[D-Trp7,9,10]-Substance P

Effect of the tachykinin antagonist, [D-Pro4, D-Trp7,9,10] substance P-(4-11), on tachykinin- and histamine-induced inositol phosphate generation in intestinal smooth muscle.[Pubmed:2438561]

Naunyn Schmiedebergs Arch Pharmacol. 1987 Mar;335(3):296-300.

The effect of the tachykinin antagonist, [D-Pro4, D-Trp7,9,10] substance P-(4-11), on inositol phosphate accumulation produced by tachykinins and by histamine in strips of longitudinal muscle from the guinea-pig small intestine was investigated in the presence of 12 mM Li+. The two tachykinins substance P (SP) and kassinin (20 nM-20 microM) caused an accumulation of inositol phosphates in a concentration-dependent manner. This was seen with an agonist contact time of only 30 s. SP and kassinin were roughly equipotent in inducing inositol phosphate accumulation, which is consistent with their relative potencies in causing muscle contraction. The tachykinin antagonist (20 microM) produced a shift to the right of the dose-response curves for inositol phosphate accumulation caused by SP and kassinin. However, the effect of kassinin was inhibited much more than that of SP, which is consistent with a similar differential antagonism of the contractions induced by these agonists. The tachykinin antagonist also depressed histamine-induced accumulation of inositol phosphates whereas histamine-induced contractions had previously been found unaffected by the antagonist. These findings show that the tachykinin antagonist is not totally selective with regard to agonist-induced accumulation of inositol phosphates in intestinal smooth muscle. This may suggest that the antagonist not only acts on tachykinin receptors but also has another site of cellular action.

G protein antagonists. A novel hydrophobic peptide competes with receptor for G protein binding.[Pubmed:1379592]

J Biol Chem. 1992 Aug 15;267(23):16237-43.

A substance P (SP) analog, [D-Pro4,D-Trp7,9,10] SP4-11, is known to inhibit the actions of various structurally unrelated messenger molecules as well as SP. Our studies on the effects of this peptide on the regulation of purified G proteins by receptor showed that at least some of the biological effects of the peptide can be explained by the ability of the peptide to block the activation of G proteins by receptors. Here we report that a novel truncated SP-related peptide, pGlu-Gln-D-Trp-Phe-D-Trp-D-Trp-Met-NH2, inhibited the activation of G(i) or G(o) by M2 muscarinic cholinergic receptor (M2 mAChR) or of Gs by beta-adrenergic receptor in the reconstituted phospholipid vesicles, assayed by receptor-promoted GTP hydrolysis. The inhibition by the peptide was apparently reversible and competitive with respect to receptor binding to G proteins; the inhibition could be overcome by increasing the concentration of receptor in the vesicles and was not altered by changes in the concentration of G protein. The competing effects of the peptide were used to analyze the effect of agonist on receptor-G protein interaction. The concentration change of muscarinic agonist did not alter the inhibitory effects of the peptide on M2 mAChR-promoted GTPase by G(o), which is consistent with the idea that agonist increases the regulatory efficiency of the receptor but does not alter its affinity for G proteins. This new group of compounds (G protein antagonists) is a promising tool to study receptor-G protein interaction quantitatively.