title: In vitro contractile effect of platelet-activating factor on guinea-pig myometrium.
abstract: Platelet-activating factor (PAF) evoked myometrial contractions in two different patterns, depending on whether spontaneous activity was present. In spontaneously active myometrial strips (58%), both PAF and oxytocin enhanced the amplitude of myometrial contractions. In quiescent myometrial strips, PAF induced contractions characterized by a prompt development of tension, a plateau, and a final, rapid relaxation. In 54% of these strips, PAF-induced contraction was followed by rhythmic activity. PAF contractile response was dependent upon the concentration (0.1-100 nM); the minimal effective concentration of PAF was 0.1 nM and the EC50 was 1 nM. The response to oxytocin (0.01-10 mU/ml), assumed as reference stimulus, was characterized by a prompt development of tension, which was followed by a sustained, slow contraction and relaxation. PAF response was almost completely dependent on cyclooxygenase and partially on lipoxygenase pathways, as inferred from studies with indomethacin and FPL 55712, respectively. A receptor mediated mechanism of PAF action was suggested by specific desensitization of the myometrium to a second challenge with an equimolar concentration of PAF (but not with oxytocin) and the blocking effect of CV 3988, a specific PAF receptor antagonist.
mesh_terms: D000818:Animals; D002867:Chromones / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D009215:Myometrium / Q000187:drug effects / Q000502:physiology; D010121:Oxytocin / Q000494:pharmacology; D010742:Phospholipid Ethers; D010972:Platelet Activating Factor / Q000502:physiology*; D011453:Prostaglandins / Q000502:physiology; D013844:Thiazoles / Q000494:pharmacology; D014590:Uterine Contraction / Q000187:drug effects*
chemical_list: D002867:Chromones; D010742:Phospholipid Ethers; D010972:Platelet Activating Factor; D011453:Prostaglandins; D013844:Thiazoles; D010121:Oxytocin; C037913:CV 3988; C006312:FPL 55712; D007213:Indomethacin