Domingos Valente

A tetrodotoxin-like substance found in the Brazilian frog Brachycephalus ephippium

A tetrodotoxin-like substance, denoted ephippiotoxin, was obtained from the tissue of Brachycephalus ephippium, a small pumpkin-coloured frog collected in the Atlantic Forest of the southeast region of Brazil. Ephippiotoxin is a dialyzable substance soluble in water, methanol and ethanol, but insoluble in organic solvents such as chloroform and other apolar solvents. After treatment with active charcoal (Norit-A) and purification with ion-exchange Amberlite IRC-50 resin (NH4 + form), a freeze-dried residue was obtained, with a toxicity of c. 117 micrograms/kg (mice, i.p.). Ephippiotoxin showed the same mobility as crystalline tetrodotoxin (Sankyo) when submitted to thin-layer chromatography (silica gel G) using seven different solvent systems. White mice (20 +/- 1 g) injected i.p. with either B. ephippium tissue extracts or semi-purified toxin showed partial paralysis of the hind limbs, lethargy, altered breathing rhythm and clonic convulsions. Death occurred within 1.5-30 min after injection, depending on the dose. Ephippiotoxin induced atrioventricular diastolic blockade in the toad heart. It also inhibited the response of toad striated muscle to direct and indirect electric stimulation and blocked the compound action potential of isolated frog sciatic nerve.

The respiratory metabolism of the lantern muscles of the sea urchin Echinometra lucunter L.-I. The respiratory intensity

Abstract 1. 1. The respiratory rates of the lantern muscles of the sea urchin Echinometra lucunter L. were measured at 25°C in different combinations of muscle integrity, oxygen tension and suspending medium. 2. 2. The results showed that, probably due to their low metabolism, it is irrelevant to respiration whether the isolated muscles, whole or scraped, in natural or artificial seawater, are exposed to air or to oxygen. 3. 3. The respiratory intensity of the lantern muscles is higher than that of the holothurian longitudinal muscles and this is explained by their being engaged in a more continuous activity.

Glycolytic and hexosemonophosphate enzyme activities in the lantern muscles of the sea urchins, Arbacia lixula (Linn.), Echinometra lucunter (Linn.) and Lytechinus variegatus (Lamarck)

Abstract 1. 1. Activities of nine glycolytic and related enzymes were measured in lantern muscle extracts of the echinoids Arbacia lixula, Echinometra lucunter and Lytechinus variegatus . 2. 2. The specific activities of these enzymes were comparatively low, being often the highest in L. variegatus and the lowest in A. lixula . The major differences referred to HK, PGK and G-6-PDH activities. 3. 3. Noticeable differences in LDH activities were recorded in comparison with other invertebrate muscles. The implications of these results are discussed.

A study on melanophore receptors of Papiliochromis ramirezi (teleostei, cichlidae)

Melanophores of Papiliochromis ramirezi aggregate their melanosomes in the presence of catecholamines. Their order of potency are: at 10(-4) M, norepinephrine greater than isoproterenol = epinephrine; at 10(-6) and 10(-8) M, norepinephrine = isoproterenol greater than epinephrine. These effects are antagonized not only by phentolamine but also by propranolol. The catecholamines are unable to induce pigment dispersion. Melanosome dispersion is obtained with cholinergic drugs and the order of potency is nicotine greater than acetylcholine = pilocarpine. Their effects are inhibited by atropine and also by d-tubocurarine and potentiated by physostigmine. The evidences suggest the presence of undifferentiated adrenoceptors, related to the melanosome aggregation and undifferentiated cholinoceptors related to the melanosome dispersion.

The acetylcholine contents of honeys from different bees as determined in four-point-assays

1. The acetylcholine contents of the honeys of the bees Apis mellifera, Melipona quadrifasciata, Tetragonisca jaty, Nannotrigona testaceicornis, Trigona crassipes, Trigona spinipes and Lestrimelita limao were determined in four-point assays, using the guinea-pigs ileum. 2. A preliminary dose-response assay, in each case, assured that the response of the preparation was linear for the dose of honey. 3. In the four-point assays, the analysis of variance showed that, in all cases, there was no significant variation between samples or doses of a same substance and that departures from linearity and parallelism were small. 4. The acetylcholine contents (in μg/g honey), calculated on the basis of the potencies found, were 45.72 (A. mellifera), 6.8 (M quadrifasciata), 12.04 (T. jaty), 12.57 (N. testaceicornis), 5.76 (T. crassipes), 21.15 (T. spinipes) and 26.45 (L. limao). 5. The variations found in acetylcholine content within or between species were attributed to either the pollen collected from different plant sources or differences in the efficiency of transfering the compound from pollen to honey.