Reduced renal mass in early postnatal development. glomerular dynamics in the guinea pig.

As shown previously in the neonatal guinea pig, unilateral nephrectomy at birth results in an earlier rise in superficial nephron glomerular filtration rate. To evaluate the role of glomerular dynamics in this compensatory adaptation, pressure gradients responsible for glomerular ultrafiltration in superficial nephrons were measured by micropuncture techniques in developing euvolemic guinea pigs subjected to uninephrectomy or sham operation at birth. Uninephrectomy resulted in a significant rise in mean arterial blood pressure and glomerular capillary pressure by 10 days of age. Effective filtration pressure was 30% higher in 10- and 21-day-old uninephrectomized guinea pigs compared to sham-operated littermates. However, there ws no significant increase in effective filtration pressure with normal growth from 10 to 21 days of age. Augmented pressure gradients for glomerular ultrafiltration therefore contribute significantly to early compensatory renal adaptation but not to the transitional sharp increase in superficial glomerular filtration which characterizes normal renal growth from 10 to 21 days of age. The apparent acceleration of functional glomerular maturation resulting from uninephrectomy of birth may result from the summation of differing responses to the demands of somatic growth and reduced renal mass.