INVESTIGADORES
VALDEZ Susana Ruth
artículos
Título:
Dopaminergic mechanisms involved in prolactin release after mifepristone and
Autor/es:
SOAJE, M; VALDEZ, S; BREGONZIO, C; PENISSI, A; DEIS, RP
Revista:
NEUROENDOCRINOLOGY
Editorial:
Karger
Referencias:
Año: 2006 vol. 84 p. 58 - 67
ISSN:
0028-3835
Resumen:
BACKGROUND/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, with no additional effect of naloxone. While mifepristone decreased
the intensity of TH immunoreactivity in the arcuate and periventricular nuclei
and in fibers of the median eminence, naloxone treatment had no further effect.
CONCLUSIONS: (1) A reduction of tuberoinfundibular dopaminergic (TIDA) neuron
activity is suggested by the fall of the DOPAC/DA ratio and the low expression of
MBH TH; (2) this reduction facilitates prolactin secretion by naloxone,
indicating that progesterone stimulates DA neurons to maintain low serum
prolactin; (3) naloxone action seems to depend on a previous decrease of DA tone
induced by mifepristone, without involve a direct effect on neuronal DA activity,
and (4) endogenous opioids may inhibit prolactin secretion through a
non-dopaminergic neuronal system that regulates prolactin secretion in which as
yet undetermined prolactin-releasing factors may participate.