A pharmacological study with substance K: evidence for multiple types of tachykinin receptors.

The substance P antagonist [D-Arg,D-Pro,D-Trp,Leu]SP (RPTTL-SP) produced a simple competitive antagonism of the responses to substance K (SK) and substance P (SP) in a variety of tissues. In the guinea-pig ileum and field stimulated rat vas deferens the pKB values against SK were similar to those against SP indicating a single population of receptors. In the guinea-pig urinary bladder the pKB value against SK was significantly higher suggesting the existence of at least two subtypes of tachykinin receptor in this tissue. In the hamster urinary bladder no antagonism was observed with up to 30 microM RPTTL-SP indicating the possibility of a third type of receptor.