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).
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.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D010693:Phloretin / Q000031:analogs & derivatives*; D011121:Polyphloretin Phosphate / Q000494:pharmacology*; D011458:Prostaglandins E / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011460:Prostaglandins F / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D011458:Prostaglandins E; D011460:Prostaglandins F; D011121:Polyphloretin Phosphate; D010693:Phloretin; D002118:Calcium