Rats were subjected to the same experimental conditions as experiment 2 for 6 weeks, and intestinal calcium transport was determined using an everted gut-sac technique. Calcium transport was reduced by the high sodium, vitamin K-deficient diet, and this reduction was restored by MK 4 administration (10 mg/kg). These results suggest that MK-4 improves the reduced calcium balance by increasing intestinal calcium absorption in these rats.

No abstract

No abstract