Autoregulation of Renal Blood Flow During Ovine Pregnancy

Abstract

Since the renal vasculature is vasodilated and the renal perfusion pressure (RPP) is reduced during pregnancy, the capacity to autoregulate renal blood flow (RBF) during pregnancy is unclear. Therefore, we assessed RBF auto-regulation in nonpregnant and pregnant sheep at RPP of 80, 75, 70, and 60 mmHg under control conditions, during amino acid infusion (SAP), and in sheep with nonfiltering kidneys in order to stress the normal feedback regulations of RBF. In nonpregnant animals, RBF was unchanged until RPP was reduced below 70 mmHg, but in pregnant animals the breakpoint occurred at 75-80 mmHg. The autoregulatory index (AI) was significantly higher in pregnant than in nonpregnant animals at all levels of RPP below 80 mmHg, indicating a greater impairment of RBF autoregulation during pregnancy. Amino acid infusion (SAP) elevated basal RBF similarly in all sheep and suppressed the autoregulatory curves of both groups, although to a greater extent in the pregnant sheep. Basal RBF was increased with nonfiltering kidneys in pregnant but not in nonpregnant animals. With nonfiltering kidneys, the levels of AI at 75, 70, and 60 mmHg were greater in pregnant compared with nonpregnant sheep, indicating a diminished residual autoregulatory capacity in the absence of the macula densa feedback mechanism (MDFM). In summary, ovine pregnancy is characterized by a reduced RBF autoregulatory capacity and by a reduced safety margin by which RPP can fall without reducing RBF.