Ontogeny of Single Nephron Filtration Distribution in Canine Puppies

Abstract

Summary: The ontogeny of single nephron flitration distribution was studied in 29 canine puppies two hr to 42 days old using the [¹⁴C] ferrocyanide method as modified by Coehlo (9). The ratio of ¹⁴Counts in outer cortical nephrons (OC) to counts in juxtamedullary nephrons (JM) were plotted against age for each puppy. This ratio (OC:JM) provided an index for comparing the single nephron mlomerular filtration between regions. A four-fold increase in OC:JM occurred from two days to four wk. The youngest puppy, two or old, showed a ratio of zero because no counts were detected in OC at that age.

The most rapid increase occurred in the first 8 days of life. By the fourth wk, the mean OC:JM ratio was 0.72 ± 0.06, approaching values reported by other laboratories for adult dogs. In contrast to age-related changes in OC:JM ratio, the ratio of middle cortical to JM counts showed no age-related increase. Cortical blood flow distribution was determined by the microsphere method. The ratio of blood flow to outer and inner cortex increased from 0.43 at one-half a day to a mean of 2.93 after one wk. The ratio of OC:JM single nephron nitration to OC/inner cortical nephron renal blood low was 0.36 from 3 days to 26 days (n = 12) and did not change significantly with age, indicating that changes in zonal filtration matched the alterations in cortical blood flow distribution.

Speculation: These studies suggest that although systemic arterial pressure changes probably play a role in the increasing single nephron filtration in the outer cortex of the maturing puppy, it is likely that plasma flow is a governing factor.

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