Central Nervous System and Pituitary Dopaminergic Defects in Hyperprolactinemic States
The fundamental role exerted by dopamine (DA) in the inhibitory control of prolactin (PRL) secretion at both hypothalamic and pituitary levels has been well established (Weiner and Ganong, 1978, for a review). In recent years many investigations have therefore been performed to evaluate the possible impairment of dopaminergic inhibition of PRL secretion in hyperprolactinemic states of different etiology, and much evidence in support of this possibility has indeed been obtained (Crosignani et al., 1977, 1980a; Fine and Frohman, 1978; Müller et al., 1978; Lim et al., 1979; Ferrari et al., 1980a, 1981a; Reschini et al., 1980; Frohman et al., 1981). Thus, many patients with idiopathic or adenomatous hyperprolactinemia do not increase serum PRL levels after DA receptor blockade by sulpiride administration, but a PRL response to this stimulus occurs in the same subjects during concurrent infusion of exogenous DA (Crosignani et al., 1977; Ferrari et al., 1979), indicating that lack of PRL increase after sulpiride is due to insufficient DA concentration outside the blood-brain barrier (most likely in the pituitary gland) in these conditions. Another dopaminergic defect occurring at pituitary level in some hyperprolactinemic patients is shown by the failure of PRL levels to suppress after administration of direct DA agonists like DA itself or L-dopa and bromocriptine.
KeywordsPituitary Adenoma Luteinizing Hormone Release Pituitary Level Hyperprolactinemic Patient Pituitary Microadenoma
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