Intra-amniotic administration and dietary inulin affect the iron status and intestinal functionality of iron-deficient broiler chickens.

Inulin, a linear ß-fructan, is present in a variety of plants, with relatively high levels of up to 20% in chicory root. It exhibits prebiotic properties and was shown to enhance mineral absorption. Our objectives were to assess the effect of intra-amniotic administration of inulin at 17 d of incubation on the iron status of broiler chicks (at hatch, 21 d) and to continue to monitor iron status with and without dietary inulin on these hatchlings for 42 d. The study included 3 prehatch treatment groups (n = 30): 1) inulin, inulin solution (4% inulin/0.85% saline); 2) control 1, untreated eggs; and 3) control 2, saline solution (0.85% saline). Solutions were injected into the naturally consumed amniotic fluid of 17-d-old chicken embryos (groups 1, 3). Upon hatch (93% hatchability), and from each group, 10 chicks were killed and their small intestine, liver, and cecum were removed for mRNA abundance of intestinal iron-related transporters, liver ferritin amounts, and bacterial analysis of cecal content, respectively. From the remaining chicks of each group, chicks were allocated to a standard corn-based diet (± 4% inulin, n = 10). During the trial, hemoglobin concentrations and body hemoglobin-Fe values were higher in the inulin group versus controls (P < 0.05). On d 42, birds were anesthetized and their duodenal loops were exposed. A nonocclusive catheter was inserted into the duodenal vein for blood sampling. A solution containing 58Fe (0.1 mg of Fe/10 mM ascorbic acid) added to the digested diet sample was injected into the loop. Blood samples were collected every 5 min and for 90 min postinjection and analyzed by inductively coupled argon-plasma mass spectrometry for 58Fe concentrations. At the end of the procedure, animals were killed and cecum contents and sections of the duodenum and liver were removed. Results showed that 58Fe absorption rates were at times higher in the inulin group versus the other groups. Also, mRNA abundance of DMT1 (an Fe transporter) and ferroportin in addition to liver ferritin amounts were higher (P < 0.05) in the inulin group versus controls. Results indicate that intra-amniotic administration and dietary inulin improved the iron status of iron-deficient broilers.

Using the domestic chicken (Gallus gallus) as an in vivo model for iron bioavailability.

Iron fortification of foods and biofortification of staple food crops are strategies that can help to alleviate Fe deficiency. The broiler chicken may be a useful model for initial in vivo screening of Fe bioavailability in foods due to its growth rate, anatomy, size, and low cost. In this study, we assess the broiler as a model for hemoglobin (Hb) maintenance studies and present a unique duodenal loop technique for direct measurement of intestinal Fe absorption. One-week-old chicks were allocated into Fe-deficient versus Fe-adequate treatment groups. For 6 wk, blood Hb, feed consumption, and BW were measured. At wk 7, birds were anesthetized and their duodenal loops were exposed. The loop was isolated and a nonocclusive catheter was inserted into the duodenal vein for blood sampling. A stable isotope solution containing (58)Fe (1 mg of Fe in 10 mM ascorbic acid) was injected into the loop. Blood samples were collected every 5 min and for 120 min postinjection and analyzed by inductively coupled argon-plasma mass spectrometry for (58)Fe concentrations. In the low-Fe group, Hb concentrations, total body Hb Fe, and BW were lower and Hb maintenance efficiency (indicator for dietary Fe availability) was higher than in the high-Fe group (P < 0.05). Iron absorption was higher in the Fe-deficient birds (P < 0.05). In addition, expression of proteins involved in Fe uptake and transfer [i.e., divalent metal transporter 1 (Fe uptake transporter), ferroportin (involved in Fe transport across the enterocyte), and duodenal cytochrome B reductase (reduces Fe at brush border membrane)] were elevated in the low-Fe group. These results indicate that this model exhibits the appropriate responses to Fe deficiency and has potential to serve as a model for Fe bioavailability. Such a model should be most useful as an intermediate test of in vivo Fe bioavailability observations in preparation for subsequent human studies.

Assessing potential effects of inulin and probiotic bacteria on Fe availability from common beans (Phaseolus vulgaris L.) to Caco-2 cells.

Inulin, a prebiotic, may enhance intestinal Fe absorption. Our objective was to assess the effects of supplemental inulin and 2 probiotic bacteria (B. infantis and L. acidophillus) on Fe availability to Caco-2 cells from common white and red beans (Phaseolus vulgaris L.). Cooked beans were mixed or not with supplemental inulin (4%, w/w), and then subjected to simulated gastrointestinal digestion (pepsin, pH 2; pancreatin, pH 7.2). Subsequently, the digests were incubated overnight with and without B. infantis or L. acidophilus. Ferritin formation in Caco-2 cells was used to evaluate Fe uptake. Total soluble phenols (Folin-Ciocalteau) and phytate (HPLC-electrochemical detection) were quantified, and the flavonoids profile (HPLC-PDA/UV detection) was monitored in the digests. Supplemental inulin did not affect Fe uptake from white nor red beans. Incubation with B. infantis increased total soluble phenols (TSP) in the digests and decreased Fe uptake. Incubation with L. acidophilus decreased TSP in the digest and increased Fe uptake. Variations in Fe uptake were not associated with soluble phytate concentrations in the digests. The largest change in flavonoids profile were found in the digests incubated with L. acidophilus, which decreased the soluble concentration of astragalin (kaempferol-3-O-glucoside). These results suggest that certain probiotics could increase Fe uptake from common beans.

Dietary inulin affects the expression of intestinal enterocyte iron transporters, receptors and storage protein and alters the microbiota in the pig intestine.

Inulin, a linear beta fructan, is present in a variety of plants including chicory root and wheat. It exhibits prebiotic properties and has been shown to enhance mineral absorption and increase beneficial bacteria in the colon. The aim of the present study was to assess the effect of dietary inulin on the gene expression of selected intestinal Fe transporters and binding proteins. Anaemic piglets at age 5 weeks were allocated to a standard maize-soya diet (control) or the same diet supplemented with inulin at a level of 4 %. After 6 weeks, the animals were killed and caecum contents and sections of the duodenum and colon were removed. Segments of the genes encoding for the pig divalent metal transporter 1 (DMT1) and duodenal cytochrome-b reductase (Dcytb) were isolated and sequenced. Semi-quantitative RT-PCR analyses were performed to evaluate the expression of DMT1, Dcytb, ferroportin, ferritin, transferrin receptor (TfR) and mucin genes. DMT1, Dcytb, ferroportin, ferritin and TfR mRNA levels in duodenal samples were significantly higher in the inulin group (P < or = 0.05) compared with the control. In colon, DMT1, TfR and ferritin mRNA levels significantly increased in the inulin group. Additionally, the caecal content microflora was examined using 16S rDNA targeted probes from bacterial DNA. The Lactobacillus and Bifidobacterium populations were significantly increased in the inulin group (P < or = 0.05) compared with the control group. These results indicate that dietary inulin might trigger an up regulation of genes encoding for Fe transporters in the enterocyte. The specific mechanism for this effect remains to be elucidated.

Calcium, zinc, and iron bioavailabilities from a commercial human milk fortifier: a comparison study.

Adding human milk fortifiers (HMF) to human milk (HM) is one way of overcoming the nutrient deficits found in the latter. In this study, the bioavailabilities of calcium, zinc, and iron in S-26/SMA HMF added to HM were compared with those in HM fortified with various bovine milk proteins: alpha-lactalbumin, colostrum, caseinate, casein phosphopeptides, and whey protein concentrate. The bioavailability of each mineral was assessed using an in vitro digestion/Caco-2 cell culture model. Calcium and zinc uptake by the cells was traced with radioisotopes; iron uptake was assessed via cell ferritin levels. Samples were prepared on an equal protein content basis and with added calcium, but no zinc or iron was added. Results revealed that calcium uptake from HM + S-26/SMA was not different from any of the HM fortified with the bovine milk proteins, except for unfortified HM and HM + colostrum in which calcium uptake was significantly lower (-89 and -38%, respectively). Uptake of zinc and iron were significantly higher for HM + S-26/SMA than for the other HM + fortifiers.

Dephosphorylation of sodium caseinate, enzymatically hydrolyzed casein and casein phosphopeptides by intestinal alkaline phosphatase: implications for iron availability.

Clusters of phosphoserine residues in casein bind iron with high affinity. Casein inhibits iron absorption in humans but partial hydrolysis of casein prior to ingestion diminishes this inhibition. The objective of this study was to test two hypotheses: 1. Partial hydrolysis of the peptide bonds in casein exposes phosphoserine residues to attack by intestinal alkaline phosphatase (IAP). 2. Hydrolysis of the phospho-ester linkage in phosphoserine residues in casein by IAP releases bound iron or inhibits iron chelation, thereby allowing its absorption. Test of hypothesis 1: Suspensions of sodium caseinate (SC), enzymatically hydrolyzed casein (EHC), and casein phosphopeptides (CPP) were subjected to an in vitro pepsin/pancreatin digestion and subsequently incubated in the presence of calf IAP. The rate of release of inorganic phosphate was measured with the following results (expressed as &mgr;mol phosphate released/unit of IAP/min): 0.081, 0.104, 0.139 for SC, EHC, and CPP, respectively. These results are consistent with hypothesis 1. Test of hypothesis 2: (59)Fe-citrate or (59)Fe-citrate + CPP in minimum essential media were spiked with a Na(2)WO(4) solution or water (Na(2)WO(4) is a known inhibitor of IAP) and placed on Caco-2 cell monolayers. Uptake of (59)Fe by the cells was used as an index of iron bioavailability. Na(2)WO(4) did not affect (59)Fe uptake from samples containing only iron but did slightly inhibit (by 10%) uptake from samples containing iron + CPP. These results are consistent with hypothesis 2 and provide a possible explanation for the observation that partial hydrolysis of casein improves iron bioavailability.

A comparison of iron availability from commercial iron preparations using an in vitro digestion/Caco-2 cell culture model.

The objectives of this study were to compare iron availability from commercial preparations of FeSO(4), ferrous gluconate, ferrous fumarate, and a polysaccharide-iron complex using an in vitro digestion/Caco-2 cell culture model. In addition, we sought to determine if calcium carbonate and calcium acetate (common phosphate binding agents) inhibited iron availability from an oral iron supplement when digested simultaneously. Caco-2 cell ferritin formation following exposure to simulated gastric and intestinal digests of the iron supplements was used as a measure of iron uptake and availability. Plates without cell monolayers were included in each replication of the experiment to measure the total amount of soluble iron that resulted from the in vitro digestion. Significantly more iron was taken up from the FeSO(4), ferrous gluconate, and ferrous fumarate than the polysaccharide-iron complex. Similar results comparing FeSO(4) and the polysaccharide-iron complex have been observed in humans. In addition, less iron was taken up from digests with calcium carbonate relative to calcium acetate even though similar amounts of soluble iron were observed in these experiments. The results indicate that when iron supplements and phosphate binders are consumed simultaneously, calcium acetate may be the preferred phosphate binder to maximize iron availability.

Caco-2 cell ferritin formation predicts nonradiolabeled food iron availability in an in vitro digestion/Caco-2 cell culture model.

We have adapted an in vitro digestion/Caco-2 cell model to assess Fe availability from foods, by using ferritin formation by Caco-2 cells as an indicator of Fe uptake. Ferritin formation by Caco-2 cells occurs in response to Fe uptake at concentrations of available Fe greater than that of the culture media to which the cells have been adapted. This methodology circumvents the need for using radioactive Fe and thus eliminates the costs and controversies associated with food radiolabeling. To validate this method, we measured ferritin formation in Caco-2 cells exposed to digests containing Fe of relatively high and low availability. Our objective was to determine if ferritin formation would be proportional to Fe uptake and sufficiently sensitive to be an indicator of Fe availability from food digests. Our model uses established in vitro digestion techniques coupled with uptake of Fe by Caco-2 cell monolayers. Measurement of cell ferritin was done by a commercially available RIA. Higher ferritin formation was observed in cells exposed to digests containing FeSO4 plus ascorbic acid vs, digests containing FeSO4 plus citric acid. Additional comparisons of Fe availability from digests of beef, fish, corn and green beans yielded results that demonstrate higher Fe availability (i.e., greater ferritin formation) from beef and fish digests than from digests of corn and green beans. Overall, the results document the promotional effects of ascorbic acid and animal tissue on Fe uptake as measured indirectly by ferritin formation. The results of this study indicate that ferritin formation by Caco-2 cell monolayers is highly sensitive and accurately measures food Fe availability in this in vitro system.

Decreased citrate improves iron availability from infant formula: application of an in vitro digestion/Caco-2 cell culture model.

We have applied an in vitro digestion/Caco-2 cell culture model to the assessment of iron availability from human milk and a generic cow's milk-based infant formula. Experiments were designed to determine the availability of iron from human milk relative to infant formula and whether known promoters of iron absorption would increase Caco-2 cell iron uptake and availability from the infant formula. In addition, we sought to determine if decreasing the citrate concentration in the infant formula would increase the iron uptake. Although approximately twice as much iron was in solution from digests of the infant formula relative to that of human milk, smaller or equal amounts of iron were taken up from the infant formula relative to the human milk digest. These results are qualitatively similar to in vivo studies. Addition of known iron uptake promoters to infant formula did not enhance Caco-2 cell iron uptake from the infant formula digest, indicating that the iron in the infant formula existed predominantly in a tightly bound unavailable form(s). Enzymatic pretreatment of the infant formula with citrate lyase and oxalacetate decarboxylase decreased the citrate concentration by 67% and resulted in a 64% increase of iron in solution, which corresponded to a 46% increase in the cell iron uptake. Iron uptake from the "low citrate" formula plus cysteine was 102% greater relative to the nontreated formula. The results indicate that too much citrate can reduce iron uptake, particularly if it is present at concentrations greater than promoters such as ascorbic acid and cysteine.

Iron uptake is enhanced in Caco-2 cell monolayers by cysteine and reduced cysteinyl glycine.

Human and animal studies have shown that amino acids and peptides influence iron absorption from the intestinal lumen. This study was conducted using Caco-2 cell monolayers as the experimental model to determine whether similar effects on iron absorption occur. Conditions were chosen to mimic the pH of the intestinal lumen and the most likely order whereby ferric and ferrous forms of iron would combine with various amino acids and dipeptides resulting from protein digestion. We demonstrated the enhancing effect of cysteine and reduced cysteinyl glycine on iron uptake by Caco-2 cells. The addition of glutathione to the transport media had no effect on uptake from ferrous or ferric iron complexes, nor did it affect iron solubility. Cysteine and reduced cysteinyl glycine increased iron solubility when added to a solution containing insoluble iron. This effect is different from that of ascorbate, which must be combined with soluble ferric iron at pH 2 to reduce and solubilize iron. Taken together, these observations are evidence that cysteine and reduced N-terminal cysteine peptides are capable of enhancing iron uptake from soluble and insoluble ferric iron. These results qualitatively reflect those observed in human studies. Our results indicate that glutathione requires digestion to Cys or Cys-Gly in order to promote iron uptake. The similarity between this study and human studies further reinforces that the Caco-2 cell model is a useful tool in studies of iron absorption and bioavailability.

Ferrous iron uptake but not transfer is down-regulated in Caco-2 cells grown in high iron serum-free medium.

Caco-2 cells in culture provide an attractive model for the study of human iron absorption. Because iron status has a marked effect on human iron absorption, we devised serum-free growth conditions that allow manipulation of Caco-2 cell iron stores while maintaining growth. Caco-2 cells were cultured in serum-free media containing 0-20 micromol/L added iron. Intracellular ferritin, measured by radioimmunoassay, increased 100-fold with the addition of 20 micromol/L iron to the serum-free growth medium. Iron uptake and transfer across Caco-2 cell monolayers were measured from balanced salt solutions of ferrous and ferric forms of iron. Uptake from ferrous, but not ferric, iron was inversely related to cell ferritin concentration and culture medium iron concentration. Kinetic analysis of uptake data from solutions of ferrous and ferric iron revealed saturable and nonsaturable components for ferrous iron, but only a nonsaturable component for ferric iron. Uptake by the nonsaturable pathway was not affected by cell ferritin concentration for either form of iron. Maximal uptake from a ferrous iron solution via the saturable pathway was nearly 100% greater in cells cultured under low compared with high iron conditions. Iron transfer across Caco-2 monolayers was not proportional to iron uptake, but was related to monolayer permeability. Iron uptake by Caco-2 cells was a reliable indicator of relative iron availability. We observed no difference in iron transfer that was related to the iron status of the cell monolayer. The lack of this effect suggests that this model may be inadequate for studies of iron transfer.

Caco-2 cell iron uptake from meat and casein digests parallels in vivo studies: use of a novel in vitro method for rapid estimation of iron bioavailability.

We developed a model for assessing iron bioavailability from foods which combines simulated peptic and intestinal digestion with measurement of iron uptake by Caco-2 cell monolayers. Our objective was to further validate this model by determining if meat enhances Caco-2 cell iron uptake relative to casein. Caco-2 cell monolayers were covered with Hank's balanced salt solution (HBSS) buffered with HEPES, pH 7.4. An upper chamber was created over the cells by fitting the bottom of a Costar Transwell insert with a 12,000-14,000 molecular weight cut-off dialysis membrane. This membrane allowed low molecular weight iron complexes to diffuse into the media bathing the cells and prevented damage to the cells from the digestive enzymes. Prior to digestion, each sample (homogenate of beef, chicken, fish or casein) was mixed with 59FeCl3 to achieve an iron concentration of 10 mumol/L. Following pepsin digestion (pH2), pH was adjusted to 7.4, pancreatic enzymes and bile extract were added to each digest, and an aliquot was then introduced into the upper chamber of the culture dish. During this intestinal digestion period, 59Fe uptake occurred from iron that dialyzed into the lower chamber. The 59Fe uptake from beef, chicken and fish digests was 300-400% of the 59Fe uptake from a casein digest. Our results parallel human absorption studies indicating that meat enhances iron absorption. The results suggest that digestion products of the meat proteins were at least partially responsible for the enhancement of iron uptake. Overall, this study supports the usefulness of our model as a means of assessing iron bioavailability.

Bathophenanthrolene disulfonic acid and sodium dithionite effectively remove surface-bound iron from Caco-2 cell monolayers.

Iron uptake by Caco-2 cell monolayers is commonly assessed by incubating the cells under radiolabeled iron solutions, removing the radiolabeled solution, rinsing to stop uptake and measuring the radioactivity retained by the cells. It is therefore essential to differentiate between iron that is nonspecifically bound to the cell surface from that which has been taken up by the cell. We report here on a method for removal of surface-bound iron from Caco-2 cell monolayers. We used a 140 mmol/L NaCl, 10 mmol/L PIPES, pH 6.7 solution containing 5.0 mmol/L sodium dithionite (Na2S2O4) and 5.0 mmol/L bathophenanthroline disulfonic acid to reduce, remove and chelate iron bound to the cell surface. We validated our method by demonstrating the removal of 97% of an insoluble iron complex from the apical surface of Caco-2 cell monolayers. Our data indicate that the removal solution does not damage the apical membrane and thereby does not have access to intracellular iron; thus only surface bound iron is removed. The remaining cell-associated iron represents that which has been transported into the cell. We present data on the uptake and nonspecific binding of iron from iron complexes of both ferrous and ferric forms, and show that iron removal treatment resulted in uptake measurements that agree more closely with accepted principles of iron uptake by intestinal epithelium. The iron removal method used in this study should provide investigators with a valuable tool for accurately determining iron uptake by epithelial cells in culture.

Aflatoxin B1 reduces Na(+)-P(i) co-transport in proximal renal epithelium: studies in opossum kidney (OK) cells.

In vivo studies indicate that aflatoxin B1 (AFB1) may affect the renal regulation of inorganic phosphate (P(i)), possibly by altering the renal response to parathyroid hormone (PTH). Therefore, the present study utilized opossum kidney (OK) cells, a mammalian renal epithelial cell line, to determine whether AFB1 exposure alters sodium-phosphate (Na(+)-P(i)) co-transport and the hormonal modulation thereof. OK cells are an established renal cell line with many properties analogous to the proximal renal epithelium, including receptors for PTH, insulin, and high levels of Na(+)-P(i) co-transport. PTH and insulin have been shown to decrease and increase Na(+)-P(i) co-transport, respectively, in OK cells. In the present study, AFB1-treated cells responded to PTH; however, AFB1 exposure decreased Na(+)-P(i) uptake such that additional decreases in Na(+)-P(i) uptake in response to PTH were minimal. In the presence of insulin, AFB1-treated cells were only able to increase Na(+)-P(i) uptake to levels 30% below that of control cells. The net result was that the range of the proximal renal epithelium to adjust Na(+)-P(i) co-transport in response to hormonal modulation was reduced by AFB1 exposure. Sodium-dependent L-alanine uptake was measured and was found not to be affected by the highest concentration of AFB1; thus, indicating that AFB1 exposure may have specific effects on Na(+)-P(i) uptake and does not generally inhibit Na(+)-dependent transport. These observations are evidence that AFB1 exposure may alter key elements of renal function. Such effects raise concern that AFB1 exposure may have broad physiological impact in addition to its known carcinogenic properties.

Autocrine/paracrine regulation of renal Na(+)-phosphate cotransport by dopamine.

We tested the hypothesis that dopamine (DA) acts as an autocrine/paracrine regulator of Na(+)-Pi symport in proximal tubules, using opossum kidney (OK) cells as an in vivo model. Both DA and parathyroid hormone (PTH) increased adenosine 3',5'-cyclic monophosphate (cAMP) and inhibited Na(+)-gradient-dependent uptake of 32P but not that of L-[3H]-alanine. Incubation of OK cells with L-dopa, a DA precursor, resulted in accumulation of DA (7.4 nM), a ninefold increase of cAMP in the medium, and an inhibition (-10%) of Na(+)-Pi uptake. Carbidopa, an inhibitor of aromatic-L-amino acid decarboxylase, prevented the formation of DA from L-dopa, the increase in cAMP, and the inhibition of Na(+)-Pi cotransport. Pi-replete OK cells produced more DA (+15%) from L-dopa than Pi-deprived cells; however, the endogenous DA inhibited Na(+)-Pi cotransport both in Pi-deprived and in Pi-replete cells. Thus OK cells can synthesize DA from L-dopa in a quantity sufficient to elicit both the maximum DA-stimulated cAMP accumulation and inhibition of Na(+)-Pi cotransport in the same cell population. Our data, obtained on an in vitro system, support the hypothesis proposing that DA generated in proximal tubular cells can modulate, via cAMP, the Na(+)-Pi symport in the same or adjacent cells. If present in the kidney, this pathway might represent an autocrine/paracrine system that can contribute to regulation of renal Pi homeostasis.

Reduced renal arterial perfusion pressure stimulates renin release from domestic fowl kidneys.

Systemic hypovolemia and hypotension increase plasma renin activity (PRA) in fowl, but it is not clear whether this response is mediated directly by reduced renal arterial perfusion pressure (RAPP) or indirectly via renal nerves activated when systemic baroreceptors detect hypotension. To evaluate the influence of RAPP on renin release, arterial and renal venous blood samples were collected as RAPP was reduced step-wise from 108 mm Hg (control) to 71 and 47 mm Hg. PRA in systemic arterial (aPRA) and renal venous (vPRA) plasma was measured as the rate of fowl angiotensin I (ANG I) generation. Basal vPRA (2.47 +/- 0.6 ng x ml-1 x min-1) tended to be higher than aPRA (1.24 +/- 0.3 ng x ml-1 x min-1). When RAPP was reduced to 47 mm Hg both vPRA (4.35 +/- 0.6 ng x ml-1 x min-1) and aPRA (1.91 +/- 0.3 ng x ml-1 x min-1) increased significantly. Significant negative slopes (P = 0.01) were obtained when changes in aPRA or vPRA were regressed on RAPP. Mean systemic arterial pressure did not change during reductions in RAPP, nor did angiotensinogen concentrations differ when systemic arterial (472 +/- 30 ng/ml) and renal venous (460 +/- 27 ng/ml) plasma values were compared. Renal plasma flow was fully autoregulated as RAPP was reduced from 108 to 47 mm Hg; consequently, RAPP-induced increases in vPRA cannot be attributed to hemoconcentration of secreted renin. These results demonstrate that reductions in RAPP directly stimulate renin release from domestic fowl kidneys.

Response of the avian kidney to acute changes in arterial perfusion pressure and portal blood supply.

Domestic fowl kidneys autoregulate total renal blood flow and glomerular filtration rate (GFR) over a wide range of renal arterial perfusion pressure (RAPP). Sustained (approximately 2-4 h) restriction of renal portal blood flow attenuates the autoregulatory responses. The present study was designed to assess the effects of acute (approximately 10 min) alterations of renal portal blood flow on renal function, and to dissociate the renal responses to altered renal portal blood flow from the renal responses to reductions in RAPP. The thermal pulse decay (TPD) technique and p-aminohippuric acid clearance (CPAH) were used to measure blood flow. During acute increases and decreases in renal portal blood flow, regional renal blood flow as measured by the TPD system (RBFTPD) was significantly positively correlated with total kidney blood flow represented by CPAH (RBFPAH). These results indicate that changes in total kidney blood flow induced by alteration of portal perfusion were reflected in the regional measurement of renal blood flow. Changes in renal portal blood flow did not affect the urine flow rate (UFR), GFR, or fractional excretion of sodium (FENa). Reducing RAPP from 120 to 50 mmHg significantly reduced UFR, GFR, and FENa. Overall, these results indicate that large acute changes in renal portal blood flow can significantly alter total renal blood flow without significantly affecting parameters (UFR, GFR, and FENa) primarily influenced by the renal arterial vasculature.

Mechanism of dopamine inhibition of renal phosphate transport.

Dopamine (DA) is natriuretic and phosphaturic. However, whether the effect of DA on Pi reabsorption is a consequence of its effect on sodium transport is not known. Therefore, this study was performed to determine the effect of DA on the maximal transport of phosphate (TmPi), and upon the capacity of renal proximal brush border membrane (BBM) for (Naextra-vesicular greater than Naintravesicular)-gradient-dependent transport of Pi, as compared with the transport of other solutes. Graded infusions of Pi (0, 1, 2, and 3 mumols/min) were given to thyroparathyroidectomized male Sprague-Dawley rats in the presence of vehicle (0.9% NaCl; N = 5), DA 15 micrograms/kg/min; N = 6), or parathyroid hormone ((PTH); 1 U/kg/min; N = 5). The TmPi for rats infused with DA (3.3 +/- 0.3 mumol/mL) was significantly less than the TmPi for saline control rats (4.4 +/- 0.2 mumol/mL). Rats infused with PTH exhibited the lowest TmPi (1.8 +/- 0.3 mumol/mL). No differences in sodium excretion were observed among any of the groups. Na-dependent Pi transport was studied in BBM vesicles (BBMV) prepared from rats fed a low-phosphate diet for 2 days that were anesthetized, acutely thyroparathyroidectomized, and systemically infused with DA (350 micrograms bolus, plus 35 micrograms/kg/min; N = 8), PTH (33 U/kg bolus, followed by a continuous infusion of 1 U/kg/min; N = 6), or vehicle (1 mL/kg bolus, plus 2 mL/h constant infusion of 0.9% NaCl; N = 8) for 90 min. DA significantly inhibited the Na cotransport of Pi by 22.4 +/- 4.1% (P less than 0.01) as compared with the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxin and glutathione in domestic fowl (Gallus domesticus)--II. Effects on hepatic blood flow.

1. The effect of aflatoxin on plasma aspartate aminotransferase (AST), protein, and hepatic glutathione (GSH) and hepatic blood flow (perfusion), were determined in 3-week-old male chickens. 2. Daily aflatoxin gavage (2 mg/kg body wt, in corn oil) for 5 and 10 days elevated plasma AST and hepatic GSH, and depressed plasma protein and hepatic perfusion. Also, renal GSH was elevated after 10 days of aflatoxin treatment. 3. Birds given aflatoxin for 10 days followed by a 10-day recovery period exhibited tissue GSH, plasma AST and protein levels that were not different from control, but hepatic perfusion remained depressed.

Use of a thermal pulse decay system to assess avian renal blood flow during reduced renal arterial perfusion pressure.

Using a simplified avian kidney model, renal arterial perfusion pressure (RAPP) was reduced from 120 (control) to 70 mmHg (near the glomerular filtration rate autoregulatory limit) and then to 46 mmHg (below the glomerular filtration rate autoregulatory range) in kidneys with ambient or partially restricted renal portal flow. Renal blood flow (RBF) was measured with a thermal pulse decay (TPD) system, using TPD thermistor probes inserted at three locations to evaluate regional differences in RBF. The clearance (CPAH) and extraction of p-aminohippuric acid were used to calculate renal plasma flow (RPF). CPAH, RPF, and RBF values were consistently lower for kidneys with restricted portal flow than for kidneys with ambient portal flow. Reducing RAPP to 46 mmHg did not significantly reduce CPAH, RPF, or RBF in the ambient group but did significantly reduce CPAH and RPF (regressed on RAPP) in the restricted group. RBF was not significantly affected when RAPP was reduced in the restricted group, although significant regional differences in blood flow were recorded. Renal vascular resistance decreased significantly as RAPP was reduced to 46 mmHg in the ambient group, confirming the renal autoregulatory response. In separate validation studies, significant reductions in RBF were detected by the TPD system during acute obstructions of portal and/or arterial flow. Overall, the results support previous evidence that avian RBF remains constant over a wide range of RAPPs. Observations of nonuniform intrarenal distributions of portal blood flow suggest that the portal system maintains the constancy of RBF in regions with proportionately high portal-to-arterial flow ratios.