Effects of 5-hydroxytryptamine on human isolated placental chorionic arteries and veins.
1. Effects of 5-hydroxytrypamine (5-HT) on cylindrical segments of human chorionic arteries and veins were investigated. Concentrations of 5-HT (up to 3 x 10(-6) M) produced concentration-dependent contractions; higher concentrations induced a reduction of the maximal response. These responses were antagonized by methysergide and ketanserin in a non-competitive manner. The contractions elicited by low 5-HT concentrations were more affected by methysergide (10(-7) M) than by ketanserin (10(-7) M). Ketanserin apparently increased the responses to high 5-HT concentrations in veins. Arteries appeared to be more sensitive to both drugs than veins. Single concentrations of 5-HT elicited transient contractions in both kinds of vessel. 2. Marked tachyphylaxis was seen in segments exposed to high concentrations of 5-HT or in which a concentration-response curve was determined. 3. Contractions induced by 5-HT were reduced in a Ca2+-free medium. Veins were more affected by the Ca2+ antagonists, nifedipine (10(-7) M), nicardipine (10(-5) M) and diltiazem (10(-5) M) than arteries. 4. 5-HT (10(-6) M) enhanced 45Ca2+ uptake in those vessels in which a concentration-response curve had not been previously determined. In veins, this increase was reduced by the three Ca2+ antagonists. 5. The results indicate that 5-HT responses in these vessels were greatly dependent on extracellular Ca2+. A type of 5-HT1-receptor may mediate responses to low 5-HT concentrations, while higher concentrations may activate 5-HT2-receptors. 5-HT may desensitize the latter by interconversion between a high affinity and low affinity state, as suggested by others, a change prevented in part by ketanserin.
Reviriego
J
J
Departamento de Farmacologia y Psiquiatria, Facultad de Medicina, Universidad de Extremadura, Madrid, Spain.
Marín
J
J
D001158:Arteries / Q000187:drug effects; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002132:Calcium Radioisotopes; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007650:Ketanserin / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010920:Placenta / Q000098:blood supply; D011247:Pregnancy; D012039:Regional Blood Flow / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D014680:Veins / Q000187:drug effects
D002132:Calcium Radioisotopes; D012701:Serotonin; D007650:Ketanserin; D002118:Calcium; D008784:Methysergide