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The ontogeny of renin mRNA and renin content from renal cortical slices was studied in two groups of ovine fetuses at 92-94 days (0.64 gestation) and at 138-142 days (0.96 gestation), newborn lambs (0.4-2 days old), and adult sheep. Renal renin mRNA was identified by hybridization with a 32P-labeled full length rat renin cDNA. Renal renin content was measured as nanograms of angiotensin I generated per hour (active renin). There was a significant age effect on renin mRNA levels (F = 10.0, P < 0.001); values increase significantly between 0.64 and 0.95 g (P < 0.005), remain elevated in the newborns (P < 0.05), and subsequently decline in adulthood (P < 0.005). Likewise, renal renin content was significantly higher in late gestation fetuses and newborn lambs than in early gestation and adults (F = 8.3, P < 0.003). The renal renin content was strongly correlated with renin mRNA levels (R = 0.88, P < 0.0001). These results suggest that 1) the renin gene is developmentally regulated in the ovine kidney and 2) the renal content of active renin in basal conditions is regulated, at least in part, by events at the transcriptional level.

Information recorded from structural development of kidney in swine foetuses of different age and in piglets together with functional data has shown that, notwithstanding progressing maturation, the capacity of renal corpuscles and tubules in piglets was less developed than in other species. Milk deficit or insufficient drinking water or medication may be considerable burdens on the kidney of newborn piglets and may cause stress-related damage.

In 15 fetuses with congenital nephrosis, distinct colloid-filled cystic tubular dilations were seen scattered in the renal cortex. Similar structures were not present in the controls. It is suggested that these structures are pathognomonic of congenital nephrosis in the fetus and make diagnosis possible even without electron microscopy.

The distribution of basement membrane glycoproteins (type IV collagen, laminin, fibronectin, and proteoglycans) was studied in foetal rat kidney by immunohistochemical techniques using polyclonal antibodies. From the first stages of nephron differentiation, all these glycoproteins were detectable by immunofluorescence in the tubular and glomerular basement membranes and in the mesangial matrix. As differentiation proceeded, labelling of glycoproteins progressively intensified, except for that of fibronectin, which gradually decreased in the glomerular basement membrane (GBM) and was barely observable at full differentiation. With immunoperoxidase staining in electron microscopy, all glycoproteins were seen to be widely dispersed in the spaces between the epithelial and endothelial glomerular cells so long as the GBM remained a loose structure. However, after it became a compact, 3-layered formation, type IV collagen and laminin were distributed throughout the GBM, whereas proteoglycans and anionic sites appeared as 2 rows of granules confined to the laminae rarae.

The activity of the calcium sensitive phospholipid dependent protein kinase C (PKC) was studied in cytosol and in the proximal tubular luminal membrane of rats during growth. Cytosolic activity was elevated at 14 and 21 days of age and fell to adult levels by day 60. Luminal brush border membrane activity on the other hand was low on day 14 but reached adult levels by day 21. Changes in brush border membrane PKC activity may have important consequences for the development of electrolyte transport in proximal tubular cells.

The concept of centrifugal renal development is based on renal embryogenesis. It implies a relationship between nephron age and nephron position along a cortical to medullary axis. In common usage, however, it often also implies a relationship between nephron age or position and nephron maturity. We consider here whether the ideas of centrifugal development and centrifugal maturation should in fact be considered as separate and distinct concepts. That is, we consider the possibility that nephron maturity does not necessarily correlate with nephron age. Unfortunately, pertinent reported data give no clear answer. We conclude only that further study will be required before definitive conclusions about renal developmental stages can be stated with certainty.

The embryologic development of the metanephric kidney is a regulated and sequential growth process. The induction of the early precursors of the metanephric kidney (pronephros and mesonephric) are essential first steps for the later appearance of the metanephric kidney. The pathogenesis of cystic disease can now be reexamined in light of these unique but carefully programmed growth processes with the expectation that the specific nature of the several growth disorders responsible can be more clearly defined.