Showing papers on "Toad published in 1978"

Ouabain-like activity in toad skin and its implications for endogenous regulation of ion transport

Abstract: THE demonstration that opium alkaloids of the plant kingdom mediate their effects on animals through specific receptors1 led to the discovery that endogenous molecules with opiate activity exist widely in animals2, including man. These studies raised the possibility that other potent pharmacological agents derived from plant sources might have active analogues in higher species. Thus, cardiac glycosides are found widely in the plant kingdom3; structurally similar compounds in the animal kingdom are known to exist only in the poison glands of certain toads3. The dried skins of Bufonid toads have been used in Chinese folk medicine for the treatment of cardiac failure4. Further, these poorly characterised medicinal preparations (Ch'an Su) were shown in the 1920s to contain ouabain-like compounds (bufotoxins) by chemical analysis5. However, although bufotoxins were shown to be a major constituent of the poison glands of Bufo marinus3 the possibility that similar compounds might also serve a physiological role apart from that of a defensive toxin was apparently not considered. More recently, two major observations make the consideration of such a physiological role seem reasonable. First, amphibian skin, which is a major organ for regulation of sodium and water homeostasis in these species6, has been shown to be rich in (Na+ + K+)-ATPase, the molecular mediator of sodium transport across the skin8. In fact, with toad bladder, amphibian skin has been widely used as a model of transepithelial ion transport in higher animals. Second, the pharmacological receptor for cardiac glycosides is now believed to be the (Na+ + K+)-ATPase9,10, glycoside binding to this enzyme resulting in inhibition of both ATPase activity11,12 and associated ion transport13,14. This glycoside–enzyme interaction is considered to be the basis for the cardiac stimulating activity10 for which glycosides such as ouabain and digoxin are used in the therapy of cardiac disorders. We report here that extracts of the skin of three different species of toad each contain high concentrations of a substance with all the functional properties of cardiac glycosides. The widespread existence of ouabain-like activity in an organ rich in physiologically important (Na+ + K+)-ATPase suggests a possible role for these endogenous compounds in the regulation of transepithelial ion transport.

Evidence for involvement of microtubules in the action of vasopressin in toad urinary bladder. I. Functional studies on the effects of antimitotic agents on the response to vasopressin.

Abstract: The antimitotic agents colchicine, podophyllotoxin, and vinblastine inhibit the action of vasopressin and cyclic AMP on osmotic water movement in the toad urinary bladder. The alkaloids have no effect on either basal or vasopressin-stimulated sodium transport or urea flux across the tissue. Inhibition of vasopressin-induced water movement is half-maximal at the following alkaloid concentrations: colchicine, 1.8 X 10(-6) M; podophyllotoxin, 5 X 10(-7)M; and vinblastine, 1 X 10(-7)M. The characteristics of the specificity, time-dependence and temperature-dependence of the inhibitory effect of colchicine are similar to the characteristics of the interaction of this drug with tubulin in vitro, and they differ from those of its effect on nucleoside transport. Inhibition of the vasopressin response by colchicine, podophyllotoxin, and vinblastine is not readily reversed. The findings support the view that the inhibition of vasopressin-induced water movement by the antimitotic agents is due to the interaction of these agents with tubulin and consequent interference with microtubule integrity and function. Taken together with the results of biochemical and morphological studies, the findings provide evidence that cytoplasmic microtubules play a critical role in the action of vasopressin on transcellular water movement in the toad bladder.

Evidence for involvement of microtubules in the action of vasopressin in toad urinary bladder

Abstract: Colchicine, podophyllotoxin, and vinblastine have been found to inhibit the action of vasopressin on water movement in the toad urinary bladder. Tubulin is the major colchicine binding component of toad bladder epithelial cells, accounting for approximately 3.3% of the total cell protein. More than 99% of the tubulin is found in the soluble fraction after sonication, the remainder is in the particulate fraction. Similar to the characteristics of the binding of colchicine to tubulins from other sources, the binding of colchicine to toad bladder tubulin is temperature- and time-dependent, is inhibited competitively by podophyllotoxin (K i =5.5×10−7 m), and has a binding constant of 1×106 liters/mole at 37°. Binding activity decays according to first-order kinetics and is stabilized by vinblastine. The characteristics of the interactions of colchicine and podophyllotoxin with epithelial cell tubulinin vitro closely parallel the ability of these drugs to inhibit the response to vasopressinin vitro. These results, coupled with those of functional and morphological studies, support the view that the ability, of these drugs to affect vasopressin-induced water movement across toad bladder epithelial cells is related to the depolymerization of cytoplasmic microtubules.

Role of prostaglandin E (PGE) in the modulation of the action of vasopressin on water flow in the urinary bladder of the toad and mammalian kidney.

Abstract: PGE1 and PGE2 are known to interfere with the water permeability effect of vasopressin in toad bladder and kidney. It has been proposed that endogenous prostaglandin E (PGE), synthesized within cells of vasopressin-sensitive tissues, serves to modulate the permeability changes elicited by the neurohypophyseal hormone. Direct evidence in support of this hypothesis is as follows: vasopressin increases the biosynthesis of PGE2 in renal interstitial cells and in isolated toad bladder. In the latter, inhibition of vasopressin-induced synthesis of PGE by a variety of inhibitors results in a greater water permeability response to vasopressin. It appears that vasopressin has two effects in toad bladder and kidney: (i) it activates adenylate cyclase thereby increasing the concentration of adenosine 3′,5′ monophosphate (cyclic AMP), the nucleotide responsible for the resultant increase in water permeability; and (ii) it activates a phospholipase that serves to release arachidonic acid, the precursor of PGE2 from intracellular pools. The PGE derived from the arachidonic acid diminishes adenylate-cyclase activity, in consequence of which the response of the enzyme to vasopressin is modulated.

Evidence for involvement of microtubules in the action of vasopressin in toad urinary bladder. III. Morphological studies on the content and distribution of microtubules in bladder epithelial cells.

Abstract: SummaryColchicine and other antimitotic agents have been found to inhibit the action of vasopressin and cyclic AMP on transcellular water movement in the toad bladder; functional and biochemical studies suggest that the effect of these agents is due to interference with microtubule function. To further assess this hypothesis, a quantitative ultrastructural analysis of the content and distribution of microtubules was performed on epithelial cells of bladders exposed to colchicine, vasopressin, and cyclic AMP. The content (volume density) of microtubules was estimated by a point-counting stereological technique. The results indicate that the content of assembled microtubules in the granular epithelial cells is reduced in hemibladders exposed to colchicine; this effect is dose-dependent and is estimated to be half-maximal at a colchicine concentration of 1.4×10−6m. In contrast, the content of assembled microtubules in the granular cells is slightly (∼30%) but significantly increased after exposure of hemibladders to vasopressin (100 mU/ml) or cyclic AMP (10mm). The content of microtubules in mitochondria-rich cells was not found to be significantly altered after exposure to vasopressin. The combined results of functional, biochemical, and morphological studies provide evidence that cytoplasmic microtubules in the granular epithelial cells play a critical role in the action of vasopressin on transcellular water movement in the toad bladder. Precisely how microtubules are involved in the action of the hormone remains to be determined.

Comparison of toad bladder aldosterone-induced proteins and proteins synthesized in vitro using aldosterone-induced messenger RNA as template.

Abstract: Using double-labeled isotope techniques, it can be shown that aldosterone induces the synthesis of several proteins in the mitochondria-rich (MR) cells of the toad's urinary bladder. Induced proteins have been identified both in the plasma membrane (mol wt=170,000, 85,000 and 12,000) and the cytosol (mol wt=36,000, 12,000 and 6,000) fractions of these mucosal cells. We have also shown that aldosterone (Aldo) induces the synthesis of a class of RNA having the properties of messenger RNA (mRNA). mRNA isolated from Aldo-treated mucosal cells was used as template in a cell-free protein-synthesis system prepared from rabbit reticulocytes. Preparations charged with mRNA from Aldotreated cells synthesized two proteins that were not labeled when mRNA from control tissues was used as template. The electrophoretic mobility of one of these proteins was similar to an Aldo-induced membrane protein (mol wt=70,000) found in the intact tissue.

Cholinergic agents inhibit sodium transport across the isolated toad bladder.

Abstract: Acetylcholine and carbamylcholine (carbachol) inhibited sodium transport across the toad bladder. This effect was blocked by atropine. Carbachol increased the uptake of 45Ca by isolated toad bladder epithelial cells. This increased 45Ca uptake was blocked by atropine, pentobarbital, or lanthanum chloride. The inhibitory effect of cholinergic agents on sodium transport was dependent on external calcium concentration and was abolished by decreasing external calcium from 2 to 0.2 mM or by agents (pentobarbital, lanthanum chloride) which prevent the movement of calcium into cells. Carbachol increased modestly, but significantly, the levels of cyclic GMP in isolated toad bladder epithelial cells. This effect was blocked by atropine. Whether the decrease in sodium transport produced by cholinergic agents is the result of increased intracytoplasmic calcium levels, increased cyclic GMP levels, or a combination of both remains to be established.

Partial characterization of pepsins and gastricsins and their zymogens from human and toad gastric mucosae.

Abstract: 1. 1. Three zymogens have been isolated from human gastric mucosae and two from the stomachs of the toad Caudiverbera caudiverbera. 2. 2. Human zymogens I and III were immunologically related and cross-reacted with antisera prepared against porcine pepsinogen. The third, (II), showed no cross-reactivity. 3. 3. Human zymogens I and III and toad zymogen ZII gave rise to two human pepsins and to a pepsin-like enzyme, respectively. 4. 4. Human zymogen II (gastricsinogen) and toad zymogen ZI gave rise to human gastricsin and to a gastricsin-like enzyme respectively. 5. 5. The toad enzymes showed much greater stability at neutral and alkaline pH values than the human enzymes.

Simultaneous monitoring by optical techniques of respiratory chain and intracellular pH in toad ventricle strip

Abstract: Intracellular pH and oxidative metabolism can be measured in toad ventricle strips simultaneously by the use of the pH indicator dye, neutral red, and a rapid scanning spectrophotometer. The effects of hypoxia and acidification on mechanical function are approximately additive. The decrease in tension due to slight acidification is probably through an effect on the portion of the twitch tension supported by anaerobic metabolism.

Genome size in the green toad (Bufo viridis) group

Abstract: Specimens of the green toad,Bufo viridis, from Morocco to Kirgizistan, have identical DNA amounts per erythrocyte nucleus. 1 specimen from Kirgizistan is a tetraploid. Of 3 closely related species,B. calamita andB. brongersmai have about the same DNA amount asB. viridis, whileB. latastii from Afghanistan has 36% more DNA per nucleus.

Cellular and shunt conductances of toad bladder epithelium.

Abstract: Toad urinary bladders were mounted in Ussing-type chambers and voltage-clamped. At nonzero voltages only, small fluctuations in current, ΔI, and therefore in tissue conductance, ΔG t, were detected. These fluctuations were caused by the smooth muscle of the underlying tissue which could be monitored continuously and simultaneously with the current,I. Inhibition of the smooth muscle contraction with verapamil (2×10−5 m) abolished the fluctuations inI andG t. Amiloride (10−4 m) had no significant effect on the magnitude of ΔG t, oxytocin increasedG t without affecting ΔG t, and mucosal hypertonicity produced by mannitol increased ΔG t. These results are consistent with the hypothesis that two parallel pathways exist for passive current flow across the toad urinary bladder: one, the cellular pathway, was not affected by smooth muscle activity; the other, the paracellular pathway, was the route whose conductance was altered by the action of the smooth muscle. Thus the relationship between the cellular and shunt conductances of the epithelium of the toad urinary bladder, under a variety of conditions, can be investigated by utilizing the effects of the movement of the smooth muscle.

Transport Across Insect Gut Epithelium

Abstract: Transport processes in vertebrates have been studied intensively, and very careful studies have been made on the transport of Na through the frog skin and the toad bladder. A large amount of work has also been done relating to the study of the intestine of mammals, with respect to both uncharged molecules and ions.

Localization of LH-RH-containing Neurons in the Rabbit Brain

Abstract: In the last three years immunohistologic methods have successfully been used to localize the hypophysiotrophic (releasing and inhibiting) hormones. The first releasing hormone localized by immunohistologic methods in the guinea pig by LEONARDELLI et al. in 1973 was luteinizing hormone-releasing hormone (LH-RH). The species studied so far for the histologic localization of LH-RH include guinea pig, rat, mouse, duck, toad, cat, dog, and greenfinch (BARRY and CARETTE, 1975; SETALO, 1976).

The role of cyclic AMP in parathyroid hormone action in the toad bladder.

Abstract: Parathyroid hormone (PTH) inhibited active transport of inorganic phosphate and stimulated an increase in cyclic AMP concentration in the urinary bladder of the toad,Bufo marinus. Active transport of phosphate in the toad bladder was also inhibited by an analog of cyclic AMP (dibutyryl cyclic AMP) and by other drugs (pitressin and theophylline) which increase toad bladder intracellular cyclic AMP concentration. These data support the concept that cyclic AMP may be the mediator of PTH-induced phosphate transport inhibition in the toad bladder.

A basic experimental approach in perspective of pineal and melatonin involvement in photoperiod-induced alteration of spermatogenesis in toad (Bufo melanostictus).

Abstract: Blinding decreases spermatogenesis along with Leydig cell degeneration in toad. Pinealectomy decreases spermatogenesis with an increase in Leydig cell activity. Melatonin decreases spermatogenesis as well the Leyding cells. Possibly pineal and melatonin possess an inverse relationship with light and inhibit testis.

[Glands in the skin of the fire-bellied toad (Bombina bombina(L.); Discoglossidae, Anura): type, number, size and distribution under natural and experimental conditions].

Abstract: 1 In the skin of the fire-bellied toad (Bombina bombina) 5 types of glands are found By analogy with the comparable glands of the yellow-bellied toad and the grass frog, these are called the toxic, lumpy, mucous, callous, and small glands The callous glands were omitted from the present study 2 Lumpy glands are most numerous in the middle of the back of the fire-bellied toad, their numbers decreasing progressively over the sides to the middle of the ventral surface Mucous glands are more common cranially than caudally The toxic and small glands are uniformly distributed over the body 3 On the average there are 700 glands per square cm of skin in the fire-bellied toad Of these, in the male the lumpy glands represent less than 10%, while the toxic, mucous and small glands each account for 30% In the females 50% of the total number of glands are mucous glands, and only about 10% toxic glands; lumpy and small glands occur in the same proportions as in the males Following gonadotropin injection, no change in the number of glands was observed in the male 4 The largest toxic and lumpy glands are located cranially; toward the tail their size is reduced The mucous glands have the greatest volume on the sides of the body Small glands are of similar size everywhere 5 Glands of uniform size are arranged in longitudinal rows on this toad The dorsally situated toxic, lumpy and mucous glands are larger, on the whole, than the more ventral glands of the same types 6 All 4 gland types on the body of Bombina are larger in males than in females 7 Following administration of PMS to the male there is a selective increase in volume of the toxic and lumpy glands on the dorsal surface, but no corresponding increase on the ventral surface Mucous and small glands do not change in size after hormone treatment 8 The capacity of all the glands in a cm2 of skin, in terms of mean volume, is 17 mm3 in males not treated with hormones After PMS treatment of the male the gland volume per cm2 increase to 25 mm3 The total volume per cm2 in females is only 065 mm3

THE LOSS OF SODIUM ACROSS THE SKIN OF THE DEHYDRATED TOAD, Bufo regularis (Reuss)

Abstract: A study was undertaken to determine the loss of sodium across the skin of the dehydrated, terrestrial toad Bufo regularis. Sodium loss was ascertained by placing the toad in a known volume of distilled water, and then measuring the sodium lost to the water. Although dehydration resulted in an increased plasma sodium concentration, the sodium loss across the skin was negligible. The toads rehydrated almost completely within one hour.