Review: Phosphorus in Fish Nutrition

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isoforms are IIb (see Werner & Kinne 2001), but the renal and intestinal isoforms are fairly different in sequence, except flounder that has an identical NaPi in both tissues. Pi uptake stimulator (PiUS) or inositol hexakisphosphate kinase (Schell et al. 1999) may be involved in the absorption of dietary P. Norbis et al. (1997) first isolated PiUS mRNA from rabbit duodenum. Katai et al. (1999) subsequently isolated the corresponding sequence from rat small intestine. These PiUS cRNA markedly increased Na-dependent Pi-uptake when injected into Xenopus laevis oocytes. Katai et al. (1999) further described that dietary P restriction (7 days) up-regulated PiUS genes (~2 times, per mRNA abundance) and Pi uptake from BBMV (~2 times) in the rat intestine. In fish, PiUS in both the intestine and kidney appears to be only slightly responsive to chronic dietary P restriction. Dietary regulation of Pi transport and NaPi-II mRNA/protein expression in the intestine have been studied in mammals (Hattenhauer et al., 1999; Katai et al., 1999; Huber et al., 2000; Huber et al., 2002). In mammals, the main site of dietary P absorption is the proximal small intestine (Danisi & Murer 1991), and unlike kidney, apical expression of NaPi-IIb prot ein in the small intestine, is mostly in response to longer term (days) situations (Murer et al. 2001). In rainbow trout, Avila et al. (2000) reported that active Pi transport is higher in the proximal than distal intestine. They also have functionally characterized P-transport in trout using everted intact intestinal sleeves. It was shown to have a saturable, career-mediat ed active component and a diffusive non-saturabl e component. The study also showed that the dietary Pi level did not affect Pi-uptake rat e in trout intestine at day-7, but significantly down-regulat ed Pi-uptake at day 28, indicating that the response of NaPi-II in trout intestine to dietary P concentration is not acute, but chronic. They did not measure NaPi-II protein or mRNA abundance of the tissues. Avila et al. (1999) incubated everted trout intestine for one hour in a Ringer solution containing either vitamin D3, 25(OH)D or 1,25 (OH) 2D; however, none of these pre-incubation did increase 32 P uptake from the intestine. Pyloric caeca (PC) are finger-like diverticula stemming from the duodenal region of the small intestine of many fish species. The physiological functions of PC have not been well researched; however, they are thought to be the auxiliary to the proximal small intestine because of their histological simalities. Buddington & Diamond (1987) studied PC of rainbow trout: It has about 56 PC, which collectively contribute about 70% of the total gut surface area. They also studied the contribution of PC to the total uptake capacity (of the entire gut) for glucose, the dipeptide carnosine, and nine amino acids, which ranged between 68 and 81%. Thus, the functional contribution of PC corresponds well to its contribution to the total gut surface area. A recent study has shown that Pi absorption in trout PC is largely a passive paracellular process facilitated by high luminal Pi concentrations. Approximately 89% of total Pi absorption takes place in PC, and about 92% of the Pi absorption in PC is diffusive at physiological luminal [Pi] of 20 mM (i.e., luminal [Pi] when a normal P diet is fed). This explains the fractional Pi absorption, which is continuous over the wide range of dietary P levels, even at concentrations much higher than the dietary requirement. The active Pi absorption is modulated by several factors, including temperature, luminal Pi concentration, fish P status, and in particular luminal pH. An isoform of NaPi isolated from trout PC is similar to the intestinal NaPi in base sequence, but functionally different one another. NaPi transporters are sodium-dependent symporters. Zebrafish and flounder NaPi-IIb are Na+-dependent. Trout intestinal NaPi-IIb is Na+ dependent (Avila et al., 2000). Trout PC NaPi is Na+-dependent at alkaline pH, but not at neutral pH. Pi uptake in PC is much higher at alkaline pH, and this increas e is strictly Na+-dependent, which is similar to that of the mammalian renal NaPi isoforms (Hilfiker et al., 1998; Murer et al., 2001). Danisi & Murer (1991) reported Na+-independent, active (carrier-mediated) Pi transport in rat and chick intestinal basolateral membrane and in dog renal basolateral membrane; however, the molecular identity of the transporter is unknown. Mammalian intestinal NaPi isoforms have higher transport rates at neutral to acidic pH (Berner et al., 1976; Borowitz & Ghishan, 1989; Danisi et al., 1984; Lee et al., 1986; Tenenhouse, 1999; Xu et al., 2002). Thus, intestinal NaPi are functionally different between mammals and fish. However, in chick, pig and sheep intestines, Pi transport rate is higher at alkaline pH than acidic pH (Danisi & Murer, 1991), which is similar to intestinal and renal NaPi isoforms of zebrafish, flounder and trout (Forster et al., 1997; Graham et al., 2003; Kohl et al., 1996; Nalbant et al., 1999). Since at pH higher than 7.2 divalent ions 2– – (HPO4 ) will be the dominant species than monovalent ions (H2PO4 ), the preferred ions for the fish NaPi isoforms and mammalian renal NaPi isoforms may be the divalent ion, whereas for mammalian intestinal isoforms, the preferred species may be the monovalent form. Dietary Acidification and P availability Heitzmann (1873) stated that lactic acid increased in the course of rickets and brought about dissolution of the salts of the bones. Anderson (1878) hypothesized about the etiology of scurvy as follows; "The conditions characteristic of this disease (i.e., scurvy) are always accompanied with a deficiency in the food of the materials for © 2000, 2005. Shozo H. Sugiura. All rights reserved. 38
the form ation of tissue phosphate; or if these materials be present in suffici ent quantity, examination of the food in use shows that the salts, which enter into the formation of tissue phosphate, are in an insoluble, or only partially soluble state (p. 108)." Also, he said, "The action of citric acid is remarkable. It is a complete and perfect solvent of phosphates; even tricalcic phosphate (bone phosphate) is in certain proportions completely dissolved by it (p. 115)." and said further "Citric acid also prevents the formation of insoluble phosphates of iron, magnesia and alumina . . . and the consequent loss of phosphoric acid required for the formation of tissue phosphate. It economises phosphoric acid and bases for the fabri cation of tissue phosphate for purposes of nutrition, by preventing the loss of phosphoric acid, which might otherwise form insoluble phosphates, useless in nutrition . . . the efficacy of lime juice as an anti-scorbutic depends mainly on the presence of citric acid, and is referable to the solvent powers of this acid on phosphates. (p. 117)." Baginsky (1882), a pediatrist in Berlin, fed puppies two grams of lactic acid daily, and reported that the total ash of the bones was decreas ed to an extent greater than when the acid was not fed. Weiske et al. (1885) fed hey acidified with sulfuric acid to sheep for 4 months, but did not see any effects on bone composition. In a later work, Weiske (1891) report ed that sulfuric acid, if ingested for a considerable time, lowered Ca content of both bones and muscles. Shohl & Sato (1923) reported that when an infant was given 250 cc of 0.1N HCl the amount of calcium increas ed in both the urine and feces. Wills et al. (1926) also reported that when hydrochloric acid milk, containing 20% of 0.1N acid, was fed, the calcium retention was decreased and the balance became negative. Ammonium chloride also failed to improve the balance. Hess (1929) wrote that one of the most important mechanisms for regulating the acid-bas e equilibrium of the body is the excretion of phosphate by the kidneys. Sherman et al. (1936) found that the dog oxidizes an average 99.3% of citric acid administered orally when 0.5-2.0 g of citric acid were given per kg of body weight. The unoxidized citric acid (0.7% of intake) appeared in the urine, and none found in the feces. Wright & Hughes (1976) reported dietary levels of citric acid at 4-5% (ca.3 g/kg/d) had no observable toxic effects in guinea pigs and rats compared with the control animals fed non-acidi fied diets in a 60 day feeding trial. Møllgaard (1946) showed that oxy-acids, such as tartaric, citric and lactic acids, shift the precipitation point of calcium phytate (pH 3-4) to a more alkaline reaction, which considerably improves the absorption of Ca and P from the intestine of pigs. Organic ligands, such as citric acid and EDTA, chelate minerals (e.g., Ca, Fe, Zn), which otherwise precipitate phytate P and Pi in the intestine (Vohra & Kratzer 1964; Nielsen et al. 1966; Lyon 1984). Phytate-mineral complexes, which are insoluble at pH higher than 7, have higher solubilities at lower pH (Tangkongchitr et al. 1982; Grynspan & Cheryan 1983; Nolan et al. 1987). Bonting (1952) studied long-term effects of citric acid and phosphoric acid intakes on the regulation of acid-bas e equilibrium using rats. The basal diet contained casein, dried milk, wheat flour and potato flour as the major ingredients, and the sources of P were tricalcium phosphate and disodium phosphate. Citric acid (1.2%) supplementation did not change fecal and urinary excretions of P and the balance. Phosphoric acid (0.4%) supplementation increased the P balance and the urinary P excretion markedly, while the fecal P was not increased. Calcium excretions, both fecal and urinary, and the balance of Ca and N did not change appreciably by both acids. Day (1940) reviewed citrates and its anticalci fying action. Hegsted (1960) briefly discussed about dietary citric acid intake, intestinal acidity, and among other factors that might affect Ca absorption in humans. Kirchgessner & Roth (1980) reported that apparent absorption of Ca, P, and Zn were improved by 13, 11, and 33%, respectively, and the balance of these minerals in the order named was also improved by 14, 13, and 43% by the addition of 2% fumarate (sic) in weaning pigs. The author suggested the chelating property of fumaric acid with various cations increases the absorption of the metal-fumarate complex. Radecki et al. (1988) found that the addition of fum aric acid (1.5%) to a corn-soybean meal diet improved gain and feed efficiency of weaning pigs; however, citric acid did not produce such effects. The authors also found that fumaric acid increased fecal Ca, P and Zn, and reduced urinary P. The retention or balance of Ca and P did not change; however, the retention of Zn decreas ed. Effects of dietary acidification on the general performance of piglets have been studied extensively (reviewed in Ravindran & Kornegay 1993). It has been shown that dietary citric, lactic, acetic, propionic and other organic acids have an anorectic (hypophagic) effect and reduce fat deposition in broilers when fed 3-5%, both of which seem to be desirable effects (e.g. Lessard et al. 1993). Many researchers of livestock animals and poultry confirmed significant effects of dietary acidi fication on animal growth and feed effici ency; however, the mode of action is still uncertain. It should be noted that the basal diets used in those animal studies were formulated with plant ingredients and without fish meal or animal by-product meals. Fish feeds generally contain substantial amounts of fish meal, which supplies bone phosphates that are not very effici ently absorbed by the fish, especially agastric fishes such as carps. Thus, the mode of effect of dietary acidification appears to be different between animal feeds and fish feeds. Rungruangsak & Utne (1981) prepared fish mince-based moist diets acidified with hydrochloric acid, formic acid, or sulfuric acid (2.5%, w/w). All diets were further supplemented with 0.5% propionic acid as a mold inhibitor. The dietary pH in the order named was © 2000, 2005. Shozo H. Sugiura. All rights reserved. 39
Page 1 and 2: Phosphorus in Fish Nutrition Edited
Page 3 and 4: maximizing the bone strength, blood
Page 5 and 6: author compared the differences in
Page 7 and 8: was lower and Pi/total P ratio was
Page 9 and 10: tubular secretion (as in birds and
Page 11 and 12: Knochel 2000; Haglin 2001). These c
Page 13 and 14: P intakes. Also, examining the traf
Page 15 and 16: eabsorption in the kidney, and by d
Page 17 and 18: eported the results of bal ance exp
Page 19 and 20: Dietary requirement of organic P co
Page 21 and 22: Practically, the dietary requiremen
Page 23 and 24: did not affect fish growth. The aut
Page 25 and 26: P requirement in Catfish Andrews et
Page 27 and 28: et al. (2002) reported lower temper
Page 29 and 30: est." He also recommended numerous
Page 31 and 32: freshwater fish Labeo rohita (Rora)
Page 33 and 34: Reducing phytate P by non-enzymatic
Page 35 and 36: NaCl 1%, and CaCO 3 3%. The Ca/P ra
Page 37: an exceptionally rapid absorption (
Page 41 and 42: increas e urinary P. Boling et al.
Page 43 and 44: many subsequent workers that measur
Page 45 and 46: Errors due to high dietary P levels
Page 47 and 48: availability of the test compounds
Page 49 and 50: P contents in the whole body and ve
Page 51 and 52: Barros, F. -- J. de Chim. med. T.4,
Page 53 and 54: Cromwell, G.L., Coffey, R.D., Parke
Page 55 and 56: (Sciaenops ocellatus). Aquaculture,
Page 57 and 58: Forbes & Keith 1914, pp. 436) Higur
Page 59 and 60: Kempson, S.A., Kim, J.K., Northrup,
Page 61 and 62: hypophosphatemia. Ann. Int. Med. 74
Page 63 and 64: Mellanby, E. 1924. Deficiency disea
Page 65 and 66: Ogino, C., Takeda, H., 1976. Minera
Page 67 and 68: Radunz-Neto, J., Corraze, G., Charl
Page 69 and 70: different dietary calcium levels on
Page 71 and 72: Sugiura, S.H., Dong, F.M., Rathbone
Page 73 and 74: eproduction of red sea bream. Bull.
Page 75 and 76: Table 1. Availability of Phosphoru
Page 77 and 78: (1982), 6 Watanabe et al. (1980a),
Page 79 and 80: Ash, Ca, P (muscle) 21, 31, 35, P,
Page 81 and 82: Table 3. Reference Values for Diagn
Page 83 and 84: (Vielma & Lall 1998a; 40 g), 4 (Ogi
Page 85 and 86: Figure 1. Ventral view of P-defi ci
Page 87: Figure 6. Pyloric caeca are the maj

Review: Phosphorus in Fish Nutrition

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