Influence of Dietary Sodium Intake on Renal Maturation in Unanesthetized Canine Puppies

A major difference between the kidney of the newborn and the adult animal is the reduced ability of the newborn's kidney to adequately excrete an acute salt load (1-4).

When anesthetized newborn dogs were given a normal saline load they excreted only 5% of the infused sodium after 2 hr of sodium infusion. Adult dogs given an equivalent infusion (per kg body wt) excreted 30 % of the sodium infused over the same period of time. Puppies excreted only 1-2% of the filtered sodium compared to 5-6% for the adult dog (5).

When premature infants were accidentally given normal saline instead of distilled water in their formula they developed peripheral edema and a large weight gain (6). Infants receiving a relatively high-salt diet prior to this accidental salt load developed less edema and had a smaller weight gain than infants on a lower salt content formula. This finding lead to the speculation that different concentrations of dietary sodium intake may alter the neonatal renal response to an acute salt load and volume expansion.

This study was designed, therefore, to investigate the effect of different concentrations of dietary sodium on neonatal renal function. Specifically, it compares the response to an acute sodium load in canine puppies after a period on either relatively high or a relatively low salt diet.

Materials and Methods. Experiments were carried out in 24 canine puppies 3-28 days of age. Sixteen of the 24 puppies Received a regular bitch's milk diet, hereafter referred to as “a low-sodium diet.” They were allowed to feed ad lib. from their mothers. Ten of these 16 puppies on the low-sodium diet were studied before and after an acute salt load. The other six puppies had renal function studies done only under nonsaline expansion conditions.