THE ROLE OF CAROTID CHEMORECEPTORS IN THE EFFECTS OF HYPOXIA ON RENALBLOOD-FLOW IN THE LATE-GESTATION SHEEP FETUS

Previous studies of the effect of hypoxia on fetal renal haemodynamics have demonstrated a fall, a rise or no change in renal blood flow (RB F). The underlying mechanisms are not understood but involve a balance between neural vasoconstrictor and opposing vasodilator mechanisms. S ince carotid chemoreflex mechanisms contribute to vasoconstriction in other fetal vascular beds and in the adult renal vasculature, we exami ned their effects on RBF during 1 h of acute hypoxia in late gestation fetal sheep (n = 12). Renal blood flow was measured continuously and urine collected at 15 min intervals. Seven fetuses underwent bilateral section of the carotid sinus nerves (CSD fetuses). During hypoxia CSD fetuses showed a transient initial rise in RBF (P < 0.05) and then a subsequent fall (P < 0.05) to levels comparable with that recorded in intact fetuses. There was no change in urine output in either intact o r CSD fetuses during hypoxia. Thus the initial fall in RBF during hypo xia is a carotid chemoreflex but other mechanisms, e.g. vasoconstricto r hormones, contribute to the sustained response.