Modification by prostaglandin E 2 (PGE 2 ) of the response of guinea-pig isolated vasa deferentia and atria to adrenergic stimuli.

1. Prostaglandin E(2) (PGE(2)) exerted positive cardiostimulant effects on isolated guinea-pig atria. The response was not altered by treatment of the animal with reserpine or by addition of propranolol to the organ bath. These results suggest that the cardiostimulatory actions of PGE(2) are not mediated through the release of catecholamines or stimulation of adrenoceptors.2. On the electrically driven atria, PGE(2) consistently exerted a cardiostimulant action which was not appreciably altered by changes in calcium ion in the bathing medium. PGE(2) showed no effect on the transport of calcium by the fragments of heart sarcoplasmic reticulum.3. PGE(2) reduced the responses to both noradrenaline and tyramine in the isolated atria. The shifted dose-response curve was not parallel to the original.4. PGE(2) increased the contractor response of the isolated vas deferens to nerve stimulation or to direct electrical stimulation.5. PGE(2) antagonized the increase caused by noradrenaline in contractor response of isolated vas deferens to direct electrical stimulation, whereas it affected the potentiation by noradrenaline differently when the vas deferens was contracting in response to nerve stimulation. In low concentration it inhibited and in large concentrations, it slightly enhanced the potentiation by catecholamine.6. It is concluded that PGE(2) has actions on multiple sites. It has post-junctional as well as pre-junctional effects on adrenergic neurones.