Pattern and Duration of the Inhibitory Effect of Alcohol Administered Acutely on Suckling-Induced Prolactin in Lactating Rats

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Abstract
We have characterized the pattern and duration of the inhibitory effect of acute alcohol administration on suckling-induced prolactin (PRL) release in the lactating rat. On day 2 of lactation, litters were adjusted to eight pups. On day 6, dams were implanted with an atrial catheter and experiments were conducted on day 10 of lactation. Pups were removed from the dams at 0800 hr. An extension tube filled with heparinized saline was attached to the catheter at 1300 hr. At 1400 hr, a preinfusion (PRE 0) blood sample was removed and was followed by infusion of saline (control) or alcohol in saline (0.5, 1.0, 2.0, 2.5 g/kg body weight doses) solutions. Following the removal of a postinfusion (POST 0) blood samples, pups were returned to the mother. Subsequent blood samples were obtained 10, 30, 60, 120, and 180 min after initiation of suckling. In separate groups, the effects of alcohol on basal PRL were studied by collecting blood samples, PRE 0, POST 0 and 20, 40, 60, 80, 100, and 120 min following infusion of saline or alcohol in saline to lactating rats also separated from their pups for 6 hr. Alcohol infusion did not alter basal PRL. However, suckling-induced PRL was inhibited at 10, 30, 60, and 120 min of suckling by alcohol administered at doses .gtoreq. 1.0 g/kg body weight. After 180 min of suckling, plasma PRL levels were comparable among groups. The suckling latency for the 2.5 g/kg body weight alcohol group was greater than for other groups, but the quantities of milk consumed during the 3-hr suckling period were comparable. The blood alcohol clearance rates expressed as mg/kg/hr were 220 .+-. 16, 342 .+-. 18, and 385 .+-. 24 for 1.0, 2.0, and 2.5 g/kg/body weight doses, respectively. The growth rate of the pups are judged by the litter weight on days 2, 7, 14, and 21 of lactation, did not differ. The data indicate that alcohol (administered acutely) does not affect the basal plasma PRL in lactating rats. In contrast, suckling-induced PRL release is inhibited, and this inhibitory effect lasts approximately for 2 hr for the highest alcohol dose (2.5 g/kg body weight) employed. Further, it was also observed that a blood alcohol concentration of 65 mg/dl or greater is necessary to exert the inhibitory effect on suckling-induced PRL release.