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Action of caerulein and caerulein-like peptides on "short-circuit current" and acid secretion in the isolated gastric mucosa of amphibians
No full textCaerulein produced an increase of the short-circuit current in the isolated gastric mucosa of Rana esculenta and Bufo viridis. Threshold concentrations were of the order of 10–10 M and 3×10–11 M, respectively. A dose-response relationship was observed for concentrations of the polypeptide up to 10 to 20 times the threshold. At the same time, the polypeptide also caused an increase in the secretion of hydrochloric acid by the isolated mucosa, as measured by a direct titrimetric method. The effects of caerulein were atropine-resistant, and hence not mediated through a cholinergic mechanism. The action of caerulein on short-circuit current was compared to that of a number of synhtetic caerulein-like peptides and to that of other miscellaneous stimulants of gastric acid secretion. This study allows some conclusions to be drawn as to the relationship between chemical structure and biological activity, and largely confirms results obtained with other test preparations. With the exception of some caerulein-like peptides, no other compound could compete with caerulein in its stimulant action on the isolated amphibian gastric mucosa: cholecystokinin possessed 3% of the activity of caerulein, histamine approximately 0.1%, human gastrin I, pentagastrin and carbachol barely 0.01%
A POTENT FACTOR IN EXTRACTS OF THE SKIN OF THE AUSTRALIAN FROG, PSEUDOPHRYNE CORIACEA – APPARENT FACILITATION OF TRANSMITTER RELEASE IN ISOLATED SMOOTH MUSCLE PREPARATIONS
No full textExtracts of the skin of the Australian frog Pseudophryne coriacea (PsC) displayed potent stimulant effects on isolated smooth muscle preparations of intestine and similar effects on electrically-stimulated vas deferens preparations. These effects must be ascribed to an alkaloid, related in structure to the pumiliotoxins, a class of alkaloid compounds occurring in the skin of neotropical poison frogs. On the basis of results obtained with antagonists and blocking agents, it is suggested that the extract has a pre-synaptic, neurogenic point of attack and that it acts to facilitate the release of transmitters from nerve endings. Acetylcholine is the most important agent involved in the response to the extract by the intestinal muscle and noradrenaline in the response by vas deferens preparations. However, release of other aminergic or peptidergic transmitters may participate, positively or negatively, in the response
In vitro and in vivo biological activities of PG-KII, a novel kassinin-like peptide from the skin of the Australian frog, Pseudophryne guntheri
No full textWe compared the in vitro and in vivo biological activities of PG-KII (pGlu-Pro-Asn-Pro-Asp-Glu-Phe-Val-Gly-Leu-Met-NH2), a new peptide belonging to the tachykinin family, related to kassinin, isolated and sequenced from extracts of the skin of the Australian myobatrachid frog Pseudophryne guntheri, with those of the well-known tachykinins [substance P (SP), neurokinin A (NKA), neurokinin B (NKB), and kassinin (KASS)] to study its pharmacological and receptor profile. PG-KII always proved inactive in the in vitro and in vivo (gastric emptying) NK2 bioassays. It resulted equipotent to SP and more potent than KASS, NKA, and NKB in all in vitro smooth muscle preparations preferentially activated by the NK1-selective agonists. On an in vivo NK3 receptor-mediated function, gastric acid secretion, PG-KII had a potency similar to that of NKB. In contracting guinea pig ileum, which contains NK1, NK2, NK3, and also new tachykinin receptor subtypes, PG-KII was more potent than SP, NKB, and NKA. The cholinergic antagonist, atropine, significantly reduced the guinea pig contractile activity of both PG-KII and NKB but not that of SP or NKA. Pretreatment with the NK1-selective antagonist, CP 96,345, and with the NK2-selective antagonist, MEN 10,376, modified neither the in vivo nor the in vitro effects of PG-KII. These findings indicate that PG-KII is neither an NK1 nor an NK2 receptor agonist but has a spectrum of biological actions close to that of the NK3 receptor agonists. PG-KII elicits strong contractile activity in guinea pig ileum. Administered centrally in the rat it regulates inhibition of gastric acid secretion
Radioimmunoassay of dermorphin-like peptides in mammalian and non-mammalian tissues
No full textA selective RIA for D-Ala2-Dermorphin (Der), a natural peptide extracted from amphibian skin, has been developed using an antibody raised in rabbits against Der which has been coupled to BSA through its phenolic hydroxyl groups of tyrosine residues with 2,4-Dichloro-6-methoxy-1,3,5-triazine. The cross-reactivity of this antibody with dermorphin analogs, C- and N-terminal fragments of dermorphin molecule, some opioid and gastrointestinal peptides was tested. Der-like immunoreactivity has been identified in tissue extracts of rats, frog and cephalopoda. Der-like peptides were purified by passing methanol extracts of the tissues through a Sephadex G25 column (16x100 cm) eluted with 0.1 M acetic acid at 4°C. Der-like immunoreactivity from neural tissue of Dosidicus gigas, Eledone moscata, and rat brain showed a good agreement with an authentic sample of synthetic dermorphin
Evidence of cholecystokinin release by bombesin in the dog
No full textIntravenous infusion of bombesin elicited in dogs a contraction of the gallbladder with decreased opening pressure of the choledocho duodenal junction and stimulation of pancreatic secretion. The pancreatic juice produced under the influence of bombesin was poor in bicarbonate and rich in protein. Threshold doses of the peptide were of the order of 0.25 μg kg-1h-1 and maximum protein output was obtained with 1 μg kg-1h-1. The pancreatic protein response to bombesin was very similar, in its onset and duration, to that elicited by intraduodenal infusion of L tryptophan. Infusions of bombesin repeated at short intervals produced tachyphylaxis. Antrectomy did not effect the stimulant action of bombesin on the pancreas. Atropine however, reduced the pancreatic protein response to bombesin. It is suggested that bombesin acts on the gallbladder and the exocrine pancreas through release of cholecystokinin from the duodenal mucosa. No release of secretin could be demonstrated. It is likely that the releasing activity of bombesin is limited, in the field of gastrointestinal peptides, to those belonging to the gastrin cholecystokinin family
Occurrence and polymorphism of bombesin-like peptides in the gastrointestinal tract of birds and mammals
No full textThe gastrointestinal tract of mammals and birds, especially stomach and upper small intestine, contains bombesin-like peptides. This has been unequivocally demonstrated by radioimmunoassay and bioassay. Concentrations of bombesin-like activity may range from a few ng to 500-600 ng per g fresh tissue. Last values refer to the chicken proventriculus, which has been the object of a more thorough investigation. The bombesin-like peptide of the chicken proventriculus showed a marked heterogeneity. All forms probably stem from a pro-bombesin, a large precursor molecule which is insoluble in methanol, acetone, and even boiling water, but may be cleaved by acid hydrolysis. Methanol extracts contain at least 2 forms of the bombesin-like peptide; HCl extracts at least 3 forms; HCl extracts of the residue of methanol extraction at least 4 forms. Whereas some forms - for example, the methanol extractable forms - probably pre-exist in the tissue, other forms may be artefacts arising from acid treatment. The various forms may be distinguished from each other not only by their elution profile, but also by bioassay. In fact, though all forms show the activity spectrum characteristic for the amphibian bombesin-like peptides, they present considerable quantitative differences in activity. Pro-bombesin(s) probably occur also in the rat and guinea-pig stomach; similarly, a clear-cut heterogeneity is appreciable for the bombesin-like peptide of the human gastric mucosa
Occurrence of bombesin and alytesin in extracts of the skin of three European discoglossid frogs and pharmacological actions of bombesin on extravascular smooth muscle.
No full text1. Methanol extracts of the skin of Bombina bombina and Bombina variegata variegata, two European discoglossid frogs, contain an active tetradecapeptide, bombesin. Alytesin, a tetradecapeptide strictly related to bombesin is present in extracts of the skin of Alytes obstetricans, another European discoglossid frog. The American frog Rana pipiens, contains in its skin ranatensin, an endecapeptide related to bombesin and alytesin. 2. Passage of crude skin extracts of Bombina through a column of alumina yields eluates which may be considered free of other peptide contaminants and are suitable for the isolation of bombesin in a pure form. 3. Bombesin has a stimulant action on several preparations of intestinal, uterine and urinary tract smooth muscle. Sometimes the effect is easily repeatable and shows a fair proportionality to the dose, but at other times a prompt and intense tachyphylaxis is observed. Other smooth muscle preparations are poorly sensitive or insensitive to bombesin. The rat uterus, the kitten small intestine, the guinea-pig colon and the rat urinary bladder may be used for the quantitative bioassay of bombesin. 4. Bombesin-like peptides may easily be distinguished from all other naturally occurring peptides by parallel assay. They constitute a new group of active peptides possessing a peculiar spectrum of activity
Active peptides in the skins of one hundred amphibian species from Australia and papua New Guinea
No full text1. Extracts prepared from the dried skins of approximately one hundred amphibian species from Australia and Papua New Guinea were subjected to biological screening in order to determine the nature and amounts of peptides active on smooth muscle preparations and systemic blood pressure present in these extracts. 2. The most frequently and abundantly occurring peptides were those of the caerulein, bombesin and tachykinin peptide families represented, respectively, by caerulein: litorin, Glu(OMe)2-litorin and Glu(OEt)2-litorin; uperolein and Lys5-Thr6-physalaemin. 3. Bradykinin-like peptides seem to have a rather diffuse distribution, in the species examined, but so far no peptide of this family has been isolated and sequenced. 4. The only angiotensin-like peptide ever found in amphibian skin, crinia angiotensin II, has been isolated from skin extracts of a few species, belonging to the genera Crinia, Geocrinia, Ranidella and Litoria. 5. The array of peptides occurring in amphibians from Australia and Papua New Guinea is destined to increase, because several apparently novel peptides have been identified in skin extracts by bioassay and radioimmunoassay
Polypeptides of the amphibian skin active on the gut and their mammalian counterparts.
No full text[No abstract available
Uperolein and other active peptides in the skin of the Australian leptodactylid frogs Uperoleia and Taudactylus
No full textMethanol extracts of the skin of the Australian leptodactylid frogs Uperoleia rugosa, Uperoleia marmorata and Taudactylus acutirostris contain several highly active polypeptides belonging to different peptide families. The most abundant peptide was uperolein, a tachykinin closely related to physalaemin and possessing the same spectrum of biological activity. Uperolein was present in the three species examined. Other tachykinins were represented by Rugosa uperolein II and Marmorata uperolein II, the structures of which still await full elucidation. Another peptide family represented in both Uperoleia and Taudactylus was that of bombesin like peptides. They were abundant in Uperoleia rugosa and scarce in Uperoleia marmorata and in Taudactylus. These bombesins are possibly similar to the bombesins, among which is litorin, present in the skin of other Australian leptodactylid frogs. Finally, Taudactylus contained a bradykinin like peptide and both the Uperoleia species an hitherto unclassified peptide. These new findings have further enriched the already considerable list of active peptides and biogenic amines occurring in the amphibian skin
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