Renal brush border membrane adaptation to phosphorus deprivation: Effects of fasting versus low-phosphorus diet

Abstract

Alimentary phosphorus deprivation due to a low-phosphorus diet (LPD) elicits a profound antiphosphaturia and an increase in sodium-dependent inorganic phosphate (Pi) uptake by renal cortical brush border membrane (BBM) vesicles. But, in alimentary phosphorus deprivation due to total fasting, high urinary excretion of Pi persists. In the present study, we determined whether low tubular reabsorption of Pi in fasting is due to a diminished capacity of the specific Pi transport system with the renal cortical luminal BBM or whether it is due to a reduced transepithelial reabsorption of Pi because of metabolic conditions occurring in proximal tubule cells during fasting. Sodium-dependent Pi transport in compared with fasted rats or rats fed a normal phosphorus diet. Sodium-dependent uptake of D-glucose was significantly lower in LPD rats, compared with fast animals or animals fed a normal diet. Thus, in contrast to LPD, fasting does nt elicit an increase in Pi transport and a decrease in D-glucose transport across the isolated renal BBM. The same differences in BBM transport of Pi were present also in thyroparathyroidectomized rats. Further experiments demonstrated that the adaptation of renal function and the renal BBM transport to LPD are overridden by a subsequent period of total fasting. Results of the present study show that fasting both prevents and reverses the renal response of rats to alimentary phosphorus deprivation. The differences in Pi excretion between fasted rats, LPD rats, and LPD rats subsequently fasted are attributed, at least in part, to specific adaptive changes in sodium-dependent Pi transport across the luminal BBM, rather than to alterations in other cellular (metabolic) components of transepithelial Pi reabsorption in the proximal tubule.

Renal cortex taurine content regulates renal adaptive response to altered dietary intake of sulfur amino acids.

“…We have examined the nature of the adaptive response in rats fed 3% f3-alanine in their drinking water in order to gain insight into the mechanism of the renal adaptive response to altered dietary intake of amino acids. As has been shown for the renal adaptive response in dietary phosphate depletion (7), fasting will blunt the renal adaptive response to altered sulfur amino acid intake (4). We have further examined this phenomenon by determining the effect of the presence of fi-alanine in the drinking water of these fasted animals.…”

Possible role of nicotinamide adenine dinucleotide as an intracellular regulator of renal transport of phosphate in the rat.

“…For studies in vitro of the effects of NAD and other tested compounds on transport, isolated BBM vesicles suspended in 300 mM mannitol, 5 mM Tris-Hepes (pH 8.5), were preincubated for 30 min at 20°C in the absence (controls) or in the presence of the test compound. In the subsequent period of actual measurement of BBM uptake, the test compound was included in the incubation medium at the same concentration as used for preincuba- (3,5,15) tised aind described in detail in otur previouis stud(lies (5,15,16). Final concentrations of 32Pi and D-[3H]-glucose were 0.1 and 0.05 mM, respectively.…”

“…(5, 16). HPD and LPD rats, when compared, were placed simultaneously on the different diets, were pair-fed, and were monitored, sacrificed, and analyzed simultaneously as described in detail (5,15,16).Experiments with acute effects of nicotinamide. Nicotinamide (NiAm) dissolved in 0.6 ml of isotonic saline (pH adjusted to 7.0 with NaOH) was administered as a single intraperitoneal injection to rats kept in metabolic cages.…”

“…In each BBM preparation the uptake was measured in triplicate at each time period. All solutions uised for the preparation of BBM fractions and for transport measuiremiienits were filtered throuigh a 0.45 ,um Millipore filter on the day of utse (5,15).Determiinationt of nuticleotides in renal tisstue. Acidic and alkaline extracts of' snap-frozen cortical tissue were prepared by the methods described by Klingenberg (19).…”

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

“…However, nutritional stress in different forms can produce variable effects on human health. For example, fasting (starvation) is known to produce extensive changes in the structure and functions of intestine, liver and kidney [2,5,6]. However, short-term fasting followed by re-feeding, restricted calorific intake, intermittent fasting and/or Ramadan fasting (Islamic fasting) in which Muslims fast dawn to dusk and allowed to eat after sunset to dawn for about a month have been shown to have beneficial effects in humans and experimental animals [7][8][9].…”