Abstract
Scutellariae Radix is one of the well-known tocolytic Chinese herbs. Oroxylin A is isolated from the root of Scutellaria baicalensis. The main syndrome of preterm birth is caused by uterus contractions from excitatory factors. Administration of tocolytic agents is a strategy to prevent the occurrence of preterm births. The aim of this study was to investigate the effects of oroxylin A on contractions of uterine strips isolated from non-pregnant female Wistar rats (250~350 g). Contractions of the uterus were induced with acetylcholine (Ach) (1 μM), PGF2α (0.1 μM), oxytocin (10-3 U/ml), KCl (56.3 mM), tetraethylammonium (TEA; 1 and 10 mM), 4-aminopyridine (4-AP; 5 mM), glipizide (30 μM), a nitric oxide synthase (NOS) inhibitor (LNNA; 10-3M), a β-receptor blocker (propranolol; 10 μM), and a cyclooxygenase inhibitor (indomethacin; 60 μM). The inhibitory effects of the amplitude and frequency of spontaneous contractions by oroxylin A were antagonized with Ach (IC50 22.85 μM), PGF2α (IC5027.28 μM), oxytocin (IC50 12.34 μM), TEA; 1 and 10 mM (IC50 52.73 and 76.43 μM), 4-AP (IC50 67.16 μM), and glipizide (IC5027.53 μM), but oroxylin A was not influenced by Ca2+-free medium, LNNA, propranolol, or indomethacin. Otherwise, oroxylin A-mediated relaxation of the rat uterus might occur through opening of uterine calcium-dependent potassium channels or adenosine triphosphate potassium channel activation. This suggests that oroxylin A is the tocolytic principle constituent of Scutellariae Radix, and oroxylin A may provide a lead compound for new tocolytic drug development in the future.
Highlights
After pregnancy, the endocrinology of the body of pregnant women obviously changes, including uterine contraction agonist receptors, and ion channel proteins which determine the resting membrane potential and excitability of myocytes [1]
Effects of oroxylin A on uterine contractions induced by agonists Agonists, including prostaglandine F2 (PGF2), oxytocin, and Ach, can induce intense uterine contractions
We examined the effects of oroxylin A on uterine contractions induced by these agonists
Summary
The endocrinology of the body of pregnant women obviously changes, including uterine contraction agonist receptors (such as oxytocin receptor, prostaglandin receptor, -adrenergic receptor, and corticotrophin releasing hormone receptor), and ion channel proteins which determine the resting membrane potential and excitability of myocytes [1]. Dysfunctional uterine contractions can lead to premature delivery. Spontaneous preterm labo and delivery accounts for approximately one-third of preterm births, which is the predominant cause of prenatal mortality and morbidity. The wide range of tocolytic agents in use is testament to the fact that we still do not have an ideal drug available [2]. Development of new safe and effective tocolytic agents is an important research topic. The Chinese herbs, Huang-Chi, Scutellaria baicalensis, has been widely used to treat several diseases such as inflammation, hypertension, suppressive dermatitis, diarrhea, and pyrogenic infections [3]. Oroxylin A (5,7-dihydroxy6-methoxyflavone) is a flavonoid that is an active compo-
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