Airway response by neurokinin A.

: We studied the effect of neurokinin A (NKA) on tracheal smooth muscle (TSM) contraction induced by the administration of acetylcholine (ACh) intra-arterially (ia) into the tracheal circulation or bilateral vagal stimulation in 18 mongrel dogs. In five dogs, 10(-12) to 10(-7) mol of NKA was injected selectively into the tracheal circulation. The tracheal contractile response to 10(-7) mol NKA was 3.12 +/- 0.48 g/cm, 6.3 +/- 0.7% AChmax. Plasma histamine concentration in the right atrium was measured at the peak response to NKA. Plasma histamine concentration was 3.33 +/- 2.05 ng/ml after 10(-7) mol NKA (vs 0.32 +/- 0.08 ng/ml for control, p > 0.10). In the other 5 dogs, dose-response was obtained with 10(-12) to 10(-7) mol ACh 10 min before and 10 min after administration of 10(-8) mol NKA. Frequency-response relationship also was induced by electrical stimulation of the distal cut ends of the cervical vagi in the range of frequencies 1-20 Hz (constant 30 V) at 15-s intervals 10 min before and after administration of 10(-8) NKA. Considerable potentiation of the tracheal contractile response to 10(-18) to 10(-7) mol ia ACh occurred 10 min after administration of 10(-8) mol NKA (p < 0.05). Significant potentiation of the tracheal contraction to vagal stimulation at 10-20 Hz was also observed 10 min after administration of 10(-8) mol NKA (p < 0.05). We demonstrate that the substantial contractile effects of NKA on canine tracheal smooth muscle are not related to histamine release from mast cells in the respiratory tract.(ABSTRACT TRUNCATED AT 250 WORDS)