Dopaminergic Mechanisms Involved in Prolactin Release after Mifepristone and NaloxoneTreatment during Late Pregnancy in the Rat

SOAJE, M; VALDEZ, S; BREGONZIO, C; PENISI, A; DEIS, RP

Karger

Lugar: Basel; Año: 2006 vol. 84 p. 58 - 58

ACKGROUND/AIMS: During late pregnancy, the antiprogesterone mifepristone facilitates prolactin release. This effect is enhanced by administration of the opioid antagonist naloxone, suggesting an inhibitory-neuromodulatory role of the opioid system. Since hypothalamic dopamine (DA) is the main regulator of prolactin release, in this study we explored the role of DA on prolactin release induced by mifepristone and naloxone treatment. METHODS/RESULTS: Rats on day 19 of pregnancy were used. Naloxone treatment did not modify the 3,4-dihydroxyphenylacetic acid/DA (DOPAC/DA) ratio or serum prolactin concentration in control rats. After mifepristone treatment, DA activity diminished significantly without modifying serum prolactin levels. Naloxone administration to antiprogesterone-treated rats did not change the DOPAC/DA ratio but increased serum prolactin. Tyrosine hydroxylase (TH) expression in medial basal hypothalamus (MBH) protein extracts was lowered by pretreatment with mifepristone, w