Inhibitory effect of alcohol on the established suckling-induced prolactin surge in lactating rats

The effect of acute alcohol infusion on the established suckling-induced prolactin surge in lactating rats was examined. Dams were implanted with an atrial catheter on Day 6 of lactation and blood sampling was done on Day 10. Following the separation of litters from dams for a 6-hr period, a baseline blood sample was removed via a catheter extension. Pups were weighed and returned to dams. Subsequent blood samples were obtained 10, 30, and 60 min after initiation of suckling. Dams were then infused with alcohol doses of 0, 0.5, 1.0, 2.0, or 2.5 g/kg body wt. Infusion (0.1 ml/min) was completed in approximately 30 min. Additional blood samples were obtained 10 30, 60, and 120 min after the termination of infusion. In a separate group of rats, pups were removed from the dam after the first 60 min of suckling and additional blood samples were obtained 40, 70, 90, and 150 min after removal of pups (corresponding to 10-, 30-, 60-, and 120-min samples for rats infused with various alcohol doses). Alcohol, when administered after the establishement of suckling-induced prolactin surge and resulting in blood alcohol levels equal to or greater than legal human intoxication levels, inhibited prolactin release. However, continued suckling for an extended period (120 min in the present study) overcame this inhibitory effect, even when the blood alcohol level was comparable to (2.0 g/kg group) or greater than (2.5 g/kg group) the human legal intoxication level. Furthermore, in rats with established prolactin surges, the patterns of prolactin decline that followed alcohol administration or pup removal were comparable, indicating that similar mechanism(s) may be involved.