T. Misztal et al., Short-term modulation of prolactin secretion by melatonin in anestrous ewes following dopamine- and opiate receptor blockade, EXP CL E D, 109(3), 2001, pp. 174-180
Citations number
46
Categorie Soggetti
Endocrinology, Nutrition & Metabolism
Journal title
EXPERIMENTAL AND CLINICAL ENDOCRINOLOGY & DIABETES
This study rested the: hypothesis that the dopaminergic and opioidergic sys
tems are not involved in the short-term stimulatory action of melatonin (ML
T) on the secretion of prolactin in anestrous ewes. Thus. MLT should stimul
ate prolactin release after blockade of either dopamine (DA) or opiate rece
ptors with specific antagonists at the level of the pituitary gland and cen
tral nervous system (CNS). respectively. During afternoon intracerebroventr
icular (icv.) infusion of MLT, the mean plasma prolactin concentration incr
eased significantly (P<0.001) as compared with the concentrations noted bef
ore and during the infusion of the vehicle (veh.). As a result of subcutane
ous (sc.) injection of sulpiride (SULP, DA antagonist), an increase in plas
ma prolactin concentration was observed. followed by a gradual decrease dur
ing the icy. infusion of the vehicle. MLT infused icy. significantly increa
sed (P<0.001) the secretion of prolactin in SULP+MLT-treated ewes. as compa
red with the concentration of prolactin noted during infusion of the vehicl
e in SULP+veh.-treated ewes. Naloxone (NAL. opioid antagonist) infused icy.
did not significantly affect the secretion of prolactin, however, a signif
icant (P<0.01) increase in the concentration was observed after the infusio
n. In MLT+NAL-treated awes, the plasma prolactin concentration increased si
gnificantly (P<0.001) during the infusion, as compared with the concentrati
on noted before and that in NAL-alone infused ewes. These results demonstra
te that melatonin stimulates prolactin release after the pharmacological ex
clusion of the dopaminergic input with the DA antagonist sulpiride and also
despite the presence of DA activity in the hypothalamus after NAL treatmen
t. Secondly, endogenous opioid peptides are not a major component of this m
elatonin action.