Pressure natriuresis during saline expansion in newborn and adult dogs.
Pressure natriuresis was studied in anesthetized saline-expanded adult (n = 10) and neonatal (n = 23) dogs. One group (protocol B) received ethacrynic acid and amiloride to block distal nephron function. Studies in the other group (protocol A) were done without diuretics. Renal arterial blood pressure was raised by bilateral carotid artery occlusion. Renal perfusion pressure was then lowered in steps by partially occluding the aorta proximal to the renal arteries. In protocol B carotid occlusion was associated with an increase in both absolute and fractional sodium excretion by adult and newborn dogs. Moreover, there was significant negative correlation (P less than 0.01) between absolute change in renal arterial pressure and change in tubular reabsorption of sodium per milliliter glomerular filtrate for both age groups. For each mmHg increase in blood pressure there was greater inhibition of sodium reabsorption in the puppy (0.55 mueq/ml glomerular filtrate) than in the adult (0.18 mueq/ml, P less than 0.05). In protocol A puppies, the inhibition of sodium reabsorption due to increases in renal perfusion pressure was less than that occurring in protocol B, indicating that some of the sodium escaping proximal nephron reabsorption was reabsorbed distally. Results of these studies indicate that during saline expansion pressure natriuresis is primarily a proximal tubular event, and the sensitivity of the proximal tubule to changes in renal arterial blood pressure is greater in the newborn than the adult kidney.
D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D001011:Aorta / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D002339:Carotid Arteries / Q000502:physiology; D004232:Diuretics / Q000494:pharmacology; D004285:Dogs; D005919:Glomerular Filtration Rate; D007668:Kidney / Q000254:growth & development*; D009318:Natriuresis; D012079:Renal Circulation / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology*
D004232:Diuretics; D012965:Sodium Chloride