Developmental aspects of the renal response to hemorrhage during fetal life

The renal hemodynamic and functional responses to sequential reductions of fetoplacental blood volume were studied in two groups of chronically catheterized fetal lambs: less than 120 d gestation, n = 9 and greater than 130 d gestation, n = 7. Significant decreases in renal blood flow (RBF) and increases in renal vascular resistance (RVR) not associated with changes in glomerular filtration were observed in both groups of fetuses. At the highest level of hemorrhage (level III), the percentage change (% delta) in RBF and RVR tended to be more important in the older group of fetuses (-52 +/- 8% and +155 +/- 58%) than in young fetuses (-38 +/- 6% and +68 +/- 18%). Multiple regression analysis demonstrated that in fetuses less than 130 d the % delta in RBF and RVR correlated more closely with the % delta in plasma arginine vasopressin (AVP) (the partial correlation coefficients being r = 0.61, P less than 0.05 and r = 0.73, P less than 0.01 respectively) than with angiotensin II, norepinephrine, or epinephrine. In fetuses less than 120 d gestation, the % delta in RBF correlated better with the % delta in plasma epinephrine (the partial correlation coefficient being r = 0.52, P less than 0.025) than with any other vasoactive substances. Significant decreases in urinary flow rate and free water clearance and increase in urine osmolality (Uosm) were found in both groups of fetuses. The increase in Uosm correlated closely with the rise in plasma AVP in both groups of fetuses; moreover, the slope of the regression line between plasma AVP and Uosm was similar in less than 120-d (slope 22.2) and greater than 130-d fetuses (slope 33.3), suggesting that the sensitivity of the fetal kidney to AVP is stable during the last trimester of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)