CONTRACTILE EFFECTS OF VANADATE ON AORTA RINGS FROM VIRGIN AND PREGNANT RATS

The present study was undertaken to characterize the contractile effec ts of vanadate on thoracic aorta rings from virgin and term-pregnant r ats. Vanadate caused concentration-dependent contraction in rat aortic rings with an EC(50) (concentration producing 50% maximum response) o f 0.10 mM. Contractions in response to vanadate were equivalent to the ones measured with 1 mu M phenylephrine. The effects of vanadate were not affected by indomethacin (up to 10 mu M), an inhibitor of prostan oid cyclooxygenase, but were blocked in a concentration-dependent mann er by staurosporine (0.1-1.0 mu M), an inhibitor of protein kinase C. Vanadate exhibited a significant decrease of contractile responses in aorta of pregnant as compared to virgin rats. When aortic rings were b athed in presence of different concentrations of vanadate, the concent ration-response curve to phenylephrine was shifted to the left, but ma ximum response was not affected. The potentiation of the contractions to phenylephrine by vanadate was significantly more prominent in aorta of virgin than of pregnant rats. These results suggest that the contr actile effect of vanadate on rat aorta is independent of endogenous pr ostanoids and may be mediated by protein kinase C-dependent pathway. T hese results also show that the contractile response to vanadate on th e rat aorta is impaired during pregnancy.