Different sensitivities for four calcium entry blockers of serotonin-, but not K+-induced contractions of isolated jugular vein and aorta of the rat.

We investigated the inhibitory effect of the calcium entry blockers (CEBs) nifedipine, diltiazem, flunarizine and gallopamil on K+-and serotonin (5-HT)-induced contractions of the rat jugular vein and aorta in vitro. In both tissues all four CEBs inhibited K+-induced contractions concentration-dependently in a similar manner in the same concentration range. Only a smaller contraction due to hyperosmolarity of the medium as the result of addition of 100 mmol/l KCl persisted. 5-HT-induced contractions were antagonized more strongly by nifedipine than by diltiazem and flunarizine, suggesting different sites of action. Moreover, the arterial preparation proved to be more sensitive to CEB pretreatment than the jugular vein preparation. Gallopamil influenced 5-HT-induced contractions also by an antiserotonergic effect.