Interaction of NPY and VIP in regulation of myometrial blood flow and mechanical activity

The occurrence, molecular characteristics and biological function of neuropeptide Y (NPY) has been studied in the female genital tract of non-pregnant rabbits. NPY immunoreactivity was demonstrated throughout the genital tract. Maximum concentrations were found in the salpinx (fallopian tube), 570 pmol/g (median) lower within the uterine body (1.5 pmol/g), cervix (2.8 pmol/g) and vagina (3.6 pmol/g). In vitro, NPY had a dose-dependent stimulatory effect on non-vascular smooth muscle (ED50 10(-9) mol/l) as studied by myometrial tension recordings. In vivo, NPY (50 pmol/min.kg) induced a dose-related, non-adrenergic and non-cholinergic decrease in myometrial blood flow. Small C-terminal (NPY31-36) or N-terminal (NPY1-16) fragments of NPY had no effect on myometrial blood flow. NPY was found to interact with the smooth muscle effect of VIP; the presence of VIP (10(-8) mol/l) counteracted the contraction elicited by NPY (10(-8) mol/l) returning the response to control value. VIP and NPY displayed a similar physiological antagonism on myometrial blood flow. There was a clear difference in the response to VIP and NPY as the effect of NPY on myometrial blood flow first appeared after a lag period of 2 minutes whereas the effect of VIP was almost instantaneous. It is concluded that NPY and VIP may interact in the local nervous control of genital functions.