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PubMed2005

Uncoupling protein 1 in fish uncovers an ancient evolutionary history of mammalian nonshivering thermogenesis.

Uncoupling proteins (UCPs) increase proton leakage across the inner mitochondrial membrane. Thereby, UCP1 in brown adipose tissue dissipates proton motive force as heat. This mechanism of nonshivering thermogenesis is considered as a monophyletic trait of endothermic placental mammals that emerged about 140 million years ago and provided a crucial advantage for life in the cold. The paralogues UCP2 and UCP3 are probably not thermogenic proteins but convey mild uncoupling, which may serve to reduce the rate of mitochondrial reactive oxygen species production. Both are present in endotherms (mammals and birds), but so far only UCP2 has been identified in ectothermic vertebrates (fish and amphibia). The evolution of UCPs is of general interest in the search for the origin of mammalian UCP1-mediated nonshivering thermogenesis. We here show the presence of UCP1 and UCP3 in ectothermic teleost fish species using comparative genomics, phylogenetic inference, and gene expression analysis. In the common carp (Cyprinus carpio), UCP1 is predominantly expressed in the liver and strongly diminished in response to cold exposure, thus contrasting the cold-induced expression of mammalian UCP1 in brown adipose tissue. UCP3 mRNA is only found in carp skeletal muscle with expression levels increased fivefold in response to fasting. Our findings disprove the monophyletic nature of UCP1 in placental mammals and demonstrate that all three members of the core UCP family were already present before the divergence of ray-finned and lobe-finned vertebrate lineages about 420 million years ago.

Amino Acid Sequence↗
PubMed2005

Penelope-like elements--a new class of retroelements: distribution, function and possible evolutionary significance.

Here we describe a new class of retroelements termed PLE (Penelope-like elements). The only transpositionally active representative of this lineage found so far has been isolated from Drosophila virilis. This element, Penelope, is responsible for the hybrid dysgenesis syndrome in this species, characterized by simultaneous mobilization of several unrelated TE families in the progeny of dysgenic crosses. Several lines of evidence favor the hypothesis of recent Penelope invasion into D. virilis. Moreover, when D. virilisPenelope was introduced by P element-mediated transformation into the genome of D. melanogaster, it underwent extensive amplification in the new host and induced several traits of the dysgenesis syndrome, including gonadal atrophy and numerous mutations. The single ORF encoded by PLE consists of two principal domains: reverse transcriptase (RT) and endonuclease (EN), which is similar to GIY-YIG intron-encoded endonucleases. With the appearance of a large number of PLEs in genome databases from diverse eukaryotes, including amoebae, fungi, cnidarians, rotifers, flatworms, roundworms, fish, amphibia, and reptilia, it becomes possible to resolve their phylogenetic relationships with other RT groups with a greater degree of confidence. On the basis of their peculiar structural features, distinct phylogenetic placement, and structure of transcripts, we conclude that PLE constitute a novel class of eukaryotic retroelements, different from non-LTR and LTR retrotransposons.

Animals↗
PubMed2005

DIRS-1 and the other tyrosine recombinase retrotransposons.

DIRS-1 is a retroelement from the slime mold Dictyostelium discoideum. Until recently only two related retrotransposons had been described: PAT from the nematode Panagrellus redivivus and Prt1 from the zygomycete fungus Phycomyces blakesleeanus. Analyses of the reverse transcriptase sequences encoded by these three elements suggested that they were closely related to each other and more distantly related to the Ty3/gypsy Long Terminal Repeat (LTR) retroelements. They have several unusual structural features that distinguish them from typical LTR elements. For instance, they each encode a tyrosine recombinase (YR), but not a DDE-type integrase or an aspartic protease. Although the DIRS-1-related elements are bordered by terminal repeats these differ from typical LTRs in a number of ways. In DIRS-1, for example, the terminal repeats are inverted (complementary), non-identical in sequence, and the outer edges of the terminal sequences are repeated (adjacent to each other) in the internal region. PAT has so-called "split" direct repeats in which the unrelated terminal sequences appear as direct repeats adjacent to each other in the internal region. The only repetition displayed by Prt1 is the presence of short inverted terminal repeats, but the sequenced copy of this element is believed to be a truncated version of an element with a structure resembling DIRS-1. The unusual structure of the terminal repeats of the DIRS1-like elements appears to be related to their replication via free circular intermediates. Site-specific recombination is believed to integrate the circle without creating duplications of the target sites. In recognition of these important distinctions it is proposed that the retrotransposons that encode tyrosine recombinases be called the tyrosine recombinase (or YR) retrotransposons. Recently a large number of additional YR retrotransposons have been described, including elements from fungi (zygomycetes and basidiomycetes), plants (green algae) and a wide range of animals including nematodes, insects, sea urchins, fish and amphibia, while remnants of elements related to DIRS-1 occur in the human genome. The complete set of YR retrotransposons can be divided into two major groups, the DIRS elements and the Ngaro elements, the two groups forming distinct clades on phylogenetic trees based on alignments of RT/RH and recombinase sequences, and also having some structural distinctions. A third group of transposable elements, which we call Cryptons, also carry tyrosine recombinases. These elements do not encode a reverse transcriptase and so are believed to be DNA transposons not retrotransposons. They have been detected in several pathogenic fungi, including the basidiomycete Cryptococcus neoformans, and the ascomycetes Coccidioides posadasii and Histoplasma capsulatum. Sequence comparisons suggest that the Crypton YRs are related to those of the YR retrotransposons. We suggest that the YR retrotransposons arose from the combination of a Crypton-like YR DNA transposon and the RT/RH encoding sequence of a retrotransposon.

Amino Acid Sequence↗
PubMed2006

Identification of intergenomic recombinations in unisexual salamanders of the genus Ambystoma by genomic in situ hybridization (GISH).

Unisexual salamanders in the genus Ambystoma (Amphibia, Caudata) are endemic to eastern North America and are mostly all-female polyploids. Two to four of the bisexual species, A. laterale, A. jeffersonianum, A. texanum and A. tigrinum, contribute to the nuclear genome of unisexuals and more than 20 combinations that range from diploid to pentaploid have been identified in this complex. Because the karyotypes of the four bisexual species are similar, homologous and homoeologous chromosomes in the unisexuals can not be distinguished by conventional or banded karyotypes. We chose two widespread unisexual genomic combinations (A.laterale-2 jeffersonianum [or LJJ] and A. 2 laterale-jeffersonianum [or LLJ]) and employed genomic in situ hybridization (GISH) to identify the genomes in these unisexuals. Under optimum conditions, GISH reliably distinguishes the respective chromosomes attributed to both A.laterale and A. jeffersonianum. Of four populations examined, two were found to have independently evolved homoeologous recombinants that persist in both LJJ and LLJ individuals. Our results refute the previous hypothesis of clonal integrity and independent evolution of the genome combinations in these unisexuals. Our data provide evidence for intergenomic interactions between maternal chromosomes during meiosis in unisexuals and help to explain previously observed non-homologous bivalents and/or quadrivalents among lampbrush chromosomes that were possibly initiated by partial homosequential pairing among the homo(eo)logues. To explore the utility of GISH in other members of the complex, probes developed from A. laterale were also applied to unisexuals that contained A. tigrinum and A. texanum genomes. GISH is an effective tool that can be used to identify and to quantify genomic constituents and to investigate intergenomic interactions in unisexual salamanders. GISH also has potential application to examine possible genomic evolution in other unisexuals.

Ambystoma↗
PubMed1992

Differences in optokinetic and vestibular ocular reflex performance in teleosts and their relationship to different life styles.

Horizontal eye movements in response to vestibular and optokinetic stimulation were investigated in 20 species of marine and fresh water teleosts. Most species performed spontaneous saccadic eye movements in light and in darkness. Successive saccades occurred either at irregular intervals and in different directions (few species), or in bursts of smaller saccades in one direction followed by saccades in the opposite direction (majority of species). Thus, in the latter group the lines of sight shifted cyclically from one side to the other about every 10-15 s. Eye movement responses in goldfish and toadfish were prototypical for two major functional groups. Optokinetic and vestibular nystagmus in the goldfish were much more regular and attained significantly higher gains than in the oyster toadfish. Optokinetic afternystagmus (OKAN) and per-/postrotatory nystagmus lasted about 10-12 s in the goldfish, but only 2-3 s in the oyster toadfish. Bilateral labyrinthectomy in goldfish resulted in optokinetic gains and OKAN durations that were very close to those of intact toadfish. These results indicate the presence (in goldfish) and the absence (in toadfish) of a functioning velocity storage network, respectively. Other non-ostariophysan teleosts failed to show a 'goldfish-like' response pattern as well. Ostariophysan species differed in their reflex performance as well. A 'goldfish-like' response pattern was observed in five of the seven cypriniform species and in two of the four characiform species but not in the four siluriform species. Positively correlated, combined response properties suggest that some species are better equipped for gaze stabilization at higher velocities than other species. These behavioral differences may parallel different specializations in locomotor pattern and mode of life. Absence of a functioning velocity storage network in bottom-dwelling teleosts (as in Amphibia) may be related to the sporadic, slow locomotion of these species and the resulting small requirements for continuous gaze stabilization during self-motion at higher velocities.

Animals↗
PubMed1986

Arginine vasotocin immunoreactivity in hypothalamic and extrahypothalamic areas of an amphibian brain.

The distribution of arginine vasotocin immunoreactivity (irAVT) was investigated in the brain of male rough-skinned newts (Amphibia: Taricha granulosa) using microdissection and radioimmunoassay techniques. The highest levels of irAVT were observed in the neuroendocrine hypothalamo-hypophysial system. However, detectable quantities of irAVT (greater than 0.40 ng/mg protein) also were observed in extrahypothalamic areas such as pallium, amygdala, striatum and thalamic, tectal and brainstem nuclei. No irAVT was detected in the olfactory bulb, rostral telencephalon, or in specific areas of the caudal telencephalon and diencephalon. These results indicate that, in amphibians, AVT is distributed among a wide range of brain areas and that there is regional specificity in irAVT concentrations.

Animals↗
PubMed1997

Chicken GnRH II-like peptides and a GnRH receptor selective for chicken GnRH II in amphibian sympathetic ganglia.

Amphibia, like most vertebrate species, have two forms of GnRH, namely [Arg8]GnRH (mammalian GnRH) and [His5,Trp7,Tyr8] GnRH (chicken GnRH II). The differential distribution of the two peptides in the amphibian brain suggests that they may play different roles. Mammalian GnRH, which is found predominantly in the hypothalamus, is most likely the prime regulator of gonadotropin release, while chicken GnRH II, which occurs predominantly in the midbrain and hindbrain, may play a neuromodulatory role. In amphibian sympathetic ganglia, GnRH has been demonstrated to be a neurotransmitter where its release from the presynaptic nerve terminals reversibly inhibits M current, a time- and voltage-dependent potassium current. The occurrence of GnRH in sympathetic ganglia extracts from two amphibian species was investigated. Chicken GnRH II-like immunoreactivity was detected in extracts of bullfrog (Rana catesbeiana) and platanna (Xenopus laevis) sympathetic ganglia after high performance liquid chromatography. Under the chromatographic conditions used, a second unknown peptide co-eluted with synthetic mammalian GnRH, but showed no cross-reactivity with specific mammalian GnRH antisera. To test the possibility of the presence of a chicken GnRH II receptor in sympathetic ganglion neurones, competition binding of membranes extracted from the sympathetic ganglia of the two amphibian species was investigated with 125I-labelled GnRH agonists. The binding of 125-I-[His5,D-Arg6,Trp7,Tyr8]GnRH (a chicken GnRH II agonist) to membranes from the sympathetic ganglia of both amphibian species was specific and had a higher affinity than chicken GnRH II, mammalian GnRH and a mammalian GnRH agonist [D-Ala6,NMe-Leu7,Pro9-NHEt]GnRH. These findings suggest that endogenous chicken GnRH II may play a role in synaptic transmission in the sympathetic ganglia via a receptor specific for chicken GnRH II.

Amphibians↗
PubMed1985

Further studies on the nature of neural intranuclear inclusions (Roncoroni bodies) (with 2 color plates).

It is generally accepted that chromosomes are not visible in interphase except in certain diptera, amphibia and rare unicellular organisms where they are represented by polytene, giant chromosomes. Such structures are exemplified by cells in which growth is evident by increase in size while the polytene structures increase in size rather than in number. These giant chromosomes are active metabolically, synthesizing mRNA and causing increasing activity in the corresponding cells. Experimental procedures leading to increased activity in neurones were accompanied by the appearance of nuclear inclusions which behaved very much like the polytene chromosomes metabolically and, as a result, an attempt was made to determine whether they had similar chemical behavior. This proved to be demonstrable and so it is concluded that the Roncoroni body represents a metabolically active interphase chromosomal segment and may be used as a sign of such activity.

Animals↗
PubMed1989

Amphibian and piscine iridoviruses proposal for nomenclature and taxonomy based on molecular and biological properties.

We have compared a number of properties of the well-characterized iridovirus, frog virus 3, with two other iridoviruses from amphibia, bullfrog edema virus and Lucké triturus virus, and with a piscine iridovirus, goldfish virus (GFV), to provide information for developing taxonomic classification of these viruses and establishing their ecological niche. Purified virions had similar size and shape (icosahedral) for each virus, and the genomic DNAs of each virus were methylated by a virus-induced DNA methyltransferase. The three amphibian viruses replicated equally well in fish (FHM), hamster (BHK), and human (WI-38) cell monolayer with identical cytopathology, while GFV failed to replicate in these cell lines. However, GFV replicated albeit at a slow rate, in a goldfish cell line; there was no detectable replication by the amphibian viruses in these cells. The amphibian iridoviruses had virtually similar DNA sequences, while those of GFV were markedly different. Analyses of virus-induced polypeptides in infected cells corroborated the DNA analyses; the polypeptides of the amphibian viruses were similar and distinct from those of the fish virus. Nongenetic reactivation could only be accomplished between the three amphibian viruses but not with the piscine virus. Based on these data, we suggest taxonomic and nomenclature designations of amphibian and piscine iridoviruses.

Amphibians↗
PubMed1994

Ageing in amphibians.

Limited research findings up-to-date with a few amphibian models do not permit a generalisation of ageing phenomena in the class Amphibia. Short-lived species of amphibians show gradual senescence comparable to the pattern seen in laboratory mammals. Long-lived species (mostly urodeles) continue to grow throughout life and are believed to exhibit very slow or negligible senescence which is unobtrusive. In a few species with gradual senescence, there is some evidence of an increase in mortality rate and a decrease in growth rate with advancing age. Increase in cross-linking of collagen, accumulation of age pigments (lipofuscin and melanin), decrease in metabolism and loss of immunocompetence are ageing phenomena common to both amphibians and mammals. On the other hand, persistence of neurogenesis and myogenesis, continuance of oogenesis beyond adult life and polyphyodonty are some of the features peculiar to ageing in amphibians. More authenticated reports are needed to fill up the gaps in our knowledge on amphibian senescence.

Aging↗
PubMed1991

A spontaneous melanoma-like tumor in the adult newt Triturus cristatus.

We present here a case of a spontaneous melanoma-like tumor in the adult newt Triturus cristatus, lying above the scapula. The melanized cellular mass had infiltrated the subcutaneous connective tissue. The presence of this tumor is discussed with respect to the incidence of tumors in amphibia in relation to the animals' regenerative capacity.

Animals↗
PubMed1994

Allografting of a nontransmissible, spontaneous dermal melanoma in the newt Triturus cristatus.

Regeneration-competent urodele Amphibia are highly resistant to spontaneous development of neoplasms, in comparison with other vertebrates which do not exhibit great regenerative power. This observation implies that at least one growth parameter of urodele cells might be subject to different developmental mechanisms than the cells of animals incapable of epimorphic regeneration. Therefore, keeping records concerning the incidence of tumors in urodeles and investigating those exceptional cases might prove invaluable in understanding the basic biological principles governing organ regeneration and carcinogenesis, and might therefore help in cancer therapy. The present report depicts a case of two spontaneous, dermal, melanoma-like tumors found in an adult newt Triturus cristatus. Both tumors were located in the pelvic region. Histological examinations and tumor transplantations were conducted. It was found that the tumors were melanomata. When allografted within the body cavity, their mass was progressively eliminated.

Animals↗
PubMedDate not supplied

Effects of frog-skin angiotensin II in amphibians.

The role of frog-skin angiotensin II (AII) in amphibia was studied by comparing the sodium and water permeability effects of three angiotensins (AII): frog skin (Ala-Pro-Gly-[Ile3, Val5]-Ang II), human [( Asp1, Ile5]-AII), and Japanese goosefish [( Asn1-Val5]-AII). Frog-skin AII increased the short-circuit current (SCC) significantly after it was added to the dermal side of the isolated skin of the South American frogs, Leptodactylus chaquensis and ocellatus, and the toad, Bufo arenarum, in concentrations of 10(-6) M. In frogs, the effect was significant at 15 minutes and reached 45% over control after 2 1/2 hours. The effect cannot be achieved with concentrations lower than 10(-7) M. Since amiloride (10(-4) M) blocked the SCC response, and absence of chloride in the bathing fluid did not, the effect is probably dependent on sodium transport. Human AII (10(-6) M) produced a similar response in summer frogs that had been treated with 0.1% NaCl for 14 days. Goosefish AII was ineffective at similar concentrations, and none of the angiotensins modified SCC in the toad bladder. Hydrosmotic effects could be achieved with the three angiotensins, the response being dependent on seasonal and species factors but always considerably lower than that of the neurohypophyseal peptides. Vascular reactivity of the isolated frog hindlimbs was compared by dose-response curves. Potency ratios on a molar basis against frog-skin AII was 1.136 for human AII and 1.193 for goosefish AII. The results show that the effects of the angiotensins differ in both the response of SCC to frog-skin angiotensin and its higher vascular effects.

Amphibians↗
PubMedDate not supplied

Phase I trial of technetium [Leu13] bombesin as cancer seeking agent: possible scintigraphic guide for surgery?

AIMS AND BACKGROUND: Bombesin-like neuropeptides work as neurotransmitters and growth factors at the same time. Several human cancers show overexpression of three receptors for mammalian counterparts of amphibia bombesins (ABNs), ie gastrin-releasing peptide (GRP), neuromedin B (NMB) and possibly another peptide. ABNs in turn are able to bind to mammalian and human receptors in vitro, and it is therefore interesting to study radioisotope-labeled bombesin (BN) and BN-like peptides as cancer seeking agents. METHODS AND STUDY DESIGN: Starting from the amino acid sequence of [Leu13] ABN, the Demokritos Institute has synthesized and labeled with technetium a new BN-like peptide that has the same biological characteristics as the amphibian peptide; changes were made only in the N-terminal part of the tetradecapeptide. After having obtained satisfactory results with 99mTc BN in a preclinical study, we started a phase I trial involving cancer patients as well as normal volunteers in Tomsk. Three normal volunteers, one patient with small cell lung cancer and one patient with primary prostate cancer were studied after iv injection of 185 MBq, corresponding to 0.7 micrograms of 99mTc BN. Dynamic images of the tumors were acquired for 20 mins, followed by SPET. Total body images were acquired in patients and normal volunteers 1 and 3 h after 99mTc BN acquisition. In addition, 99mTc sestamibi scintigraphy was performed in the patient with small cell lung carcinoma. RESULTS: No relevant side effects were observed. Both tumors were well visualized on early 1-2 mins images with planar as well as tomographic imaging. Total body images showed radioactivity in the liver, kidneys and thyroid gland. The stomach and spleen were ever imaged. Radioactivity was found in the urinary bladder 4 mins after injection in the patient with prostate cancer. Three-hour total body scans showed radioactivity in the duodenum. In the patient in whom also 99mTc sestamibi scintigraphy was performed, thyroid uptake was much higher with sestamibi than with 99mTc BN, whereas the uptake of small cell lung carcinoma was higher with 99mTc BN than with sestamibi. CONCLUSIONS: 99mTc BN is able to clearly image tumors with BN receptor overexpression. Our first impression is that in the future this radiopharmaceutical may serve as a cancer seeking agent and, due to its high tumoral uptake, also as a radiotracer for radioisotope-guided surgery.

Bombesin↗
PubMed1984

Increase in 3,5,3'-triiodothyronine (T3)-binding sites in tadpole erythrocyte nuclei during spontaneous and T3-induced metamorphosis.

The change in T3-binding sites in larval and adult type red blood cell (RBC) nuclei during metamorphosis was studied with the use of Scatchard plots. The number of binding sites per nucleus or the maximum binding capacity (MBC) in the larval type RBC (containing larval hemoglobins) increased from 240 at stage X to 410 at stage XVIII. The apparent Kd also increased from 170 pM at stage X to 260 pM at stage XVIII. At stages XX-XXI, adult type RBCs (containing adult hemoglobins) accounted for 22% of the RBC population. At stage XXII, adult RBCs increased to 54%. In the separated larval and adult RBCs from stage XXII, obtained by Percoll gradient centrifugation, the MBC in larval RBCs had increased to 930 sites/nucleus, a 4-fold increase over stage X, with a Kd of 760 pM; adult RBCs had 1150 sites/nucleus and a Kd of 1530 pM. In contrast, when T3 binding was measured in the whole RBC population from stage XXII tadpoles, the MBC and Kd in larval and adult RBC were estimated at 780 sites/nucleus with a Kd of 640 pM and 1200 sites/nucleus with Kd of 2300 pM, respectively. After metamorphosis, the larval RBCs disappeared and were replaced by adult RBCs. The MBC in adult RBC had declined to 350 sites/nucleus at stage XXV (froglet). The Kd of adult RBC decreased to 790 pM at stage XXV. When stage XVII tadpoles were given a single injection of T3, a 2-fold increase in MBC and Kd was observed after 14 days at 20 C. The values observed for T3-treated animals (870 sites/nucleus with a Kd of 660 pM) were close to the values for the larval RBCs at stage XXII in spontaneous metamorphosis. The MBC and apparent dissociation constant of control animals (400 sites/nucleus; Kd of 270 pM) were almost the same as at stage XVIII in spontaneous metamorphosis. Treatment with PRL (10 micrograms/10 g tadpole every 2 days) had no effect on the T3-binding sites of RBC nuclei. This dose is adequate to stimulate tail fin growth and inhibit hind limb growth. The same dose of PRL did not affect the T3-induced increase in the MBC and Kd of the T3-binding sites. The results are discussed in terms of the positive regulation of the number of T3 receptors by thyroid hormones. The metamorphic response in amphibia appears to require an increase in the number of T3-binding sites (Receptor Induction).

Animals↗
PubMed1984

Role of exogenous and endogenous prostaglandins in steroidogenesis by isolated frog interrenal gland: evidence for dissociation in adrenocorticotropin and angiotensin action.

The role of prostaglandins (PGs) in the regulation of glucocorticoid and mineralocorticoid production by the frog interrenal (adrenal) gland was studied in vitro by means of continuous perifusion. No change in corticosteroid production was observed upon perifusion with PGA1 or PGA2 (up to 10(-6) M). Conversely six other primary PGs, and the prostacyclin I2 (PGI2), significantly stimulated corticosteroidogenesis: the order of potency being PGE1 greater than PGI2 greater than PGE2 greater than PGB2 greater than PGB1 greater than PGF2 alpha greater than PGF1 alpha. The ability of the PGs to stimulate corticosterone and aldosterone production indicated that PGs may contribute to corticosteroid biosynthesis and that endogenous PGs could act as mediators for certain corticosteroid-stimulating factors. The essential role of endogenous PGs for spontaneous corticosteroid biosynthesis was demonstrated by the marked inhibition of corticosterone and aldosterone production induced by indomethacin (IDM) and meclofenamic acid, two specific inhibitors of cyclooxygenase which reduced significantly PG formation in the interrenal tissue. Stimulation of steroidogenesis by ACTH or cAMP was not affected by infusion of IDM or meclofenamic acid. In addition, ACTH did not modify the production of PGs by interrenal tissue. In contrast, the stimulatory effect of the angiotensin II analog [Sar1-Val5] AII, was markedly reduced in the presence of these two PG synthetase inhibitors and a direct stimulatory effect of the AII analog on PGE2 release was demonstrated. The effects of a supramaximal dose of [Sar1-Val5] AII could not be enhanced by PGE1 indicating that the corticosteroid response to angiotensin II is dependent upon endogenous PG synthesis, whereas the additivity of the stimulatory effects of PGE1 and a maximal dose of ACTH confirmed that PGs are not involved in the mechanism of action of ACTH. These results show that endogenous and exogenous PGs are implicated in corticosteroidogenesis in the frog. Since, in fish and amphibia the adrenocortical tissue is in close contact with the kidney (a major source of PGEs) these results may suggest a physiological relationship between the kidney and the interrenal gland in lower vertebrates. In addition, our results provide the first evidence that the action of angiotensin II on both corticosterone and aldosterone production may be mediated by PGs, whereas ACTH and cAMP stimulate corticosteroidogenesis through another mechanism. Thus, our data support the concept that ACTH and angiotensin II activate the early steps of corticosteroid biosynthesis via different pathways.

Adrenal Glands↗
PubMed1984

An osmometric method for the bioassay of vasotocin and related peptides in the toad bladder.

This study describes a new method for quantitating the antidiuretic activity of 8-arginine vasotocin (AVT) and related peptides on the isolated toad urinary bladder. The method is based on measuring changes in the osmolality of the surface fluid film of bladders that have been filled with a dilute solution and suspended in humidified air. Eight microliters of Ringer's fluid containing a known concentration of hormone are applied to small paper discs (0.7 cm in diameter), and the discs are then placed with fine forceps onto the outer surface of the bladder to which they adhere. The hormone increases the permeability to water of the epithelium that is underneath the area of the disc, and as water moves from the interior of the bladder along its osmotic gradient to the outer surface of the bladder, the Ringer's fluid in the disc becomes diluted. The magnitude of this dilution is quantitated by removing the discs to a vapor pressure osmometer at timed intervals. A supramaximal dose of AVT reduced disc fluid osmolality by 188 mosmol/kg H2O within 15 min. Similar maximal responses were observed with 8-arginine vasopressin (AVP), oxytocin, and 8-lysine vasopressin, although the potencies of these hormones diminished in the order listed above. AVT was 112-fold more potent than AVP, and AVP, in turn, was 329-fold more potent than 8-lysine vasopressin. The lower limit at which AVT was detected in this assay was 0.25 pg/disc (3 X 10(-11) M). The intra- and interassay variabilities for AVT were 14% and 28% (+/- SD), respectively. This assay is suitable for measuring the biological activity of hormone analogs lacking vasopressor activity, such as desmopressin, which was found to have a hydroosmotic activity of 8.3 +/- 2.4 U/mg. After osmotic stimulation, AVT was detected in toad plasma at a concentration of 1.4 X 10(-10) M. Therefore, this method has the requisite sensitivity for measuring this hormone in biological fluids of amphibia, reptiles, fish, and birds.

Animals↗
PubMed1988

Iodothyronine 5'-deiodinase activity in the amphibian Rana catesbeiana at different stages of the life cycle.

In a previous study, 5' deiodinase (5'D) activity was detected in skin but not in other tissues of premetamorphic tadpoles. When these tadpoles were stimulated to metamorphic climax by treatment with thyroid hormone, activity was increased in skin and was found also in gut and tail tissue. In the present study, 5'D activity was studied at various stages of spontaneous development from early prometamorphosis through metamorphic climax and including the adult frog. 5'D activity was detected in gut and skin at all stages studied and in metamorphosing tail tissue. It was minimal or absent in all other tissues examined. Activity in prometamorphic skin was comparable to that previously observed in premetamorphic skin but increased significantly during metamorphic climax and remained at this level in the adult. 5'D activity was not observed in tail tissue until resorption commenced and when present could not be correlated with tadpole stage or tail length. In both skin and tail, the 5'D activity exhibited values for Michaelis-Menten constant (Km) for rT3 and T4 in the nanomolar range. During prometamorphosis, the 5'D activity in gut exhibited a value for the rT3 Km in the micromolar range. As the tadpoles entered metamorphic climax, the rT3 Vmax of this activity in gut decreased and a second type of 5'D activity, with a Km for rT3 in the nanomolar range, was detected in this tissue. By stage XXI, only the latter component was observed, and its activity increased significantly during metamorphic climax. In the adult frog, 5'D activity in gut was comparable to that seen at the onset of climax. The adult frog also exhibited T3 5D activity in all tissues studied. These observations, together with those reported in the previous study, indicate that gut and skin are the principal T3-generating organs in anuran amphibia and suggest that increased activity of the 5'D system, at the time in the life cycle that the tissues require increased amounts of thyroid hormone, is an important part of thyroid hormone economy in this species.

Aging↗