Dopaminergic stimulation of pituitary but not hypothalamic estrogen receptors in ovariectomized rats

This study was designed to examine the role of catecholamines and serotonin in the regulation of estrogen receptors (ER) in the medial basal hypothalamus (MBH) and anterior pituitary gland (AP) of adult ovariectomized rats. Plasma PRL and LH were also determined. Injection of alpha-methyl tyrosine (alpha-MT) resulted in the significant reduction of norepinephrine and dopamine (DA) content in the MBH, and of plasma LH levels as well as in the significant elevation of plasma PRL levels. This treatment also resulted in the significant reduction of ER concentration in the AP. The elevation in plasma PRL by alpha-MT was reversed by the simultaneous injection of bromocriptine (BC), a DA agonist, which also partially reversed the alpha-MT reduction of ER concentrations in the AP. BC had no effect on plasma LH levels. The ER concentration in the MBH was not significantly changed by any of these treatments. The reduction of serotonin content in the MBH by the injection of p-chlorophenylalanine had no effect on the ER concentration in either the MBH or AP, nor did it have any effect on plasma PRL levels. However, p-chlorophenylalanine treatment did decrease plasma LH levels. Neonatal treatment of female rats with monosodium glutamate which has been reported to destroy part of the MBH, resulted in a significant reduction in body and pituitary weight and in a significant elevation of plasma PRL levels in adults (2 months old). This treatment also resulted in a significant reduction in the AP and MBH ER concentration. Injection of BC to adults reversed the effects of neonatal monosodium glutamate treatment on plasma PRL levels and on the pituitary ER concentration, but had no effect on the ER concentration in the MBH. BC had no effect on the AP or MBH ER concentration in control rats, although it did as expected reduce the plasma PRL levels in these animals. Plasma LH levels were not significantly changed by any of these treatments. Injection of the DA antagonist, haloperidol, to adult rats resulted in a significant elevation of plasma PRL and in a significant reduction of ER concentration in the AP. Haloperidol treatment did not affect the binding affinity of these receptors. Overall, these data suggest that DA is involved with the regulation of ER in the AP.