Mediation by 5-HT2 Receptors of 5-Hydroxytryptamine-Induced Contractions of Human Placental Vein

Abstract 1. In isolated human placental chorionic vein segments, 5-hydroxytryptamine (5-HT; 10 −8 to 5×10 −5 M) elicited concentration-dependent contractions with EC 50 =5.5 (5.2–5.7)×10 −8 M) and E max =93.1±7.3% of 75 mM KCl-induced contraction. 2. The agonist of 5-HT 2 receptors, α-methyl-5-hydroxytryptamine, and the selective agonist of 5-HT 1 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-HT 3 receptor, 2-methyl-5-hydroxytryptamine, reached a maximum averaging 36.7±5.1% of the maximal response to KCl. 3. The 5-HT 1 and 5-HT 3 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-HT 2 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 2 receptors mediate contraction of the human placental vein with no obvious role for 5-HT 1 -like, or 5-HT 3 receptors.