MATURATIONAL CORRELATES OF NEPHRON STRUCTURE AND FUNCTION DURING DEVELOPMENT

Abstract

Glomerulo-tubular(GT) relationships in the developing kidney have been characterized as immature, with anatomical and functional glomerular preponderance. Previous studies have not differentiated renal immaturity from other possible causes of GT imbalance. Glucose titration experiments were performed in 13 puppies from 2-51 days of age in which volume expansion(VX) was avoided (A), given 20ml/kg 0.9%, saline IV(B) and observed(C). Proximal tubular length(L) and diameter of Bowman's capsule(D) were measured by microdissection studies. Maximal tubular reabsorption of glucose(TmG) and inulin clearance(Cin) increase with age(r=.96)*, with dry kidney weight(DKW)(r=.72)** and with L(r=.84)*. DKW increased with L(r=.61)**. Cin decreased with D(r=-.58)**. Glucose threshold increased from 133 to 210mg/dl from 2-23 days(r=.84)* but did not increase thereafter. The pattern of functional splay (S) <3 weeks of age was greater than that observed >3 weeks. TmG/Cin(3.37±.28,m±SD) did not change with age(r=.54). During B a decrease in TmG** without change in Cin resulted in a decrease in TmG/Cin(2.97±.67)** and an increase in S at all ages. During C, TmG increased, Cin did not change and TmG/Cin increased to 3.60±.99**, values not different from A. S resembled that noted in A at saturation. It is concluded that increments in TmG, Cin and DKW during development, are related to nephron growth and that GT balance for glucose obtains from birth in the canine kidney whose response to VX is qualitatively similar to the adult at every stage of morphological development. *p<.001, **p<.05