RT Journal Article SR Electronic T1 Comparison of the activity of the cis and trans isomer of vitamin K1 in vitamin K-deficient and coumarin anticoagulant-pretreated rats. JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 330 OP 333 VO 209 IS 3 A1 J Lowenthal A1 G M Vergel Rivera YR 1979 UL http://jpet.aspetjournals.org/content/209/3/330.abstract AB The cis and trans isomers of vitamin K1 have been prepared at a purity of better than 99.5% and tested for effect on plasma level of factor VII in coumarin anticoagulant-pretreated and vitamin K-deficient rats. Both isomers show activity, but in coumarin anticoagulant-pretreated animals the cis isomer has approximately 10% and in vitamin K-deficient approximately 1% of the activity of the trans isomer. The cis isomer also shows slower onset and rate of increase of the response. Reduction of the 2',3'-double bond of the phytyl side chain of either isomer to the same 2',3'-dihydro derivative of vitamin K1 leaves the activity of the trans isomer unchanged but increases the activity of the cis isomer to that of the trans isomer. The results suggest that the phytyl side chain not only serves to increase lipid solubility, but may play a more direct functional role.