Toad

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

Decreased effectiveness of aldosterone on active sodium transport by the isolated toad bladder in the presence of other steroids.

Abstract: Aldosterone can stimulate the active transport of sodium by the isolated toad bladder in vitro. Corticosterone, cortisol, 17\g=b\-oestradioland progesterone had no such effect despite incubation of the preparation with more than 100 times the smallest effective concentration of aldosterone. When the serosal surface of the membranes was exposed to 10 \g=m\g% d\x=req-\ aldosterone combined with 100 times this concentration of corticosterone, cortisol or progesterone, the stimulating action of aldosterone was reduced. Spirolactone SC 9420 failed to exert by itself a significant effect on the isolated toad bladder in vitro, but this compound blocked the stimulation by aldosterone of active sodium transport in vitro when present at concentrations 50 times those of aldosterone. When the concentration ratio was 10:1, a hormonal effect could be demonstrated, except at the highest concentration of the drug used. Stimulation of the active transport of sodium has been observed on exposure of the serosal surface of the urinary bladder of the toad, Bufo marinas, to aldosterone in vitro (Crabbé 1961 b). It therefore seemed appropriate to deter¬ mine whether other steroid hormones, capable of inducing sodium retention when injected into mammals, had properties analogous to those of aldosterone on this preparation. * Work done during tenure of a Research Fellowship of the Helen Hay WhitneyFoundation, 1959-1962. Present address: Laboratory of experimental Surgery (Section on Endocrinology), Hôpital St. Pierre, Louwain, Belgium. Downloaded from Bioscientifica.com at 12/01/2018 11:12:48AM via free access The possibility of interference on the part of some steroids with the action of aldosterone as a sodium-retaining agent at the renal tubule site, was also thought worthy of evaluation by means of the toad bladder preparation which presumably allows a more direct experimental approach to such a problem, than studies involving the the whole animal. The urinary bladder of the toad is morphologically a simple biological membrane capable of transporting sodium from its mucosal to its serosal surface in the absence of an electro¬ chemical potential gradient for this ion (Leaf et al. 1958), and this active process can be conveniently and accurately measured by the short-circuit current method of Ussing 8c Zerahn (1951). Aldosterone excepted, none of the steroid hormones used so far has proved capable of a significant stimulation of active sodium transport by the isolated toad bladder in vitro. In the presence of relatively large concentration of some of them, however, the effect of aldosterone on sodium transport was weakened. A steroidal spirolactone, devoid by itself of a demonstrable effect on the preparation, blocked at suitable concentrations the stimulation of active sodium transport induced by aldosterone. MATERIALS AND METHODS Toads Bufo marinus, were used, of both sexes. They were maintained half-immersed in water for at least 2 days prior to sacrifice, because this procedure was found to enhance the response of their urinary bladders to aldosterone (Crabbé 1961 b). After pithing the animal, both bladder halves were mounted in rapid succession as dia¬ phragms between lucite chambers (inner diameter 20 mm) for measurements of transmembrane potential and short-circuit current during incubation of the paired mem¬ branes in aerated frog Ringer's solution.* All readings were corrected for junction potentials. Solutions of ¿-aldosterone in frog Ringer's fluid ranged in concentration of from 2 X IO-7 m (7.2 «g/100 ml) to 5 X 10-° m (180 /tg/100 ml). Progesterone, cortisol. corticosterone and 17/?-oestradiol, all sparingly hydrosoluble in the alcoholic form, were first dissolved in ethanol added in amounts such that its final concentration in in¬ cubation fluid did not exceed 0.1 % (v/v). Under these conditions ethanol inhibited neither the action of aldosterone on sodium transport nor the transmembrane potential. At any rate, whenever a solution containing ethanol was used, both membranes serving for the paired experiment were exposed to it. Spirolactone SC 9420 was dissolved in frog Ringer's fluid; at saturation, such solutions contain approximately 5 X 10~5M (2.1 mg/100 ml) of the substance, as indicated by measurements performed with a fluorometric method (Gochman Sc Gantt 1962). The steroids were added at the beginning of the experiments to the solution on the serosal surface of the membrane. Incubation, carried out at room temperature lasted at least 3 hours before addition, in some instances, of 0.5 or LO U commercial vasopressin (Pitressin, Parke, Davis and Co.) to the solution to which the serosal sur* Composition in miu/litre: NaCl, 115; NaHCO:î, 2.5; KC1, 2.0; CrCl,, 1.0. Downloaded from Bioscientifica.com at 12/01/2018 11:12:48AM via free access face of the toad bladder was exposed; measurements were then made at short intervals for an additional 20-minute period. After completion of the incubation, the bladder tissue was blotted and weighed. One series of 8 toads received a subcutaneous injection of 50 /tg ¿/-aldosterone 21 monoacetate, in 0.05 ml ethanol diluted to 0.25 ml with frog Ringer's fluid, 16-20 hours before sacrifice. In order to find out if aldosterone could be displaced from the toad bladder tissue by other steroids, the following experiment was carried out. Toad bladder tissue was immersed in 3 tubes containing 7-3H d-aldosterone (S. .: 20 μ /μ ) at a concentra¬ tion of 10-8 M in aerated frog Ringer's fluid with 0.25% ethanol (v/v). In addition, corticosterone was present in one of the tubes, and SC 9420 in another one, the con¬ centration of both steroids being 2.5 X IO-4 M. After incubation for 4 hours, the pieces of tissue

Effect of Chlorpropamide on the Permeability of the Urinary Bladder of the Toad and the Response to Vasopressin, Adenosine-3″,5″-monophosphate and TheophyUine

Abstract: Chlorpropamide, which is reported to decrease urine volume and promote the formation of hypertonic urine in patients with pituitary diabetes insipidus, has no effect on the osmotic permeability of the urinary bladder of the toad, Bufo marinus. The sulfonylurea compound markedly potentiates the effect of vasopressin and theophylline, both of which increase the osmotic permeability of the toad bladder by increasing the intracellular concentration of cyclic 3′,5′-AMP. Unexpectedly, the response of the toad bladder to exogenous cyclic 3′,5′-AMP is inhibited by chlorpropamide. Therefore, the mechanism of action of chlorpropamide remains obscure. Nevertheless, it is clear that under certain conditions the drug does alter the permeability of vasopressin-sensitive tissues both in man and in the toad bladder. (Endocrinology 84: 411,1969)

Lack of teratogenicity of microcystin-LR in the mouse and toad

Abstract: Microcystin-LR (MC-LR) is a cyanobacterial toxin generated by the organism Microcystis aeruginosa. Although the hepatotoxicity of this chemical has been characterized, the potential developmental toxicity in vertebrates has not been well studied. The purpose of this study was to elucidate the effects of this toxin on the in vivo and in vitro development of mammals and the development of an Anuran (toad). Initial acute toxicity experiments with female CD-1 mice were accomplished with MC-LR administered i.p. in saline. Lethality occurred at 128 and 160 µg kg −1 and histopathology revealed massive hepatic necrosis with diffuse hemorrhage. Developmental toxicity studies were done with MC-LR administered i.p. for 2-day periods: gestation days 7–8, 9–10 or 11–12. Doses used ranged from 2 to 128 µg kg−1. On gestation day 17, fetuses were weighed and analyzed for gross morphological and skeletal defects. No treatment-related differences were seen in litter size, viability, weight or the incidence of anomalies. Groups of dams dosed with 32–128 µg kg−1 on gestation days 7–8, 9–10 or 11–12 were allowed to give birth and the growth and development of their pups were followed postnatally. There were no significant effects noted in the offspring of the treated dams. Neurulation-staged CD-1 mouse conceptuses were exposed to 50–1000 nM MC-LR in whole embryo culture for 24 h. No significant increase in abnormalities or developmental delays was observed. Finally, exposure of the developing toad. Bufo arenarum was done from stage 17 (tail bud) for 10 days at concentrations of 1–20 mg l−1. No effect on morphological development or survival was noted in any exposed groups. These data indicate that microcystin does not appear to affect development adversely in the mouse (in vivo or in vitro) or the toad at the doses and exposure parameters used. Copyright © 2002 John Wiley & Sons, Ltd.