Effect of furosemide on renal function of the newborn piglet.

The effects of development of renal function on the response of newborns to furosemide was evaluated in an animal model, the newborn piglet. Three ages of piglets were used: 5-day-old, 20-day-old, and 50-day-old. Intravenous administration of furosemide (2 mg/kg) produced a prompt natriuresis in all animals. The natriuresis after furosemide was greatest in the older piglets (110 microEq/min for 50-day-old piglets were 210 microEq/min for 5-day-old piglets). However, the fractional sodium excretion at the peak of the response was near 20% in animals in each age group. Neither the time of peak response nor duration of natriuresis was affected by age. Potassium excretion increased after furosemide and remained elevated after both urine flow and sodium excretion had returned to control. The pattern of potassium excretion was identical for each of the three age groups. Thus, while renal maturation does not markedly affect the response to furosemide, both newborns and older piglets continue to excrete relatively large amounts of potassium after sodium excretion returns to control.