Evaporative water loss and oxygen uptake in two casque-headed tree frogs, Aparasphenodon brunoi and Corythomantis greeningi (Anura, Hylidae)

Evaporative water loss (EWL) and oxygen uptake ((V) over dot o(2)) was measured in two species of tree frogs with cranial co-ossification, Aparasphenodon brunoi and Corythomantis greeningi. Both species use their head to seal the entrance of bromeliads, tree holes or rocky crevices used as shelters. EWL was significantly reduced in sheltered individuals of both species as compared with those exposed nude to desiccation. EWL per unit area through the head surface was significantly lower than the body skin for A. brunoi but not for C., greeningi. EWL per unit surface area through C. greeningi body skin was about 50% that of A. brunoi, indicating a less permeable skin in the former species. The relationship between cranial coossification and EWL is discussed. ((V) over dot o(2)) in A. brunoi was comparable with other anurans of similar size, whereas in C. greeningi, it was lower than predicted from body mass. Moreover, ((V) over dot o(2)), in C. greeningi showed less sensitivity to temperature increase than in A. brunoi. C. greeningi occurs in a drier environment than A. brunoi, and this appears to be reflected in their EWL and ((V) over dot o(2)) characteristics. (C) 1997 Elsevier B.V.

Oxygen-uptake in snakes - is there a reduction in fossorial species

Oxygen uptake of the fossorial blind snake (Typhlops reticulatus) and the semifossorial coral snake (Micrurus ibiboboca) was measured at 20 and 30 degrees C. Oxygen uptake of blind snakes was within the normal range, whereas oxygen uptake of coral snakes was in the lower end of values reported for snakes. The results do not support the hypothesis of reduced oxygen uptake in fossorial reptiles.

ONTOGENIC VARIATION OF OXYGEN-UPTAKE IN THE PITVIPER BOTHROPS MOOJENI (SERPENTES, VIPERIDAE)

The scaling of oxygen uptake was measured along the ontogeny, in the neotropical pitviper Bothrops moojeni. Allometric relationship between oxygen uptake and body mass, quantified for juveniles, sub-adults and adults, showed the same mass coefficient and exponent. The uniformity of mass constants along ontogeny suggests that B. moojeni is energetically homomorphic. Variation in mass seem to be the sole determinant of oxygen uptake, and structural modifications have no effect on the metabolic rate. Applications of the homomorphism principle to assess variations in mass coefficient and exponent for intraspecific analysis of metabolism in reptiles are discussed. B. moojeni had an oxygen consumption in the range reported for viperids, but lower than that for colubrid snakes of similar size. Possible causative reasons for this pattern is discussed.

LOW-PROTEIN DIET IMPAIRS GLUCOSE-INDUCED INSULIN-SECRETION FROM AND CA-45 UPTAKE BY PANCREATIC RAT ISLETS

Glucose-induced insulin secretion rom and Ca-45 uptake by isolated pancreatic islets, derived from rats fed with normal (NPD) or low protein diet (LPD), were studied. Insulin secretion from both types of islets in response to increasing concentrations of glucose followed an S-shaped pattern. However, basal secretion observed at substimulatory concentrations of glucose (0-5.6 mM), as well as maximal release, obtained at 16.7 mM or higher glucose concentrations were significantly reduced in islets from LPD. Furthermore, in LPD rat islets, the dose-response curve to glucose was clearly shifted to the right compared with NPD islets, with the half-maximal response occurring at 8.5 and 14.4 mM glucose for NPD and LPD islets, respectively. In islets from NPD rats, the Ca-45 content, after 5 or 90 min in the presence of 8.3 mM glucose, was higher than that observed for islets kept at 2.8 mM glucose and increased further at 16.7 mM glucose. After 5 min of incubation, the Ca-45 uptake by LPD islets in the presence of 8.3 mM glucose was slightly higher than basal values (2.8 mM glucose); however, no further increase in the Ca-45 uptake was noticed at 16.7 mM glucose. In LPD islets a significant increase in Ca-45 uptake over basal values was registered only at 16.7 mM glucose, after 90 min of incubation. These data indicate that the poor secretary response to glucose observed in islets from LPD rats may be related to a defect in the ability of glucose to increase Ca2+ uptake and/or to reduce Ca2+ efflux from beta-cells.

Trypanosoma cruzi: identification and characterization of a novel ribosomal protein L27 (TcrL27) that cross-reacts with an affinity-purified anti-Sm antibody

Small nuclear ribonucleoproteins (snRNPs)are involved in trans-splicing processing of pre-mRNA in Trypanosoma cruzi. To clone T. cruzi snRNPs we screened an epimastigote cDNA library with a purified antibody raised against the Sm-binding site of a yeast sequence. A clone was obtained containing a 507 bp-insert with an ORF of 399 bp and coding for a protein of 133 amino acids. Sequence analysis revealed high identity with the L27 ribosomal proteins from different species including: Canis familiaris, Homo sapiens, Schizosaccharomyces pombe and Saccharomyces cerevisiae. This protein has not been previously described in the literature and seems to be a new ribosomal protein in T. cruzi and was given the code TcrL27. To express this recombinant T. cruzi L27 ribosomal protein in E. coli, the insert was subcloned into the pET32a vector and a 26 kDa recombinant protein was purified. Immunoblotting studies demonstrated that this purified recombinant protein was recognized by the same anti-Sm serum used in the library screening as well as by chagasic and systemic lupus erythemathosus (SLE) sera. Our results suggest that the T. cruzi L27 ribosomal protein may be involved in autoimmunity of Chagas disease.

Yield and nitrogen uptake of peanuts as affected by lime, cobalt, and molybdenum

Peanut response to lime has been associated to calcium (Ca) nutrition, but a higher nitrogen (N) uptake has been observed in limed plots probably due to an increase in molybdenum (Mo) availability. A two-year experiment was conducted to study the effects of Mo, cobalt (Co), and liming on peanut yields and N nutrition. Peanut seeds were treated with Mo and/or Co and grown in soil with base saturation about 13, 41, 57, and 71%. There was no effect of seed treatment with Co on peanut yields or N nutrition. Liming and Mo application increased N contents in the leaves. Nitrogen uptake was increased by Mo and liming in cv. Tatu and only by liming in cv. Tupa. Manganese (Mn) contents in the leaves were decreased by liming. The higher yields were observed when the Ca/Mn ratio in the leaves was above 25. In acid soils, low availability of Mo and Mn toxicity can impair N acquisition by peanut plants and decrease grain yields.

Thiabendazole uptake and persistence in lemons following postharvest dips at 50 degrees C

Thiabendazole (TBZ) uptake and degradation rate in lemon fruits, following prestorage dipping at 50 degrees C in mixtures containing different amounts of fungicide, was compared with those measured after treatment at standard room temperature. TBZ residues were strictly dependent upon the amount of fungicide. Following 1,200 ppm TBZ dipping at 20 degrees C residue uptake in fruit was the same that would have been accumulated with ca. 150 ppm fungicide at 50 degrees C, a value that can be calculated due to the linear relationship between the residue in fruit after treatment and fungicide concentration TBZ residues showed great persistence during fruit storage: after 13 weeks at 8 degrees C and 1 week at 20 degrees C residues in fruit averaged ca. 70% of their initial values. In this study it was shown that it is possible to employ remarkably low amounts of TBZ (ca. 150 mg kg(-1)), when applied in combination with water at 50 degrees C, and keep the same residues of fruit treated at room temperature with high amounts of TBZ (1,200 mg kg(-1)).

MODULATION OF PARASITEMIA AND ANTIBODY-RESPONSE TO TRYPANOSOMA-CRUZI BY CYCLOPHOSPHAMIDE IN CALOMYS-CALLOSUS (RODENTIA, CRICETIDAE)

Calomys callosus a wild rodent, previously described as harboring Trypanosoma cruzi, has a low susceptibility to infection by this protozoan.Experiments were designed to evaluate the contribution of the immune response to the resistance to T. cruzi infection exhibited by C. callosus. Animals were submitted to injections of high (200 mg/kg body weight) and low (20 mg/kg body weight) doses of cyclophosphamide on days -1 or -1 and +5, and inoculated with 4 x 10(3) T. cruzi on day O. Parasitemia, mortality and antibody response as measured by direct agglutination of trypomastigotes were observed. Two hundred mg doses of cyclophosphamide resulted in higher parasitemia and mortality as well as in suppression of the antibody response. A single dose of 20 mg enhanced antibody levels on the 20th day after infection, while an additional dose did not further increase antibody production. Parasitemia levels were not depressed, but rather increased in both these groups as compared to untreated controls. Passive transfer of hyperimmune C. callosus anti-T. cruzi serum to cyclophosphamide immunosuppressed animals resulted in lower parasitemia and mortality rates. These results indicate that the immune response plays an important role in the resistance of C. callosus to T. cruzi.

CIRCADIAN OSCILLATORY PATTERNS OF OXYGEN-UPTAKE IN INDIVIDUAL WORKERS OF THE ANT CAMPONOTUS-RUFIPES

Respiratory rates of individual workers of Camponotus rufipes Fabricius (Hymenoptera: Formicidae) were measured at 25-degrees-C and LD 12:12 h (lights on 06.00 hours), DL 12:12 h (lights on 18.00 hours), LL (850 lux) and DD (red light, 20-30 lux), using the micro-Warburg technique. Worker ants were collected from natural nest during the winter of 1987 in a woodland park in the region of Rio Claro, São Paulo, Brazil. The respiration of ants showed a circadian rhythm with acrophase ranging from 20 h 41 min to 01 h 18 min and from 10 h 32 min to 12 h 22 min at LD and DD, respectively. In constant darkness the rhythmometric variables were similar to those presented by ants kept at LD 12:12 h. Under constant light no circadian rhythm in the respiration rates was found. A reduction in the amplitude was observed, indicating an inhibitory effect of this light regime on the respiration process.

RESPONSE TO TEMPERATURE IN THE OXYGEN-UPTAKE OF AWAKE AND DORMANT FROGS (AMPHIBIA, LEPTODACTYLIDAE)

In southeastern Brazil the leptodactylid frogs Leptodactylus fuscus and Physalaemus fuscomaculatus enter dormancy during the dry season. Oxygen uptake was measured in awake and dormant groups of both species in a temperature range at which these frogs are usually exposed throughout the year. Oxygen uptake was lower for dormant groups at high temperature, and a lack of response to temperature was reported between 20 - 25 C in the dormant group of both species. This temperature-intensitive range can be considered an adaptive feature to save fat reserves during dormancy.