RENAL AUTOREGULATION IN MIDTERM AND LATE-PREGNANT RATS

OBJECTIVES: The normal kidney autoregulates (that is, maintains) renal blood flow over a wide range of arterial blood pressures. During normal pregnancy blood pressure falls and the kidney vasodilates. The purpose of this study was to investigate whether renal autoregulatory ability was influenced during pregnancy in the normal rat. STUDY DESIGN: Experiments were conducted on three groups of anesthetized rats, studied in the virgin state, at midterm, and late in pregnancy (gestation lasts 22 days in the rat). Renal blood flow was measured by electromagnetic flow probe at normal renal perfusion pressures, during elevation in renal perfusion pressure with bilateral carotid occlusion, and at subnormal renal perfusion pressures after application of an aortic snare. RESULTS: Blood pressure was similar in midterm and virgin rats but lower in late pregnancy in the control state. Control renal blood flow was similar between virgin and late-pregnant rats but significantly elevated at midterm. During elevation in blood pressure with bilateral carotid occlusion, autoregulation was maintained in all three groups. During graded aortic occlusion, renal autoregulatory ability was lost. The autoregulatory threshold was between 90 and 100 mm Hg for midterm pregnant and virgin rats and was slightly lower at about 88 mm Hg for late-pregnant rats. CONCLUSIONS: Midterm pregnant rats are able to autoregulate renal blood flow as well as virgins are in spite of underlying gestational renal vasodilatation. The slight shift in renal autoregulatory threshold seen in late-pregnant rats may prevent the kidney from hypoperfusion during late-gestation hypotension.