Renal osmotic effect of mannitol in the neonatal and adult dog.
The renal response to mannitol loading was studied in 21 newborn dogs aged 1-19 days and in 12 adult dogs. One group of animals (protocol B) underwent distal nephron blockade with ethacrynic acid and amiloride prior to and during infusion of mannitol to estimate proximal tubule function. The other group of animals (protocol A) received mannitol without the diuretics. Mannitol was infused at progressively increasing dosages, resulting in progressively increasing mannitol excretion rates. For all groups of animals, as mannitol excretion rates increased, urine flow and sodium, potassium, and chloride excretion rates increased. However, there was no correlation between mannitol excretion and bicarbonate excretion. The osmotic effect of mannitol was quantitated from the slope of the plot of mannitol excretion vs. sodium excretion (dNa/dMan). In both pups and adults dNa/dMan was greater in protocol B (1.47 for pups, 0.70 for adults) than in protocol A (0.18 for pups, 0.07 for adults). In addition, in protocol B dNa/dMan was greater in the newborn than in the adult and decreased logarithmically with age in pups. In protocol B, as mannitol excretion increased, the urine-to-plasma sodium ratio declined in adults but did not change in pups. Urine-to-plasma osmolality ratio remained at unity throughout the experiment in both age groups in protocol B. These results indicate that 1) the osmotic effect of mannitol is greater in the immature than in the mature kidney, and 2) the greater osmotic effect in the neonatal kidney is related to inability of the immature proximal tubule to generate and sustain a transtubular sodium gradient.
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001834:Body Water / Q000378:metabolism; D004285:Dogs; D005260:Female; D005919:Glomerular Filtration Rate; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008353:Mannitol / Q000494:pharmacology*; D009318:Natriuresis / Q000187:drug effects; D009399:Nephrons / Q000502:physiology; D009995:Osmosis / Q000187:drug effects*; D011188:Potassium / Q000652:urine
D008353:Mannitol; D011188:Potassium