Age-Dependent Differences in Active and Inactive Renin in the Lamb Fetus

Abstract

Most studies examining the developmental aspects of renin secretion in fetal lambs have focused on measurements of active renin. Data from these studies demonstrated age-dependent differences in renin release in vivo and in vitro. However, little information is available concerning gestational changes in total (active and inactive) renin. Therefore, we have measured the renin concentration in plasma, amniotic fluid and various tissues before and after trypsin treatment (for total renin) using 7 fetuses at 0.61-0.79 gestation (immature) and 7 fetuses at 0.88-0.97 gestation (mature). We found that active and total renin levels in plasma and kidney tissues were significantly lower in immature than in mature fetuses, while inactive renin levels were not different. We also found that the amniotic fluid, the adrenal gland, the placenta and membranes all contained low levels of active and total renin that were not different between groups. These results suggest that, over the last third of gestation, maturation influences the regulation of active renin in the kidney and plasma. The data also indicate that the renin concentration in the amniotic fluid, the adrenals, the placenta and membranes is regulated differently than that in the plasma and the kidney.