Actions of D 600 on isolated rabbit aorta.

1. The actions of D 600 (10(-9)-10(-4) M) on various phases of NE- or Ca2+-induced contractions of rabbit isolated aorta were determined in Ca2+-free medium. 2. D 600 inhibited the slow phase of contraction with EC50 approximately equal to 3 X 30(-8) M, but affected the rapid phase of contraction only at 10(-4) M. 3. D 600 increased the relaxation that followed the rapid phase of NE-induced contraction in Ca2+-free medium with EC50 approximately equal to 1.5 X 10(-5) M. 4. The method described might be useful for further studies on Ca2+-antagonists.