Changes in oviductal VIP content induced by sex steroids and inhibitory effect of VIP on spontaneous oviductal contractility

The content of vasoactive intestinal polypeptide (VIP) in rabbit oviducts was determined using a radioimmunoassay technique. Treatment with oestrogen (polyestradiolphosphate) alone for 5 days caused a significant increase in oviductal VIP content, whereas addition of progesterone during the last 3 days of an 8 day polyestradiol-phosphate treatment resulted in a return of VIP content to control levels. The effect of VIP on oviductal smooth muscle contractility was investigated using an in vitro system. It was found that VIP caused a reduction of spontaneous contractile activity in doses as low as 10(-10) M and this reduction in motor activity was strictly dose dependent with an ED50 value similar to that reported for the VIP activity on rabbit myometrial smooth musculature.