Search

Plasma renin activity (PRA) has been measured by microassay on capillary and venous blood sampled simultaneously in 21 subjects; there is no significant difference between these two groups of PRA values. PRA values in normal infants, children and adults have been measured with this microassay and the results are similar to those previously published by authors using different radioimmunological assays.

The aim of this work was to investigate the presence of inactive renin (IR) in plasma of normal infants and children and nephrectomized children and to study the plasma IR response to stimulation of the renin-angiotensin system (orthostasis) in children. The study was performed in 10 normal infants (2 days to 1 yr old), 28 normal children (1-15 yr old), 8 nephrectomized children (8-14 yr old), and 7 normal adults (20-40 yr old). IR was calculated as the difference in renin activity in trypsin-treated (1500 micrograms/ml) plasma, e.g. total renin (TR), and in untreated plasma, e.g. active renin (AR). IR was not detectable in most infants in the supine position, but their AR values were high (8.8-30 ng/ml X h). Moreover, in some of these infants, trypsin appeared to degrade renin activity, since TR values were lower than AR values. IR was detectable in 3 infants and 27 children, but their AR values were in a lower range (0.3-10 ng/ml X h). Trypsin degradation of renin activity was not found in either children or adults. With increasing age (2 days to 40 yr), AR decreased while IR and the IR to TR ratio increased significantly (P less than 0.001). A significant (P less than 0.001) inverse relationship was found between the IR and AR values of subjects 2 days to 40 yr old. IR was detectable in all nephrectomized children and represented 25% of normal values, while AR was undetectable (less than 0.1 ng/ml X h). In children in the upright position, IR decreased and AR increased significantly (P less than 0.001) in a reciprocal manner. TR did not change. These data suggest 1) that trypsin degradation of renin activity and absence of trypsin-activated IR are specific to infants with high AR levels, and 2) that IR might be activated in vivo into AR, especially after changes in position in children. IR could be a prorenin playing a physiological role in children.

Circadian rhythms of plasma renin activity (PRA) and plasma aldosterone (PA) were studied in eight healthy children, 7 to 15 years old. Blood samples were obtained at 7:00 AM, 10:00 AM, 1:00 PM, 4:00 PM, 5:00 PM, 8.00 PM, and midnight on day 1 and 4:00 AM and 7:00 AM on day 2. Children had normal activity during this test. Intra- and interindividual changes were noted in PRA in plasma taken in the upright position. Mean PRA values for samples taken in the upright position were maximal at 1:00 PM (7 ng/ml/hr) and minimal at 5:00 PM (4.1 ng/ml/hr). Mean PRA in the supine position was maximal at 4:00 AM on day 2 (5.6 ng/ml/hr), and its rise was statistically significant compared with the mean PRA at 7:00 AM on the same day (3.9 ng/ml/hr). Plasma aldosterone varied without any definite pattern. No correlation was found between PRA and PA and 24-hr urinary sodium excretion.

We compared plasma active and inactive renin (prorenin) concentrations and activities in infants and children, as measured with a newly available direct immunoradiometric assay kit for active renin and a widely used enzymatic renin assay (plasma renin activity). The study was performed in 57 healthy infants and children under steady-state conditions and in eight subjects after orthostatic stimulation. Our study; (i) reports concentrations for active and inactive renin determined by the immunoradiometric assay in normal infants and children; (ii) confirms, by use of the immunoradiometric assay, the previously described decrease in plasma active and inactive renin, as measured by the enzymatic assay, with increasing age; and (iii) shows close correlations between the results obtained by immunoradiometric and enzymatic assays for active and inactive renin in normal infants and children.