[Relation between plasma renin and other variables. An evaluation in the Venezuelan population]

The plasma renin activity (PRA) was determined by radioimmunoassay in 102 subjects with normal blood pressure. In this group, 56 were female and 46 male, their ages ranged between 13 and 90 years, they were not receiving any medication and their diet contained normal amounts of sodium and potassium. In addition to the PRA measurements, their weight, height, blood pressure, hemoglobin, hematocrit, serum and urinary sodium, potassium, chloride as well as proteinuria and creatinine clearance were studied. A significative correlation was found between the PRA and age. However, no correlation was found between PRA and urinary sodium. The subjects were also divided in three groups: I. less than 30 years old. II. between 30 and 60 years old, and III. over 60 years. A significative correlation between PRA and urinary sodium was found in group II. These results in group II could be explained by the finding of a daily urinary sodium excretion below 250 mEq. Age has a definite influence between PRA and urinary sodium. We found that important changes in the response of the yuxtaglomerular apparatus to the intake of sodium develop around the age of 60. In group II is where we found a more stable equilibrium in PRA. In group I, the response of the PRA to a low intake of sodium was faster and violent, where as in group III the response was slower. Finally we think it is very important in these type of studies to follow very strict methodology, because it is the only way to establish comparisons between the different ethnic groups.