Postnatal development of oxidative enzymes in various rat nephron segments: effect of weaning on different diets

Activities of fumarase and 3-hydroxyacylCoA dehydrogenase (3-OHDH) were determined in homogenates of rat kidneys between day 21 of gestation and postnatal day 10 and in single isolated nephron segments at postnatal days 16, 21, and 30, and in adult segments. For 3-OHDH activity, main developmental changes were found in proximal convoluted (PCT) and straight tubules (PST) and were characterized by an overshoot of adult level from postnatal days 21 to 30 (59.7 +/- 3.0 and 37.5 +/- 3.4 at day 21 vs. adult values 27.1 +/- 1.5 and 22.7 +/- 1.5 mol.kg dry wt-1.h-1). When rats were precociously weaned on day 16 and fed a diet containing lipid to equal 13% of total caloric intake, a significant decrease in 3-OHDH activity was observed in some parts of the nephron. These changes could be prevented by maintaining early weaned animals on high-fat diet providing 70% of total calories as lipid. Results suggest that changes in fat content of diet during kidney maturation can in part regulate 3-OHDH activity in some nephron segments. Fumarase activity increased 2.6-fold in the medullary thick ascending limb between days 16 and 30; pattern of development was similar to the one reported for Na(+)-K(+)-ATPase activity in this segment. High levels of both enzymes were reached noticeably earlier during development in PCT and PST than in medullary thick ascending limb, which emphasizes metabolic heterogeneity of developing rat kidney nephron.