Myotropic effects of proctolin analogues, modified in position 2 of the peptide chain, on the foregut of the locust Schistocerca gregaria

Autor: Danuta Konopińska, Jane M. Hinton, H. Bartosz-Bechowski, Richard H. Osborne
Rok vydání: 1996
Předmět:
Zdroj: Journal of Insect Physiology. 42:449-454
ISSN: 0022-1910
DOI: 10.1016/0022-1910(95)00130-1
Popis: Proctolin (H.Arg.Tyr.Leu.Pro.Thr.OH) caused dose-dependent contraction of the isolated foregut of the locust Schistocerca gregaria at concentrations ranging from 10 −8 , m to 2 × 10 −6 , m . Of the ten analogues evaluated, [Phe( p -NH 2 ) 2 ]-, [Tyr( m -NH 2 ) 2 ]- and [Phe( p -OEt) 2 ]-proctolin are dose-dependent supra agonists while [Phe( p -OMe) 2 ]- and [ l -DOPA 2 ]-proctolin are supra agonists only when applied at a single dose of 5 × 10 −7 , m . Construction of dose response curves showed that [Phe( p -OMe) 2 ]-, [ l -DOPA 2 ]-, [Phe( p -NH 2 ) 2 ]- and [Phe( p -NO 2 ) 2 ]-proctolin are partial agonists incapable of causing a maximum response equivalent to that induced by the parent pentapeptide. [Cha(4-OMe) 2 ]-, [Afb( p -OH) 2 ]- and [Afb( p -NO 2 ) 2 ]-Proctolin are weak agonists with intrinsic activities equivalent to only 12.7%, 7.9% and 3.5% respectively of that of proctolin. [α-Me- l -Tyr 2 ]- and [Afb( p -NO 2 ) 2 ]-Proctolin (10 −8 , m –10 −6 , m are potent non-competitive antagonists of proctolin induced tissue contraction, reducing the maximum response of applied proctolin to 16% and 23% respectively when used at a dose of 10 −6 , m . From analysis of the myotropic effects of the analogues investigated in this study, we conclude that the agonist actions of proctolin are dependent on the presence of either a para substituted Phe or a meta substituted Tyr in position 2 of the peptide chain. These data show that the ideal substituents on the aromatic ring are groups containing oxygen and nitrogen atoms.
Databáze: OpenAIRE
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