Toad

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

Inhibition of vasopressin-stimulated prostaglandin E biosynthesis by chlorpropamide in the toad urinary bladder. Mechanism of enhancement of vasopressin-stimulated water flow.

Abstract: Chlorpropamide is known to enhance the water permeability response of the toad urinary bladder to vasopressin and to theophylline In other studies, we have shown that prostaglandin E synthesis by the toad bladder inhibits the water permeability response to arginine vasopressin and to theophylline In this study, the effect of chlorpropamide on vasopressin-, theophylline-, and cyclic AMP-stimulated water flow and on prostaglandin E biosynthesis was investigated in the toad urinary bladder in vitro Chlorpropamide inhibited prostaglandin E biosynthesis during vasopressin-, theophylline- and cyclic AMP-stimulated water flow Tolbutamide and glyburide, two other sulfonylurea compounds, also enhanced vasopressin-stimulated water flow and inhibited vasopressin-stimulated prostaglandin E biosynthesis We conclude that the mechanism of enhancement on vasopressin-stimulated water flow by the sulfonylureas is the inhibition of prostaglandin E biosynthesis

Urinary acidification and carbonic anhydrase distribution in bladders of Dominican and Colombian toads

Abstract: A comparative analysis of the acidifying capacity and distribution of carbonic anhydrase was made in isolated bladders of toads,Bufo marinus, obtained from the Dominican Republic (D) and Colombia (C). In the absence of exogenous CO2 and HCO3−, mucosal acidification was observed in 10 of the 18 C toad bladders examined and in only one of 18 D toad bladders. In approximately half of the C toad bladders the rate of acidification was measurable by means of the pH stat method; the average rate in this group was 0.22±0.03 μmoles/hour in the absence of exogenous CO2 and 0.35±0.04 μmoles/hour in the presence of 1% CO2. Rates were not measurable in D toad bladders with or without CO2. Staining of whole stretched bladders for carbonic anhydrase revealed a population of enzyme-containing mucosal cells accounting for 4.6% of the surface area in C toad bladders and 0.8% in D toad bladders. Electron histochemistry of both bladders identified the carbonic anhydrase-containing cells as mitochondria-rich cells.

A novel signalling pathway originating in mitochondria modulates rat skeletal muscle membrane excitability.

Abstract: Single skeletal muscle fibres from rat and cane toad were mechanically skinned and stimulated either electrically by initiating action potentials in the sealed transverse (t-) tubular system or by ion substitution causing depolarisation of the t-system to pre-determined levels. Depression of mitochondrial ATP-producing function with three diverse mitochondrial function antagonists (azide: 1-10 mM; oligomycin 1 microg ml-1 and carbonyl cyanide 4-trifluoromethoxyphenylhydrazone (FCCP) 1 microM), under conditions in which the cytosolic ATP was maintained high and constant, invariably reduced the excitability of rat fibres but had no obvious effect on the excitability of toad fibres, where mitochondria are less abundant and differently located. The reduction in excitability linked to mitochondria in rat fibres appears to be caused by depolarisation of the sealed t-system membrane. These observations suggest that mitochondria can regulate the functional state of mammalian muscle cells and have important implications for understanding how the balance between ATP utilisation and ATP production is regulated at the cellular level in general and in mammalian skeletal muscle fibres in particular.

A dynorphin-like opioid in the central nervous system of an amphibian.

Abstract: We have provided evidence for the existence of a biologically active opioid in toad (Bufo marinus) brain that is immunoreactive with antiserum raised against dynorphin (1-13). Compared with porcine dynorphin, this opioid is similar in apparent molecular weight on the basis of gel permeation chromatography and is more hydrophobic on the basis of high-performance liquid chromatography. After purification, its opioid biological activity was demonstrated on the guinea pig ileum myenteric plexus-longitudinal muscle preparation. It was found to be less potent, and to have a similar sensitivity to antagonism by naloxone, in comparison with porcine dynorphin. Because it is immunoreactive with antiserum specific for porcine dynorphin, it probably has considerable sequence homology. Generally, the tissue distribution of immunoreactive dynorphin in the toad is similar to that in the rat, with highest concentrations in the neurointermediate lobe of the pituitary. However, the anterior lobe of the toad pituitary contains considerably lower concentrations than are found in the rat anterior lobe. There appear to be three size classes of immunoreactive dynorphin in toad neural tissue, each with apparent molecular weight below 12,000, similar to the size classes of immunoreactive dynorphin found in pig and rat. However, in toad spinal cord (and possibly in brain) there is immunoreactive dynorphin of greater apparent molecular weight, which has not been reported in mammalian tissue. The contribution of each molecular size to the total immunoreactivity varies from tissue to tissue and is different from that observed in the rat.