Current Studies on Urotensins

Recent studies on urotensins I and II and experiments on urophysialfunction are described. Chemical and pharmacological studies showed that: (i) The isoelectricpoints of urotensins I and II are pI 5.5 ± 0.05 and 5.9± 0.05, respectively; (ii) two active peaks of urotensinI are obtained by gel chromatography of HCl-extracted urophyseson Bio-Gel P⁶, one corresponding to a substance of mol wt 4000,the other, mol wt 2000; (iii) the rat-hypotensive activity ofurotensin I affects peripheral blood vessels at an undeterminedreceptor site(s) and is not mediated by cholinergic, adrenergic,or histaminergic receptors or the corresponding transmittersubstances; and (iv) urotensins I and II increase blood pressureand urine flow in the American eel (Anguilla rostrata). Urophysial content of urotensin II in the white sucker (Catostomuscommersoni) was high during about 3 months preceding spawningand was considerably lower during the remainder of the year.Pituitary content of isotocin is significantly higher in malesuckers after spawning as compared with the content before spawning.The reverse was found on urophysial content of urotensin IIin the male fish.     

Chemical Properties and the Physiological and Pharmacological Actions of Urophysial Peptides

Recent advances in urophysial research are reported and currentresearch in this laboratory on the urophysial peptides (urotensinI, urotensin II) of Catostomxts commersoni is summarized. UrotensinI has been purified by gel filtration, electrofocussing, ultrafiltrationand ion exchange chromatography. Three similar utotensin I peptideswere found. The main peptide was shown to be a straight chainpeptide with about 36 amino acid residues. Pressor-diureticeffects in fish have been observed. The peptide produces a long-lastinglowering of mammalian blood pressure by peripheral vasodilatation.Urotensin II has been isolated and purified. It appears to contain23 amino acids including two disulphidebridges. It is a potentpressor-diuretic-smooth muscle contracting agent in the fish,without any known pharmacological actions in mammals. UrotensinIII: the existence of this activity as a separate chemical entityhas not been established, but urophysectomy was shown to lowerblood Na⁺ without an increase in renal excretion. UrotensinIV has been shown to be similar to, or identical with, argininevasotocin. Urotensin IV could not be found in the urophysisof Catostomus (gel filtration, bioassays, immunohistochemistry).Similarities and differences between the hypothalamic and caudalneurosecretory systems and their active principles are analysed.