Haplosporosomes, sporoplasmosomes and their putative taxonomic relationships in rhizarians and myxozoans.

This paper reviews current knowledge of the structure, genesis, cytochemistry and putative functions of the haplosporosomes of haplosporidians (Urosporidium, Haplosporidium, Bonamia, Minchinia) and paramyxids (Paramyxa, Paramyxoides, Marteilia, Marteilioides, Paramarteilia), and the sporoplasmosomes of myxozoans (Myxozoa - Malacosporea, Myxosporea). In all 3 groups, these bodies occur in plasmodial trophic stages, disappear at the onset of sporogony, and reappear in the spore. Some haplosporidian haplosporosomes lack the internal membrane regarded as characteristic of these bodies and that phylum. Haplosporidian haplosporogenesis is through the Golgi (spherulosome in the spore), either to form haplosporosomes at the trans-Golgi network, or for the Golgi to produce formative bodies from which membranous vesicles bud, thus acquiring the external membrane. The former method also forms sporoplasmosomes in malacosporeans, while the latter is the common method of haplosporogenesis in paramyxids. Sporoplasmogenesis in myxosporeans is largely unknown. The haplosporosomes of Haplosporidium nelsoni and sporoplasmosomes of malacosporeans are similar in arraying themselves beneath the plasmodial plasma membrane with their internal membranes pointing to the exterior, possibly to secrete their contents to lyse host cells or repel haemocytes. It is concluded that these bodies are probably multifunctional within and between groups, their internal membranes separating different functional compartments, and their origin may be from common ancestors in the Neoproterozoic.

Patterning of sodium ions and the control of electrons in sodium cobaltate.

Sodium cobaltate (Na(x)CoO2) has emerged as a material of exceptional scientific interest due to the potential for thermoelectric applications, and because the strong interplay between the magnetic and superconducting properties has led to close comparisons with the physics of the superconducting copper oxides. The density x of the sodium in the intercalation layers can be altered electrochemically, directly changing the number of conduction electrons on the triangular Co layers. Recent electron diffraction measurements reveal a kaleidoscope of Na+ ion patterns as a function of concentration. Here we use single-crystal neutron diffraction supported by numerical simulations to determine the long-range three-dimensional superstructures of these ions. We show that the sodium ordering and its associated distortion field are governed by pure electrostatics, and that the organizational principle is the stabilization of charge droplets that order long range at some simple fractional fillings. Our results provide a good starting point to understand the electronic properties in terms of a Hubbard hamiltonian that takes into account the electrostatic potential from the Na superstructures. The resulting depth of potential wells in the Co layer is greater than the single-particle hopping kinetic energy and as a consequence, holes preferentially occupy the lowest potential regions. Thus we conclude that the Na+ ion patterning has a decisive role in the transport and magnetic properties.

Visualizing the dynamics of soil aggregation as affected by arbuscular mycorrhizal fungi.

Stable soils provide valuable ecosystem services and mechanical soil stability is enhanced by the presence of arbuscular mycorrhizal fungi (AMF). Soil aggregation, which is the major driver of mechanical soil stability, is often treated as a static phenomenon, even though aggregate turnover is continually ongoing. In fact, some breakdown of macroaggregates is necessary to allow new aggregate formation and inclusion of new organic matter into microaggregates. We determined how aggregate turnover times were affected by AMF by tracking movement of rare earth elements (REE), applied as their immobile oxides, between aggregate size classes, and using X-ray fluorescence microscopy to spatially localize REEs in a sample of aggregates. Here we show that AMF increased large macroaggregate formation and slowed down disintegration of large and small macroaggregates. Microaggregate turnover was increased in the presence of AMF. Internal aggregate organization suggested that although formation of microaggregates by accretion of soil to particulate organic matter is common, it is not the only mechanism in operation.

Sporogony of Tetracapsuloides bryosalmonae in the brown trout Salmo trutta and the role of the tertiary cell during the vertebrate phase of myxozoan life cycles.

Tetracapsuloides bryosalmonae is the myxozoan that causes the commercially and ecologically important proliferative kidney disease of salmonid fish species. Immunohistochemistry and electron microscopy were used to examine the development of this parasite within the kidney of the brown trout Salmo trutta. The main replicative phase of T. bryosalmonae is a cell doublet composed of a primary cell and a single secondary cell. Engulfment of one secondary cell by another to form a secondary-tertiary doublet (S-T doublet) heralded the onset of sporogony whereupon the parasite migrated to the kidney tubule lumen. Within the tubule, the parasite transformed into a pseudoplasmodium and anchored to the tubule epithelial cells via pseudopodial extensions. Within each pseudoplasmodium developed a single spore, composed of 4 valve cells, 2 polar capsules and 1 sporoplasm. The pseudoplasmodia formed clusters suggesting that large numbers of spores develop within the fish. This examination of T. bryosalmonae suggests that the main replicative phase of freshwater myxozoans within vertebrates is via direct replication of cell doublets rather than through the rupturing of extrasporogonic stages, while tertiary cell formation relates only to sporogony. Taken in conjunction with existing phylogenetic data, 5 distinct sporogonial sequences are identified for the Myxozoa.

Sacculogenesis of Buddenbrockia plumatellae (Myxozoa) within the invertebrate host Plumatella repens (Bryozoa) with comments on the evolutionary relationships of the Myxozoa.

Members of the phylum Myxozoa are obligate parasites, primarily of aquatic organisms. Their phylogeny has remained problematic, with studies placing them within either the Bilateria or Cnidaria. The discovery that the enigmatic Buddenbrockia plumatellae is a myxozoan that possesses distinct bilaterian features appeared to have finally resolved the debate. B. plumatellae is described as a triploblastic 'worm-like' organism, within which typical myxozoan malacospores form. Using EM we examined the early development of the B. plumatellae 'worms' within the bryozoan host Plumatella repens. The initial development involved numerous unicellular, amoeboid pre-saccular stages that were present within the basal lamina of the host's body wall. These stages migrate immediately beneath the peritoneum where a significant host tissue reaction occurs. The stages aggregate, initiating the formation of a 'worm'. The base of a developing 'worm' forms a pseudosyncytium which resolves into an ectoderm surrounding a mesendoderm. The pseudosyncytium is directly anchored into neighbouring host cells via masses of striated fibres. The replication of the ectodermal and mesendodermal cells extends the developing 'worm' into the coelom of the host. The mesendoderm resolves to form a mesoderm and an endoderm. Myogenesis appears to be initiated from the anchored end of the 'worm' and develops along the mesoderm. The aggregation and differentiation of amoeboid pre-saccular stages to initiate the 'worm' draws analogies to the sacculogenesis observed for Tetracapsuloides bryosalmonae, B. plumatellae's sister taxon within the class Malacosporea. The development of a multicellular, spore forming organism, from single cells does not correlate to any bilaterian or cnidarian species. Current phylogenies indicate the Myxozoa are basal bilaterians along with the Acoela and Mesozoa. Comparison with these other basal groups may help to resolve the placement of Myxozoa within the tree of life.

Endogenous inhibitors (GALFs) of 11beta-hydroxysteroid dehydrogenase isoforms 1 and 2: derivatives of adrenally produced corticosterone and cortisol.

Two isoforms of 11beta-HSD exist; 11beta-HSD1 is bi-directional (the reductase usually being predominant) and 11beta-HSD2 functions as a dehydrogenase, conferring kidney mineralocorticoid specificity. We have previously described endogenous substances in human urine, "glycyrrhetinic acid-like factors (GALFs)", which like licorice, inhibit the bi-directional 11beta-HSD1 enzyme as well as the dehydrogenase reaction of 11beta-HSD2. Many of the more potent GALFs are derived from two major families of adrenal steroids, corticosterone and cortisol. For example, 3alpha5alpha-tetrahydro-corticosterone, its derivative, 3alpha5alpha-tetrahydro-11beta-hydroxy-progesterone (produced by 21-deoxygenation of corticosterone in intestinal flora); 3alpha5alpha-tetrahydro-11beta-hydroxy-testosterone (produced by side chain cleavage of cortisol); are potent inhibitors of 11beta-HSD1 and 11beta-HSD2-dehydrogenase, with IC50's in range 0.26-3.0 microM, whereas their 11-keto-3alpha5alpha-tetrahydro-derivatives inhibit 11beta-HSD1 reductase, with IC50's in range 0.7-0.8 microM (their 3alpha5beta-derivatives being completely inactive). Inhibitors of 11beta-HSD2 increase local cortisol levels, permitting it to act as a mineralocorticoid in kidney. Inhibitors of 11beta-HSD1 dehydrogenase/11beta-HSD1 reductase serve to adjust the set point of local deactivation/reactivation of cortisol in vascular and other glucocorticoid target tissues, including adipose, vascular, adrenal tissue, and the eye. These adrenally derived 11-oxygenated C21- and C19 -steroidal substances may serve as 11beta-HSD1- or 11beta-HSD2-GALFs. We conclude that adrenally derived products are likely regulators of local cortisol bioactivity in humans.

Transmission of freshwater myxozoans during the asexual propagation of invertebrate hosts.

The phylum Myxozoa contains over 1350 species almost all of which are considered to be obligate parasites of aquatic animals. The phylum is composed of two classes, the Myxosporea and the Malacosporea, species of which are important pathogens responsible for severe economic losses in cultured fisheries. The life cycles of freshwater Myxozoa are believed to involve horizontal, indirect transmission, involving an invertebrate (oligochaetes or bryozoans) and a vertebrate host (fish or amphibians). Here, we describe myxozoan propagation through the fragmentation of invertebrate hosts to form new infected individuals. The two hosts examined are an oligochaete Lumbriculus variegatus infected with an unidentified myxosporean (Triactinomyxon sp.) and the bryozoan Fredericella sultana infected with the malacosporean Tetracapsuloides bryosalmonae which causes proliferative kidney disease, a major constraint of the European rainbow trout industry. Such intra-clonal propagation is a novel form of vertical transmission that is likely to be widespread within the Myxozoa and could form an important method by which some of these parasites maintain and proliferate within the aquatic environment.

Severe, chronic proliferative kidney disease (PKD) induced in rainbow trout Oncorhynchus mykiss held at a constant 18 degrees C.

Proliferative kidney disease (PKD), caused by the myxozoan parasite Tetracapsuloides bryosalmonae, is well documented as a seasonal disease of rainbow trout Oncorhynchus mykiss. Water temperatures influence the course of the infection both within the fish and the invertebrate host, the recovery of fish from the disease being accelerated with decreasing water temperatures. During this study, groups of rainbow trout were held at a constant temperature (18 degrees C) for a sustained period of time following initial exposure to T. bryosalmonae. While the majority of these fish had recovered from the clinical disease after 9 mo, 10% remained infected, showing clinical signs of disease. A histological study revealed that the majority exhibited very high parasite loads and unusually severe symptoms of PKD. This demonstrates that while most rainbow trout can recover from PKD independent of water temperature, there exists a sub-population that cannot.

The effects of castration and treatment with testosterone on the biliary excretion of (3H)aldosterone in rats.

The rate of excretion of aldosterone radiometabolites into the bile duct cannulation, and the intravenous injection of (3H)aldosterone, was demonstrated to be markedly increased in male rats following castration. In 1 h, 72% of the injected 3H-radioactivity was excreted in the bile of castrated male rats compared with 26% in the intact male control rats. Castration of the males led to the increased biliary excretion of aldosterone metabolites and the elimination of the sex-dependence of this process in rats. The ovariectomy of female rats did not substantially increase the rate of excretion of aldosterone metabolites via the bile. Castrated male rats treated with testosterone excreted aldosterone metabolites into the bile at a slower rate. A similar treatment of ovariectomized female rats with testosterone also significantly slowed the rate of biliary excretion of the aldosterone metabolites. These findings suggest that the presence of androgens plays an important role in regulating the routes of hepatic metabolism of aldosterone and the rates of clearance of aldosterone and its metabolites from the plasma into the bile of rats.

The "mineralocorticoid-like" actions conferred on corticosterone by carbenoxolone are inhibited by the mineralocorticoid receptor (type I) antagonist RU28318.

We have previously demonstrated, in adrenalectomized male rats, that the liquorice derivative carbenoxolone (CS) can confer mineralocorticoid (MC)-like activity upon the glucocorticoid corticosterone (B) and amplify the Na(+)-retaining actions of aldosterone (Aldo) and deoxycorticosterone (DOC). The purpose of the present study was to determine whether the MC-like effects of B and the amplified actions of ALDO and DOC in the presence of CS are mediated via the occupation of type I (MC) receptors. In adrenalectomized male rats, B (100 micrograms/rat) alone produced a significant kaliuresis, but no antinatriuresis. This kaliuresis was blocked by the type I (MC) receptor antagonist RU28318 (300 micrograms/rat). In the presence of CS (2.5 mg/rat), B produced a significant Na+ retention, and the kaliuretic activity of B was significantly enhanced. This CS-induced antinatriuresis produced by B was significantly reduced by RU28318, as was the amplified kaliuresis. The MC effects of either Aldo (0.05 micrograms/rat) or DOC (5 micrograms/rat) alone were, as expected, reduced by RU28318 (300 micrograms/rat). As previously reported, CS amplified only the Na(+)-retaining actions of Aldo and DOC, and it was also possible to reduce these amplified effects with RU28318. The present study demonstrates that in the presence of CS, the MC actions of B, Aldo, and DOC are mediated to a large extent via the occupation of type I (MC) receptors.

The antinatriuretic and kaliuretic effects of the glucocorticoids corticosterone and cortisol following pretreatment with carbenoxolone sodium (a liquorice derivative) in the adrenalectomized rat.

Carbenoxolone Sodium (CS), a chemical derivative of liquorice is known to be associated with hypertension, increased sodium retention and hypokalemia. The present studies describe the effects of CS on the renal actions of the glucocorticoids Corticosterone (B) and Cortisol (F) on sodium and potassium in adrenalectomized male rats. B (50, 100 and 500 micrograms/rat) and F (1 mg/rat) were found to possess no intrinsic antinatriuretic activity which is represented by a decrease in the Na+ to creatinine ratio; while only B (500 micrograms/rat) demonstrated kaliuretic effects as indicated by an increase in K+ to creatinine ratios. B and F showed very significant antinatriuretic and kaliuretic properties following pretreatment with CS (2.5 mg/rat). CS alone was not found to be antinatriuretic at this dosage. Further experiments demonstrated that lower dosages of CS (500 and 1,000 micrograms/rat) also cause B to exhibit Na+ retaining and K+ excreting properties. Thus, we have demonstrated that pretreatment with CS can confer mineralocorticoid-like activity upon the glucocorticoids B and F.

Biliary excretion of [3H]aldosterone and its sex dependence in adrenalectomized rats.

The rate of excretion of 3-H-radioactivity via the bile into the intestine following intravenous injection of [3-H]aldosterone, was demonstrated to be rapid and sex-dependent in adrenalectomized rats. Within 1 h, female rats excreted into the intesting via the bile greater than 95% of the injected dose of [3-H]aldosterone, compared to 47% in the male rats. In both the male and female rats, greater than 90% of the total radioactivity excreted into the intestine represented dichloromethane nonextractable polar derivatives of aldosterone (NEPD). Similarly, the quantities of NEPD recovered in the bile following bile duct cannulation of the rats, were also sex-dependent. These findings account for the rapidity and sex-dependence of the rates of clearance of aldosterone and its metabolites from the plasma of adrenalectomized rats. The sex hormones appear to influence not only the extent and the routes of metabolism of aldosterone in the liver, but also the rates of clearance of aldosterone and its metabolites from the plasma into the bile.

Induction of flavokinase (EC 2.7.1.26) by aldosterone in the rat kidney.

The effect of aldosterone on rat renal flavokinase (EC 2.7.1.26) enzymic activity and concentration was investigated in bilaterally adrenalectomized male Sprague-Dawley rats. Flavokinase enzymic activity was measured in the 100,000 X g supernatant of renal cortex and red medulla and was increased after 3 h by 19% and 42%, respectively, as a result of aldosterone (1.5 micrograms/100 g BW) administration. Dual isotope labeling studies revealed increases of 20-30% and 20-35% in the incorporation of [3H]- and [35S]methionine into rat renal cortical and red medullary flavokinase, respectively, as a result of aldosterone administration. The aldosterone-dependent increases in methionine incorporation were blocked when the mineralocorticoid receptor antagonist spirolactone (SC 26304; 150 micrograms/100 BW) was administered 30 min before aldosterone. The relative concentrations of renal flavokinase also increased by 40% in both the cortex and red medulla 3 h after aldosterone treatment, as determined by an enzyme-linked immunosorbent assay (ELISA). These increases were abolished by actinomycin D (100 micrograms/100 g BW) and cycloheximide (200 micrograms/100 g BW), given 1 h before aldosterone administration. The mineralocorticoid receptor antagonists SC 26304 (225 micrograms/100 g BW) and progesterone (500 micrograms/100 g BW) were also able to inhibit the aldosterone-dependent increase in renal flavokinase concentration. The effect of aldosterone on renal flavokinase concentration was studied from 30 min to 8 h after aldosterone administration. There appeared to be maximum increases of 23-30% and 25-32% after 2.5-3.5 h in the renal cortex and red medulla, respectively. 5 alpha-Dihydroaldosterone, a metabolite of aldosterone with mineralocorticoid activity, was also able to increase renal flavokinase concentrations by approximately 40%. However, dexamethasone, a potent glucocorticoid with little or no mineralocorticoid activity, appeared to have no effect on renal flavokinase, as observed by ELISA. These data suggest that the increase in the relative concentration of renal flavokinase may be due to increased biosynthesis of flavokinase, and ultimately, that renal flavokinase may be an aldosterone-induced protein whose synthesis is mediated through the mineralocorticoid receptor and RNA synthesis.

The metabolism and binding properties of 3H-aldosterone in plasma and its sex dependence in adrenalectomized rats.

The rates of clearance of plasma 3-H radioactivitivity following intravenous injection of 3-H aldosterone was demonstrated to be sex-dependent in adrenalectomized rats. The perchantage plasma radioactivity which is CH-2CL-2extractable is greater in female than in male rats from 5 min to 90 min postinjection; however the quantities of CH2-CL2-extractable label are not significantly different until 60 min postinjection. The quantities of nonextractable, water-soluble metabolites of adosterone (NEPD), which are markedly greater in the plasma of males, reach peak levels 30 min after injections of aldosterone, during the latent period of the hormone.N females, these polar metabolites (NEPD)are rapidly cleared from the blood. The quantities of 3-H-radioactivity associated with the plasma binding proteins are similar in both males and females. The unbound levels of aldosterone and its metabolities are significantly greater in the plasma of males. These findings indicate that the sex hormones may influence not only the metabolism of aldosterone in rats, but also the plasma levels of unmetabolized aldosterone and its metabolites.

Further studies of the mineralocorticoid activity of 19-oxo-deoxycorticosterone.

Antinatriuretic and kaliuretic activities of 19-oxo-deoxycorticosterone (19-oxo-DOC) were measured in male adrenalectomized rats and compared with those of aldosterone. No significant effects of 19-oxo-DOC or aldosterone were observed in the lag period (i.e. the first hour post injection). In the subsequent 2 h, rats injected with 25 micrograms 19-oxo-DOC excreted less than half the sodium and more than twice the potassium compared to rats injected with vehicle alone. Overall mineralocorticoid activity (based on changes in urinary Na+/K+), antinatriuretic activity (based on changes in urinary Na+/creatinine) and kaliuretic activity (based on changes in urinary K+/creatinine) of 19-oxo-DOC were all in the range of 1:100th-1:200th that of aldosterone. These results are not in agreement with a recent report suggesting that 19-oxo-DOC possesses antinatriuretic activity but no kaliuretic activity.

Mineralocorticoid activity of 19-hydroxyaldosterone, 19-nor-aldosterone, and 3 beta-hydroxy-delta 5-aldosterone: relative potencies measured in two bioassay systems.

The mineralocorticoid (MC) activities of 19-hydroxyaldosterone (19-OH-Aldo) and 19-nor-aldosterone (19-nor-Aldo) were tested in adrenalectomized male rats. Potency was assessed by three criteria. Overall MC activity is expressed as the ability to decrease the urinary Na+ to K+ ratio; antinatriuretic activity is represented by decreases in the urinary Na+ to creatinine ratio, and kaliuretic activity by increases in the K+ to creatinine ratio. All measurements were made on urine collected 1-3 h postinjection. In this assay, 19-OH-Aldo was 1/100th to 1/140th as active as Aldo, and 19-nor-Aldo possessed MC activity similar to that of Aldo; both steroids possessed antinatriuretic and kaliuretic activities. In contrast, when assayed in vitro in the isolated toad urinary bladder, the natriferic responses of both 19-OH-Aldo and 19-nor-Aldo (10(-8), 10(-7), and 10(-6) M) were not significantly different from those caused by equivalent concentrations of Aldo. 3 beta-Hydroxy-delta 5-Aldo is active as a MC in the adrenalectomized male rat, being 1/20th to 1/35th as active as Aldo, but, in contrast to 19-OH-Aldo, was less active in the isolated toad bladder system. 19-OH-Aldo, 19-nor-Aldo, and 3 beta-hydroxy-delta 5-Aldo could represent important new classes of Aldo analogs.

11 alpha- and 11 beta-hydroxyprogesterone, potent inhibitors of 11 beta-hydroxysteroid dehydrogenase (isoforms 1 and 2), confer marked mineralocorticoid activity on corticosterone in the ADX rat.

The effects of 11 alpha- and 11 beta-hydroxyprogesterone (11 alpha-OHP, 11 beta-OHP), on the activity of the glucocorticoid inactivating enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) were studied. 11 alpha-OHP and 11 beta-OHP were potent inhibitors of both 11 beta-HSD1 in rat liver microsomes and 11 beta-HSD2 in lysates of JEG-3 cells, a human choriocarcinoma cell line. In addition, both progesterone metabolites were markedly potent in conferring mineralocorticoid activity upon B in the adrenalectomized rat. These results provide insight into the structural properties required of inhibitors of 11 beta-HSD activity and indicate a possible role for endogenous 11 beta-HSD inhibitors in the regulation of glucocorticoid-induced Na+ retention.

The role of aldosterone in the development of hypertension in spontaneously hypertensive rats.

A continuous sc infusion of aldosterone for 2 weeks (10 micrograms/day) markedly increased the blood pressure of male, adrenalectomized (ADX), spontaneously hypertensive rats (SHR) from 142 to 178 mm Hg, which was similar to the increase seen in a group of sham-operated SHR. The blood pressure in a group of ADX SHR maintained without aldosterone declined from 141 to 119 mm Hg during the 2 weeks after surgery. Wistar Kyoto (WKY) and Sprague-Dawley (SD) rats treated in an identical fashion remained normotensive throughout. Adrenalectomy caused hyperkalemia in all strains of rat. Plasma potassium levels in aldosterone-treated WKY and SD rats were lower than those in sham-operated controls, but were similar to those in corresponding groups of SHR. Acute renal responses of ADX male rats showed that SHR reabsorbed more water and sodium of an injected isotonic saline load than WKY rats and excreted less potassium than either WKY or SD rats. Sensitivity to aldosterone in the three strains of rats was compared using the urinary sodium to creatinine and potassium to creatinine ratios 1-3 h postinjection of aldosterone. Decreases in the urinary ratio of sodium to creatinine in response to various doses of aldosterone (0-1.25 micrograms aldosterone) were similar for the three strains of rat. ADX SHR appeared to be less responsive to the kaliuretic actions of aldosterone than WKY and SD rats. The present studies show that aldosterone is essential to the development of hypertension in SHR. The hypertensinogenic actions of aldosterone in these rats may be related to a blunted kaliuretic response to mineralocorticoids.

Antinatriuretic and kaliuretic activities of the reduced derivatives of aldosterone.

The mineralocorticoid activities of the two dihydro- and the four tetrahydroisomers of the ring A-reduced derivatives of aldosterone were tested in adrenalectomized male rats. Potency was assessed by three criteria. Overall mineralocorticoid activity is expressed as the ability to reduce the urinary Na+/K+ ratio; antinatriuretic activity is represented by decreases in urinary Na+/creatinine; kaliuretic activity is shown by increases in K+/creatinine. All measurements were made on urine collected in the period 1-3 h postinjection. Measurements of overall activity indicate that the potency of aldosterone is greater than 5 alpha-dihydroaldosterone (DHA) greater than 3 alpha, 5 alpha-tetrahydroaldosterone (THA) greater than 3 alpha, 5 beta-THA greater than 3 beta, 5 alpha-THA greater than 5 beta-DHA greater than 3 beta, 5 beta-THA. Measurements of individual cation effects indicated that reduced derivatives generally, and the 5 alpha-reduced derivatives in particular, have greater antinatriuretic than kaliuretic activity. For example 5 alpha-DHA possesses between 7% and 17% of the antinatriuretic activity of aldosterone but only 0.7-2.7% of the kaliuretic activity. 5 alpha-DHA and 3 alpha, 5 beta-THA at concentrations of 10(-7)M were also shown to have mineralocorticoid activity in the isolated toad bladder; both caused an increase in the short circuit current across this epithelium although not to the level shown by a similar concentration of aldosterone. 5 beta-DHA appeared to be inactive at this dose.