EXPERIMENT A L STUDY / ORIGINAL AR T ICLE

It has been proposed that low birth weight (LBW) results in a reduction in glomerular number that may, in turn, predispose an individual to develop hyper- tension in adulthood. Glomerular number is reduced in animal models of intra-uterine malnutrition using a vari- ety of techniques. However, the relevance of such ex- treme models to man is uncertain. The purpose of this study was to evaluate whether animals with naturally oc- curring LBW, which have not received any manipulation in utero, have a reduction in glomerular number, altered glomerular volume and abnormal urine albumin excre- tion. Litters from female rats delivering at term on the same day were weighed and sexed at birth. From each lit- ter 2 males with the lowest birth weight (LBW n=18) and 2 males with a birth weight closest to the litter mean (nor- mal birth weight (NBW) n=18) were selected and cross- fostered onto periparturient lactating dams. LBW rats weighed 6.7±0.6 g compared with 7.2±0.6 g for NBW rats (P=0.03). After weaning all rats were weighed week- ly and underwent metabolic studies at 4, 8, 12 and 16 weeks. Following perfusion fixation, glomerular number and mean glomerular volume were estimated using stan- dard stereological techniques. There was no significant difference between LBW and NBW rats with respect to glomerular number (24 499±2 078 vs. 24 825±1 818), mean glomerular volume and urine albumin excretion, and no rats had a glomerular number outside the normal range. This study suggests that naturally occurring LBW has little influence on renal development, glomerular number and volume.