Nijland M J, Chao C R, Ross M G
Department of Obstetrics and Gynecology, School of Medicine, Harbor-University of California, Los Angeles, Torrance 90502, USA.
Am J Obstet Gynecol. 1997 Nov;177(5):1105-12. doi: 10.1016/s0002-9378(97)70024-3.
Fetal swallowing contributes importantly to amniotic fluid volume regulation as the primary route of fluid resorption, reaching 500 to 1000 ml/day near term. Near-term ovine fetal swallowing activity occurs predominantly during low-voltage electrocortical activity. In view of the potential to pharmacologically alter electrocortical activity, we hypothesized that fetal administration of a centrally acting cholinergic antagonist may be used to modulate fetal swallowing activity. To explore cholinergic modulation of swallowing activity, we examined fetal swallowing and electrocortical activity in response to central and peripheral cholinergic suppression by atropine sulfate.
Singleton ovine fetuses (n = 6) were chronically prepared with vascular catheters and thyrohyoid, nuchal, and thoracic esophageal electromyogram and biparietal electrocortical electrodes. Swallowing and electrocortical activity were monitored for 2 hours before and after intravenous injection (1 ml of 0.15 mol/L sodium chloride) of atropine sulfate (1 mg/kg). On a subsequent day an identical study was performed with use off atropine methyl nitrate (3 mg/kg), an atropine analog that does not cross the blood-brain barrier.
Atropine sulfate decreased low-voltage electrocortical activity (56% +/- 5% to 14% +/- 4%), increased high-voltage electrocortical activity (40% +/- 5% to 81% +/- 5%), and did not change intermediate electrocortical activity (4% +/- 1% to 5% +/- 1%). Fetal swallowing activity decreased from 46 +/- 12 to 12 +/- 2 swallows per hour after atropine sulfate administration. Atropine methyl nitrate had no discernible effect on either fetal electrocortical or swallowing activity. Fetal arterial pressure, plasma osmolality, pH, PCO2, and PO2 did not change.
Central cholinergic antagonism suppresses low-voltage fetal electrocortical and swallowing activity in the ovine fetus. Studies exploring spontaneous or induced fetal swallowing should consider the behavioral state of the fetus when conclusions are drawn about changes in the swallowing activity.
胎儿吞咽作为羊水吸收的主要途径，对羊水量的调节起着重要作用，足月时胎儿每天吞咽量达500至1000毫升。足月绵羊胎儿的吞咽活动主要发生在低电压皮质电活动期间。鉴于药理学方法有可能改变皮质电活动，我们推测给胎儿使用中枢作用的胆碱能拮抗剂或许可用于调节胎儿吞咽活动。为探究吞咽活动的胆碱能调节作用，我们检测了胎儿对硫酸阿托品引起的中枢和外周胆碱能抑制的吞咽及皮质电活动反应。
对单胎绵羊胎儿（n = 6）长期植入血管导管、甲状舌骨肌、颈部及胸段食管肌电图电极和双顶皮质电极。静脉注射（1毫升0.15摩尔/升氯化钠）硫酸阿托品（1毫克/千克）前后2小时监测吞咽及皮质电活动。随后一天，使用不透过血脑屏障的阿托品类似物硝甲阿托品（3毫克/千克）进行相同研究。
硫酸阿托品使低电压皮质电活动降低（从56%±5%降至14%±4%），高电压皮质电活动增加（从40%±5%增至81%±5%），中间电压皮质电活动无变化（从4%±1%至5%±1%）。给予硫酸阿托品后，胎儿吞咽活动从每小时46±12次降至12±2次。硝甲阿托品对胎儿皮质电活动及吞咽活动均无明显影响。胎儿动脉压、血浆渗透压、pH值、PCO₂和PO₂均未改变。
中枢胆碱能拮抗作用可抑制绵羊胎儿的低电压皮质电活动及吞咽活动。在对吞咽活动变化得出结论时，探索自发或诱导性胎儿吞咽的研究应考虑胎儿的行为状态。
