Abstract
The inverse relationship between zinc (Zn++) and prolactin (PRL) was detected in in vitro studies, whereas in vivo results are contradictory. In order to evaluate this controversial subject we studied patients with hyperprolactinemia. Basal serum Zn++ levels and serum PRL response to acute and chronic oral Zn++ administration were evaluated in seven patients with prolactinomas and one with idiopathic hyperprolactinemia. Serum PRL levels did not change after acute oral Zn++ administration (37.5 mg), although Zn++ levels increased from 1.11±0.15 to 2.44±0.39 μg/mL (P<0.05). ZnZn++ administration (47.7 mg daily) during 60 days increased serum Zn++ levels from 1.11 ± 0.15 to 1.59 ± 0.58 μg/mL (p < 0.05) but caused no change in serum PRL levels. The TRH tolerance test (200 μg) was performed before and after 60 days of Zn++ administration, and PRL response to TRH was unchangeable and similar in both tests. We concluded that acute or chronic Zn++ administration does not inhibit PRL secretion in basal condition or by TRH effect in hyperprolactinemic patients.
Highlights
Zn plays an important role in animal and human metabolism, as a constituent or activating cofactor of more than 300 different enzymes
It was even hypothesized by Koppelman that PRL is a major Zn regulating hormone and that the suppression of PRL by Zn is a part of a negative feedback regulatory system The aim of this paper is to study basal serum Zn levels, the serum PRL levels after acute and chronic Zn*/ administration, and TRH-induced PRL secretion after chronic Zn administration in hyperprolactinemic patients
Acute oral Zn// ingestion There was a significant increase of serum Zn+/ levels during the test when compared with the basal levels, p < 0.05 (Table I)
Summary
Zn plays an important role in animal and human metabolism, as a constituent or activating cofactor of more than 300 different enzymes. The spectrum of their action includes intermediary metabolism, DNA and RNA synthesis, gene expression, immunocompetence, behaviour, and several endocrine functions []. Many studies have shown that Zn+/ can interact with many hormones especially with PRL [z3]. An inverse relationship between serum Zn+/and plasma PRL levels is a common finding in human chronic renal failure. The administration of oral Zn to a group of uremic hypozincemic men decreased their high PRL levels and these levels were inversely correlated to serum Zn concentrations[7]. In normal male and female subjects and in lambs, acute Zn administration decreased plasma
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