Tachykinin receptors involved in the contractile effect of the natural tachykinins in the rat gastric fundus.

1. The receptors involved in mammalian tachykinin-induced contractions of longitudinal smooth muscle strips of the rat gastric fundus were characterized pharmacologically. 2. Substance P (SP), neurokinin A, neurokinin B and senktide contracted the strips in a concentration-dependent manner with a potency order of neurokinin A > or = senktide > neurokinin B > substance P. The contractions were not influenced by tetrodotoxin and atropine. 3. L 659877, a NK2B-receptor-preferring antagonist reduced neurokinin A- and neurokinin B-induced contractions (estimated pKB 6.9 and 6.3, respectively) but had less pronounced effects on SP-induced contractions and none on contractions induced by senktide. MEN 10376, an NK2A-receptor-preferring antagonist, reduced the neurokinin A-induced contractions (estimated pKB 5.2), while dactinomycin, reduced the neurokinin A-induced contractions only to a minor extent at 10(-4) M. 4. CP 96345, an NK 1-receptor antagonist, reduced substance P- and neurokinin A-induced responses, but also reduced the contractions induced by KCl and methacholine. RP 67580, another non-peptide NK1-receptor antagonist had no effect on the substance P-, neurokinin A- and neurokinin B-induced contractions up to a concentration of 3 x 10(-6) M. 5. These results suggest that the mammalian tachykinins induce contractions of the longitudinal smooth muscle strip of the rat gastric fundus by direct action at muscular NK2B- and NK3-receptors.