Glomerular filtration rate, effective renal bloodflow, and maximal tubular excretory capacity in infancy

Summary

• Glomerular filtration, effective renal plasma flow, and maximal tubular excretory capacity have been measured in twenty-one normal infants ranging in age from one-half to 110 weeks.

• When corrected for surface area, the adult mean value for the filtrationrate is reached in some infants in ten to twenty weeks, for effective renal plasma flow and maximal tubular excretory capacity in thirty weeks.

• If the body surface area is used as an index to general metabolism, the filtration rate, renal blood flow, and tubular excretory mass are adjusted before the end of the first year to the metabolic requirements of the body. However, in the first two or three months of life the three functions develop at different rates. The fact that the normal adult value of the C_PAH/Tm_PAH ratio is observed served in nearly every infant suggests that the renal blood flow increases in served in nearly every infant suggests that the renal blood flow increases in proportion to the development of the renal tubules. The C_M/TMPAH and C_M/C_PAH ratios in early infancy are, however, higher than the adult values, indicating functional imbalance between glomeruli and tubules in favor of the former. This imbalance might be related to increased glomerular pressure, disproportionally large glomerular surface, or decreased PAH extraction ratio; it is suggested that large glomerular surface and increased pressure are, perhaps, responsible for glomerular hyperfunction.