THE SYSTEMIC HEART OF OCTOPUS-VULGARIS - EFFECTS OF EXOGENOUS ARACHIDONIC-ACID AND CAPABILITY FOR ARACHIDONATE METABOLISM

The actions of exogenous arachidonic acid on the performance of the is olated and perfused systemic heart of Octopus vulgaris (collected in t he Bay of Naples in 1992), and the potential of this heart for eicosan oid synthesis are described. Arachidonic acid induces positive chronot ropic and inotropic effects. The positive inotropic effect is apparent only at the lowest concentration used (10(-7) M) and in the paced hea rt preparations, in which a negative relationship between stroke volum e and heart rate has been demonstrated. Using 10(-5) M arachidonate, w hich induces the greatest chronotropic effect, a reduction of inotropi sm is evident which is due to the above negative relationship between stroke volume and heart rate. These effects are scarcely affected by t he cyclooxygenase and lipoxygenase inhibitors, indomethacin (IM) and n ordihydroguaiaretic acid (NDGA), respectively. On the coronary system of this heart arachidonic acid displays a potent vasoconstrictory acti on (ca. 100 percent increase of coronary resistance). This effect is p otentiated by IM and reduced by NDGA. C-14-arachidonate is metabolized by the octopus ventricle homogenate into the lipoxygenase products (a ssayed as hydroxy acids) more actively than into cyclo-oxygenase produ cts (prostanoids: PGE(2), PGD(2), PGF(2 alpha), and 6-keto-PGF(1 alpha )). On the other hand, the Ca ionophore A23187 enhances the production of cyclooxygenase metabolites much more than of lipoxygenase metaboli tes.