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

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Abstract
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.