Prolactin activation of phospholipase A activity in membrane preparations from mammary glands

The addition of prolactin to the 150,000 x g sedimented fraction of mammary gland homogenates increased by about two-fold the rate of [3H]-arachidonic acid released from phosphatidyl choline. This enhanced activity was observed during incubation periods of 1-3 hours and occurred with prolactin concentrations ranging between 2.5 and 100 mug per 300 mul. The enhanced rate of arachidonic acid release from phosphatidyl choline suggests that prolactin stimulates phospholipase A activity and this may be the primary site of action of prolactin in the mammary gland. Specificity of the prolactin effect is suggested by the fact that growth hormone at 100 mug per 300 mul had no effect on the rate of [3H]-arachidonic acid release from phosphatidyl choline.