Mediation by 5-HT2 receptors of 5-hydroxytryptamine-induced contractions of human placental vein

1. In isolated human placental chorionic vein segments, 5-hydroxytryptamine (5-HT; 10(-8) to 5 x 10(-5) M) elicited concentration dependent contractions with EC50=5.5 (5.2-5.7)x10(-8) M) and E-max=93.1+/-7.3% of 75 mM KCl-induced contraction. 2. The agonist of 5-HT2 receptors, alpha-methyl-5-hydroxytryptamine, and the selective agonist of 5-HT1 receptors, N,N-dipropyl-5-carboxamidotryptamine and 5-carboxamidotryptamine, induced pronounced concentration related contractions, which reached 71.1+/-6.0%, 53.0+/-5.0% and 75.0+/-7.8% at the highest dose tested, respectively. The agonist of 5-HT3 receptor, 2-methyl-5-hydroxytryptamine, reached a maximum averaging 36.7+/-5.1% of the maximal response to KCl. 3. The 5-HT1 and 5-HT3 receptor antagonists, methiothepin and metoclopramide (10(-7) to 10(-6) M) did not alter the response to 5-HT. However, ketanserin (10(-7) to 10(-6) M), a 5-HT2 receptor antagonist, induced significant inhibition of the concentration-response curve to 5-HT. 4. Contractile responses to 5-carboxamidotryptamine and 2 methyl 5 hydroxytryptamine were not affected by methiothepin and metoclopramide, respectively, whereas ketanserin significantly attenuated the contractile response to these agonists. 5. In conclusion, our study shows that 5-HT? receptors mediate contraction of the human placental vein with no obvious role for 5-HT1-like, or 5-HT3 receptors. (C) 1998 Elsevier Science Inc.