Inhibitory action of lanthanum(La) on PGF2 alpha - induced contraction of guinea-pig stomach muscle.

The effects of lanthanum(La) on contractions induced by prostaglandin F2 alpha(PGF2 alpha) or isotonic K+ were investigated in the isolated stomach muscle of guinea-pig. Low concentrations of La( 0.1-1 microM) inhibited the contraction to PGF2 alpha 1 microM in a dose-dependent manner, without affecting the tonic contraction to isotonic K+. 0.1 and 1 microM La shifted the dose-response curve for PGF2 alpha( 0.001 - 1 microM) to the right and reduced the maximum response. The IC50 of La against PGF2 alpha and K+ were 0.6 microM and 30 microM, respectively. These results support the suggestion that PGF2 alpha -induced contraction in the stomach muscle depends mainly on the intracellular release of sequestered Ca, which would be depleted or immobilized by La.