Altered renal function in growth-restricted newborn piglets

The effect of intrauterine growth restriction (IUGR) on renal hemodynamics and excretory functions was studied in 76 newborn piglets 12-27 h old. The experiments were performed on anesthetized animals divided into normal-weig ht piglets and IUGR piglets according to their birth weight. The "normal-we ight" category included animals with a birth weight >40th percentile (pigle ts heavier than 1,220 g); the IUGR category included animals with a birth w eight >5th and <10th percentiles (piglets with a birth weight between 733 g and 853 g). Cardiac output and renal blood flow were measured by the color ed microsphere technique. Urine was collected from catheters placed in the ureters. This animal model of naturally occurring growth retardation in swi ne gives asymmetric growth with an increase in the mean ratio of brain weig ht to liver weight from 1.02 to 1.85 (P<0.01). Thus there was only a small reduction in brain weight (11%). In contrast, the reduction in the weight o f liver (50%) and kidney (46%) was proportional to that in body weight (46% ). Heart rate, cardiac out put, arterial blood gases, and pH were similar i n normal-weight and IUGR piglets, but arterial blood pressure and arterial glucose content were significantly reduced in IUGR piglets (P<0.01). Moreov er, IUGR piglets had higher plasma catecholamine levels (P<0.05). Renal blo od flow and renal vascular resistance were similar in the normal-weight and in the IUGR groups. However, in IUGR animals, glomerular filtration rate w as significantly less than in the controls (P<0.05). Normal-weight and IUGR newborn piglets reabsorbed sodium very efficiently, the fractional sodium excretion was less than 1% in both groups. We conclude that renal blood flo w is maintained in relation to kidney and body weight in IUGR newborns, but that important renal excretory functions are compromised due to IUGR.