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 microM) inhibited to the contractile response in all preparations. The magnitude of inhibition by NPY was dependent on frequency of stimulation in each organ, the inhibition being in general much greater (80-100%) at low frequencies (2-5 Hz) than at high frequencies (30-40% at 10-100 Hz). The vas deferens and urethra exhibited nearly maximal inhibition (90-100%) over a broader range of stimulus frequencies (1-20 Hz), while the bladder exhibited a more prominent inhibition at frequencies of stimulation below 2 Hz. When tested at 20 Hz stimulation the urethra and vas deferens were very sensitive (70-90% inhibition) to both types of NPY, whereas bladder strips were much less sensitive to NPY and the effect differed with the two types of NPY (16% inhibition with human NPY and 39% inhibition with porcine NPY). In the urinary bladder, NPY inhibited the cholinergic component of the contractile response, while in the urethra adrenergic transmission was primarily affected. These studies suggest that NPY, which is present in both cholinergic and adrenergic neurons in the pelvic ganglia, may have an important role in the neural control of the lower urinary tract by participating in autoinhibition at autonomic nerve terminals as well as in the heterosynaptic interactions between the cholinergic and adrenergic pathways.