Measurement of prolactin

Kahan I, Papanastasiou-Dimandi A, D Costa M, Diamandis E. A time-resolved immunofluorometric assay for the measurement of prolactin in serum. 

Tanalta T, Shiu RP, Gout PW, Beer C% Noble RL, Friesen HG. A new sensitive and specific assay for lactogenic hormones Measurement of prolactin and growth hormones in human serum. J Clin Endocrinol Me tab 1980 51 1058-63. 

In addition to the common neural mechanism, primer pheromones have a common endocrine effect expressed principally by changing prolactin secretion from the anterior pituitary. Our own studies have shown that lowering prolactin by injections of bromocriptine (a dopamine agonist) is able to reproduce the actions of all the described primer pheromones in female mice with identical timing (Keverne, 1982). Direct measurement of prolactin has also demonstrated that exposure of female mice to males results in rapid decreases of serum prolactin (Ryan and Schwartz, 1980). Such decreases in prolactin are probably brought about by increases in the release of hypothalamic dopamine from the tuberoinfundibular dopaminergic (TIDA) neurons into the hypophyseal portal circulation. Indeed, our recent studies show there to be an increase in the synthesis of dopamine in this... 

In combination with clinical symptoms, at least three repeated measures of serum prolactin levels greater than 20 ng/mL (20 mcg/L) are needed to confirm the diagnosis because prolactin,... 

Two parallel groups of healthy volunteers received 20 mg of citalopram (n = 12) or placebo (n = 6) once daily for 10 d in a randomized, double-blind fashion, followed by concomitant selegiline, 10 mg once daily for 4 d. The safety of this drug combination was assessed by measurements of blood pressure, heart rate, body temperature, and inquiries for adverse events. Blood samples were taken for the analysis of serum concentrations of selegiline, citalopram, and their metabolites. In addition, plasma was obtained to measure prolactin, epinephrine, norepinephrine, and 3,4-dihydroxyphanolglycol (DHPG), the urinary excretion of norepinephrine and 5-hydroindoleacetic acid (5-HIAA), the urinary metabolite of serotonin. 

Serum hormone concentrations reflect both the rate of secretion and clearance by peripheral tissues. In parallel with our studies on prolactin secretion we have evaluated the effects of dietary fat on the metabolic clearance rate of prolactin. Rats were initially treated with ergocryptine to suppress endogenous prolactin secretion. We then measured the disappearance of immuno-reactive prolactin from the sera after a single intravenous injection of prolactin. No significant effect of dietary fat on the clearance of prolactin was observed (Figure 4). 

The role of cyclic AMP as modulator of prolactin secretion was first suggested by the finding of a stimulatory effect of cyclic AMP derivatives (17-22) and inhibitors of cyclic nucleotide phosphodiesterase activity such as theophylline and IBMX (22-26) on the secretion of this hormone. More convincing evidence supporting a role of cyclic AMP in the action of dopamine on prolactin secretion had to be obtained, however, by measurement of adenohypophysial adenylate cyclase activity or cyclic AMP accumulation under the influence of the catecholamine. As illustrated in Fig. 1, addition of 100 nM dopamine to male rat hemipituitaries led to a rapid inhibition of cyclic AMP accumulation, a maximal effect (30% inhibition) being already obtained 5 min after addition of the catecholamine. Thus, while dopamine is well known to stimulate adenylate cyclase activity in the striatum (27, 28), its effect at the adenohypophysial level in intact cells is inhibitory. Dopamine has also been found to exert parallel inhibitory effects on cyclic AMP levels and prolactin release in ovine adenohypophysial cells in culture (29) and purified rat mammotrophs (30). Using paired hemipituitaries obtained from female rats, Ray and Wallis (22) have found a rapid inhibitory effect of dopamine on cyclic AMP accumulation to approximately 75% of control. 

For the evolution of histological findings, measurement of pituitary prolactin concentrations should be considered as an additional source of information. 

CRITICAL ASSESSMENT OF THE METHOD The method is of interest because the results can be correlated with measurements of pituitary TSH and prolactin secretion, and tissue content of these hormones. In a number of studies it has been shown, that changes in the secretion of thyroid hormone in the treated animals as well as administration of hormonally active compounds can change the hypothalamic TRH content in characteristic manner (Emerson and Utiger 1975, Schwinn et al. 1976, Simpkins et al. 1976). 

They are now many modifications of different sensitivity and limit of detection (Utiger 1979, Spencer 2004). In the endocrine safety pharmacology in rats and dogs, the TRH test injection with measurement of the serum TSH response is an established tool for assessment of changes at the level of thyroid hormone secretion, with consecutive modification of the pituitary TSH and prolactin response. 

The two phases of prolactin activation of TIDA neurons (rapid tonic and delayed induction components) suggest that the level of activity of these DA neurons reflects both amount of circulating prolactin at the time of measurement (tonic component) and the past history of blood levels of this hormone (induction component). That is, animals treated chronically in such a way as to maintain high circulating concentrations of prolactin exhibit an exaggerated stimulatory response to acute injections of prolactin. Conversely, chronic hypoprolactinemia causes a reduced response to the acute administration of this hormone (Demarest et al., 1985a). 

The rapid (i.e. less than 4 h) activation of TH in the median eminence by prolactin that constitutes the tonic component of prolactin stimulation does not require protein synthesis, but is probably associated with effects on the catalytic properties of this enzyme. Pasqualini and coworkers (1994) demonstrated in vitro that prolactin acts directly on TH in the mediobasal hypothalamus to trigger the phosphorylation of this enzyme. This effect, possibly mediated by protein kinase C, makes the enzyme less susceptible to inhibition by newly synthesized DA. That is, prolactin-induced short-term activation of TH results from the removal of end-product inhibition of the enzyme. Conversely, the acute reduction in TH activity measured in vitro in median eminence removed from rats 4 h after administration of bromocriptine is prevented by the coadministration of prolactin (Arbogast and Voogt, 1995). This can also be prevented by an inhibitor of phosphoprotein phosphatases, suggesting that rapid suppression of TH activity secondary to the bromocriptine-induced hypoprolactinemia may also result from dephosphorylation of the enzyme. 

Gerder, A., Grosclaude, J., Strasburger, C. J., Nir, S., and Djiane, J. (1996). Real-time kinetic measurements of the interactions between lactogenic hormones and prolactin-receptor extracellular domains from several species support the model of hormone-induced transient receptor dimerization. J. Biol. Ghent. 271(40), 24482-24491. 

A study in 11 healthy subjects found that paroxetine 20 mg daily for 16 days had no effect on the response to a 6-mg dose of subcutaneous sumatriptan, as measured by prolactin levels. The sumatriptan levels remained unaltered, its cardiovascular effects were unchanged and no clinically significant adverse effects occurred. Other studies report that the concurrent use of sumatriptan and SSRIs (fluoxetine 20 to 60 mg daily, fluvoxamine 200 mg daily, paroxetine 20 to 50 mg daily, sertraline 50 to 100 mg daily) was successful and uneventful. No adverse effects have been noted in 148 other patients. However, a case report describes a 65-year-old woman who had been taking paroxetine 20 mg [daily] for a number of years, who developed confusion, strange behaviour, sinus tachycardia, hypertension and hyperthermia shortly after starting sumatriptan. The serotonin syndrome was diagnosed, and she recovered completely on withdrawal of the two drugs. ... 

Explants of mammary gland of pregnant mice were cultured with insulin, prolactin and hydrocortisone in different combinations and incubated with radioactive adenine and adenosine. Radioactivity incorporated and measurements of apparent activities of several enzymes of purine metabolism were done by the methods of Henderson et al7 ... 

Other neurochemical studies have not been carried out in lead-exposed humans. It is difficult to measure neurochemical functions in vivo without recourse to such techniques as cerebrospinal fluid collection. However, the reported effects of lead exposure in rodents on plasma concentrations of prolactin (Govoni et al., 1978) and other pituitary hormones (Petrusz et al., 1979), and tetrahydrobiopterin (Leeming and Blair, 1980 McIntosh et al., 1982) would suggest that similar studies in humans might be considered. 

This immunosensor-type assay uses ferrocene methanol as co-substrate (redox mediator) of glucose oxidase (GOD). The various steps of the assay, shown in Fig. 8.20, are as follows (1) Covalent immobilization of protein A on graphite-polystyrene screen-printed electrodes (SPEs) (2) Addition of the rabbit IgG to be quantified which is captured specifically by protein A (3) Addition of a biotinylated goat anti-rabbit antibody (4) Addition of avidin-GOD conjugate (5) Addition of glucose and ferrocene methanol (6) Measurement of catalytic current by flow injection immunoassay. The voltammetric current corresponds to the one-electron oxidation of the ferrocenyl group to ferricinium. The electrode can subsequently be regenerated up to 30 times. The feasibility of the assay has been demonstrated for the case of monoclonal mouse anti-human prolactin (PL) with a detection limit of 0.02 pg mL [90]. 

Clemens, J.A., Okimura, T. and Smalstig, E.B. (1993) Dopamine agonist activities of pergolide, its metabolites, and bromocriptine as measured by prolactin inhibition. 

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