Mechanisms subserving the physiological nocturnal relative hypoprolactinemia of healthy older men: Dual decline in prolactin secretory burst mass andbasal release with preservation of pulse duration, frequency, and interpulse interval - A general clinical research center study

Citation
A. Iranmanesh et al., Mechanisms subserving the physiological nocturnal relative hypoprolactinemia of healthy older men: Dual decline in prolactin secretory burst mass andbasal release with preservation of pulse duration, frequency, and interpulse interval - A general clinical research center study, J CLIN END, 84(3), 1999, pp. 1083-1090
Citations number
54
Categorie Soggetti
Endocrynology, Metabolism & Nutrition","Endocrinology, Nutrition & Metabolism
Journal title
JOURNAL OF CLINICAL ENDOCRINOLOGY AND METABOLISM
ISSN journal
0021972X → ACNP
Volume
84
Issue
3
Year of publication
1999
Pages
1083 - 1090
Database
ISI
SICI code
0021-972X(199903)84:3<1083:MSTPNR>2.0.ZU;2-J
Abstract
Increasing age is accompanied by decrements in randomly obtained, fasting, or frequently sampled serum PRL concentrations. The precise neuroendocrine mechanisms underlying such relative hypoprotactinemia in aging are incomple tely understood. In the present study, we sampled blood at 2.5-min interval s overnight in 11 young (aged 21-34 yr) and 8 older (aged 62-72 yr) healthy men for subsequent chemiluminescence-based assay of serum PRL concentratio ns. The mean (+/- SEM) serum PRL concentration was significantly reduced at 4.3 +/- 0.78 mu g/L in older men compared with 9.5 +/- 1.2 mu g/L in young volunteers (P = 0.0049). PRL concentrations correlated with serum testoste rone (r = 0.473; P = 0.041), dehydroepiandrosteroen sulfate (r = + 0.455, P = 0.05), and insulin-like growth factor I (r = 0.494; P = 0.032) levels. D econvolution analysis was used to evaluate combined pulsatile and basal mod es of PRL secretion. In older men, discrete PRL secretory bursts were marke d by a significantly (2.4-fold) attenuated mass of hormone secreted per bur st (amount of PRL secreted per unit distribution volume), viz. 1.6 +/- 0.23 (older) vs. 3.9 +/- 0.57 mu g/L (young; P < 0.01). In contrast, PRL secret ory burst frequency, interpulse interval, and pulse duration were invariant of age. Concomitantly, basal PRL secretion was reduced by 2-fold in older subjects, namely to 0.00030 +/- 0.00027 (older) vs. 0.00065 +/- 0.0002 mu g /L/min(young; P < 0.01). The amount of total PRL secretion that was pulsati le averaged 82 +/- 5.3% in young and 99 +/- 0.13% in older men (P = 0.012), indicating preferential loss of the basal mode of PRL release in aging. Assuming that basal PRL secretion mirrors functional pituitary lactotroph c ell secretory mass, whereas pulsatile PRL release reflects effective (net) intermittent hypothalamic drive to responsive lactotroph cells, then our re sults suggest both an attrition in lactotroph cell mass and an impoverishme nt of net positive hypothalamic (agonistic) input to lactotrophs in older m en. Given the multiple roles of PRL reported in experimental animals (e.g. on the one hand to support immune function and adrenal androgen biosynthesi s and on the other hand to activate intraprostatic growth factors), we sugg est that the nocturnal relative hypoprolactinemia observed in healthy aging men may have both adaptive and maladaptive clinical implications to target tissues.