Colostomy of the duck (Anas platyrhynchos): A surgical technique and an assessment of its chronic effects on osmotic balance

Genetic rescue of Leishmania deficiency in porphyrin biosynthesis creates mutants suitable for analysis of cellular events in uroporphyria and for photodynamic therapy

Leishmania was found deficient in at least five and most likely seven of the eight enzymes in the heme biosynthesis pathway, accounting for their growth requirement for heme compounds. The xenotransfection of this trypanosomatid protozoan led to their expression of the mammalian genes encoding delta-aminolevulinate (ALA) dehydratase and porphobilinogen deaminase, the second and the third enzymes of the pathway, respectively. These transfectants still require hemin or protoporphyrin IX for growth but produce porphyrin when ALA was supplied exogenously. Leishmania is thus deficient in all first three enzymes of the pathway. Uroporphyrin I was produced as the sole intermediate by these transfectants, further indicating that they are also deficient in at least two porphyrinogen-metabolizing enzymes downstream of porphobilinogen deaminase, i.e. uroporphyrinogen III co-synthase and uroporphyrinogen decarboxylase. Pulsing the transfectants with ALA induced their transition from aporphyria to uroporphyria. Uroporphyrin I emerged in these cells initially as diffused throughout the cytosol, rendering them sensitive to UV irradiation. The porphyrin was subsequently sequestered in cytoplasmic vacuoles followed by its release and accumulation in the extracellular milieu, concomitant with a reduced photosensitivity of the cells. These events may represent cellular mechanisms for disposing soluble toxic waste from the cytosol. Monocytic tumor cells were rendered photosensitive by infection with uroporphyric Leishmania, suggestive of their potential application for photodynamic therapy.

Heme metabolism of Plasmodium is a major antimalarial target

The malarial parasite manifests unique features of heme metabolism. In the intraerythrocyte stage it utilizes the host hemoglobin to generate amino acids for its own protein synthesis, but polymerizes the acquired heme as a mechanism for detoxification. At the same time the parasite synthesizes heme de novo for metabolic use. The heme biosynthetic pathway of the parasite is similar to that of hepatocytes and erythrocytes. However, while the parasite makes its own delta-aminolevulinate (ALA) synthase that is immunochemically different from that of the host, it imports ALA dehydrase and perhaps the subsequent enzymes of the pathway from the host red cell. Many schizonticidal drugs such as chloroquine and artemisinin act by interfering with the heme metabolism of the parasite and there is scope to design new molecules based on the unique features of this metabolic machinery in the parasite.

Metabolism of aldosterone in the colostomized duck (Anas platyrhynchos): partial characterization of urinary metabolites

1. Chronically colostomized ducks were injected with [4-14C]-aldosterone to study the metabolism of aldosterone and the pattern of metabolite excretion via the kidney. 2. Nearly half of the injected dose was excreted as radiometabolites during the first 24 hr; the largest amounts being excreted during the first 3 hr after injection. 3. Ion-exchange chromatography showed that monosulfate, disulfate, glucuronide, acidic, and neutral metabolites were excreted during each collection period, and that their relative proportions changed with time after injection of [4-14C]-aldosterone. 4. HPLC analysis of the neutral radiometabolites revealed 15 major peaks with retention times corresponding to both polar and reduced derivatives of aldosterone. 5. Only small quantities of unaltered labelled aldosterone were excreted. 6. Treatment of the birds with SKF 525-A caused a decrease in the total quantity of radiometabolite excreted and a change in the proportions of neutral and acidic metabolites in the cloacal fluid. 7. The decreases that occurred in the absolute amounts of some of the polar metabolites excreted by the birds treated with SKF-525A suggests that they may be hydroxylated and at least part of the aldosterone metabolizing system in the duck is cytochrome P450 dependent.

Differential energetic metabolism during Trypanosoma cruzi differentiation. I. Citrate synthase, NADP-isocitrate dehydrogenase, and succinate dehydrogenase

The activities of the mitochondrial enzymes citrate synthase (citrate oxaloacetatelyase, EC 4.1.3.7), NADP-linked isocitrate dehydrogenase (threo-Ds-isocitrate:NADP+ oxidoreductase (decarboxylating), EC 1.1.1.42), and succinate dehydrogenase (succinate: FAD oxidoreductase, EC 1.3.99.1) as well as their kinetic behavior in the two developmental forms of Trypanosoma cruzi at insect vector stage, epimastigotes and infective metacyclic trypomastigotes, were studied. The results presented in this work clearly demonstrate a higher mitochondrial metabolism in the metacyclic forms as is shown by the extraordinary enhanced activities of metacyclic citrate synthase, isocitrate dehydrogenase, and succinate dehydrogenase. In epimastigotes, the specific activities of citrate synthase at variable concentrations of oxalacetate and acetyl-CoA were 24.6 and 26.6 mU/mg of protein, respectively, and the Michaelis constants were 7.88 and 6.84 microM for both substrates. The metacyclic enzyme exhibited the following kinetic parameters: a specific activity of 228.4 mU/mg and Km of 3.18 microM for oxalacetate and 248.5 mU/mg and 2.75 microM, respectively, for acetyl-CoA. NADP-linked isocitrate dehydrogenase specific activities for epimastigotes and metacyclics were 110.2 and 210.3 mU/mg, whereas the apparent Km's were 47.9 and 12.5 microM, respectively. No activity for the NAD-dependent isozyme was found in any form of T. cruzi differentiation. The particulated succinate dehydrogenase showed specific activities of 8.2 and 39.1 mU/mg for epimastigotes and metacyclic trypomastigotes, respectively, although no significant changes in the Km (0.46 and 0.48 mM) were found. The cellular role and the molecular mechanism that probably take place during this significant shift in the mitochondrial metabolism during the T. cruzi differentiation have been discussed.

Effects of aldosterone and corticosterone on cloacal water and electrolyte excretion of constantly-loaded intact and colostomized ducks (Anas platyrhynchos)

1. Doses of aldosterone (50, 100 and 200 micrograms per kg body wt) evoked similar changes in Na+ and K+ excretion by intact and colostomized ducks loaded with either distilled water or 0.5 isotonic saline (70 mM NaCl, 1.5 mM KCl); both antinatriuretic and antikaliuretic responses were observed. 2. The lowest dose of aldosterone had no effect on electrlyte excretion in intact and colostomized ducks loaded with a solution containing more K+ than Na+ (74 mM KCl, 36 mM NaCl) but the higher doses caused an antinatriuretic response in both groups; a retention of K+ occurred only in intact birds given this solution. 3. The lower dose of corticosterone (1.25 mg per kg body weight) caused both antidiuresis and antinatriuresis in intact birds, but in colostomized birds the decrease in Na+ excretion was not accompanied by an antidiuresis. 4. The higher dose of corticosterone (2.50 mg per kg body wt) caused a significant increase in K+ excretion in colostomized birds, whereas no kaliuresis was ever observed in intact birds. 5. Intact and colostomized birds loaded with 0.5 isotonic saline showed no responses to the lower dose of corticosterone, whereas the higher dose had an antikaliuretic effect in intact birds and an antinatriuretic effect in colostomized birds. 6. Corticosterone had no effect on cloacal water and electrolyte excretion by intact and colostomized birds given loads containing more K+ than Na+.

Patterns of cloacal water and electrolyte excretion in constantly-loaded intact and colostomized ducks (Anas platyrhynchos)

1. The patterns of cloacal water and electrolyte excretion were qualitatively similar in intact and chronically colostomized ducks given oral loads of either distilled water or electrolyte solution. 2. The rates of Na+ and K+ excretion were each selectively increased in birds loaded with solutions containing a relatively higher concentration of each ion. 3. Compared to the intact birds, the colostomized birds showed lower rates of electrolyte excretion following administration of identical electrolyte loads and thus appeared to be retaining electrolyte. 4. At the same time, a significant antidiuresis of similar magnitude occurred in each group of saline-loaded birds. 5. The possible contributions of renal and post-renal mechanisms to the overall conservation of water in intact and colostomized ducks are discussed.