Contractile effect of vanadate and other vanadium compounds on the rat vas deferens

Sodium metavanadate (NaVO3), vanadium pentoxide (V2O5) and vanadyl sulphate (VOSO4), evoked rhythmic and tonic contractions of the normal and reserpinized rat isolated vas deferens. Contractions were not observed by the use of vanadium trichloride (VCl3) The order of potency of these compounds, for their maximum contractile effects was NaVO3 greater than V2O5 greater than VOSO4 greater than VCl3. Differences in pD2 values were less than 0.5 long units in relation to the first compound. Vanadium-induced contractions were blocked by Ca2+ deprivation, nifedipine, Mg2+, Mn2+, Ni2+ and Co2+, indicating the involvement of a loosely bound or extracellular calcium-dependent mechanism. It is still unclear whether this calcium translocation was related, or not, to changes in Na+, K+-ATPase activity. Since ouabain blocked the action of vanadyl or vanadate non-competitively, it is concluded that vanadium compounds and ouabain induce their effects by interacting with different sites in vas deferens, both of which may or may not be located on the (Na+, K+)ATPase enzyme complex.