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 (NANC) response of the rat urinary bladder was studied. Electrical stimulation of muscle strips from 3-month-old female Wistar rat urinary bladders in the presence of autonomic blockers (atropine 10^-6 mol/l, propanolol 10^-6 mol/l, phentolamine 10^-6 mol/l, and guanethidine 10^-6 mol/l) showed NANC contraction accounting for 60% of the maximum contractile 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 frequencies (3-10 Hz) were enhanced (p < 0.05; n = 9). However, no significant differences were observed at higher frequencies (20-40 Hz). With repetitive 4-Hz stimulation, alpha chymotrypsin caused a 19% increase in the NANC contractile response (p < 0.05; n = 8). It is postulated that the NANC 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.