Effects of prostaglandins on rat cardiac adenylate cyclase

A significant stimulatory action of PGE₁ on adenylate cyclase of the particulate membrane preparation of rat heart was observed at 1 × 10^?4 M. PGE₁ caused a positive inotropic effect on isolated spontaneously beating rat atria at 1 × 10^?5 M, and an increase in atrial cyclic AMP level at 1 × 10^?6 M. PGE_2α had no effect on these enzyme preparations. Our results suggest that: (i) The inotropic response of isolated spontaneously beating rat atria to PGE₁ may be connected with an increase in cyclic AMP level; (ii) the effect of prostaglandins on heart in vivo must be indirect, because the concentrations needed to stimulate isolated atria and particulate adenylate cyclase were high, compared with the doses effective in vivo.