Denervation of arterial chemoreceptors and baroreceptors in fetal lambs in utero.

Arterial baroreceptors and chemoreceptors were denervated in eight fetal lambs in utero. Carotid sinus and carotid body denervation was accomplished by stripping the carotid artery rostral and caudal to the origin of the occipital and lingual arteries. Aortic bodies were denervated by section of the superior laryngeal nerve and aortic nerve in the neck. The anatomy relevant to the technique is presented. The effectiveness of the denervation was tested by injection of 20 micrograms phenylephrine. The slowing of the fetal heart rate normally present in the intact lambs was abolished in the denervated fetuses. Denervation of the carotid and aortic chemoreceptors abolished the reflex bradycardia following injection of 200 micrograms cyanide or following acute hypoxemia produced by uterine blood flow reduction for 20 s. These results indicate that the baroreflex and chemoreflex can be elicited in utero and eliminated by the method we described. The preparation we present allows the study of the role of the arterial chemoreceptors and baroreceptors in normal fetal cardiovascular regulation and in fetal responses to stress.