Levels of neurokinin A, neurokinin B and substance P in rabbit iris sphincter muscle.

We investigated the contents of neurokinin A, neurokinin B and substance P in the rabbit iris sphincter muscle, combining HPLC and radioimmunoassay, as our previous reports indicated that a slow component of neurogenic contractions of this muscle is most probably mediated by such tachykinins. The concentrations of these tachykinins were 44.3 +/- 8.7 fmol/mg protein, 35.3 +/- 10.2 fmol/mg protein and 186.8 +/- 29.8 fmol/mg protein (N = 4), respectively. These results demonstrated that neurokinin A, neurokinin B and substance P are all present in the rabbit iris sphincter muscle.