PHARMACOLOGY OF PROCTOLIN RECEPTORS IN THE ISOLATED FOREGUT OF THE LOCUST SCHISTOCERCA-GREGARIA - IDENTIFICATION OF [ALPHA-METHYL-L-TYROSINE(2)]-PROCTOLIN AS A POTENT RECEPTOR ANTAGONIST
As. Gray et al., PHARMACOLOGY OF PROCTOLIN RECEPTORS IN THE ISOLATED FOREGUT OF THE LOCUST SCHISTOCERCA-GREGARIA - IDENTIFICATION OF [ALPHA-METHYL-L-TYROSINE(2)]-PROCTOLIN AS A POTENT RECEPTOR ANTAGONIST, Journal of insect physiology, 40(7), 1994, pp. 595-600
1. Proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) caused dose-dependent contract
ion of the foregut of the locust Schistocerca gregaria. 2. Of the nine
new analogues tested, five stimulated tissue contraction, the most po
tent being [p-fluoro-L-phenylalanine(2)]-proctolin which caused a maxi
mum response 35% greater than that induced by proctolin. 3. The demons
tration that [3'-mono-iodo-L-tyrosine(2)]-proctolin is a potent agonis
t provides a physiological basis for the use of the [I-125] derivative
of this peptide to study proctolin binding sites in insect tissues. 4
. The tripeptide Arg-Tyr-Thr was devoid of agonist action but reduced
the myotropic activity of proctolin. 5. Cyclic proctolin and [alpha-me
thyl-L-tyrosine(2)]-proctolin reduced the maximum response to proctoli
n by 37 and 88%, respectively when used as antagonists at concentratio
ns of 5 x 10(-6) and 10(-6) M, respectively. The demonstration that [a
lpha-methy-L-tyrosine(2)]-proctolin is a potent proctolin receptor ant
agonist means that it is now possible to characterize the receptors th
at the parent pentapeptide activates to bring about its physiological
effects.