Levodopa Suppression of Prolactin in Nonpuerperal Galactorrhea

161

A B S T R A C T Prolactin secretion in normal adults is characterized by periods of episodic secretion which increase in magnitude during sleep. In this study, we report the 24-h mean prolactin concentrations, prolactin secretory patterns, and associated pituitary hormone function in nine patients (seven women and two men) with hyperprolactinemia of diverse etiologies. Four of the women and one of the men had clinically demonstrable pituitary tumors, one boy had a hypothalamic tumor, and the three other women had "functional" hyperprolactinemia. The 24-h mean prolactin concentrations derived from averaging the 20-min interval samples for 24 h ranged from 28.6 to 1,220 ng/ml. The plasma prolactin patterns in these patients showed persistence of episodic secretion in all and loss of the normal sleepwake difference in plasma prolactin in seven of nine. Three of the patients with galactorrhea and comparable 24-h mean prolactin concentrations (58.3, 59.7, and 64.3 ng/ml) showed similar prolactin secretory patterns despite different etiologic mechanisms. Evaluation of the secretory patterns of luteinizing hormone (LH) in these patients showed loss of normal pulsatile LH release and a low 24-h mean LH concentration in the patient with the pituitary tumor, while the two patients without clinically demonstrable pituitary tumors ("post-pill" galactorrhea and "idiopathic" galactorrhea) showed normal LH secretory patterns and 24-h mean LH concentrations. The 24-h mean cortisol concentrations and secretory patterns were normal in five of the seven patients who had these parameters measured. The patient with the hypothalamic tumor had a low 24-h mean cortisol concentration and production rate and absent response to metyrapone. The patient with "idiopathic" galactorrhea had an elevated 24-h mean cortisol concentration but normal cortisol production rate and urinary 17-hydroxycorticoid excretion. Growth hormone secre-

Section: Subjectsmentioning

confidence: 99%

Hypothalamic-Pituitary Function in Diverse Hyperprolactinemic States

Boyar¹,

Kapen²,

Finkelstein³

et al. 1974

161

“…These observations have led to the hypothesis that the pathogenesis of at least some growth hormone-and ACTH-secreting pituitary tumors may involve excessive stimulation by growth hormone and ACTH-releasing factors. Administration of L-dopa to patients with PRL-secreting tumors has not given evidence for altered neuroendocrine regulation in that, suppression of PRL secretion has generally been observed (16,17). However, the site of L-dopa action was not documented in these patients, inasmuch as the suppressive effects of L-dopa could have occurred by a direct action on the pituitary as well as by CNS mediation.…”

Section: Introductionmentioning

confidence: 99%

“…The administration of L-dopa, the immediate biosynthetic precursor of dopamine, is also followed by a decrease in PRL secretion and has been widely used to demonstrate PRL suppressibility (16,17). However, there are multiple sites at which exogenously administered L-dopa can exert its effects on PRL secretion.…”

Section: Introductionmentioning

confidence: 99%

Loss of Central Nervous System Component of Dopaminergic Inhibition of Prolactin Secretion in Patients with Prolactin-Secreting Pituitary Tumors

Fine¹,

Frohman²

1978

137

A B S T R A C T The administration of L-dopa suppresses prolactin (PRL) secretion in normal subjects and in patients with hyperprolactinemia, although it is not known whether this effect, which requires the conversion of dopa to dopamine, is mediated peripherally or through the central nervous system. To distinguish between these effects, 10 normal subjects (6 male, 4 female) and 8 patients with hyperprolactinemia associated with pituitary tumors were given L-dopa, 0.5 g alone, or 0.1 g after a 24-h pretreatment with carbidopa, 50 mg every 6 h, which produces peripheral dopa decarboxylase inhibition. Similar degrees of PRL suppression were observed in normal subjects (basal plasma PRL 13+2 ng/ml) after L-dopa alone (48±+4%) and after L-dopa plus carbidopa (58+6%). In patients with pituitary tumors and elevated plasma PRL (73+14 ng/ml), L-dopa alone led to PRL suppression comparable with that in normal subjects (47±+6%). However, L-dopa plus carbidopa resulted in only minimal suppression of plasma PRL (19+4%) which was significantly less than after L-dopa alone (P < 0.001). Urinary homovanillic acid excretion, which reflected peripheral dopa decarboxylation was similar in controls and tumor patients after L-dopa both alone and after carbidopa pretreatment.

“…Recent studies on human prolactin have indicated the primary importance of hypothalamic mechanisms in the regulation of secretion of this hormone by the pituitary (1)(2)(3). A large body of experimental observations in animals and of pharmacological studies in the human has indicated the presence of catecholaminergic mechanisms in the hypothalamic regulation of prolactin secretion.…”

Section: Introductionmentioning

confidence: 99%

Stimulation of Human Prolactin Secretion by Intravenous Infusion of L-Tryptophan

MacIndoe¹,

Turkington²

1973

196

A B S T R A C T Previous studiesThese results support the concept that the effect of L-tryptophan on the secretion of human prolactin is mediated through its conversion to serotonin and are consistent with reported experimental observations that serotonin may participate in the reciprocal regulation of prolactin and gonadotropins. INTRODUCTIONRecent studies on human prolactin have indicated the primary importance of hypothalamic mechanisms in the regulation of secretion of this hormone by the pituitary (1-3). A large body of experimental observations in animals and of pharmacological studies in the human has indicated the presence of catecholaminergic mechanisms in the hypothalamic regulation of prolactin secretion. In these studies we report an additional substance that can reciprocally regulate the secretion of prolactin and gonadotropins, the amino acid L-tryptophan. Effects observed with the intravenous infusion of this amino acid appear to relate to the presence of a serotonergic pathway mediating neuroendocrine regulation of prolactin secretion (4, 5) and provide an additional means of probing the human hypothalamic-pituitary axis.