The increased Rrs induced by MCh was maintained for 30 minutes despite waning of MCh concentration over that period , measured as attenuated renarrowing when the DI was taken 30 minutes after compared with immediately after the last dose ( 7 min post-DI , -36.2 11.8 vs. 14.4 13.2 % ; 12 min post-DI , -39.5 9.8 vs. 15.2 17.8 % ) .