Metabolic clearance and production rates of prolactin in man

Pituitary Hyperplasia Due to Longstanding Primary Hypothyroidism: A Case Report and Comprehensive Review of the Literature

Hypothyroidism is a frequently diagnosed endocrine disorder. Common signs and symptoms include fatigue, cold intolerance, hoarseness, dry skin, constipation, a slow relaxation phase of deep tendon reflexes, and bradycardia. However, some patients may exhibit atypical signs and symptoms, which can result in diagnostic confusion. Pituitary hyperplasia resulting from longstanding primary hypothyroidism was first described by Niepce in 1851. It is usually asymptomatic, but sometimes, in addition to symptoms of overt hypothyroidism, patients may complain of headaches, hypopituitarism, visual field impairment, and hyperprolactinemia. Furthermore, on imaging, pituitary hyperplasia can be mistaken for a pituitary adenoma. Distinguishing between the two is crucial, as their management differs; the former often responds to thyroid hormone replacement therapy, while the latter might need treatment with surgery and/or radiotherapy. Here we describe a patient who developed pituitary hyperplasia in the setting of longstanding uncompensated primary hypothyroidism due to a lack of compliance with levothyroxine replacement therapy. We also review the clinical, laboratory, and radiologic findings of the case reports available in the literature up to now in order to improve the knowledge and the care of the disease.

Investigation of the effects of atorvastatin and Lactobacillus acidophilus on some hormones and oxidative stress in experimental hypercholesterolemia

AIM

The investigation of serum leptin, ghrelin, insulin, seratonin hormones, NO, total oxidant/antioxidant status and brain cannaboid 1 receptor protein and apoptotic cell levels in atorvastatin and Lactobacillus acidophilus administrated experimental hypercholesterolemia was aimed in the project.

METHODS

In the study, 5 experimental groups were formed. Group 1 was fed with standard rat chow, and Group 2 was fed with 2% cholesterol added standard rat chow for 8 weeks. Group 3 was fed with 2% cholesterol feed and received atorvastatin (20 mg/kg/day) for the last 4 weeks. Group 4 was given L. acidophilus (2 ×10⁸ cfu/kg/day). Group 5 was given atorvastatin and L. acidophilus probiotic in the last 4 weeks of the experiment period. After the experimental period, blood samples were taken from each rat. Rats were sacrificed and brain tissues were taken for analyzes. In sera samples, leptin, ghrelin, insulin, serotonin hormones and NO levels were measured with ELISA. In brain samples, cannabinoid 1 receptor proteins and apoptosis levels were measured by ELISA. Total oxidant and antioxidant levels were investigated with using Rel Assay Kits.

RESULTS

The addition of cholesterol to feeds increased the levels of serum cholesterol, insulin and leptin levels; on the other hand, reduced the levels of serotonin and ghrelin. In hypercholesterolemia, total oxidant and NO levels were increased, and total antioxidant levels were decreased.

CONCLUSION

The results showed that administrations of L. acidophilus and atorvastatin might be recommended for treatment of hypercholesterolemia.

Prolactin and Its Altered Action in Alzheimer's Disease and Parkinson's Disease

BACKGROUND

Prolactin (PRL) is one of the most diverse pituitary hormones and is known to modulate normal neuronal function and neurodegenerative conditions. Many studies have described the influence that PRL has on the central nervous system and addressed its contribution to neurodegeneration, but little is known about the mechanisms responsible for the effects of PRL on neurodegenerative disorders, especially on Alzheimer's disease (AD) and Parkinson's disease (PD).

SUMMARY

We review and summarize the existing literature and current understanding of the roles of PRL on various PRL aspects of AD and PD.

KEY MESSAGES

In general, PRL is viewed as a promising molecule for the treatment of AD and PD. Modulation of PRL functions and targeting of immune mechanisms are needed to devise preventive or therapeutic strategies.

The forgotten effects of thyrotropin-releasing hormone: Metabolic functions and medical applications

Thyrotropin-releasing hormone (TRH) causes a variety of thyroidal and non-thyroidal effects, the best known being the feedback regulation of thyroid hormone levels. This was employed in the TRH stimulation test, which is currently little used. The role of TRH as a cancer biomarker is minor, but exaggerated responses to TSH and prolactin levels in breast cancer led to the hypothesis of a potential role for TRH in the pathogenesis of this disease. TRH is a rapidly degraded peptide with multiple targets, limiting its suitability as a biomarker and drug candidate. Although some studies reported efficacy in neural diseases (depression, spinal cord injury, amyotrophic lateral sclerosis, etc.), therapeutic use of TRH is presently restricted to spinocerebellar degenerative disease. Regulation of TRH production in the hypothalamus, patterns of expression of TRH and its receptor in the body, its role in energy metabolism and in prolactin secretion are addressed in this review.

Serum Concentrations of Ghrelin and Leptin according to Thyroid Hormone Condition, and Their Correlations with Insulin Resistance

BACKGROUND

Thyroid hormones can influence energy metabolism and insulin sensitivity via their interaction with adipocytokines and gut hormones. The aims of this study were to evaluate differences in serum ghrelin and leptin concentrations according to thyroid hormone levels, and to investigate the correlation of insulin resistance.

METHODS

A total of 154 patients (57 hyperthyroid patients, 61 euthyroid patients, and 36 hypothyroid patients; mean age, 47.9 years) were enrolled. Serum leptin, ghrelin, and insulin levels were measured and insulin resistance was calculated using the formula of the homeostasis model assessment of insulin resistance (HOMA-IR).

RESULTS

There were no differences in mean concentrations of ghrelin or leptin among the three groups. There were no significant differences in insulin levels between the groups (P=0.06), although hyperthyroid patients had borderline statistically significantly higher levels of insulin than did euthyroid subjects by post hoc test (26.4 μIU/mL vs. 16.1 μIU/mL, P=0.057). Regarding HOMA-IR index, the mean levels were highest in the hyperthyroid group among those of the three groups (hyperthyroid vs. euthyroid vs. hypothyroid, 6.7 vs. 3.8 vs. 4.4, P=0.068). Plasma levels of ghrelin were significantly negatively correlated with age, insulin, glucose, body mass index (BMI), and HOMA-IR. Plasma levels of leptin showed significant positive correlation with BMI and triglyceride. There were no significant correlations among thyroid hormone, thyrotropin, ghrelin, leptin, or insulin.

CONCLUSION

The present study found that serum ghrelin, leptin, and insulin levels didn't differ according to thyroid function conditions. Further studies with larger numbers of patients are required to establish a direct relationship between plasma ghrelin, leptin, and thyroid hormone.

Predictions of in vivo prolactin levels from in vitro K(i) values of D(2) receptor antagonists using an agonist-antagonist interaction model

Prolactin elevation is a side effect of all currently available D(2) receptor antagonists used in the treatment of schizophrenia. Prolactin elevation is the result of a direct antagonistic D(2) effect blocking the tonic inhibition of prolactin release by dopamine. The aims of this work were to assess the correlation between in vitro estimates of D(2) receptor affinity and pharmacokinetic-pharmacodynamic model-based estimates obtained from analysis of clinical data using an agonist-antagonist interaction (AAI) model and to assess the value of such a correlation in early prediction of full prolactin time profiles. A population model describing longitudinal prolactin data was fitted to clinical data from 16 clinical phases 1 and 3 trials including five different compounds. Pharmacokinetic data were modeled for each compound and the prolactin model was both fitted in per-compound fits as well as simultaneously to all prolactin data. Estimates of prolactin elevating potency were compared to corresponding in vitro values and their predictability was evaluated through model-based simulations. The model successfully described the prolactin time course for all compounds. Estimates derived from experimental preclinical data and the model fit of the clinical data were strongly correlated (p<0.001), and simulations adequately predicted the prolactin elevation in five out of six compounds. The AAI model has the potential to be used in drug development to predict prolactin response for a given exposure of D(2) antagonists using routinely produced preclinical data.

Prolactin secretion in healthy adults is determined by gender, age and body mass index

Background

Prolactin (PRL) secretion is quantifiable as mean, peak and nadir PRL concentrations, degree of irregularity (ApEn, approximate entropy) and spikiness (brief staccato-like fluctuations).

Hypothesis

Distinct PRL dynamics reflect relatively distinct (combinations of) subject variables, such as gender, age, and BMI.

Location

Clinical Research Unit.

Subjects

Seventy-four healthy adults aged 22–77 yr (41 women and 33 men), with BMI 18.3–39.4 kg/m².

Measures

Immunofluorometric PRL assay of 10-min samples collected for 24 hours.

Results

Mean 24-h PRL concentration correlated jointly with gender (P<0.0001) and BMI (P = 0.01), but not with age (overall R² = 0.308, P<0.0001). Nadir PRL concentration correlated with gender only (P = 0.017) and peak PRL with gender (P<0.001) and negatively with age (P<0.003), overall R² = 0.325, P<0.0001. Forward-selection multivariate regression of PRL deconvolution results demonstrated that basal (nonpulsatile) PRL secretion tended to be associated with BMI (R² = 0.058, P = 0.03), pulsatile secretion with gender (R² = 0.152, P = 0.003), and total secretion with gender and BMI (R² = 0.204, P<0.0001). Pulse mass was associated with gender (P = 0.001) and with a negative tendency to age (P = 0.038). In male subjects older than 50 yr (but not in women) approximate entropy was increased (0.942±0.301 vs. 1.258±0.267, P = 0.007) compared with younger men, as well as spikiness (0.363±0.122 vs. 0463±2.12, P = 0.031). Cosinor analysis disclosed higher mesor and amplitude in females than in men, but the acrophase was gender-independent. The acrophase was determined by age and BMI (R² = 0.186, P = 0.001).

Conclusion

In healthy adults, selective combinations of gender, age, and BMI specify distinct PRL dynamics, thus requiring balanced representation of these variables in comparative PRL studies.

Abolition of endocrine dimorphism in hyperthyroid males? An argument for the positive feedback effect of hyperoestrogenaemia on LH secretion

Our aim was (i) to investigate the hypothalamo-hypophyseal-gonadal axis in hyperthyroid Indian males, (ii) to rule out the modulatory role of adrenal steroids on it and (iii) to determine if the simultaneous rise in oestradiol and luteinising hormone (LH) in hyperthyroid males is due to a positive feedback action of oestradiol on pituitary LH release. Age- and BMI-matched men were divided into two groups, I, euthyroid subjects (n = 17) and II, hyperthyroid patients (n = 12) on the basis of their thyroid hormone levels. Serum levels of thyroid-stimulating hormone, triiodothyronine, thyroxine, LH, follicle-stimulating hormone (FSH), prolactin, E(2), T, P(4), sex hormone binding globulin and dehydroepiandrosterone sulphate (DHEAS) were assayed. Mean levels of T and E(2) were approximately two times higher in group II in comparison with group I. DHEAS levels were similar in both groups ruling out any adrenal involvement. Mean serum LH level was 2.6 folds higher in group II in comparison with group I. Mean serum levels of FSH were higher in group II, it was marginally nonsignificant. On the basis of these and previous observations, we hypothesise that endocrinological dimorphism in human male and female is not rigid; a sustained rise in serum oestradiol probably induces a positive feedback action on pituitary leading to elevated gonadotrophin levels.

Comparison of the agonist-antagonist interaction model and the pool model for the effect of remoxipride on prolactin

AIMS

The tolerance to the prolactin response following administration of antipsychotic drugs has been modelled as a depletion of a prolactin pool (pool model) and a model where the tolerance is explained by a feedback loop including the dopamine interaction of prolactin release (agonist-antagonist interaction model, (AAI model)). The AAI model was superior to the pool model when analyzing data from clinical trials of risperidone and paliperidone. Here we evaluated the two models using the remoxipride data, designed to challenge the short-term prolactin response, from which the original pool model was built.

METHODS

The remoxipride data were collected from a study where eight healthy male subjects received two remoxipride infusions on five occasions. The intervals between the first and second dose on each occasion were 2, 8, 12, 24 and 48 h, respectively. The pool and AAI models were fitted using NONMEM.

RESULTS

According to the objective function values the pool model with a circadian rhythm function fitted the data slightly better, while the AAI model was better in describing the circadian rhythm of prolactin. Visual predictive checks revealed that the models predicted the prolactin profiles equally well.

CONCLUSIONS

According to the analysis performed here, a previous analysis of several clinical studies and literature reports on prolactin concentrations, it appears that the dopamine feedback mechanism included in the AAI model is better than the storage depletion mechanism in the pool model to estimate the bio-rhythm of prolactin time-course and the tolerance development across different populations, drugs, treatment schedules and time.

An agonist-antagonist interaction model for prolactin release following risperidone and paliperidone treatment

A mechanistic pharmacokinetic/pharmacodynamic model is presented, characterizing the time course of prolactin in healthy as well as schizophrenic subjects following the administration of various doses and formulations of the antipsychotic drugs risperidone and paliperidone. Prolactin concentrations from nine studies (1,462 subjects) were analyzed in NONMEM. A competitive agonist-antagonist interaction model described the competition between these drugs and dopamine for the D(2) receptors that regulate prolactin release. Tolerance development was explained by a feedback loop with prolactin stimulating dopamine release, whereas models wherein tolerance is described in terms of depletion of a prolactin pool did not explain the data well. The diurnal prolactin rhythm was described by a two-period cosine function. Baseline prolactin was health-status dependent and higher in women than in men, although the drug-induced release was less than proportional to baseline. This quantitative mechanism-based model is the first to describe prolactin release in patients, and it confirms that paliperidone and risperidone have similar potencies for prolactin release.

Biphasic effects of moderate drinking on prolactin during lactation

BACKGROUND

Contrary to the popular lore that encourages women to drink alcohol as an aid to lactation, we previously showed that alcohol consumption disrupted lactational performance and the hormonal milieu of the lactating mother in the short term.

METHODS

Thirteen lactating women participated in a 4-session, double-blind, 2 x 2 within-subject study to test several hypotheses related to the effects of alcohol on prolactin (PRL) responses and milk yield over time. The two within-subject factors were beverage condition (control or 0.4 g/kg dose of alcohol) and pumping condition (pumping occurred at fixed intervals once or twice during the 5.3-hour session). Plasma PRL, blood alcohol concentrations (BAC), and milk yield were measured.

RESULTS

Alcohol consumption increased basal PRL levels (p < 0.0001) and modified the PRL response to pumping (p < 0.0001) but the directionality of the response depended on when pumping occurred along the BAC curve. Pumping enhanced PRL response when it occurred during the ascending BAC limb but blunted the response when it occurred during the descending limb, providing evidence that the effects were transient and of a biphasic nature. The slower the alcohol was metabolized, the greater the relative PRL response to breast pumping (p < 0.05). The dynamics of the PRL response between pumping sessions was also altered if women drank. If women pumped within the hour after drinking alcohol, the PRL response during the next pumping some 1.5 hours later, was delayed by a few minutes. Milk yield was significantly lower after drinking alcohol but such deficits were not significantly related to PRL or the speed at which alcohol was eliminated.

CONCLUSIONS

Effects of alcohol on suckling-induced PRL were biphasic in nature, but could not explain the deficits in lactational performance. Such findings provide further evidence that the dynamic changes in neuroendocrine state are integrally involved in alcohol's effects over time and underscore the complexity of lactation.

Nipple discharge

By performing a thoughtful evaluation including a detailed history and careful physical examination, appropriate studies can be selected to allow the practitioner to arrive at the correct diagnosis of nipple discharge in a nonmorbid, expeditious, and inexpensive manner. This article has presented a simple, cost-effective, minimally morbid algorithm for the evaluation of nipple discharge.

Hypothalamic-pituitary-testicular axis and seminal parameters in hyperthyroid males

Information on the effect of abnormal thyroid function on male reproduction is less available than that for the female. To assess the effects of hyperthyroidism on hypothalamic-pituitary-testicular axis and on spermogram parameters, 25 male patients (19-47 years old) suffering from active Graves' disease were studied. Serum luteinizing hormone (LH), follicle stimulating hormone (FSH), and prolactin (PRL) were measured before and after administration of 100 microg GnRH plus 200 microg thyrotropin-releasing hormone (TRH). Testosterone (T), estradiol (E2), and 17-hydroxyprogesterone (17-OHP) were determined before and after 5000 IU human chorionic gonadotropin (HCG) administration. Serum sex hormone-binding globulin (SHBG), cortisol-binding globulin (CBG), androstenedione and bioavailable testosterone (bioT), and bioavailable estradiol (bioE2) were also measured. Spermograms according to World Health Organization (WHO) criteria were determined in 21 patients. Hormonal and seminal studies were repeated in six patients after 7 to 19 months of euthyroidism achieved after treatment for hyperthyroidism. As a control group, 10 normal men were evaluated. Impaired sexual function, gynecomastia, and low testicular volume were found in 12, 6, and 3 hyperthyroid patients. Mean basal LH was significantly higher than the control group (7.8 +/- 4.7 vs. 5.0 +/- 1.9 mIU/mL, respectively, p < 0.02), with hyperresponse to GnRH. The response of PRL to TRH was lower in patients versus control group (30 minutes: 3.9 +/- 3.4 and 12.0 +/- 2.8 ng/mL, p < 0.01). Basal levels of steroids and SHBG were significantly higher in patients than in normal men (T: 9.3 +/- 3.3 vs. 5.4 +/- 1.6 ng/mL, p < 0.005; E2: 62.2 +/- 25.2 vs. 32.1 +/- 11.0 pg/mL, p < 0.005; 17-OHP: 2.4 +/- 0.9 vs. 1.1 +/- 0.5 ng/mL, p < 0.001; SHBG: 102.3 +/- 37.3 vs. 19.0 +/- 5.0 nmol/L, p < 0.01). The maximal increment of T and 17-OHP after HCG was lower in hyperthyroid patients than in normal men (p < 0.019 and p < 0.001, respectively). Basal bioT was lower in patients than controls (1.7 +/- 0.8 and 3.1 +/- 1.9 ng/mL, p < 0.02). The following incidence of abnormal semen parameters was found: asthenospermia 85.7%, hypospermia 61.9%, oligospermia 42.9%, necrospermia 42.9% and teratospermia 19.0%. In euthyroidism, a normalization of 85% of seminal alterations was observed in the limited number of patients evaluated. Our results confirm that hyperthyroidism causes marked alterations of the gonadotropic and PRL axis and dramatically affects spermatic function. BioT measurement was useful to identify hypoandrogenism in these patients in spite of the high concentration of total testosterone. The restoration of most semen parameters when euthyroidism was achieved suggests that the alterations were induced by the Graves' disease.

Genetic and environmental influences on prolactin secretion during wake and during sleep

To delineate the contributions of genetic and environmental factors in the regulation of human prolactin (PRL) secretion, the 24-h profile of plasma PRL was obtained at 15-min intervals in 10 pairs of monozygotic and 10 pairs of dizygotic twins. Sleep was monitored polygraphically. PRL secretory rates were derived from plasma concentrations by deconvolution. Diurnal (24-h) variations were quantified by a regression curve to define nadir, acrophase, and amplitude. Pulses of PRL secretion were identified using a computerized algorithm. A procedure specifically developed for twin studies was used to partition the variance into genetic and environmental contributions. Significant genetic effects were identified for daytime PRL concentrations, rhythm amplitude, and overall wave-shape of the daily PRL profile. In contrast, environmental effects were dominant for mean concentrations during sleep, total secretory output during sleep, overall 24-h concentrations, and total 24-h secretion. However, when interindividual variations in sleep fragmentation were taken into account, the estimates of genetic variance for PRL concentrations and secretion during sleep approached statistical significance. Significant genetic influences were identified for slow-wave sleep (SWS). Because SWS is associated with increased nocturnal PRL secretion, it is possible that genetic effects on PRL secretion during sleep reflect genetic influences on SWS. In conclusion, genetic factors determine partially both the basal daytime concentrations of PRL and the temporal organization of PRL secretion over the 24-h cycle in normal young men.

Clomipramine-induced sleep disturbance does not impair its prolactin-releasing action

The present study was undertaken to examine the role of sleep disturbance, induced by clomipramine administration, on the secretory rate of prolactin (PRL) in addition to the direct drug effect. Two groups of supine subjects were studied under placebo-controlled conditions, one during the night, when sleeping (n = 7) and the other at daytime, when awake (n = 6). Each subject received a single 50 mg dose of clomipramine given orally 2 hours before blood collection. Plasma PRL concentrations were analysed at 10 min intervals and underlying secretory rates calculated by a deconvolution procedure. For both experiments the drug intake led to significant increases in PRL secretion, acting preferentially on tonic secretion as pulse amplitude and frequency did not differ significantly from corresponding control values. During the night clomipramine ingestion altered the complete sleep architecture in that it suppressed REM sleep and the sleep cycles and induced increased wakefulness. As the relative increase in PRL secretion expressed as a percentage of the mean did not significantly differ between the night and day time studies (46 +/- 19% vs 34 +/- 10%), it can be concluded that the observed sleep disturbance did not interfere with the drug action per se. The presence of REM sleep was shown not to be a determining factor either for secretory pulse amplitude and frequency, as, for both, mean nocturnal values were similar with and without prior clomipramine ingestion.

Vasoactive intestinal peptide-induced prolactin release in hypothyroid patients

VIP is an established prolactin-releasing factor. VIP gene expression at the anterior pituitary level and the central nervous system is regulated by thyroid hormones. On the other hand, primary hypothyroidism leads in many cases to amenorrhea, galactorrhea and hyperprolactinemia. In this study we assessed prolactin responses to VIP (75 micrograms iv infusion over 12 min) in a group of six hypothyroid women (mean age +/- SE, 38.8 +/- 3.3 yr; serum TSH levels, mU/L, 116.3 +/- 23.9), before treatment and after normalization of thyroid hormone levels during thyroxine (T4) replacement therapy (100-150 micrograms/day over 12-16 weeks). Furthermore, we assessed if VIP infusion had any effects on serum GH levels in these patients. In hypothyroid women, VIP infusion increased serum prolactin concentrations with peak levels being attained at 15 min (28.8 +/- 3.4 micrograms/L). The Area Under the Curve (AUC) was 1921 +/- 103 micrograms/L/2h. PRL responses to VIP were unchanged after T4 therapy, both in terms of peak levels (28.7 +/- 2.2 micrograms/L, NS) and of AUC (2079 +/- 261 micrograms/L/2h, NS). Serum GH levels were unaffected by VIP administration. In conclusion our study shows that, in hypothyroid patients, restoration of normal thyroid hormone levels by thyroxine replacement therapy does not affect lactotroph responsiveness to VIP. Therefore, our data do not support the hypothesis that VIP might contribute to the hypothyroid-induced hyperprolactinemia seen in man.

Osteopenia in men with a history of delayed puberty

BACKGROUND AND METHODS

The effect of delayed puberty on peak bone mineral density in men is unknown. To determine whether such a delay reduces normal peak bone density and leads to osteopenia during adulthood, we measured radial bone mineral density by single-photon absorptiometry and spinal bone mineral density by dual-energy x-ray absorptiometry in 23 men who had a history of constitutionally delayed puberty and 21 men who underwent normal puberty. Their mean ages were 26 and 24 years, respectively. The groups were matched for other factors known to affect bone mass.

RESULTS

The mean (+/- SD) radial bone mineral density was significantly lower in the men with a history of delayed puberty than in the normal men (0.73 +/- 0.07 vs. 0.80 +/- 0.05 g per square centimeter; P less than 0.0002). Spinal bone mineral density was also significantly lower in the men with delayed puberty than in the normal men (1.03 +/- 0.10 vs. 1.13 +/- 0.11 g per square centimeter; P less than 0.003). Radial bone density was at least 1 SD below the mean value for the normal men in 15 of the 23 men with a history of delayed puberty, and spinal bone density was similarly decreased in 10 of the 23.

CONCLUSIONS

Adult men with a history of constitutionally delayed puberty have decreased radial and spinal bone mineral density. These findings suggest that the timing of puberty is an important determinant of peak bone density in men. Because the peak bone mineral density achieved during young adulthood is a major determinant of bone density in later life, men in whom puberty was delayed may be at increased risk for osteoporotic fractures when they are older.

Mathematical model for in vivo pharmacodynamics integrating fluctuation of the response: application to the prolactin suppressant effect of the dopaminomimetic drug DCN 203-922

We propose a general pharmacokinetic-pharmacodynamic model that integrates the rhythmic fluctuation of hormone secretion for the description of the hormone-lowering effect of a drug. The mathematical model takes into account the variation in response observed after administration of a placebo and the drug. It is assumed that the change with time in the physiological response during the placebo period results from fluctuations in the concentration of hypothetical endogenous molecules. The mathematical formulation for predicting the response after drug intake is derived assuming competitive interaction of these "molecules" with the active species for binding to receptors. The suggested "fluctuation model" was implemented in order to describe the time course of the prolactin (PRL) plasma level after administration of two oral doses (2.5 and 5.0 mg) of the dopaminomimetic compound DCN 203-922 (DCN) to 9 healthy male subjects. Its performance was compared with that of conventional modeling approaches, in which the circadian changes after placebo are neglected and the hormone baseline is assumed to be constant. The new model provided a better description of the time course of PRL in most subjects. It was used for prediction of the amplitude and duration of the PRL suppressant effect after single and chronic administration of DCN at various dosage regimens as well as after changes in drug absorption.

Reproductive endocrinologic alterations in female asymptomatic obesity

Excess body fat has been clearly associated with an increased risk of oligo-ovulation and endometrial/breast carcinoma. The connection has been assumed to lie within derangements of the metabolic/endocrine compartments, particularly of estrogens and androgens. To differentiate the effect of obesity from its related disease process, an attempt has been made to define the reproductive-endocrinologic alterations encountered in otherwise asymptomatic obese women. Androgen metabolism is accelerated in obesity. It is not clear whether the increased clearance precedes or follows the accelerated production of androgens. A servocontrol mechanism appears to be operative in these asymptomatic individuals, maintaining plasma steroid levels normal. The unbound fraction of T may be somewhat increased in overweight women with predominantly upper body fat deposition. The increased clearance of androgen may arise from an obesity-related depression in SHBG concentration (e.g., for T, E2, delta 5-diol, etc.). Adipose tissue, by virtue of the lipid solubility of most of these steroids, concentrates androgens, estrogens, and progesterone. This steroid sequestration not only contributes to the obesity-related increase in androgen clearance but also leads to an extremely enlarged total body steroid pool. Fat tissue sequestration also increases the concentration of androgens in the vicinity of adipose stromal cells, possibly encouraging their aromatization. Adipose tissue also has a moderate degree of 17-hydroxysteroid dehydrogenase activity, which appears to stimulate the conversion of A to T. Finally, alterations in peripheral and hepatic conjugation and an accelerated urinary excretion may contribute to the elevated clearance of androgens. The accelerated PR of androgens may simply result as compensation for the elevated MCR in obesity. Nonetheless, evidence of alteration(s) in adrenocortical steroidogenesis has been presented suggesting a selective obesity-related enhancement in adrenal androgen secretion. These remain to be confirmed. Nonetheless, adrenocortical abnormalities may arise secondary to the influence of other circulating and intra-adrenal factors, including insulin, prolactin, estrogens, and androgens. It is not known whether the accelerated androgen metabolism or the aberrant adrenal steroidogenesis improve with weight reduction. Excess body fat increases androgen aromatization which, together with an obesity-related decrease in SHBG, is associated with mildly elevated levels of E1 and free E2 in postmenopausal women. Although premenopausal obese individuals have the same tendency, the far greater ovarian estrogen secretion overshadows any differences. The bulk of aromatization activity in fat lies in the stromal comportment. The major substrate for peripheral estrogen production is A. Testosterone also contributes to the estrogen pool via its conversion to E2.(ABSTRACT TRUNCATED AT 400 WORDS)

A dose rising study of the safety and effects on serum prolactin of SK&F 101468, a novel dopamine D2-receptor agonist

1. SK&F 101468, a non phenolic indolone derivative, has been characterised preclinically as a novel, potent and specific dopamine D2-receptor agonist. 2. Its tolerability and effects on serum prolactin were investigated in 14 healthy male volunteers in a study of the first administration of SK&F 101468 to man. 3. Doses between 80 micrograms and 2.5 mg caused statistically significant (P less than 0.05) lowering of basal and food stimulated serum prolactin, relative to placebo, over a 6 h post treatment period. 4. SK&F 101468 was well tolerated up to 1 mg with symptoms of nausea and postural hypotension at higher doses.

Diagnostic work-up of hyperprolactinemic disorders

Substantial advances have been made in the understanding of chronic hyperprolactinemia. The diagnostic effort should be directed at excluding physiological and pharmacological causes of chronic hyperprolactinemia, both of which are reversible and are not likely to be of grave consequence. Subsequently further efforts should be made to rule out obvious pathological entities, in particular, treatable hypothyroidism. Finally, the diagnosis of prolactinoma must be entertained. It relies on the biochemical determination of prolactin as well as direct imaging of the pituitary.

Bone mineralization in women following successful treatment of Hodgkin's disease

PURPOSE

Women with Hodgkin's disease in whom a cure has been achieved may be at risk for osteoporosis because of therapy-induced premature menopause. Our objective was to gather information regarding the integrity of bone mass in such long-term cancer survivors.

SUBJECTS AND METHODS

Bone mineral density was measured using photon absorptiometry in five groups of women: 11 patients with Hodgkin's disease and ovarian failure (Group I); six patients with Hodgkin's disease and ovarian failure who received estrogen replacement (Group II); 15 patients with Hodgkin's disease and normal ovarian function (Group III); 16 premenopausal control subjects (Group IV); and 11 postmenopausal control subjects (Group V). All patients with Hodgkin's disease were in remission and had completed treatment more than five years earlier.

RESULTS

Subjects in Group I were found to have significantly decreased radial (p = 0.0009), lumbar spine (p = 0.002), and femoral neck (p = 0.0001) bone mineral density measurements compared with those in subjects in Group IV; the bone mineral density measurements at all sites of subjects in Group I were no different than those of subjects in Group V. Subjects in Group III had bone density measurements that were similar to those in Group IV, although the radial bone mineral density value was significantly lower (p = 0.0004). Determination of serum gonadotropins and estradiol was consistent with the menstrual status defining the five groups. No secondary causes for decreased bone mineral density values could be detected, since the mean serum levels of parathyroid hormone, calcium, phosphorus, and vitamin D metabolites were similar among the groups, and all prolactin levels were normal.

CONCLUSION

We have identified a new population of patients with a high risk of osteoporosis, and these results emphasize the importance of treatment-related ovarian failure in the pathogenesis of osteoporosis.

Clinically silent hypersecretion of growth hormone in patients with pituitary tumors

Hypersecretion of growth hormone (GH) was found in three women aged 25 to 35 years old, with somatotroph adenomas without clinical stigmata of acromegaly. The patients had previously been diagnosed as having nonfunctioning pituitary macroadenomas, with extrasellar extension. Concentrations of GH were elevated preoperatively in all subjects and could not be suppressed during oral glucose tolerance testing. Somatomedin-C concentrations were elevated in two patients. Immunocytochemical studies of surgically obtained tumor tissue demonstrated sparse positive staining for GH in all subjects. Gel-chromatographic analysis of serum and tumor tissue samples demonstrated that the immunoactive GH was authentic GH. On pathological examination, the tumor was cellular in all cases, consisting of partly acidophilic and partly chromophobic cells. Electron microscopic analysis of one tumor showed a cell composition not previously described. These studies further characterize GH hypersecretion in a subset of patients with clinically nonfunctioning pituitary macroadenomas.

Hormone production in clinically nonfunctioning pituitary adenomas

Pituitary tumors in which no excess hormone secretion can be identified clinically have been considered as nonfunctioning or null-cell adenomas. Immunocytochemical data presented here suggest that many of these tumors contain subunits of the glycoprotein hormones. Of 160 patients referred for pituitary surgery, 37 (23%) had no evidence of excess hormone secretion on preoperative endocrine evaluation. Immunocytochemical staining of these tumors was carried out using antibodies specific for prolactin, growth hormone, adrenocorticotropic hormone, the beta subunits of luteinizing hormone (beta-LH), follicle-stimulating hormone (beta-FSH), and thyroid-stimulating hormone (beta-TSH), and the alpha subunit. One or more of these pituitary hormones were detected in 73% of cases. The alpha and beta subunits were detected most frequently, being found in 68% of cases; 27% had staining for one or more beta subunits and 37.9% had staining for both alpha and beta subunits. The incidence was: beta-FSH in 58%, beta-LH in 47%, beta-TSH in 33%, and the alpha subunit in 42%. Staining for multiple glycoprotein hormones was common (52%), and mixed glycoprotein hormones and prolactin cell types were found in 16% of cases. These data suggest that most apparently nonfunctioning pituitary tumors contain immunoreactive hormones and the majority of these are subunits of the glycoprotein hormones. Since the glycoprotein hormone beta subunits must combine with the alpha subunit to produce biologically active hormones, the production of the subunits alone may not have endocrine manifestations.

Hypothalamic dysfunction following whole-brain irradiation

The authors describe 15 cases with evidence of hypothalamic dysfunction 2 to 9 years following megavoltage whole-brain x-irradiation for primary glial neoplasm. The patients received 4000 to 5000 rads in 180- to 200-rad fractions. Dysfunction occurred in the absence of computerized tomography-delineated radiation necrosis or hypothalamic invasion by tumor, and antedated the onset of dementia. Fourteen patients displayed symptoms reflecting disturbances of personality, libido, thirst, appetite, or sleep. Hyperprolactinemia (with prolactin levels up to 70 ng/ml) was present in all of the nine patients so tested. Of seven patients tested with thyrotropin-releasing hormone, one demonstrated an abnormal pituitary gland response consistent with a hypothalamic disorder. Seven patients developed cognitive abnormalities. Computerized tomography scans performed a median of 4 years after tumor diagnosis revealed no hypothalamic tumor or diminished density of the hypothalamus. Cortical atrophy was present in 50% of cases and third ventricular dilatation in 58%. Hypothalamic dysfunction, heralded by endocrine, behavioral, and cognitive impairment, represents a common, subtle form of radiation damage.

Increase in bone mass after treatment of hyperprolactinemic amenorrhea

Hyperprolactinemia occurs in 25 to 30 percent of young women with amenorrhea, and this condition is known to be associated with osteopenia. To determine whether the osteopenia is affected by treatment of hyperprolactinemia, we studied 32 women with hyperprolactinemic amenorrhea prospectively for 12 to 72 months to investigate the effects of sustained hyperprolactinemia or return of gonadal function on bone mass. We studied 18 patients using direct photon absorptiometry before and after normalization of serum prolactin levels. Initial bone densities ranged from 0.55 to 0.77 g per square centimeter (mean +/- 1 SD, 0.64 +/- 0.05)--densities significantly lower (P less than 0.001) than those of controls (0.71 +/- 0.04 g per square centimeter). After therapy, bone density increased significantly (P less than 0.001), to 0.67 +/- 0.05 g per square centimeter, but remained lower (P less than 0.05) than normal. Fourteen patients were followed without therapy. Their initial bone densities ranged from 0.62 to 0.75 g per square centimeter (mean, 0.67 +/- 0.04)--values significantly lower (P less than 0.02) than those in controls. There was a significant decrease (P less than 0.002) in bone density over time in this group. We conclude that (1) treatment of hyperprolactinemia increases bone mass in most amenorrheic women with osteopenia, (2) normalization of serum prolactin levels in such women is associated with prevention of bone loss, and (3) a subset of untreated women with hyperprolactinemia have progressive osteopenia, which could have adverse long-term health consequences.

Description of the time course of the prolactin suppressant effect of the dopamine agonist CQP201-403 by an integrated pharmacokinetic-pharmacodynamic model

Six male volunteers (mean age 24 years) received a single oral dose of 0.025 mg CQP201-403 and placebo in a randomised double-blind crossover design. Fifteen plasma samples were collected over 48 h and were assayed by radioimmunoassay for drug substance and prolactin (PRL). Three of the samples were drawn during sleep on the first study day. The pharmacological effect (E%) of CQP201-403 was expressed as reduction in plasma PRL levels. The pharmacokinetic (PK)-pharmacodynamic (PD) model consisted of two kinetic compartments and an effect compartment linked to the central compartment. A sigmoid Emax model (Hill equation) described the relationship between the drug concentration in the effect compartment and E%. Curve-fitting of PK and PD data provided individual parameter estimates which served to generate computer-simulated PK and PD profiles after single and multiple doses in order to: investigate the in vivo concentration-effect relationship; evaluate the consequence of dosage reduction on the steady-state PD profile; and study the robustness of the response to changes in drug potency and bioavailability.

Decreased fetal cord prolactin concentration in diabetic pregnancies

Infants of diabetic mothers are known to have a greater incidence of respiratory distress syndrome than normal control infants. Fetal lung maturation is modulated by a large number of hormones. To further investigate a possible role of hormonal modulators of lung maturation in infants of diabetic mothers, fetal cord prolactin, estrone, estradiol, thyroxine, triiodothyronine, and triiodothyronine-resin uptake index levels were measured in infants of diabetic mothers (n = 40) and nondiabetic mothers (n = 40) at term. Infants of diabetic mothers had significantly lower mixed-cord serum prolactin levels (p less than 0.0005) than control infants. There was no significant difference in cord serum thyroxine, triiodothyronine-resin uptake index, triiodothyronine, estrone, or estradiol levels between the infants of diabetic mothers and the infants of control mothers. These findings raise the possibility that decreased fetal prolactin levels may be associated with, or contribute to, the delayed lung maturation reported with diabetic pregnancies.

Cysteamine decreases prolactin responsiveness to thyrotropin-releasing hormone in normal men

Cysteamine depletes pituitary and plasma prolactin in rats. It acts through a nondopaminergic mechanism to alter both immunoactive and bioactive prolactin. The effect of cysteamine on prolactin secretion is reported in normal men. Six normal subjects received a control thyrotropin-releasing hormone (TRH) test at 0900 using 200 micrograms TRH intravenously; serum prolactin and TSH were measured at -10, 0, 10, 20, 30, 60, and 90 min after administration of TRH. Serum calcium and parathyroid hormones levels were measured at -10 min. Seven or more days later, they received cysteamine hydrochloride 15 mg/kg body weight orally every 6 hours for 5 doses. One hour after the last dose, the TRH test was repeated. Peak serum prolactin levels following TRH, prolactin levels at the 10-min time point, and total area from 0 to 30 min under the prolactin secretory curve were significantly decreased by cysteamine administration. TSH levels were unchanged. Serum calcium levels were significantly decreased by cysteamine administration, but parathyroid hormone levels were unchanged. It was concluded that cysteamine reduced TRH-stimulated prolactin secretion. Cysteamine also decreases serum calcium levels and suppresses the anticipated rise in serum parathyroid hormone levels. These effects on serum calcium and parathyroid hormone are similar to those previously shown for WR2721, another sulfhydryl compound. Cysteamine should be further considered as an alternative drug in the treatment of hyperprolactinemia and as a therapeutic agent for hypercalcemia.

Immunoreactive prolactin like material in the urine of women

Immunoreactive prolactin-like material (Ir Prl) was detected in urines of eugonadal women during the luteal phase and in urines of pregnant and lactating women. The levels of Ir Prl urinary excretion per 24 h and of elimination per 100 ml of glomerular filtrate were highest in lactating women as compared to pregnant women; levels in pregnant women were elevated as compared to eugonadal subjects. Iv injection of thyrotropin releasing hormone (TRH, 200 micrograms) caused increased levels of urinary Ir Prl. The physiochemical characteristics of urinary Ir Prl of lactating women were investigated by filtrating urine samples on Ultragel Aca 54 in presence or absence of Trasylol. Urines, supplemented with Trasylol and analyzed either immediately or after storage at room temperature for 24 h, contained in addition to the 23,000 Mr monomeric form (25.2 +/- 7.4%), two fractions of high (greater than or equal to 70,000) or low (less than 23,000) molecular weight, respectively. The latter material largely predominated (73.5 +/- 7.3%). Urines kept at room temperature for 24 h without Trasylol showed variable but significant decreases in the monomer form with a parallel increase in high MW and fragmented forms. The extent of degradation of the monomer was directly proportional to the proteolytic activity of the urines as estimated by the Azocoll breakdown test. Contrary to what was observed with the urinary endogenous monomeric Prl, human pituitary Prl remained unaltered upon incubation in Trasylol-free urines up to 45 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiologic concentrations of dopamine fail to suppress prolactin secretion in patients with idiopathic hyperprolactinemia or prolactinomas

Several investigators have suggested that normal responsiveness to dopamine is exhibited by pituitary lactotrophs in patients with idiopathic hyperprolactinemia and prolactinomas. These studies, however, have employed dopamine infusion rates that produced supraphysiologic serum dopamine concentrations. In order to further examine this issue, we infused graded doses of dopamine to normal men and women as well as to patients with idiopathic hyperprolactinemia and prolactinomas. Dopamine infusion rates as low as 0.004 micrograms/kg/min, which were associated with physiologic serum dopamine levels, produced significant (p less than 0.01) suppression of prolactin in normal women and in normal males (p less than 0.05). In contrast, a 10-fold increase in the dopamine infusion rate, 0.04 micrograms/kg/min, was required in the hyperprolactinemic subjects to produce prolactin suppression similar to that found in the control subjects. Hence, prolactin secretion in both tumors and other hyperprolactinemic states is associated with a resistance to suppression by dopamine.

Prolactin response to thyrotropin-releasing hormone (TRH) in patients with hypothalamic-pituitary disease

The prolactin (PRL) response to thyrotropin-releasing hormone (TRH) was evaluated in 686 patients over a 4-year period. Of the 170 control subjects tested, none had a blunted PRL response to TRH. Eighty patients with prolactinomas documented by surgery were tested. Ninety-five percent (76 of 80) of these patients had an abnormally blunted PRL response to TRH. Of the 87 patients with a prolactinoma who did not undergo surgery, 98% (85 of 87) had a blunted PRL response to TRH. Many patients with other pituitary and hypothalamic diseases (pituitary tumors other than prolactinomas [Cushing's disease, acromegaly, chromophobe adenoma], craniopharyngioma) also had an abnormal PRL response to TRH (79 of 153, 52%). In the majority of patients with hyperprolactinemia due to dopamine antagonist medications, TRH stimulation did not produce a normal rise in PRL. The TRH test may be helpful in confirming the diagnosis of prolactinoma, but it is not a decisive factor in the diagnosis or management of this entity.

Diminution of prolactin and increase of thyrotrophin response to thyrotrophin releasing hormone occurring independently of changes in basal level of these hormones during treatment of hypothyroidism

In order to study the effect of rising thyroid hormone levels in hypothyroidism upon prolactin responses to TRH, in relation to changes in basal prolactin concentration and to changes in TSH responses, we followed 18 patients by performing TRH tests before and after 14, 28, 42 and 56 d on gradually increasing levothyroxine dosages, plus a final test when euthyroidism was achieved. Basal prolactin rose initially, at day 14, followed by a return on days 28, 42 and 56 to a level similar to the pretherapeutic value, while at euthyroidism prolactin had fallen below the original value. The area under the prolactin response curve on TRH stimulation was unchanged at 14 d, notwithstanding the rise of basal prolactin concentration. At 28, 42 and 56 d the responses declined progressively along with basal prolactin concentrations that remained equivalent to the pretreatment level. The TSH response to TRH rose at 14, 28, and 42 d along with a continuous downward course of basal TSH. Thus, substitution with L-thyroxine inhibited the responsivity of prolactin but enhanced that of TSH to TRH. The fact that these changes occurred in opposite directions, appears to rule out a negative feed-back effect of T4 on hypothalamic TRH secretion. The effects on responses were shown to occur independently of those on basal secretion of prolactin and TSH.

Dopaminergic modulation of TSH and its subunits: in vivo and in vitro studies

We have studied the effects of dopamine on the secretion of TSH and its subunits in vivo and in vitro. Four normal controls, seven patients with primary hypothyroidism, two patients with peripheral resistance to thyroid hormone (PRTH), and two patients with alpha-secreting pituitary tumours underwent a 3-h dopamine infusion (4 micrograms/kg/min). Serial blood samples were drawn for TSH, PRL, alpha, and TSH-beta subunit. In normal subjects, TSH fell from 2.1 +/- 0.9 (+/- SE) to 0.7 +/- 0.1 microU/ml (P less than 0.05), and alpha declined from 1.5 +/- 0.4 to 1.0 +/- 0.1 ng/ml (P less than 0.01). TSH-beta was at or slightly above the detection limits of the assay before and after dopamine. In hypothyroidism, basal serum TSH was 81 +/- 14 microU/ml. With dopamine, TSH fell to 35 +/- 8 microU/ml (P less than 0.001), while alpha decreased from 3.2 +/- 0.4 to 2.0 +/- 0.3 ng/ml (P less than 0.01). Serum TSH-beta also declined from 0.97 +/- 0.06 to 0.57 +/- 0.05 ng/ml (P less than 0.001). A similar fall in TSH and alpha was seen in the two patients with PRTH. In normals and hypothyroid patients, the percentage change in alpha concentration was significantly less than that observed for intact TSH. This is due presumably to the contribution of the gonadotrophs to the circulating alpha pool. TSH and TSH-beta were undetectable in the two pituitary tumour patients, and alpha declined only slightly in each patient after dopamine. The in vitro effects of dopamine were studied using cultured bovine anterior pituitary cells. Dopamine (10(-4)-10(-8) mol/l) did not change basal TSH, alpha, or TSH-beta release. However, dopamine at all doses significantly blunted TRH (10(-7) mol/l)-stimulated TSH and TSH-beta release, and blunted TRH-mediated alpha release at the two highest dopamine doses. These data suggest that dopamine modulates both TSH and TSH subunit secretion. These effects may be exerted directly at the level of the thyrotroph.

No evidence for a peripheral effect of L-DOPA on plasma prolactin in the rat

Male and female rats with two permanently indwelling intravenous catheters were infused for 2 hours with ovine prolactin. During equilibrium conditions the effects of intravenously injected L-DOPA and benzerazide (a blocker of dopa-decarboxylase) on steady state levels of ovine prolactin were measured. A dose of 4.5 mg L-DOPA per 100 gr body weight (b.w.) caused a transient increase of plasma ovine prolactin. A dose of 0.3 mg L-DOPA/100 gr b.w. had no effect, neither in males nor in females, while benzerazide (20 mg/100 gr b.w.) had only a slight effect. The experiments suggest that L-DOPA does not affect the peripheral uptake of prolactin from the plasma.

The effect of thyroid hormones on prolactin secretion by cultured bovine pituitary cells

The effect of thyroid hormones and thyrotropin releasing hormone (TRH) on prolactin (PRL) secretion has been studied using a primary calf anterior pituitary cell culture system. After mechanical and enzymatic dispersion, cultured pituitary cells were preincubated with T3 or T4 for 48 hr prior to a 24 hr experimental incubation. T3 stimulated the release of PRL into the medium in a dose-related fashion, with an ED50 of 3 nM; at 10 nM T3, a maximal 52 +/- 5% stimulation (p less than 0.001) was observed. T4 at 100 nM stimulated medium PRL 27 +/- 10% (p less than 0.05); the ED50 for T4 was 20 nM. Neither T3 nor T4 affected intracellular PRL content. The stimulation of medium PRL by T3 was observed in medium containing 10% euthyroid as well as 10% charcoal-stripped hypothyroid calf serum. The relative stimulation by TRH of PRL release into the medium was significantly diminished by 10 nM T3 in euthyroid and stripped hypothyroid serum medium, but only as a consequence of the stimulation of basal medium PRL by T3; there was no change in maximal TRH-stimulated PRL release. In medium supplemented with unstripped hypothyroid serum, however, T3 did decrease absolute TRH-stimulated PRL release.

Familial thyroid hormone resistance

Three phenotypically normal family members were discovered to have elevated thyroid function (T4, free T4, T3, 123I uptake), but were clinically euthyroid. Further evaluation of pituitary and peripheral indices of thyroid hormone action was consistent with the diagnosis of peripheral resistance to thyroid hormone. Basal metabolic rate, serum cholesterol, pulse wave arrival time (QKd), and serum sex hormone binding globulin levels were all normal. Serum TSH was inappropriately elevated for the degree of thyroid hormone excess, while serum alpha subunit levels were normal. TSH responses to TRH (200 micrograms) were commensurate with the basal TSH levels, and decreases in TSH were observed after T3, dexamethasone, and bromocriptine administration. Analysis of thyroid hormone binding to an extract of mononuclear leukocyte nuclei disclosed no abnormalities. The reason for these patients' resistance to thyroid hormones remains to be elucidated. The proper diagnosis of this syndrome may be difficult. Assessment of pituitary TSH secretory dynamics and peripheral indices of thyroid hormone action should be performed in all hyperthyroxinemic patients who do not have obvious symptoms and signs of thyrotoxicosis.