Quantitative changes in the canine glomerular vasculature during development: Physiologic implications

Quantitative changes in the canine glomerular vasculature during development: Physiologic implications. The apparent discrepancy between functional glomerulotubular balance and morphologic glomerular preponderance observed in developing animals has prompted us to reexamine the changes in glomerular geometry that occur as a function of age. In both superficial and juxtamedullary nephrons, calculations of the glomerular corpuscular volume made from measurements of diameter underestimated the increase in glomerular capillary volume. The measurements were obtained with a new method based on neutron activation of the chromium contained in a silicone rubber compound injected into the renal vasculature. The glomerular capillary surface area (SA GC ) of the juxtamedullary nephrons fell from 0.112 ± (SEM) 0.029 to 0.064 ± 0.011mm 2 between 1 and 3 weeks of age and rose thereafter to 0.417 ± 0.026mm 2 in the adult. No superficial glomeruli were detectable in 1-week-old puppies. Between 3 weeks and adulthood, the SA GC of the superficial nephrons rose from 0.033 ± 0.005 to 0.370 ± 0.014mm 2 . Values in both superficial and juxtamedullary glomeruli observed at 6 weeks were midway between those found at 3 weeks and adulthood. The increase of about 10-fold in the superficial nephron SA GC appears to represent the major determinant of the 25-fold increase in single nephron glomerular filtration rate observed during development. Changes in the size of the glomerular arterioles were small, indicating that the overall fall in renal vascular resistance known to occur during maturation is due predominantly to the genesis of new nephrons in the superficial cortex, which act as resistors In parallel. Modifications quantitatives des vaisseaux glomerulaires au cours du developpement: Implications physiologiques. La discordance apparente entre un equilibre glomerulo-tubulaire fonctionnel et la preponderance morphologique du glomerule observee chez les animaux en cours de developpement nous a incite a reevaluer les modifications de la geometrie glomerulaire qui survient en fonction de l'âge. Dans les nephrons superficiels et juxtamedullaires le calcul du volume glomerulaire a partir de mesures de diametre sous-estime l'augmentation du volume capillaire glomerulaire qui peut etre obtenu par une nouvelle methode fondee sur l'activation neutronique du chrome contenu dans les elastomeres de silicone injecte dans les vaisseaux renaux. La surface capillaire glomerulaire (SA GC ) des nephrons juxtamedullaires diminuent de 0,112 ± (SEM) 0,029 a 0,064 ± 0,011mm 2 de 1 a 3 semaines puis augmentant jusqu'a 0,417 ± 0,026mm 2 chez l'adulte. Il n'a pas ete detecte de glomerule superficiel chez des choits de 1 semaine. Entre 3 semaines et l'âge adulte SA GC des nephrons superficiels augmente de 0,033 ± 0,005 a 0,370 ± 0,014mm 2 . Les valeurs observees a 6 semaines dans les glomerules superficiels et juxtamedullaires etaient intermediaires entre celles obtenues a 3 semaines et a l'âge adulte. L'augmentation de 10 fois de SA GC des nephrons superficiels represente le determinant majeur de l'augmentation de 25 fois de la filtration glomerulaire observee au cours du developpement. Les modifications de taille des arterioles du glomerule etaient minimes, ce qui indique que la diminution de la resistance vasculaire renale, dont on connait la survenue au cours de la maturation, est due essentiellement a la genese de nouveaux nephrons dans le cortex superficiel, nephrons qui agissent comme des resistances en parallele.