Novel recordings of renal sympathetic nerve activity in conscious fetal sheep and newborn lambs.

This study describes a technique for measuring efferent renal sympathetic nerve activity (RSNA) during the perinatal period. Experiments were carried out in four chronically instrumented fetal sheep (gestational age, 134-140 days) and 6 newborn lambs (postnatal age, 3-7 days). Surgery, performed under halothane anesthesia, consisted of routine catheter insertions and placement of a Doppler flow probe around the left renal artery. In addition, bipolar platinum electrodes were placed on a branch of the left renal postganglionic nerve. At least 24 h after surgery RSNA was measured in conscious fetal and newborn animals. RSNA was pulse synchronous, reduced with pressor agents, and completely inhibited during ganglionic blockade. Using this method, we have provided direct evidence of efferent renal sympathetic nerve traffic in utero and in the immediate postnatal period. This technique opens new avenues into the investigation of the role of the sympathetic nervous system during the perinatal period.