PGE2α의 rat적출심방에 대한 작용을 ouabain의 작용과 비교하여 다음과 같은 결과를 얻었다. PGE2α의 양성변력성작용은 ouabain의 작용에 비해 potency가 강하고 efficacy는 낮았다. Ouabain은 PGE2α의 양성변시성작용과 유사한 양성변시성 경향을 나타내었는데 이 점에 대해 추후의 탐구가 요구된다. PGE2α(3 × 10-8M)의 작용은 저칼슘농도(1.4mM)에서 ouabain(3 × 10-3M)보다 현저히 (≤0.05 ~ p≤0.00)강하게 나타났고, medium내에 첨가되는 Ca++에 대하여도 보다 예민하게 반응하였다. 저칼륨 medium(2.8mM) 또는 medium내 K+첨가는 PGE2α보다 ouabain의 작용에 더 큰 영향을 미쳤다. PGE2α와 ouabain의 작용에 미치는 lidocaine (1 × 10-5M이상의 고농도)의 영향은 매우 흡사하여 별다른 차이점을 볼 수 없었다. Propranolol (3 × 10-6M)로써 전처치하여 아드레나린성 β수용체를 봉쇄한 적출심방에서 PGE2α 양성변력성 및 양성변시성 작용은 방해를 받지 않았다. 이상의 결과로 보아 PGE2α는 ouabain의 Na+, K+-ATPase 억제기전파는 달리 PGE2α 고유의 막수용체에 작용하여 Ca++의 세포내 유입을 촉진시키는 기전으로 작용하는 것으로 추측되며, 그 수용체의 등정(identification)은 추후의 연구과제로 남는다.
Comparative effects of PGE2α and ouabain on the isolated rat(Sprague-Dowley) atria were studied. The isolated rat atria were prepared for isometric myography in the isolated organ bath containing Feigen s solution perfused with 95% O2 and 5% CO2, and the pH of the medium was maintained at 7.4. The cumulative concentration-response relationship revealed the positive inotropic effects of both drugs with the higher potency of PGE2α and the higher efficacy of ouabain. PGE2α showed a positive chronotropic effect, but ouabain showed a tendency of increasing the contraction rate. In low-Ca(1.4 mM) medium, the positive inotropic and chronotropic effect of PGE2α(by 3 × 10-8M) were preponderant (p<0.05 ~ p<0.005) over those of ouabain(by 3 × 10-3M). Ca++-addition(cumulative, to 2.8, 4.2, 5.6, and 7.0 mM) into the medium evoked the more sensitive response in the PGE2α group than in the ouabain group. In low-K(2.8 mM) medium, the PGE2α(3 × 10-8M) group and the ouabain(3 × 10-3M) group showed similar tensions(DT and RT) and contraction rates. And both group showed significantly(p<0.05p<0.01) higher tensions and contraction rates than those of the control group. By the cumulative addition of the K+(to 4.2, 5.6, 7.0 and 8.4 mM), only the DT of the PGE2α group was sustained at signifcantly(p<0.05 ~ p<0.01) higher level than the DT of the control group. The K+-addition inhibited the positive inotropic effect of ouabain significantly (p<0.05). The cumulative addition of lidocaine in high concentrations (1 × 10-5 to 1 × 10-3M) evoked no significant influence on the intropic activities of PGE2α and ouabain, but significant β-blockade with propranolol could not inhibit the positive intropic and chronotropic effect of PGE2α. In conclusion, it is presumed that PGE2α may have some more active mechanism of accelerating the influ× of Ca++ across the cell membrane of the isolated rat atria as compared with ouabain, and the action site may be located at the cell membrane. As a supposition which needs further investigations, it is presumed that PGE2α may have its specific membrane receptors on the atrial muscle or sinus node cells.
