Toad

About: Toad is a research topic. Over the lifetime, 1624 publications have been published within this topic receiving 28732 citations.

Glyoxylate cycle in toad urinary bladder: possible stimulation by aldosterone.

Abstract: A homogenate of the toad urinary bladder epithelial cell layer has the two enzymatic activities unique to the glyoxylate cycle--isocitrate lyase (threo-Ds-isocitrate glyoxylate-lyase, EC 4.1.3.1) and malate synthase [L-malate glyoxylate-lyase (CA-acetylating), EC 4.1.3.2]--as well as the capacity to carry out CN-insensitive palmitoyl-CoA oxidation. When tissue is incubated in the presence of a fatty acid substrate, tissue glycogen levels increase. Additionally, in the presence of aldosterone, glycogen levels are higher. These data demonstrate the presence of glyoxylate cycle enzymes in tissue of a higher animal and raise the possibility that such tissue can convert lipid to carbohydrate.

Action of aldosterone and vasopressin on the active transport of sodium by the isolated toad bladder.

Abstract: Summaries – Résumés Action of aldosterone and vasopressin on the active transport of sodium by the isolated toad bladder By Crabbé, J. and Weer, P. de: J. Physiol., Lond. 180: 560-568 (1965). The isolated urinary bladder of the toad, Bufo marinus, was incubated in the presence, on its mucosal side, of 24Na and 14C-carboxyl inulin added to sodium-Ringer’s diluted to 1i5 with choline-Ringer’s. The serosal surface was exposed to straight sodium-Ringer’s. Active sodium transport by the tissue was stimulated upon removal of sodium from the animal environment, by treatment of the toad with aldosterone, or by addition to the incubation solution of vasopressin. The short-circuit current, taken as a reflection of active sodium transport in the experimental conditions selected, agreed closely with the flux of 24Na from the mucosal to the serosal surface of the membranes. The amount of radioactive sodium in toad-bladder tissue was found, after correction for sodium present in the inulin space on the mucosal side, to be directly proportional to the short-circuit current in the case of untreated bladders. The results obtained with membranes stimulated by the above treatments conformed with the same current-tissue sodium relation. It is concluded that aldosterone and vasopressin alter the diffusion barrier at the mucosal surface of the cells to allow more sodium to reach the sodium ‘pump’ at the serosal surface. Author’s address: Dr. J. Crabbé. Section of Endocrinology, Laboratory of Experimental Surgery, University Clinics St. Pierre, L·ouvain (Belgium). Effects of spinal section and renal denervation on the renal response to blood volume expansion By Pearce, J.W. and Sonnenberg, H.: Canadian J. Physiol. Pharmacol. 43: 211 (1965). Expansion of the blood volume with ‘artificial blood’ infusion was previously shown to cause diuresis and natriuresis in anaesthetized dogs (1). As the magnitude of response was related to the state of prehydration as reflected in some parameter other than the initial or expanded blood volume, the possibility of extravascular fluid volume receptors was considered. In the present work, artificial blood infusion failed to produce increased renal excretion in chronic high-spinal dogs. This observation was considered best explained as the result of interruption of nervous pathways essential to a reflex mechanism. In other dogs, unilateral renal denervation did not significantly alter the time course of response or the magnitude of the diuresis, but did result in a reduced natriuresis. As there was no qualitative difference between the responses of the innervated and denervated kidneys in each animal, it is concluded that renal motor nerve supply is not involved in the effector limb of the reflex, which must then be humoral. Bilateral renal denervation led to a marked reduction in natriuretic response to infusion and, while not reducing the diuretic response, significantly delayed the maximum increase in urine flow. These effects, like those of spinal section, are attributed to the loss of sensory pathways. The hypothesis is advanced that receptors of extracellular fluid volume with spinal 64 Summaries – Resumes

Electrophoretic Analysis of Axonally Transported Proteins in Toad Retinal Ganglion Cells

Abstract: As a preliminary step to studying changes in axonal transport in regenerating neurons, we have analyzed the composition and organization of polypeptides normally axonally transported in a neuronal system capable of regeneration, i.e., the retinal ganglion cells of the toad, Bufo marinus. We labeled proteins synthesized in the retina with 35S-methionine and subsequently used one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis to analyze labeled, transported proteins in tissues containing segments of the axons (the optic nerve, optic tract, and optic tecta) of the retinal ganglion cells. The transported polypeptides could be divided into five groups according to their apparent transport velocities. Many of the polypeptides of each group were electrophoretically similar to polypeptides of corresponding groups previously described in rabbit and guinea pig retinal ganglion cells, and in some cases, additional properties of the polypeptides indicated that the transported materials of the two vertebrate classes were homologous. These results serve two purposes. First they establish the retinal ganglion cells of the toad Bufo marinus as a model system in which changes in gene expression related to regeneration may be studied. Second they show that the organization and many aspects of the composition of axonal transport in retinal ganglion cells have been conserved in animals as unrelated as amphibians, and mammals.

Cloning and Functional Characterization of the Amphibian Mesotocin Receptor, a Member of the Oxytocin/Vasopressin Receptor Superfamily

Abstract: Mesotocin is the oxytocin-like hormone found in most terrestrial vertebrates from lungfishes to marsupials, which includes all non-mammalian tetrapods (amphibians, reptiles, and birds). It has the largest distribution in vertebrates after vasotocin found in all non-mammalian vertebrates and isotocin identified in bony fishes. In this study, we report the cloning and functional characterization of the cDNA for the mesotocin receptor (MTR) from the urinary bladder of the toad Bufo marinus. The cloned cDNA encodes a polypeptide of 389 amino acids that shows the greatest similarity to the teleost fish isotocin receptor and to mammalian oxytocin receptors with mutations in extracellular loops which are involved in ligand binding. When expressed in COSM6 cells, MTR exhibits the following relative order of ligand affinity: mesotocin > vasotocin = oxytocin > vasopressin > hydrin 1, isotocin, hydrin 2. Injection of MTR cRNA into Xenopus laevis oocytes induces membrane chloride currents in response to mesotocin, which indicates the coupling of the mesotocin receptor to the inositol phosphate/calcium pathway. This response is inhibited by an oxytocin antagonist, but not by a vasopressin antagonist specific for V2 vasopressin receptors. MTR mRNA is not only found in toad urinary bladder, but also in kidney, muscle, and brain tissue of the toad as revealed by Northern blot analysis and reverse-transcriptase PCR. The results suggest a variety of functions for mesotocin and its receptor including, in particular, an involvement in the regulation of water and salt transport.