Comparison between inulin clearance and endogenous creatinine clearance in newborn normal weight and growth restricted newborn piglets.

The effect of intrauterine growth restriction (IUGR) and acute oxygen deprivation on renal plasma flow (RPF), renal excretory function (Inulin clearance and endogenous creatinine clearance) and urine flow were studied in twenty newborn piglets 12 to 27 hours old. The experiments were performed on anesthetized animals divided into normal weight piglets and intrauterine growth restricted (IUGR) piglets according to birth weights. The "normal weight" category included animals with a birth weight > 40th percentile (piglets heavier than 1220 g); the IUGR category included animals with a birth weight > 5th and < 10th percentiles (piglets with a birthweight between 733 g and 853 g). This animal model of naturally occurring growth restriction in swine gives asymmetric growth with an increase in the mean ratio of brain weight to liver weight from 1.02 to 2.02 (p < 0.01). There was only a small reduction in brain weight (11%). In contrast, the reduction in weight of liver (55%) and kidney (41%) was proportional to that in body weight (48%). Arterial blood pressure, heart rate, arterial blood gases, pH and RPF were similar in normal weight and IUGR piglets. However inulin clearance and creatinine clearance were significantly lower in the growth restricted piglets (p < 0.01). Severe hypoxia induced a moderate tachycardia, combined with pronounced metabolic acidosis and strongly reduced renal plasma flow and renal excretory function in both groups (p < 0.05). Comparison between inulin and creatinine clearances in normal weight and IUGR piglets revealed a markedly higher clearance of creatinine as of inulin at every experimental stages (p < 0.05, p < 0.01). Alterations of renal excretion due to severe hypoxia and early recovery were similar in both animal groups investigated. Regression analysis rendered a linear correlation between inulin clearance and creatinine clearance among the experimental stages for normal weight as well as IUGR piglets (p < 0.001). Thus, endogenous creatinine clearance is suggested to be a reliable indicator for renal excretory function in newborn piglets. It accurately reflects proportional effects of long-term alterations of renal function due to intrauterine growth restriction as well as acute effects of severe oxygen deprivation. However, using standard methods of plasma and urine creatinine measurement, quantitative determination of GFR by endogenous creatinine clearance is not possible.