THE DOSE-DEPENDENT EFFECT OF BHT (BUTYLATED HYDROXYTOLUENE) ON VITAMIN-K-DEPENDENT BLOOD-COAGULATION IN RATS

Earlier studies have reported a reduction of vitamin K-dependent blood clotting factor activity and incidence of haemorrhagic death in rats fed butylated hydroxytoluene (BHT); however, the vitamin K status of t he animals used in these studies was claimed to be inadequate. The aim of the study reported here was to determine the effect of BHT on vita min K-dependent clotting factors in vitamin K-sufficient and vitamin K -supplemented rats. Rats given BHT (3000 mg/kg body weight) for up to 21 days, in a diet containing a minimum of 3 ppm vitamin K-3 (six time s the recommended requirement), showed decreased vitamin K-dependent b lood clotting factor activities, demonstrated by increases in factor-s pecific clotting time assays. Clotting times were prolonged within 7 d ays, significantly increased within 14 days (P < 0.001) and maximally increased 5.5-fold at 21 days (P < 0.05). Supplementation with a furth er 250 ppm vitamin K-3 reversed this effect. BHT did not increase prot hrombin time (PT), the usual index of clotting. However, in a similar 14-day investigation, a small but significant increase in PT (up to 15 1%, P < 0.005) was seen within 7 days. Further vitamin K supplementati on was incapable of reversing this effect completely. A similar trend was shown by activated partial thromboplastin time. The 1/51 dilution Thrombotest, a more sensitive indicator of vitamin K-dependent clottin g factor activity in the rat, was significantly increased (more than f our fold, P < 0.01) within 7 days. This increase was fully reversed by further vitamin K supplementation. Prolongation of Thrombotest time w as significant at a BHT dose level of 600 mg/kg body weight per day an d this could be reversed by further supplementation of only 3.0 ppm vi tamin K. However, at dose levels of 125 mg BHT/kg body weight per day or less, no clotting defects were observed. These studies confirm that chronic administration of more than 600 mg BHT/kg/day to rats supplie d with recommended amounts of vitamin K can depress clotting factors a nd precipitate haemorrhagic deaths. When further vitamin K is provided , these deaths could be prevented even though not all clotting abnorma lities may be reversed. This study disproves the proposal that BHT-rel ated clotting factor defects are confined to rats of inadequate vitami n K status, but shows that such effects do not occur at dose levels lo wer than 600 mg/kg/day. The results further indicate that rats receivi ng a high dose of BHT have a higher vitamin K requirement than would o therwise be considered necessary. However, as BHT produces no clotting defects in these animals receiving an intake 1000 times the acceptabl e daily intake, such clotting effects are most unlikely to indicate a human safety problem for BHT.