d-Lysergic acid diethylamide (LSD) produced dose-dependent contractions (EC50, 17.9 +/- 2.1 nM) on isolated ovine uterine artery of late pregnancy, which were competitively antagonized by ketanserin. The maximal contraction to LSD was 51% of the 5-HT response. LSD competitively antagonized (pA2 9.21) contractions produced to 5-hydroxytryptamine (5-HT). The results indicate that LSD is a partial...