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At least 973 records · Page 54Linked to original sources
PubMed1992

Decreased docosahexaenoic acid levels in retina and pigment epithelium of frogs fed crickets.

Whole retina, rod outer segments, and retinal pigment epithelium of frogs (Rana pipiens) fed crickets for more than 1 year had significantly lower levels of docosahexaenoic acid (22: 6n-3) than the same tissues of frogs fed crickets for less than 1 month. Decreases in 22:6n-3 levels in these tissues were compensated for by increases in the n-6 polyunsaturated fatty acids (PUFAs), primarily 22:5n-6. There were no changes in the levels of saturated, monoenoic, or dienoic acids. Analysis of diacyl phospholipid molecular species (PLMS) revealed decreases in both the 22:6(n-3)-containing dipolyenoic molecular species in phosphatidylethanolamine and phosphatidylserine, and the monopolyenoic molecular species in phosphatidylcholine. These PLMS were replaced by species containing 22:5n-6 or other n-6 PUFAs. Examination of fatty acid methyl esters of total lipids extracted from crickets revealed that less than 1 mol% fatty acids were of the n-3 family, while more than 30 mol% were of the n-6 family. Thus, frogs raised on an n-3-deficient diet have reduced levels of n-3 PUFA in their retinas, rod outer segments, and retinal pigment epithelium. Although such changes have been reported for mammals, this is the first report of the effects of n-3 deficiency on the lipids of amphibians.

Animals↗
PubMed1992

Light stimulates in vivo inositol lipid turnover in frog retinal pigment epithelial cells at the onset of shedding and phagocytosis of photoreceptor membranes.

We have developed an experimental model to study in vivo inositol lipid metabolism in frog retinal pigment epithelial (RPE) cells, including the effect of light on phospholipase C-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate. RPE cells were rapidly isolated after either brief light or dark periods. Light and electron microscopy showed complete detachment of the retina from the RPE cells, and that the RPE cell suspensions were devoid of photoreceptor cell outer segments. Frog tissues were labeled in vivo for 20 hr by intravitreal injection of [3H]inositol (4 microCi, 4 microliters per eye) within a 24-hr constant illumination period. Following 1 hr of darkness (priming period), frogs were intravitreally injected with LiCl (0.5 M, 4 microliters per eye) 15 min before the onset of either 30-min light stimulation or an additional 30 min of darkness (controls). In order to preserve endogenous inositol phosphate pools present after dark and light exposure, the RPE cells were harvested in the shortest time possible, at low temperatures (18-20 degrees C), and in the presence of 10 mM LiCl. Total [3H]inositol-labeled water-soluble products (inositol plus inositol phosphates) were increased by 86% after 30 min of light. Inositol trisphosphate (IP3) showed the highest accumulation (a 5.5-fold increase), followed by inositol bisphosphate (1.9-fold increase) and inositol monophosphate (1.4-fold increase). Free [3H]inositol also accumulated (2.8-fold increase), reflecting only a partial inhibition of phosphomonoesterase by LiCl. These changes were paralleled by a 12% decrease in 3H-labeled phosphatidylinositol with no significant difference in the labeling of polyphosphoinositides.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The role of ornithine decarboxylase and polyamines in regeneration of the frog sciatic nerve.

The current study examined both in vivo and in vitro the effects of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), on regeneration of sensory axons from a local crush of the adult frog sciatic nerve. If daily injections of DFMO started at the same time as crushing and continued throughout the regeneration period (7 days) the outgrowth in vivo of new sensory axons was reduced by about 30%. If DFMO injections started 2 days after crushing, the outgrowth distance did not differ from control values. The sensory axons of a cultured frog sciatic nerve with the attached spinal ganglia start to regenerate from a local crush applied 7 days after the start of the incubation. Five days after crushing the outgrowth distance was 4.5 mm. At the end of the culturing period (7 + 5 days) both the putrescine and spermidine concentrations in the ganglia had increased about 2.5 times, whereas the spermine concentration remained constant. The presence of 10 mM DFMO throughout the culturing period, 7 + 5 days, almost depleted putrescine and prevented the spermidine increase in the ganglia without affecting the regeneration distance. In the nerve putrescine was only reduced by 55% and the other polyamines were unaffected by DFMO. The results show that DFMO influences the early onset of regeneration in vivo. The in vitro results indicate that this is not due to a close mechanistic relationship between the perikaryonal ODC/polyamine system and nerve regeneration. The question of whether polyamines are of local importance for regeneration of the frog sciatic nerve cannot be answered by the present results.

Animals↗
PubMed1992

Effects of freezing a segment of peripheral nerve on subsequent protein release and axonal regeneration in the frog.

Previous studies in frogs have shown that axons from the proximal stump of a cut nerve will grow toward the distal stump, possibly in response to diffusible trophic factors produced by cells of the nerve sheath. In the present experiments, the synthesis and release of proteins in vitro, from proximal and distal stumps of frog sciatic nerves, were studied 1, 4, and 14 days after nerve section in vivo. Using two-dimensional gel electrophoresis to separate released proteins, a marked increase in the synthesis of two lipoproteins of 37 and 67 kDa was seen, initially in both proximal and distal stumps, but by 14 days these proteins were produced exclusively by the distal stump. To see if the production of these proteins was correlated with subsequent reinnervation of the distal stump, isolated nerve segments were removed from the frogs and either replaced immediately or frozen (to kill sheath cells) and replaced. After 2 weeks, the pattern of newly synthesized proteins released by both the frozen and nonfrozen nerve segments was similar although freezing severely impaired the reinnervation of the nerve segment. These results suggest that although the 37- and 67-kDa lipoproteins may have a role in nerve regeneration, their presence per se is not sufficient to support the reinnervation of a distal stump of a cut peripheral nerve and that additional factors may therefore be required.

Animals↗
PubMed1983

The absence of the long 3'-non-translated region in mRNA coding for eye lens alpha A2-crystallin of the frog (Rana temporaria).

The nucleotide sequence of a cloned cDNA (clone pRt(1)297; GENE (1982) 17, 131) coding for a 18 kDa polypeptide of the frog eye lens has been determined. The sequence, 791 nucleotide in length has only one long open reading frame (447 nucleotides). The derived amino acid sequence in this frame has greater than 90% homology with the region 25-173 of alpha A2-crystallin amino acid sequence from a related frog species Rana pipiens. The 5'-terminal part of mRNA corresponding to the first 24 amino acids of alpha A2-crystallin has been lost in cloning and substituted by an artefactual sequence. The 3'-terminal part appears to be intact as follows from the presence of the universal poly(A) addition site and poly(A) tract. The 3'-nontranslated region present in frog alpha A2-crystallin mRNA (130 nucleotides) is about 4-times shorter than in mammalian alpha A2-crystallin mRNA. Intact alpha A2-crystallin mRNA with a size of about 700 nucleotides as determined by Northern blot hybridization is about twice smaller than corresponding mammalian mRNAs.

Amino Acid Sequence↗
PubMed1988

The amino acid sequences of frog heart atrial natriuretic-like peptide and mammalian ANF are closely related.

Despite few studies conducted in non-mammalian species, there has been a number of reports pertaining to the occurrence of a natriuretic-like substance in lower organisms. Thus, an immunoreactive substance reacting with antibodies directed against mammalian atrial natriuretic factor has previously been detected both in heart atria and ventricles of a chordate, the frog. This substance was isolated and purified from frog heart atria and its amino acid sequence established. The sequence, Ala-Pro-Arg-Ser-Ser-Asp-Cys-Phe-Gly-Ser-Arg-Ile-Asp-Arg-Ile-Gly-Ala-Gln- Ser-Gly - Met-Gly-Cys-Gly-Arg-(Phe), is highly homologous to known mammalian ANF sequences. However, when aligned with the complete mammalian ANF precursor sequence at positions 121 to 151, it exhibits a single amino acid insertion at position 129 and other substitutions at positions 121, 125, 133, 135, 144, 147 and 148. Some evidence is also presented concerning the occurrence of uncleaved frog pronatriodilatin, the precursor form of ANF. This study represents the first report pertaining to the structure of a non-mammalian ANF and its precursor.

Amino Acid Sequence↗
PubMed1995

Asn-265 of frog kainate binding protein is a functional glycosylation site: implications for the transmembrane topology of glutamate receptors.

Kainate binding proteins (KBPs) from frog and goldfish brain are glycosylated, integral membrane proteins. These KBPs are homologous (35-40%) to the C-terminal half of AMPA and kainate receptors which have been shown to form glutamate-gated ion channels. We report here that the frog KBP has three functional N-glycosylation sites. Of particular interest, Asn-265, a residue located between two putative membrane spanning regions of the frog KBP, is a functional N-glycosylation site. A mutation of Ser-267 to Gly renders this site non-functional as shown using an in vitro translation system and by transient expression in human embryonic kidney (HEK 293) cells. The mutant receptor protein (S267G), when expressed in HEK cells, binds kainate with high affinity (Kd = 16 nM). These results further support a topology with three transmembrane segments for KBPs and, by sequence homology, for glutamate-gated ion channels.

Amino Acid Sequence↗
PubMed1996

Molecular cloning of frog secretogranin II reveals the occurrence of several highly conserved potential regulatory peptides.

Secretogranin II (SgII) is an acidic secretory protein present in large dense core vesicles of neuronal and endocrine cells. Based on the sequence of a peptide derived from the processing of SgII in the brain of the frog Rana ridibunda, degenerate oligonucleotides were used to clone the cDNA encoding frog SgII from a pituitary cDNA library. This cDNA encodes a 574 amino acid protein which exhibits 46-48% sequence identity with mammalian SgII and contains 11 pairs of basic amino acids. Four potential processing products delimited by pairs of basic residues exhibited a much higher degree of identity (68-82%) with the corresponding mammalian SgII sequences. The frog SgII mRNA is approximately 4 kb in length and is differentially expressed in the brain and endocrine tissues. The present data reveal that several SgII-derived peptides have been highly conserved during evolution, suggesting that these peptides may play important neuroendocrine regulatory functions.

Amino Acid Sequence↗
PubMed1983

Catecholamine and divalent cation effects on frog liver adenylate cyclase.

Frog liver adenylate cyclase was characterized with respect to divalent cation interaction and hormonally stimulated activities. The enzyme catalyzed the synthesis of cyclic [32P]3',5'-AMP from alpha-32P-labeled ATP. The activity of the enzyme was linear with time and protein concentration. The Km for ATP was 0.5 mM, in the presence or absence of stimulators. The temperature optimum was 25 degrees. GTP (10(-4) M) increased the stimulation of adenylate cyclase by epinephrine. Similar activities were obtained using 5 mM Mg2+ or Mn2+. At higher concentrations, both ions inhibited epinephrine-stimulated, but not basal or fluoride-stimulated activities. Approximately equivalent hormonal stimulation was obtained with maximal stimulating concentrations of epinephrine, isoproterenol, glucagon, and prostaglandin E1. Norepinephrine was less stimulatory. Only catecholamine-stimulated activities were inhibited by propranolol (10(-5) M). The data suggest that catecholamines stimulate frog liver adenylate cyclase through interactions with beta adrenergic receptors. The adenylate cyclase in frog liver differs from its mammalian counterpart in its response to temperature and maximally stimulatory concentrations of hormones.

Adenylyl Cyclases↗
PubMed1984

Cardiac actions and structural--activity relationship of parathyroid hormone on isolated frog atrium.

The hypercalcemic and hypotensive actions of parathyroid hormones (PTH), parathyroid extract, and synthetic PTH-(1-34) have been reported in many different animals. However, their cardiac action was only recognized recently. In the present study, experiments were designed to examine (1) whether PTH possesses any cardiac action on the isolated frog atrium, and (2) the importance of methionine and arginine of bPTH-(1-34) in cardiac action. Six different bPTH analogs were tested in frog atria in vitro: bPTH-(1-34); H2O2-treated bPTH-(1-34); [Nle8, Nle18, Tyr34]-bPTH-(1-34); H2O2-treated [Nle8, Nle18, Tyr34]-bPTH-(1-34); arginine-modified bPTH-(1-34); and arginine-regenerated bPTH-(1-34) (Nle-norleucine). bPTH-(1-34) produced positive chronotropic and inotropic responses. Oxidation with hydrogen peroxide abolished both actions of bPTH-(1-34). [Nle8, Nle18, Tyr34]-bPTH-(1-34) also possesses this cardiac-stimulating property. The H2O2 treatment of this analog did not alter the chronotropic action, but a decrease in the inotropic action was observed. The arginine-modified bPTH-(1-34) was much less potent than its native hormone, while the reversal of the arginine modification partially restored the biopotency. From these data, it is concluded that (1) bPTH-(1-34) possesses both positive chronotropic and inotropic effects on the frog atrium, (2) the cardiac actions of bPTH-(1-34) may be closely related with its hypotensive property, (3) methionines are not necessary for the cardiac actions, and (4) arginines are important for the cardiac-stimulating effects of bPTH.

Animals↗
PubMed1985

Effect of photic manipulation on the level of melatonin in the retinas of frogs (Rana tigrina regulosa).

The level of melatonin in the frog (Rana tigrina regulosa) retina was studied at midlight and middark in a 12L:12D cycle and under different lighting conditions. It was found that the frog displayed a diurnal rhythm of melatonin in the retina with high levels in the dark period. When the animal was subjected to an extended dark period, the level of retinal melatonin was significantly (P less than 0.05) increased. In addition, the normal low level of retinal melatonin in the light period was significantly (P less than 0.05) increased after dark treatment, and the normal high level of retinal melatonin in the dark period was significantly (P less than 0.05) lowered following light exposure. These results suggest that synthesis and secretion of melatonin in the frog retina is controlled by environmental lighting. This supports the hypothesis that melatonin plays an important role in the regulation of the photomechanical changes of eye pigmentation, an important element in the control of light sensitivity and acuity in the eyes of vertebrates. Moreover, these findings suggest that the photoreceptor may be a neuroendocrine or neurohumoral transducer which transduces the environmental lighting into neuroendocrine or neurohumoral secretion, melatonin.

Animals↗
PubMed1986

In vitro study of frog (Rana ridibunda Pallas) interrenal function by use of a simplified perifusion system. VIII. Structure-activity relationship of synthetic ACTH fragments and gamma-MSH.

The present study was undertaken to determine the structure-activity relationships of ACTH analogs on corticosteroid production by frog adrenal gland. Rana ridibunda interrenal dice were perifused with amphibian culture medium for 10 hr. Corticosterone and aldosterone concentrations were measured in the effluent perifusate using sensitive and specific radioimmunoassay methods. Perifusion of interrenal fragments with increasing concentrations of synthetic human ACTH 1-39 (ranging from 6.25 X 10(-11) to 10(-9) M) led to a linear log-dose increase in both corticosterone and aldosterone secretion. Thus, this model made it possible to compare the steroidogenic potency of several ACTH analogs. Synthetic alpha-MSH and its des-N alpha-acetyl derivative were found to be approximately equipotent, and 5 X 10(3) times less active than authentic ACTH. The short-chain analog ACTH 1-10 was 2 X 10(4) times less potent than ACTH whereas ACTH 4-10 was totally inactive. A fragment of the N-terminal region of the proopiomelanocortin molecule, gamma 3-MSH, caused a dose-related stimulation of steroid secretion. However, in contrast to what has been observed in the rat, gamma 3-MSH did not potentiate the corticotropic action of ACTH on frog interrenal gland. Since processing of proopiomelanocortin in frog intermediate lobe generates high amounts of alpha-MSH and des-N alpha-acetyl alpha-MSH, these results suggest that in amphibians, several peptides other than ACTH may be involved in the control of corticosteroidogenesis.

Adrenal Glands↗
PubMed1990

The vasorelaxant effect of atrial natriuretic peptide in the frog.

The vasorelaxant effect of atrial natriuretic peptide (ANP) in two species of frogs, Rana catesbeiana and R. tigrina, were studied in vitro. Isolated arterial strips were prepared from the aortic loop, dorsal aorta, iliac, and femoral arteries in the frog. These were stimulated to contract with KCl, norepinephrine, or arginine vasotocin. When maximal contraction was attained, ANP was added to assess if it could relax the strips. Data show that ANP is vasorelaxant in these preparations. The sensitivity of these tissues depends on the contractile agents, e.g., KCl-stimulated preparations from R. catesbeiana did not respond to ANP. Data also suggest that ANP action elicited in the frog vascular tissue is due to an inhibitory effect on the mobilization of the intracellular calcium store and/or calcium influx from extracellular space to initiate contraction.

Animals↗
PubMed1990

Neurohypophysial hormones and cardiac activity in the frog, Rana tigrina, and in the snake, Ptyas mucosa.

The cardiac effects of neurohypophysial hormones (NH) in the frog, Rana tigrina, and in the snake, Ptyas mucosa, were studied in isolated atrial preparations. Arginine vasopressin (AVP), vasotocin (AVT), isotocin (ISN), mesotocin (MSN), and oxytocin (OXY) produced dose-related positive chronotropic and inotropic responses in the frog atria. AVT was the most potent. In the snake, AVP, AVT, MSN, and OXY produced dose-related positive inotropic but not chronotropic changes. OXY was the most potent. Data indicate that there is a direct action of NH on the heart in both animals, the atrial rate and tension responses to NH are not coupled, and judging by the efficacy, AVT and OXY might be the natural NH in the frog and snake, respectively, which may account for the high concentrations required of other NH to be cardiac stimulating.

Animals↗
PubMed1990

Indirect evidence for a physiological role exerted by a "testicular gonadotropin-releasing hormone" in the frog, Rana esculenta.

The possible physiological role of a putative testicular gonadotropin-releasing hormone (GnRH)-like material was studied in the frog, Rana esculenta. We have investigated (a) changes of mitotic index (MI) of primary spermatogonia (SPG) in GnRH agonist (GnRH-Ag)-treated testes in vitro; (b) changes of androgen concentrations in testes of intact frogs treated with a GnRH antagonist (GnRH-Ant); (c) variations of mitotic index of primary SPG in intact GnRH-Ant-injected animals and in testes incubated with GnRH-Ant; (d) changes of MI in hypophysectomized (PDX) animals treated with hypophysis (PD) homogenate, and hCG alone or in combination with GnRH-Ant; and (e) changes of androgen concentrations in plasma PDX frogs treated with hCG and hCG plus GnRH-Ant. Our results indicate that while GnRH-Ag induced accumulation of primary SPG mitosis, GnRH-Ant inhibited androgen production and natural occurring mitosis accumulation. Therefore, GnRH-Ant may counteract an endogenous peptide working into the testis.

Androgens↗
PubMed1992

Changes of LH level in the pituitary gland and plasma in hibernating frogs, Rana temporaria.

Pituitary and plasma luteinizing hormone (LH) levels were measured in female frogs, Rana temporaria, during and immediately after hibernation (0-4 degrees in darkness; 22-25 weeks) to study regulation of gonadotropin leading to posthibernation ovulation. Pituitary LH content began to rise progressively during the last third of hibernation (e.g., from starting levels of 5.3 +/- 0.09 micrograms/gland, 1.5 micrograms/mg between 8 and 11 weeks, to 18.6 +/- 9.7 micrograms/gland, 5.0 +/- 2.7 micrograms/mg at 19-22 weeks). Plasma LH increased in parallel, but with some delay (from 10 +/- 8 to 25 +/- 24 ng/ml). Frogs kept in light at low temperatures showed similar responses. Release of LH (rise in plasma levels with a drop in pituitary content) was observed during 32 hr immediately after termination of hibernation in association with the onset of ovulation. These data indicate the existence of regulatory mechanisms operating during hibernation under conditions of constant cold. Altogether, these and our previous results obtained after surgical deafferentiation of median eminence support the hypothesis of a progressive reduction of a CNS inhibition that results in the release of GnRH during hibernation in this frog.

Analysis of Variance↗
PubMed1992

In vitro study of the effect of adenosine on frog adrenocortical cells.

Previous reports have shown that adenosine in rat inhibits both spontaneous and ACTH-induced release of corticosteroids through activation of adenosine A1 receptors. In the present study, we have investigated the possible effect of adenosine in the secretion of corticosteroids in amphibians using a perfusion technique for frog adrenocortical slices. Infusion of adenosine, at concentrations ranging from 10(-7) to 10(-4) M, had no effect on the basal output of corticosterone and aldosterone by frog interrenal cells. Similarly, adenosine did not affect the response of frog adrenocortical slices to ACTH, vasoactive intestinal peptide, or angiotensin II. The stable adenosine A1 receptor agonist N6-phenylisopropyl adenosine (PIA) was also totally devoid of effect on the spontaneous or ACTH-induced release of corticosteroids. These results show that in amphibians, adenosine does not modulate adrenal steroidogenesis.

Adenosine↗
PubMed1980

A theoretical proposal to account for visual computation in a frog's retina.

Our theoretical account for visual computation in a frog's retina is based on the concepts that: (a) outer retinal layers provide three spatial channels of information pertaining to local spatio-temporal properties of retinal stimuli; (b) prominent specialisation in a frog's retina is the result of a non-linear lateral interaction at the inner plexiform layer; (c) ganglion cell firing frequency is determined by a local computation wherein signals from processes above are either excitatory, facilitatory or defacilitatory. General though concrete expressions for the processing at different layers are developed from these concepts. They result in a unified model for ganglion retinal cells in frog, from which the various extreme groups of ganglia can be deduced. The model leaves a natural margin to fit intermediate types, both found and likely to be found.

Animals↗