Effect of a selective inhibitor of epinephrine synthesis, SK&F 64 139, on prolactin secretion in the rat.

The participation of central epinephrine in prolactin secretion was investigated in rats by testing the effects of SK&F 64 139, a selective inhibitor of phenylethanolamine-N-methyltransferase. The drug is reported to dramatically reduce brain epinephrine concentration without affecting norepinephrine or dopamine levels. When SK&F 64 139 was administered (40 mg/kg, ip) to male rats or to female rats during diestrus or proestrus, plasma prolactin levels were not different from those of control groups. Lactating and ovariectomized rats, however, responded to the same SK&F 64 139 dose with an increase in plasma prolactin levels: 210.02 +/- 22.72 vs 378.66 +/- 42.57 (mean +/- SEM) for control of lactating rats, and 4.35 +/- 0.52 vs 6.21 +/- 0.60 ng/ml for control ovariectomized rat. These results suggest that epinephrine may play a functional inhibitory role in prolactin secretion in the lactating and ovariectomized rat.