Effect of fasting and fasting-refeeding on the structure, metabolism and transport functions of renal cortical proximal tubules from different kidney regions

Abstract

and HMP-shunt pathway but enzymes of gluconeogenesis were increased by fasting in rat intestine and kidney [2,10]. BBM biomarker enzymes and transport of Pi was also decreased by 1, 3, and 5 d fasting in superficial and juxta-medullary cortex of rat kidney [10]. Now we have determined the effect of fasting and fasting-re-feeding on the enzymes of carbohydrate metabolism, BBM in the homogenates and/ or BBMVs prepared from whole (BBMV-WC), superficial (BBMV-SC) and juxta-medullary cortex (BBMV-JMC) of rat kidney. The transport of Pi was also simultaneously determined under same experimental conditions in freshly prepared BBM vesicles. The results show that fasting caused significant decrease in metabolic enzymes involved in energy generation that caused decrease in transport functions of the kidney but re-feeding prevented the effect of fasting and caused increase in energy metabolism, BBM integrity and transport of Pi.In conclusion, the results show that the kidney has much greater capacity to adapt and try to keep positive balance of various ions and nutrients under acute situations. Material and methodsWistar rats were purchased from All India Institute of Medical Sciences (New Delhi, India). AbstractThe effect of fasting and fasting-re-feeding was studied on certain serum parameters; enzymes of brush border membrane and carbohydrate metabolism; transport of Pi in different anatomical parts of rat kidney. Fasting decreased the activities of lactate dehydrogenase (LDH), malate dehydrogenase (MDH) but increased the activities of glucose-6-phosphatase (G6Pase) and fructose 1, 6-bisphosphatase (FBPase); glucose-6-phosphate dehydrogenase (G6PDH) and malic enzyme (ME). Activities of brush border membrane (BBM) and the transport of Pi in BBM vesicles prepared from superficial and juxta-medullary cortex were also decreased. The feeding of a normal diet to fasted rats reversed the effect of fasting on various parameters. The activities of BBM enzymes and Pi transport elevated to above fasting levels close to control values. Kinetic parameters determined for BBM enzymes and Pi transport affected by fasting and/or re-feeding by alteration in the V max and K m values. The enzymes of glucose degradation decreased but those of its production increased by fasting were also returned back towards control values by re-feeding. Serum Pi, phospholipids and cholesterol affected by fasting were also normalized by re-feeding. The results show that fasting caused significant decrease in metabolic enzymes involved in energy generation caused decrease in transport functions of the kidney but re-feeding could ameliorate the effect of fasting. In conclusion, the results show that the kidney can adapt too much greater extent under acute situations Abbreviations: AlkPase: Alkaline phosphatase; BBM: Brush border membrane; BUN: Blood urea nitrogen; BBMV: Brush border membrane vesicle; FBPase: Fructose 1,6-bisphosphatase; G6PDH: Glucose-6-phosphate dehydrogenase; GGTase: ɤ-glutamyl transferase;