EFFECT OF ALPHA-CHYMOTRYPSIN ON THE NONADRENERGIC, NONCHOLINERGIC CONTRACTION OF THE RAT URINARY-BLADDER IN-VITRO

The role of peptides in mediating the nonadrenergic, noncholinergic (N ANC) response of the rat urinary bladder was studied. Electrical stimu lation of muscle strips from 3-month-old female Wistar rat urinary bla dders in the presence of autonomic blockers (atropine 10(-6) mol/l, pr opanolol 10(-6) mol/l, phentolamine 10(-6) mol/l, and guanethidine 10( -6) mol/l) showed NANC contraction accounting for 60% of the maximum c ontractile responses at 40 Hz. Frequency-response studies showed that in the presence of alpha-chymotrypsin (2 U/ml, 30-min incubation), the NANC contractile responses to electrical stimulation at lower frequen cies (3-10 Hz) were enhanced (p < 0.05; n = 9). However, no significan t differences were observed at higher frequencies (20-40 Hz). With rep etitive 4-Hz stimulation, alpha chymotrypsin caused a 19% increase in the NaNC contractile response (p < 0.05; n = 8). It is postulated that the WANG response of the rat bladder smooth muscle is composed of an excitatory (contractile) and an inhibitory (relaxant) component. Some peptide(s) is/are responsible for mediating the inhibitory response.