EXOGENOUS OXYTOCIN ATTENUATES SUCKLING-INDUCED PROLACTIN-RELEASE BUT NOT MATERNAL OR INFANT BEHAVIOR IN LACTATING RATS

The influence of exogenous oxytocin (OT) on maternal and infant behavi or over 60 min of suckling, which followed 6 h of isolation, was inves tigated on Day 12 of lactation in rats. Mothers administered 1 IU of O T or saline through an indwelling atrial catheter and their litters in dicated a similar nursing and suckling pattern, which was estimated by the crouching time of the mothers and the number of stretch reactions performed by the litters during a suckling period. To assess the alte ration of the suckling intensity by OT administration, the plasma prol actin (PRL) level was determined by an Nb, lymphoma cell bioassay. In the control group, the plasma PRL level increased and reached a peak a t 45 min after the onset of suckling in 60% of the animals. The suckli ng-induced PRL release was completely inhibited and/or markedly delaye d by OT administration. The difference in body weight of the litters b efore and after a suckling period was estimated as an index of the amo unt of milk suckled by the litters. There was no difference in the amo unt of milk between the control and OT-treated groups during a 60-min suckling period. However, it was significantly greater in the OT-treat ed group during the first 20 min of the suckling period. These results indicate that a dose of OT is a factor in the attenuation of the inte nsity of suckling done by the pups, whereas the nursing and suckling b ehavior is not influenced by OT administration. (C) 1998 Elsevier Scie nce Inc.