(Leu sup 9. phi. (CH sub 2 NH)Leu sup 10 )-neurokinin A(4-10) (MDL 28,564) distinguishes tissue tachykinin peptide NK sub 2 receptors

The neurokinin A analogue, MDL 28,564 (Asp-Ser-Phe-Val-Gly-Leu-CH{sub 2}NH-Leu-NH{sub 2}), inhibited {sup 125}I-NKA binding to hamster urinary bladder NK{sub 2} receptors with a K{sub I} of 130 nM. For rat submaxillary gland NK{sub 1} receptors and cerebral cortical NK{sub 3} receptors, the K{sub I}'s for MDL 28,564 were >250 {mu}M and >500 {mu}M, respectively. MDL 28,564 did not relax dog carotid artery (NK{sub 1} tissue) or contract rat portal vein (NK{sub 3} tissue). In guinea pig trachea tissues, MDL 28,564 stimulated phosphatidylinositol turnover and induced contraction with maximum effects similar to those of neurokinin A. In hamster urinary bladder tissue, MDL 28,564 stimulated phosphatidylinositol turnover with maximum effect only 10% of that of neurokinin A, did not produce sustained contraction itself and antagonized NKA-induced contraction. MDL 28,564 also produced full contraction in rabbit pulmonary artery (NK{sub 2} tissue) but was inactive in rat vas deferens (NK{sub 2} tissue). These data with MDL 28,564 are consistent with the NK{sub 2} receptors in guinea pig trachea and rabbit pulmonary artery being different form those in hamster urinary bladder and rat vas deferens.