Self-assembling ultrashort NSAID-peptide nanosponges: multifunctional antimicrobial and anti-inflammatory materials

This paper outlines the design, synthesis and characterisation of innovative NSAID-peptide gelators which demonstrate antimicrobial and anti-inflammatory properties and have potential use as multifunctional materials for biomedical applications.

Transport characteristics and morphology of the colon and coprodeum in two wild birds of different habitats, the rock ptarmigan (Lagopus mutus) and the common murre (Uria aalge)

Dietary salt intake in domestic fowl affects epithelial transport and morphology of the lower intestine (colon and coprodeum). This study investigated lower intestinal morphology and transport activity in two wild bird species with natural diets containing either low or high salt. Tissues from rock ptarmigan (Lagopus mutus) and common murres (Uria aalge) were sampled for histology and electrophysiological analyses. The ptarmigan exists on a low salt diet, while the murre lives on a high protein and high salt diet. The ptarmigan colon and coprodeum had villi/folds and crypts and the epithelium contained absorptive epithelial cells, mitochondria-rich cells and goblet cells. The colon had significant amiloride-inhibitable Isc, 5-15 μA/cm(2), with no glucose-stimulated Isc, and no significant phloridzin inhibition. The coprodeum also had high amiloride-inhibitable Isc. This transport pattern corresponded to that of chickens on low-salt diets. However, the ptarmigan colon also had a significant lysine/leucine-stimulated Isc of 3±1.0 μA/cm(2). The short U. aalge colon was similar to that of ptarmigans, but with no villi. It demonstrated a significant lysine/leucine-stimulated Isc (11±3.5 μA/cm(2)) with no amiloride-inhibitable Isc, similar to the high-salt chicken colon, but with no Na(+)-glucose cotransport. The murre coprodeum was inert to all substances and showed high resistance (1000 Ω·cm(2)), with a multilayered squamous epithelium. Despite some variations possibly associated with dietary protein intake, we conclude that natural high and low salt diets in different avian species are associated with different lower intestinal transport patterns, providing for post-renal adjustments in ion and water excretion.

Antimicrobial efficacy of an innovative emulsion of medium chain triglycerides against canine and feline periodontopathogens

OBJECTIVES

To test the in vitro antimicrobial efficacy of a non-toxic emulsion of free fatty acids against clinically relevant canine and feline periodontopathogens

METHODS

Antimicrobial kill kinetics were established utilising an alamarBlue(®) viability assay against 10 species of canine and feline periodontopathogens in the biofilm mode of growth at a concentration of 0·125% v/v medium chain triglyceride (ML:8) emulsion. The results were compared with 0·12% v/v chlorhexidine digluconate and a xylitol-containing dental formulation. Mammalian cellular cytotoxicity was also investigated for both the ML:8 emulsion and chlorhexidine digluconate (0·25 to 0·0625% v/v) using in vitro tissue culture techniques.

RESULTS

No statistically significant difference was observed in the antimicrobial activity of the ML:8 emulsion and chlorhexidine digluconate; a high percentage kill rate (>70%) was achieved within 5 minutes of exposure and was maintained at subsequent time points. A statistically significant improvement in antibiofilm activity was observed with the ML:8 emulsion compared with the xylitol-containing formulation. The ML:8 emulsion possessed a significantly lower (P < 0·001) toxicity profile compared with the chlorhexidine digluconate in mammalian cellular cytotoxicity assays.

CLINICAL SIGNIFICANCE

The ML:8 emulsion exhibited significant potential as a putative effective antimicrobial alternative to chlorhexidine- and xylitol- based products for the reduction of canine and feline periodontopathogens.

CFTR mediated chloride secretion in the avian renal proximal tubule

In primary cell cultures of the avian (Gallus gallus) renal proximal tubule parathyroid hormone and cAMP activation generate a Cl(-)-dependent short circuit current (I(SC)) response, consistent with net transepithelial Cl(-) secretion. In this study we investigated the expression and physiological function of the Na-K-2Cl (NKCC) transporter and CFTR chloride channel, both associated with Cl(-) secretion in a variety of tissues, in these proximal tubule cells. Using both RT-PCR and immunoblotting approaches, we showed that NKCC and CFTR are expressed, both in proximal tubule primary cultures and in a proximal tubule fraction of non-cultured (native tissue) fragments. We also used electrophysiological methods to assess the functional contribution of NKCC and CFTR to forskolin-activated I(SC) responses in filter grown cultured monolayers. Bumetanide (10 μM), a specific blocker of NKCC, inhibited forskolin activated I(SC) by about 40%, suggesting that basolateral uptake of Cl(-) is partially mediated by NKCC transport. In monolayers permeabilized on the basolateral side with nystatin, forskolin activated an apical Cl(-) conductance, manifested as bidirectional diffusion currents in the presence of oppositely directed Cl(-) gradients. Under these conditions the apical conductance appeared to show some bias towards apical-to-basolateral Cl(-) current. Two selective CFTR blockers, CFTR Inhibitor 172 and GlyH-101 (both at 20 μM) inhibited the forskolin activated diffusion currents by 38-68%, with GlyH-101 having a greater effect. These data support the conclusion that avian renal proximal tubules utilize an apical CFTR Cl(-) channel to mediate cAMP-activated Cl(-) secretion.

Adaptive strategies for post-renal handling of urine in birds

Birds are a diverse vertebrate class in terms of diet and habitat, but they share several common physiological features, including the use of uric acid as the major nitrogenous waste product and the lack of a urinary bladder. Instead, ureteral urine refluxes from the urodeum into the more proximal coprodeum and portions of the hindgut (colon or rectum and ceca). This presents a potential problem in that hyperosmotic ureteral urine in contact with the permeable epithelia of these tissues would counteract renal osmotic work. This review describes and provides examples of different strategies used by avian species to balance renal and post-renal changes in urine composition. The strategies described include: 1. a "reptilian" mode, with moderate renal concentrating ability, but high rates of post-renal salt and water resorption; 2. the "mammalian" strategy, in which the coprodeum effectively functions like a mammalian urinary bladder, preserving the osmotic concentrating work of the kidney; 3. an interaction strategy, in which post-renal transport processes are hormonally regulated in order to optimize renal function under varying conditions of salt or water stress; 4. the salt gland strategy seen in marine or estuarine birds with functional salt glands, in which post-renal transport mechanisms are used to conserve urinary water and to recycle excess NaCl to the nasal salt glands. Finally, we also describe some features of an as-yet unstudied group of birds, the birds of prey. At least some species in this group are relatively good renal concentrators, and would be predicted to have post-renal mechanisms to preserve this work. This new synthesis illustrates the marked diversity of adaptive mechanisms used by avian species to maintain osmotic homeostasis.

Expression of SPAM1 (PH-20) in the Murine Kidney Is Not Accompanied by Hyaluronidase Activity: Evidence for Potential Roles in Fluid and Water Reabsorption

BACKGROUND

A role for Sperm Adhesion Molecule 1 (SPAM1) hyaluronidase in murine kidney, where Spam1 transcript levels have been reported to be higher in males, has not been clarified.

METHODS

Spam1 RNA and protein were studied using RT-PCR, in situhybridization, Western blotting, immunohistochemistry and hyaluronic acid substrate gel electrophoresis. Urine volume and osmolality were studied in wild-type and Spam1 null mice.

RESULTS

While RT-PCR supported a tendency of higher RNA expression in males, no sex difference for the protein was detectable in the cortex, medulla, and urine. Transcripts were predominantly localized in the proximal tubules and glomeruli, with lower levels in the medulla. Similarly, Western blotting and immunohistochemistry revealed that SPAM1 is more abundant in the cortex. Hyaluronidase activity was absent at neutral and acidic pH: suggesting non-enzymatic role(s) for SPAM1. Wild-type and Spam1 null mice given free access to water showed significantly reduced urine volumes (p < 0.01; n = 12) in the latter. Baseline urine osmolality was similar in both, leading to a significantly (p < 0.05) lower osmolar output in the nulls. After water deprivation (24 h), a significant (p < 0.01) increase in urine osmolality was seen only for wild-type mice.

CONCLUSION

SPAM1 is implicated in fluid reabsorption and urine concentration.

Vitamin C transport and SVCT1 transporter expression in chick renal proximal tubule cells in culture

The characteristics of vitamin C (ascorbic acid, ASC) transport were studied in polarized cultured monolayers of the chick (Gallus gallus) renal proximal tubule in Ussing chambers. Under voltage clamp conditions, monolayers responded to apical addition of ASC in a dose-dependent manner, with positive short circuit currents (I(SC)), ranging from 3 microA/cm(2) at 5 microM ASC to a maximal response of 27 microA/cm(2) at 200 microM, and a half-maximal response at 40 microM. There was no effect of basolateral addition of ASC, indicating a polarized transport process. The oxidized form of ASC, dehydroascorbic acid had negligible effects. The I(SC) response to ASC was completely eliminated with Na(+) ion replacement, and was also eliminated by bilateral reduction of bath Cl(-), from 137 to 2.6 mM. There was significant inhibition of the I(SC) responses to 30 microM ASC by the flavanoid quercetin (50 microM) and by 100 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and 5-ethylisopropylamiloride (EIPA), blockers of anion exchangers and sodium-proton exchangers, respectively. There was no inhibition, however, by the chloride channel blocker 5-nitro-2(3-phenylpropylamino)benzoic acid (NPPB). Phorbol 12-myristate 13 acetate (PMA), the phorbol ester activator of protein kinase C, caused a 37% decrease in the I(SC) response to ASC. Chicken-specific primers to an EST homolog of the human vitamin C transporter SVCT1 (SLC23A1) were designed and used to probe transporter expression in these cells. RT-PCR analysis demonstrated the presence of chicken SVCT1 in both cultured cells and in freshly isolated proximal tubule fragments. These data indicate the presence of an electrogenic, sodium-dependent vitamin C transporter (SVCT1) in the chick renal proximal tubule. Vitamin C transport and conservation by the kidney is likely to be especially critical in birds, due to high plasma glucose levels and resulting high levels of reactive oxygen species.

Endocrine regulation of ion transport in the avian lower intestine

The lower intestine (colon and coprodeum) of the domestic fowl maintains a very active, transporting epithelium, with a microvillus brush border, columnar epithelial cells, and a variety of transport systems. The colon of normal or high salt-acclimated hens expresses sodium-linked glucose and amino acid cotransporters, while the coprodeum is relatively inactive. Following acclimation to low salt diets, however, both colon and coprodeum shift to a pattern of high expression of electrogenic sodium channels, and the colonic cotransporter activity is simultaneously downregulated. These changes in the transport patterns seem to be regulated, at least in part, by aldosterone. Our recent work with this tissue has focused on whether aldosterone alone can account for the low salt pattern of transport. Other work has looked at the changes in morphology and in proportions of cell types that occur during chronic acclimation to high or low salt diets, and on a cAMP-activated chloride secretion pathway. Recent findings suggesting effects of other hormones on lower intestinal transport are also presented.

PTH stimulates a Cl(-)-dependent and EIPA-sensitive current in chick proximal tubule cells in culture

The electrophysiological effects of parathyroid hormone (PTH) were studied in a primary cell culture model of the chick (Gallus domesticus) proximal tubule. In this model, confluent monolayers are grown on permeable filters and exhibit vectorial transport, including glucose-stimulated current. Under short-circuit conditions, PTH, at 10(-9) M, induced a positive current [short-circuit current (I(sc))] response, with an average 2-min peak response of 14.30 +/- 1.58 microA/cm(2) over the baseline I(sc,) followed by a slow decay. The PTH response was dose dependent, with a half-maximal response at 5 x 10(-9) M and maximal response at 5 x 10(-8) M. Forskolin and dibutyryl-cAMP also stimulated I(sc), as did the phosphodiesterase inhibitor IBMX. In contrast, the phorbol ester PMA inhibited baseline I(sc). The PTH response was nearly abolished by apical addition of 100 microM EIPA, an inhibitor of Na(+)/H(+) exchangers, and partially blocked by the Cl(-) channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB; 100 microM) and glibenclamide (300 microM). Higher doses of EIPA or NPPB alone (500 microM) were almost fully effective, with no or slight additional effects of NPPB or EIPA, respectively. The anion exchange inhibitor DIDS (100 microM) and the Na(+) channel blocker amiloride (10 microM) had no effect. Bilateral reduction of Cl(-) in the buffer, from 137 to 2.6 mM, abolished the PTH response; increasing Cl(-) concentration restored the I(sc) response, with a half-maximal effect at 50 mM. These data suggest that, in the chick proximal tubule, PTH activates both an Na(+)/H(+) exchanger and a Cl(-) channel that may be functionally linked.

Regulation of transepithelial phosphate transport by PTH in chicken proximal tubule epithelium

The effect of parathyroid hormone (PTH) and activation of protein kinase C (PKC) and protein kinase A (PKA) on transepithelial P(i) transport was examined in monolayers of chick proximal tubule cells in primary culture (PTCs). Acute exposure of the PTCs to PTH (10(-9) M, basolateral side) significantly decreased the net reabsorption of P(i) by approximately 66%. There was no effect after the addition of PTH to the luminal side. Activation of PKC by phorbol 12-myristate 13-acetate (PMA; 0.1 microM) dramatically decreased net P(i) reabsorption by approximately 60%. Bisindolylmaleimide I (BIM; 1 microM), a highly selective PKC inhibitor, prevented PMA-induced inhibition. Activation of adenylate cyclase/PKA by forskolin (10 microM) mimicked the effect of PTH by significantly reducing net P(i) reabsorption by one-half. Addition of H-89 (10 microM), a potent inhibitor of PKA, abolished forskolin-induced inhibition. PTH inhibition was blocked by either BIM or H-89. Tissue electrophysiology remained stable after all treatments. There was a decreased immunoreactivity of the luminal Na+-P(i) cotransporter NaPi-IIa after PTH treatment. These data indicate that PTH inhibition of P(i) reabsorption in this in vitro system is mediated by PKC and PKA.

Aldosterone suppresses expression of an avian colonic sodium-glucose cotransporter

Transport in the colon of the domestic fowl switches from sodium-linked hexose and amino acid cotransport on high-salt intake to amiloride-sensitive sodium channel expression on low-salt (LS) diets. The present experiments were designed to investigate the role of aldosterone in suppression of the colonic sodium-glucose luminal cotransporter (SGLT). LS-adapted hens were resalinated with or without simultaneous aldosterone treatment. Changes in the electrophysiological responses and SGLT protein expression levels were examined at 1, 3, and 7 days of treatment. Serum aldosterone levels fell from approximately 400 pmol/l in LS-adapted hens to values below the detection limit (<44 pmol/l) after 1 day of resalination. At the same time, glucose-stimulated short circuit current (I(SC)) increased from 20.9 +/- 8.7 to 56.3 +/- 15.5 microA/cm(2), whereas amiloride-sensitive I(SC) decreased from -68.9 +/- 12.7 microA/cm(2) on LS to +0.6 +/- 12.0 microA/cm(2). Glucose-stimulated I(SC) increased further at 3 and 7 days of resalination, whereas amiloride-sensitive I(SC) remained suppressed. When resalinated birds were simultaneously treated with aldosterone, the LS pattern of high amiloride-sensitive I(SC) and low glucose-stimulated I(SC) was maintained. Immunoblotting results from the same tissues demonstrated that SGLT-like protein expression increased following resalination. Aldosterone treatment completely blocked this effect. These results demonstrate that aldosterone suppresses both activity and protein expression of hen colonic SGLT. Resalination either through decreased aldosterone or other factors may be able to activate SGLT activity independently of increases in protein expression.

Characterization of a primary cell culture model of the avian renal proximal tubule

Methods have been developed for producing functional, transporting monolayers of avian proximal tubule (PT) cells. A highly homogenous fraction of PT fragments was prepared by enzymatic digestion (collagenase + Dispase) of chick (3- to 5-day-old) kidneys, followed by Percoll gradient centrifugation. The PT fraction was enriched in glucose-6-phosphatase, a proximal enzyme marker, and reduced in specific activity of hexokinase, a distal marker. PT fragments were grown to confluence in serum-free media on collagen-coated permeable filter supports. Electron microscopy of confluent monolayers revealed numerous microvilli and mitochondria, central cilia, and tight junctions, all characteristic of PT cells. gamma-Glutamyltranspeptidase, a proximal brush-border enzyme, showed threefold higher activity on apical than on basolateral sides of the monolayer. The electrophysiological characteristics of monolayers were investigated by voltage-clamp techniques. Monolayers displayed low transepithelial resistances (40-60 Omega . cm2), lumen-negative potentials, and baseline currents of 6-12 microA/cm2 (with or without 5 mM glucose). Both alpha-methyl-D-glucose (2 mM), a nonmetabolizable hexose, and phenylalanine (2 mM) significantly stimulated short-circuit current when added to the mucosal side of glucose-free monolayers. Phloridzin, a specific inhibitor of Na+-coupled glucose transport, significantly inhibited short-circuit current, as did 10(-5) M amiloride. Monolayers also expressed net secretory transport of urate. This cell culture preparation may provide a useful working model for the study of avian PT transport.

Transport characteristics of the colonic epithelium of the Japanese quail (Coturnix coturnix)

The colon of the domestic fowl sustains a reabsorptive Na+ current on both high- and low-sodium diets. However, there is a marked shift in the apical transport step under these two extreme conditions, from amino acid/hexose cotransport on high-salt diets to amiloride-sensitive Na+ channels on low-salt diets. The present experiments were performed to study colonic Na+ transport in another galliform species, the Japanese quail (Coturnix coturnix). Birds were maintained on a commercial game feed containing 0.18% Na+ (78 mumoles/g), an intermediate level of salt intake. Experiments were performed on unstripped colons in standard Ussing chambers with bicarbonate/CO2 buffer solution on both sides. Baseline values (n = 11) for PD (3.13 +/- 0.68 mV) and short circuit current (SCC, 30.87 +/- 7.79 microA/cm2) were lower than those reported for chickens on a similar diet, whereas tissue resistance (76.06 +/- 4.19 omega.cm2) was similar. Addition of amino acids (4 mM leucine + lysine) increased SCC by 10.85 +/- 1.97 microA/cm2. Both phloridzin (1 mM) and amiloride (10(-5) M) decreased SCC, by 7.05 +/- 1.26 and 9.64 +/- 2.68 microA/cm2, respectively. Thus, on this diet the quail colonic epithelium maintains both amino acid/hexose cotransporter activity and amiloride sensitive channel activity. Arginine vasotocin (10(-6) M) caused a small, but consistent decrease in SCC, while acetazolamide increased SCC. Aldosterone (128 micrograms/kg), given 4 hr prior to the experiment (n = 4) significantly reduced the amino acid stimulated SCC. These results confirm, for the Japanese quail, the presence of multiple apical Na+ entry mechanisms in colonic epithelium. Amino acid cotransporter activity, in particular, appears to be highly sensitive to aldosterone suppression.

Mucosal acidification and an acid microclimate in the hen colon in vitro

Experiments were performed on isolated, stripped colonic epithelia of low-salt-adapted hens (Gallus domesticus) in order to characterize acid secretion by this tissue. With symmetric, weak buffer solutions, colonic epithelia acidified both mucosal and serosal sides. Titration measurements of the mucosal acidification rate (pH-stat technique) averaged 1.63 +/- 0.25 microEq.cm-2.h-1. Mucosal acidification was also evident in colons from high-salt-adapted birds and in low-salt-adapted coprodeum, but was completely abolished in the high-salt coprodeum. Mucosal acidification by low-salt-adapted colonic epithelium was unaffected by sodium replacement, mucosal amiloride (10(-3) mol.l-1), and serosal ouabain (5 x 10(-4) mol.l-1), although all three treatments significantly reduced or reversed the short-circuit current. Acetazolamide (10(-3) mol.l-1, serosal) reduced mucosal acidification by 15% and simultaneously increased short-circuit current by a similar amount. Colonic epithelia incubated in glucose-free solutions had significantly lower acidification rates (0.59 +/- 0.13 microEq.cm-2.h-1, P < 0.002 versus controls) and addition of glucose (15 mmol.l-1), but not galactose, partially restored acidification to control levels. Anoxia (N2 gassing) completely inhibited short-circuit current, but reduced acidification by only 30%. A surface microclimate pH, nearly 2 pH units more acidic than the bath pH of 7.1-7.4, was measured in low-salt-adapted colon and coprodeum. The acid microclimate of both tissues was partially attenuated by adaptation to a high-salt diet. Colonic microclimate pH was dependent on the presence of glucose and sensitive to the bath pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the parathyroid hormone antagonist [Tyr34]bPTH-(7-34)amide on avian renal phosphate transport

The in vivo parathyroid hormone antagonist, [Tyr34]bPTH-(7-34)amide, was tested for its ability to block endogenous parathyroid hormone (PTH) activity in parathyroid-intact European starlings. The inhibitor was infused at two dose levels, 0.005 and 0.05 mg/hr. A third group received a vehicle/control infusion. High-dose infusion led to rapid and significant decreases in plasma calcium and in both absolute and relative phosphate (Pi) excretion. Low-dose infusion significantly reduced plasma calcium, but had no effect on Pi excretion. Plasma Pi tended to increase with time in all three groups. Removal of the antagonist after 140 min of high-dose infusion led to a rapid recovery of relative Pi excretion, and a subsequent overshoot to more than twice the original control level. To further test the ability of the antagonist to block endogenous PTH activity, an EGTA challenge was used to induce hypocalcemia and subsequent elevation of circulating PTH levels. In vehicle-infused birds, EGTA challenge led to a doubling of relative Pi excretion, but in birds receiving the high-dose infusion, no effect of EGTA was observed. These results demonstrate that [Tyr34]bPTH-(7-34)amide can completely block endogenous PTH activity in birds at the receptor level, including the hormone response of the renal Pi secretory transport mechanism.

Micropuncture study of proximal tubule pH in avian kidney

Transepithelial potentials (PD) and pH gradients were measured by in vivo micropuncture in superficial proximal tubules of anesthetized European starlings. The average PD for 46 tubules was 2.24 +/- 1.17 mV (mean +/- SD), lumen negative. Only a single lumen-positive potential was recorded, even though late proximal segments are accessible to micropuncture. Proximal luminal pH, measured with single-barrel pH-sensitive microelectrodes, averaged 7.62 +/- 0.26. The pH of peritubular blood, also measured with microelectrodes, was 7.58 +/- 0.15. Correction of the luminal pH for the average PD resulted in a value of 7.58. A few measurements made with double-barrel microelectrodes indicated a pH in proximal tubules of 7.65 +/- 0.08 with a PD of -3.32 +/- 1.47 mV. Thus there appears to be no transepithelial pH gradient across these tubules. On the other hand, pH measurements of cortical collecting ducts averaged 6.40 +/- 0.37, indicating significant acidification in more distal segments. Starlings made acutely acidotic by HCl infusion had significantly reduced arterial and renal cortical pH values, but there was still no significant pH gradient across the proximal tubule. In conclusion, these superficial "reptilian-type" proximal tubules do not appear to have the capacity to maintain a pH gradient. Based on this and on the lack of lumen-positive chloride diffusion potentials, there appears to be no early proximal preferential bicarbonate reabsorption by these nephrons.

Kidney function in domestic fowl with chronic occlusion of the ureter and caudal renal vein

A previously published technique for producing renal insufficiency in chicks involves ligating the caudal renal vein together with the ureter near the midpoint of the kidney. This ligation occludes the normal route (caudal renal vein) by which blood exits the medial and posterior kidney divisions. The present study was conducted to evaluate kidney function following chronic caudal renal vein and ureter occlusion. The ureters and caudal renal veins of 2 to 3-week-old chicks were clamped with hemostatic clips (Clamp Group), and kidney function evaluations were conducted when the birds reached 14 weeks of age. Plasma values [osmolality, Na, K, Ca, inorganic P (Pi)] of control, sham, and clamp groups did not differ significantly. Plasma uric acid concentrations did not differ when the control and clamp groups were compared. Clamping the ureter near the midpoint of the kidney caused a significant reduction in the number of filtering glomeruli per kidney, but due to compensatory hypertrophy the kidney weights of the groups did not differ significantly. Kidney function comparisons (urine flow rates, glomerular filtration rates, renal plasma flow rates, urine pH, fractional excretion of Na, K, Ca, Pi, and uric acid) revealed a significant reduction in Na and K excretion by the clamp group, but other renal function parameters did not differ significantly. These experiments demonstrate that chickens have a remarkable capacity to survive significant reductions in renal mass and to adapt to major disruptions of blood flow patterns.

Avian renal responses to oxidized and nonoxidized bPTH(1-34)

The hypotensive, hypercalcemic, and hyperphosphaturic responses to bovine synthetic 1-34 amino acid parathyroid hormone [bPTH(1-34)] were simultaneously evaluated in anesthetized laying hens, and compared to the same responses to oxidized (0.3% hydrogen peroxide) bPTH(1-34) prepared from the same commercial batch of hormone. The oxidized and nonoxidized hormones were administered intravenously into separate groups of animals, which were also receiving a constant intravenous infusion of inulin and p-aminohippuric acid (PAH) to serve as renal clearance test markers. bPTH(1-34) caused a 33.25 +/- 7.05 mm Hg decrease in mean arterial blood pressure. The corresponding change in response to the oxidized hormone preparation was a 10.75 +/- 1.49 mm Hg decrease, a significant reduction in hypotensive activity compared to the intact hormone. In contrast, oxidation had no influence on the hypercalcemic or hyperphosphaturic (relative clearance of phosphate, CPO4/CIn) responses to bPTH(1-34), both preparations causing significant and parallel increases in these variables. Both hormone preparations also caused increases in urine flow rate, GFR, CPAH, CCa/CIn, CK/CIn, CNa/CIn, and urine pH. However, on the basis of percentage change from the respective control periods, only CNa/CIn and urine pH showed significant differences between the two hormone preparations, with the intact hormone causing greater natriuresis and urine alkalinization than the oxidized hormone. The failure of peroxide oxidation to significantly affect the renal hyperphosphaturic response to bPTH(1-34) in chickens contrasts with results reported on mammalian species, and may be related to differences in the mechanism of renal phosphate transport between these groups.

Micropuncture study of urate transport by superficial nephrons in avian (Sturnus vulgaris) kidney

Tubule fluid samples from proximal tubules of superficial, reptilian-type nephrons of the European starling (Sturnus vulgaris) were obtained by micropuncture and, along with plasma samples, were analyzed for urate by high performance liquid chromatography with electrochemical detection, as well as for the elements sodium, chloride, calcium, magnesium, phosphorus and potassium by electron microprobe analysis. All proximal tubules sampled showed net secretion of urate, but the magnitude of transport was highly variable. Mean fractional delivery of urate to the point of micropuncture was 4.04 +/- 0.37 (mean +/- SE, n = 40 tubules). Fractional delivery of urate could not be correlated with fractional delivery of any of the measured elements or with relative fluid absorption. Samples collected from surface segments of cortical collecting ducts suggest that, although much net secretion of urate occurs early within the proximal tubule of superficial nephrons, some additional secretion may occur in more distal segments. Fractional excretion of urate at the level of the cloaca averaged 4.72 +/- 0.97 for nine birds, confirming the result of overall net secretion of urate previously reported for other avian species. These results clearly demonstrate the presence of significant secretory transport of urate in the proximal tubule of superficial reptilian-type nephrons, but do not rule out the possibility of additional secretory or reabsorptive fluxes at other sites.

Micropuncture of superficial nephrons in avian (Sturnus vulgaris) kidney

Single nephron glomerular filtration rate (SNGFR), fluid absorption, and tubule transport of sodium, chloride, calcium, magnesium, potassium, and phosphate were evaluated under control (2.5% mannitol infusion) conditions by micropuncture of superficial, reptilian-type nephrons of European starlings (Sturnus vulgaris). SNGFR averaged 0.36 nl . min-1 . Sodium, chloride, and water were transported at equivalent rates with about 24% of the filtered load absorbed up to the point of micropuncture. Calcium was absorbed continuously along these tubules in excess of sodium and fluid, whereas magnesium appeared to undergo net secretion early and net absorption late in the tubules. Potassium transport varied considerably, with all tubules from a single bird generally showing either net potassium absorption or no net transport. In the latter group, data for a few tubules suggested net potassium secretion. For phosphate, individual tubules from a single bird were capable of either net absorption or net secretion. Mean fractional delivery of phosphate for all tubules was 1.62, but secretion rates apparently can exceed filtration rates for phosphate by as much as 6 times.