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) x 10^-8 M) and E(max) = 93.1 ± 7.3% of 75 mM KCl-induced contraction. 2. The agonist of 5-HT₂ receptors, α-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-HT₂ receptors mediate contraction of the human placental vein with no obvious role for 5-HT₁-like, or 5 HT₃ receptors.