Blanco C E, Dawes G S, Hanson M A, McCooke H B
J Physiol. 1984 Jun;351:25-37. doi: 10.1113/jphysiol.1984.sp015229.
Carotid chemoreceptor activity was detected in each of fourteen halothane or pentobarbitone anaesthetized exteriorized fetal lambs of 90-143 days gestational age. Activity was about 5 Hz at a Pa,O2 of 25 mmHg and it increased as Pa,O2 was reduced, either by compressing the umbilical cord or by reducing the (FIO2) oxygen fraction of the gas used to ventilate the ewe. Activity increased briskly when 1-2 ml CO2-saturated saline was injected retrogradely into the lingual artery, but not when saline of pH 7.4 or fetal arterial blood was injected. In two fetuses near-term chemoreceptor activity was recorded continuously whilst the umbilical cord was ligated and ventilation with air started. Activity increased 200-500% as Pa,O2 fell, but then fell to below control as Pa,O2 rose. We suggest that these changes in activity reflect those occurring naturally at birth. No spontaneous chemoreceptor activity could be detected on the day of birth in twelve pentobarbitone anaesthetized lambs delivered vaginally or by Caesarean section at 135-146 days. Single baroreceptor activity could however be recorded in these lambs, and chemoreceptor activity could be elicited by hypercapnia. Spontaneous chemoreceptor activity was detected in six of seven lambs more than 2 days old. In eight conscious lambs the steady-state respiratory response to isocapnic hypoxia was variable on the day of birth. In six of these lambs the response was significantly greater by the third day. We conclude that the arterial chemoreceptors are active and responsive in the fetus, but quiescent in the lamb on the day of birth when Pa,O2 has risen. The hypoxic sensitivity of the chemoreceptors is reset from the fetal to the adult range over the next few days.
在14只孕龄为90 - 143天、用氟烷或戊巴比妥麻醉并暴露在外的胎羊中，均检测到了颈动脉化学感受器活动。在动脉血氧分压（Pa,O2）为25 mmHg时，活动频率约为5 Hz，随着Pa,O2降低，活动频率增加，降低Pa,O2的方式有两种，一是压迫脐带，二是降低用于给母羊通气的气体中的氧分数（FIO2）。当向舌动脉逆行注射1 - 2 ml二氧化碳饱和盐水时，活动迅速增强，但注射pH 7.4的盐水或胎儿动脉血时则无此现象。在两只接近足月的胎儿中，在结扎脐带并开始用空气通气时，连续记录化学感受器活动。随着Pa,O2下降，活动增加200 - 500%，但随后随着Pa,O2上升，活动降至对照水平以下。我们认为这些活动变化反映了出生时自然发生的情况。在12只于135 - 146天经阴道分娩或剖宫产、用戊巴比妥麻醉的羔羊出生当天，未检测到自发的化学感受器活动。然而，在这些羔羊中可记录到单个压力感受器活动，高碳酸血症可诱发化学感受器活动。在7只出生超过2天的羔羊中，有6只检测到自发的化学感受器活动。在8只清醒的羔羊中，出生当天对等碳酸血症性低氧的稳态呼吸反应各不相同。其中6只羔羊在第三天时反应明显增强。我们得出结论，动脉化学感受器在胎儿期是活跃且有反应的，但在出生当天羔羊体内处于静止状态，此时Pa,O2已经上升。在接下来的几天里，化学感受器的低氧敏感性从胎儿水平重置为成人水平。
