The decreases in plasma prolactin (PRL) levels in lactating rats that follow the separation of mother and pups have been studied. Blood samples were taken via an indwelling cannula from conscious primiparous animals between days 5 and 11 of lactation. Significant depressions of plasma prolactin levels have been detected within 3 min of separation. These decreases in hormone levels were most pronounced after 3 min, and continued up to the end of the 1st hour, but did not change during the 2nd hour. Disappearance of PRL from the blood during the first 3 min was identical to that occurring after hypophysectomy. Pretreatment of mothers, 90 min prior to separation, with α-methyl-p-tyrosine (250 mg/kg i.p.), pimozide (2 mg/kg i.p.), or haloperidol (2 mg/kg i.p.), completely blocked the decreases in PRL levels. L-Dopa (20 mg/rat i.p.) counteracted the inhibitory effect of α-methyl-p-tyrosine. These data suggest that separation of lactating rats from their litter resulted in a marked and complete blockade of PRL release from pituitary. They also suggest that a dopaminergic mechanism plays an important role in this inhibition of PRL release.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Endocrine and Autonomic Systems
- Cellular and Molecular Neuroscience