Objective: To determine if the increase in intrarenal renin content that occurs in late gestation in the fetal lamb results from an increase in the proportion of cells containing renin, an increase in the amount of renin per renin-containing cell, or both.
Methods: Kidney cells with a density of 1.062 g/mL were isolated from ovine fetuses at 100-104 days gestation (n = 6, immature) and at 131-139 days gestation (n = 6, mature). This fraction was enriched with renin-containing cells. Total renin (TR) and active renin (AR) were measured by their ability to generate angiotensin I (AI). Renin mRNA was measured by RNase protection assay. The presence of renin in cells and the capacity to release it were identified by immunocytochemistry and cell immunoblot analyses. Data were analyzed by analyses of variance.
Results: The TR and AR in isolated cells increased from 3.7 +/- 0.3 and 2.5 +/- 0.2 micrograms AI/microgram protein . hr-1 in immature fetuses to 6.2 +/- 0.7 and 5.0 +/- 0.6 micrograms AI/microgram protein . hr-1 in mature fetuses (P < .01). The percentage of immunopositive renin cells (PC) was greater in mature (40.6 +/- 4.3) than in immature fetuses (15.2 +/- 1.2) (P < .01). The TR/PC and AR/PC were also higher in mature (8.2 +/- 0.6 and 6.6 +/- 0.4 ng AI/h . pc-1) than in immature animals (6.5 +/- 0.6 and 4.4 +/- 0.4 ng AI/h . pc-1) (P < .01).
Conclusions: The data indicate that the increase in TR and AR occurring during development in fetal lamb kidney results from an increase in both the number of renin-containing cells and in the renin content per cell.