Vi. Melnikova et al., PROLACTIN SECRETION AND ITS DOPAMINE INHIBITORY CONTROL IN RAT FETUSES, European journal of endocrinology, 139(3), 1998, pp. 337-342
This study has determined in rats the ontogenetic schedule of the onse
t of pituitary prolactin (PRL) synthesis and release as well as of the
establishment of the dopamine (DA) inhibitory control of PRL secretio
n. RIA recognized PRL traces in the pituitary at the 18th embryonic da
y (E18), although a clearly detectable amount of this hormone was firs
t measured at E20, suggesting the onset of PRL synthesis. The PRL leve
l in the pituitary increased significantly by E22, in females to a hig
her extent than in males. Decapitation of fetuses did not cause any ch
ange in the PRL plasma level in males showing no PRL release from the
pituitary until term. Conversely, there was a slight but significant f
all of plasma PRL in decapitated females, suggesting PRL release from
the pituitary. An inhibition of DA receptors on lactotropes of fetuses
resulted in an increased level of plasma PRL at E20, but not at Els,
while the pituitary content of PRL remained unchanged. The same treatm
ent at E22 caused a significant increase of the PRL concentration in p
lasma and a concomitant fall in the pituitary that could be prevented
by preliminary encephalectomy, These data show that the tuberoinfundib
ular DA system begins to inhibit PRL release from lactotropes between
E20 and E22, completely arresting PRL release from the pituitary in ma
les but not in females.