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  • Title: Role of calcium in the mechanism of action of the prostaglandins E1 and F2 alpha as well as of their antagonist polyphloretin phosphate (PPP).
    Author: Petkov V, Radomirov R, Petkov O.
    Journal: Acta Physiol Pharmacol Bulg; 1978; 4(4):27-35. PubMed ID: 752228.
    Abstract:
    The contractile effect of PGE1 on guinea-pig ileum is not changed either by increase (to 4 mM) or by decrease (to 1 mM) of the Ca++ content in Krebs solution. The decrease of Ca++ in the medium intensifies the contractile effect of PGE2 alpha. Reduction of Ca++ weakens the antagonistic effect of PPP (100 micrograms/ml) against PGF2 alpha. PPP has a marked aftereffect with respect to the effects of PGF2 alpha--in cases of normal Ca++ content in the Krebs solution this aftereffect appears upon longer (10 min) contact of PPP with the intestinal segment, while in cases of changed Ca++ content it appears already after 2-min PPP action. It is concluded that in order to induce contractions in the guinea-pig ileum, PGE1 and PGF2 alpha utilize the internal Ca++. It is assumed that PGF2 alpha increases the reactivity of the anionic sites of the smooth-muscle membrane for Ca++. As a result of this, the complex compounds of Ca++ at its higher concentration make more difficult the realization of the contractile process. It is assumed that Ca++ is needed for the maximum manifestation of the antagonistic effect of PPP.
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