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Definition
Xenopsin, an octapeptide isolated from the skin of Xenopus laevis.  It is involved in the modulation of gastrointestinal functions.

Discovery
The octapeptide xenopsin was first discovered by Araki et al., in the skin of amphibians 1.

Structural Characteristics
Xenopsin is one of the peptides found in amphibian skin, first isolated consists of eight amino acids and is present in relatively high amounts in skin extracts from Xenopus laevis. The octapeptide bears a striking sequence resemblance to mammalian neurotensin and shares a number of its biological properties 2.

Xenopsin-Related Peptides:
Xenin, a Xenopsin-related Peptide, in the human gastric mucosa: As immunohistochemistry has indicated the presence of xenopsin immunoreactivity in man. The elutes extracted by HPLC were monitored with a radioimmunoassay for amphibian xenopsin. Determination of the amino acid sequence revealed 25–amino acid peptide having 6 C-terminal amino acids in common with amphibian xenopsin 3. The sequence of this peptide, termed xenin 25, is M-L-T-K-F-E-T-K-S-A-R-V-K-G-L-S-F-H-P-K-R-P-W-I-L.

Mode of Action
In an experiment conducted, the effects of synthetic xenopsin on endocrine pancreas and gastric antrum in anesthetized dogs were studied. Synthetic xenopsin was administered into the superior pancreaticoduodenal artery and plasma insulin, glucagon and gastrin in the superior pancreaticoduodenal vein and gastrin in the right gastroepiploic vein were measured radioimmunologically. Administration of 10 µg of xenopsin per kg of body weight brought about a hyperglycemic response and rapid and sharp elevations of the hormones in the pancreatic vein. Plasma gastrin level in the gastric vein also showed an immediate and sharp increase following xenopsin administration. Xenopsin appeared more potent inducer of the glucagon. Taken together, it can be concluded that xenopsin acts directly on endocrine pancreas and gastric antrum to secrete their hormones 4.

Functions

Effect of xenopsin on blood flow, hormone release, and acid secretion: A study investigated the effects of the neurotensin analogue xenopsin on regional blood flow, central hemodynamics, and stimulated acid secretion in awake conscious dogs. Organ blood flow, estimated using the radioactive microsphere technique, was significantly increased during the xenopsin infusion to the adrenals, pancreas, and ileum. There was no change in mean arterial pressure or cardiac output (measured by thermodilution). Along with changes in blood flow, there was a significant increase in the hormone output from the pancreas. These included rises in plasma pancreatic polypeptide, insulin, and glucagon. There also was a rise in plasma cortisol levels during the infusion. Substance P levels rose slowly but significantly during the xenospin infusion. There was no change in plasma gastrin levels. Xenopsin produced a significant inhibition of tetragastrin-stimulated gastric acid output. Thus, xenopsin appears to have region-specific influence on blood flow that correlates with region-specific hormonal secretion. In addition, xenopsin, like its mammalian analogue neurotensin, is an inhibitor of stimulated gastric acid secretion. A mammalian xenopsin like peptide may well be involved in the modulation of gastrointestinal function 5.

Xenopsin stimulates exocrine pancreatic secretion in the dog: In a study, the octapeptide xenopsin, stimulated exocrine pancreatic secretion of bicarbonate and protein in conscious dogs and increases the volume of secretion. This effect has been shown in the dose range of 1.25 up to 160 pmoles kg–1min–1.  The high potency of this peptide is suggestive of a possible physiological role of xenopsin in mammals 6.

References

  1. Araki K, Tachibana S, Uchiyama M, Nakajima T, Yasuhara T (1973). Isolation and structure of a new active peptide "Xenopsin" on the smooth muscle, especially on a strip of fundus from a rat stomach, from the skin of Xenopus laevis. Chem. Pharm. Bull., 21(12):2801-2804.
  2. Araki K, Tachibana S, Uchiyama M, Nakajima T & Yasuhara T (1975). Isolation and structure of a new active peptide xenopsin on rat stomach strip and some biogenic amines in the skin of Xenopus laevis. Chem. Pharm. Bull. (Tokyo)., 23(12):3132-3140.
  3. Feurle GE, Hamscher G, Kusiek R, Meyer HE, Metzger JW (1992). Identification of Xenin, a Xenopsin-related Peptide, in the Human Gastric Mucosa and Its Effect on Exocrine Pancreatic Secretion. The Journal of Biological Chemistry., 267(31):22305-22309.
  4. Kawanishi K, Goto A, Ishida T, Kawamura K, Nishina Y, Machida S, Yamamoto S, Ofuji T (1978). The effects of xenopsin of endocrine pancreas and gastric antrum in dogs. Horm Metab Res., 10(4):283-286.
  5. Zinner MJ, Kasher F, Modlin IM, Jaffe BM (1982). Effect of xenopsin on blood flow, hormone release, and acid secretion. AJP - Gastrointestinal and Liver Physiology,  243(3):195-199.
  6. Feurle GE, Baca I, Knauf W, Schwab A, Araki T, Carraway R (1982). Xenopsin stimulates exocrine pancreatic secretion in the dog. Cellular and Molecular Life Sciences, 38(6):679-680. 

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