Plasma prolactin levels in parental male rats: effects of increased pup stimuli.

The effects of pup exposure on plasma prolactin (PRL) levels were measured in unrestrained, steriod-primed, orchidectomized parental rats. Castrated adult male rats were treated with estradiol and progesterone for 3 weeks and then exposed to rat young until parental behavior was induced. Blood samples were then collected from parental males in both the presence and the absence of pups. Samples were obtained through the use of indwelling cannulas connected via polyethylene tubing to syringes located outside each subject's cage. Despite the intense pup stimulation provided by exposure to nine rat pups, acute rises in plasma PRL levels were not observed in these unrestrained parental male rats. Parental male rats, therefore, do not appear to have the capacity to secrete prolactin in response to acute exposure to young.