The Renin–Angiotensin System in Newborn Dogs

Abstract

A detailed evaluation of the rennin–angiotensin system by concurrent determinations of plasma renin activity, renal renin activity, and juxtaglomerular index in newborn dogs during the first 15 days of extrauterine life is described. Findings show that the plasma renin activity is significantly higher for the first 2 weeks of extrauterine life when compared with the values found in adult dogs, and that the renal renin activity is slightly greater despite a very low juxtaglomerular index with a few granular cells, mostly located in the juxtamedullary cortex. Stimulation (peritoneal dialysis) of renin release resulted in a marked increase in plasma renin activity. The juxtaglomerular index was not modified by the stimulation whereas the renal renin activity decreased slightly. From these results, it is suggested that the formation and secretion of renin is well developed in kidneys of newborn dogs despite the absence of demonstrable juxtaglomerular cell granules.