Dual excitatory and smooth muscle-relaxant effect of β-phenylethylamine on gastric fundus strips in rats

beta-Phenylethylamine (beta-PEA) is a trace amine with chemical proximity to biogenic amines and amphetamines. It is an endogenous agonist of trace amine-associated receptors (TAARs) that acts as a neuromodulator of classic neurotransmitters in the central nervous system. At high concentrations, beta-PEA contracts smooth muscle, and a role for TAARs in these responses has been postulated. The high dietary intake of trace amines has been associated with such symptoms as hypertension and migraine, especially after the intake of foods containing such compounds. In gastrointestinal tissues, TAAR expression was reported, although the effect of beta-PEA on gastric contractile behaviour is unknown. Here, isolated strips that were obtained from the rat gastric fundus were stimulated with high micromolar concentrations of beta-PEA. Under resting tonus, beta-PEA induced contractions. In contrast, when the strips were previously contracted with KCl, a relaxant response to beta-PEA was observed. The contractile effect of beta-PEA was inhibited by 5-hydroxytryptamine (5-HT) receptor antagonists (i.e., cyproheptadine and ketanserin) but not by the TAAR(1) antagonist EPPTB. In gastric fundus strips that were previously contracted with 80 mmol/L KCl, the relaxant effect of beta-PEA intensified in the presence of 5-HT receptor antagonists, which was inhibited by EPPTB and the adenylyl cyclase inhibitor MDL-12,330A. The guanylyl cyclase inhibitor ODQ did not alter the relaxant effects of beta-PEA. In conclusion, beta-PEA exerted dual contractile and relaxant effects on rat gastric fundus. The contractile effect appeared to involve the recruitment of 5-HT receptors, and the relaxant effect of beta-PEA on KCl-elicited contractions likely involved TAAR(1).