A COMPARISON OF INHIBITORY EFFECTS OF NEUROPEPTIDE-Y ON RAT URINARY-BLADDER, URETHRA, AND VAS-DEFERENS

The effects of human and porcine neuropeptide Y (NPY) on electrically induced contractions of smooth muscle strips from rat urinary bladder, urethra, and vas deferens were investigated. NPY (10 nM-10 muM) inhib ited the contractile response in all preparations. The magnitude of in hibition by NPY was dependent on frequency of stimulation in each orga n, the inhibition being in general much greater (80-100%) at low frequ encies (2-5 Hz) than at high frequencies (30-40% at 10-100 Hz). The va s deferens and urethra exhibited nearly maximal inhibition (90-100%) o ver a broader range of stimulus frequencies (1-20 Hz), while the bladd er exhibited a more prominent inhibition at frequencies of stimulation below 2 Hz. When tested at 20 Hz stimulation the urethra and vas defe rens were very sensitive (70-90% inhibition) to both types of NPY, whe reas bladder strips were much less sensitive to NPY and the effect dif fered with the two types of NPY (16% inhibition with human NPY and 39% inhibition with porcine NPY). In the urinary bladder, NPY inhibited t he cholinergic component of the contractile response, while in the ure thra adrenergic transmission was primarily affected. These studies sug gest that NPY, which is present in both cholinergic and adrenergic neu rons in the pelvic ganglia, may have an important role in the neural c ontrol of the lower urinary tract by participating in autoinhibition a t autonomic nerve terminals as well as in the heterosynaptic interacti ons between the cholinergic and adrenergic pathways.