Effects of natural tachykinins on porcine lower urinary tract smooth muscle

1 The aim of our study was to ascertain the possible differences and/or sim ilarities in natural tachykinin activity in vitro on lower urinary tract of large-sized animals as compared with data obtained in laboratory animals. 2 Besides tachykinins normally present in mammals, namely substance P (SP), neurokinin A (NKA) and neurokinin B (NKB), we tested non-mammalian tachyki nins, such as eledoisin (ELED), physalaemin (PHYS), kassinin (KASS) and PG- kassinin II (PG-KASS II). 3 NKA, KASS and ELED were found to be the most potent peptides in contracti ng detrusor strips from porcine bladder. In particular, NKA showed a pD(2) of 7.14, whereas KASS and ELED showed pot values of 7.20 and 7.22, respecti vely. The activity of NKB and PG-KASS II corresponded to 72.4 and 55.0% res pectively of that of NKA. SP and PHYS activity corresponded to only 2% of t hat of NKA. 4 NKA (pD(2) 7.92) was the most active peptide in contracting bladder neck tissues as well. ELED and KASS were found to have lower, similar pD(2) valu es (7.62 and 7.70, respectively), whereas NKB and PG-KASS II were much less active (pD(2) 7.12 and 6.74, respectively). Moreover, SP and PHYS showed a n activity range lower than 2% of that of NKA. 5 The reported results confirm that, on pig vesical neck and detrusor, NK1 receptors represent a minority as compared with NK2 and NK3 receptors. By c ontrast, the presence of NK2 receptors is demonstrated by a greater potency of NKA. The presence of NK3 receptors both on detrusor and neck is evidenc ed by NKB activity and by results achieved with PG-KASS II.