Petra Kok

Sensitivity and specificity of pulse detection using a new deconvolution method

Quantifying pulsatile secretion from serial hormone concentration measurements (deconvolution analysis) requires automated, objective, and accurate detection of pulse times to ensure valid estimation of secretion and elimination parameters. Lack of validated pulse identification constitutes a major deficiency in the deconvolution field, because individual pulse size and number reflect regulated processes that are critical for the function and response of secretory glands. To evaluate deconvolution pulse detection accuracy, four empirical models of true-positive markers of pituitary (LH) pulses were used. 1) Sprague-Dawley rats had recordings of hypothalamic arcuate nucleus multiunit electrical activity, 2) ovariectomized ewes underwent sampling of hypothalamo-pituitary gonadotropin-releasing hormone (GnRH pulses), 3) healthy young men were infused with trains of biosynthetic LH pulses after GnRH receptor blockade, and 4) computer simulations of pulsatile LH profiles were constructed. Outcomes comprised sensitivity, specificity, and receiver-operating characteristic curves. Sensitivity and specificity were 0.93 and 0.97, respectively, for combined empirical data in the rat, sheep, and human (n = 156 pulses) and 0.94 and 0.92, respectively, for computer simulations (n = 1,632 pulses). For simulated data, pulse-set selection by the Akaike information criterion yielded slightly higher sensitivity than by the Bayesian information criterion, and the reverse was true for specificity. False-positive errors occurred primarily at low-pulse amplitude, and false-negative errors occurred principally with close pulse proximity. Random variability (noise), sparse sampling, and rapid pulse frequency reduced pulse detection sensitivity more than specificity. We conclude that an objective automated pulse detection deconvolution procedure has high sensitivity and specificity, thus offering a platform for quantitative neuroendocrine analyses.

Effects of Continuous Versus Intermittent Exercise, Obesity, and Gender on Growth Hormone Secretion

CONTEXTnObesity attenuates spontaneous GH secretion and the GH response to exercise. Obese individuals often have low fitness levels, limiting their ability to complete a typical 30-min bout of continuous exercise. An alternative regimen in obese subjects may be shorter bouts of exercise interspersed throughout the day.nnnOBJECTIVEnThe objective of the study was to examine whether intermittent and continuous exercise interventions evoke similar patterns of 24-h GH secretion and whether responses are attenuated in obese subjects or affected by gender.nnnDESIGNnThis was a repeated-measures design in which each subject served as their own control.nnnSETTINGnThis study was conducted at the University of Virginia General Clinical Research Center.nnnSUBJECTSnSubjects were healthy nonobese (n = 15) and obese (n = 14) young adults.nnnINTERVENTIONSnSubjects were studied over 24 h at the General Clinical Research Center on three occasions: control, one 30-min bout of exercise, and three 10-min bouts of exercise.nnnMAIN OUTCOME MEASURESnTwenty-four hour GH secretion was measured.nnnRESULTSnCompared with unstimulated 24-h GH secretion, both intermittent and continuous exercise, at constant exercise intensity, resulted in severalfold elevation of 24-h integrated serum GH concentrations in young adults. Basal and pulsatile modes of GH secretion were attenuated both at rest and during exercise in obese subjects.nnnCONCLUSIONSnThe present data suggest that continuous and intermittent exercise training should be comparably effective in increasing 24-h GH secretion.

Estrogen Supplementation Selectively Enhances Hypothalamo-Pituitary Sensitivity to Ghrelin in Postmenopausal Women

CONTEXTnSex-steroid hormones amplify pulsatile GH secretion by unknown mechanisms. Ghrelin is the most potent natural GH secretagogue discovered to date. A plausible unifying postulate is that estradiol (E(2)) enhances hypothalamo-pituitary sensitivity to ghrelin (a physiological effect). The hypothesis is relevant to understanding the basis of hyposomatotropism in aging and other relatively hypogonadal states.nnnOBJECTIVEnOur objective was to test the hypothesis that E(2) supplementation potentiates ghrelins stimulation of pulsatile GH secretion.nnnSETTINGnThe study was conducted at an academic medical center.nnnSUBJECTSnHealthy postmenopausal women (n = 20) were included in the study.nnnINTERVENTIONSnSeparate-day iv infusions of saline vs. five graded doses of ghrelin were performed in volunteers prospectively randomly assigned to receive (n = 8) or not receive (n = 12) transdermal E(2) for 21 d were performed.nnnMEASURESnGH secretion was estimated by deconvolution analysis and abdominal visceral fat mass determined by computerized axial tomography were calculated.nnnRESULTSnE(2) supplementation augmented ghrelins stimulation of basal (nonpulsatile) GH secretion by 3.6-fold (P = 0.022), increased GH responses to low-dose ghrelin by 2.9-fold (P = 0.035), did not alter ghrelin efficacy, and elicited more regular patterns of acylated ghrelin concentrations during saline infusion (P = 0.033). Abdominal visceral fat negatively determined responses to ghrelin (R = -0.346; P < 0.005).nnnCONCLUSIONSnTransdermal E(2) supplementation potentiates GH secretion stimulated by physiological but not pharmacological concentrations of acylated ghrelin, and concomitantly regularizes patterns of bioactive ghrelin secretion in postmenopausal women. Accordingly, the estrogen milieu appears to control sensitivity of the hypothalamopituitary unit to acylated ghrelin.

Cortisol production rate is similarly elevated in obese women with or without the polycystic ovary syndrome.

CONTEXTnThe pituitary-adrenal axis in obesity and polycystic ovary syndrome (PCOS) is marked by increased urinary excretion of cortisol and its metabolites. It is not as yet clear whether the increased cortisol production in PCOS is related to obesity per se.nnnINTERVENTION AND METHODSnWe investigated 15 obese PCOS women with a body mass index of 30-54 kg/m(2) and 15 healthy obese controls (body mass index 31-60 kg/m(2)) with a regular menstrual cycle. Patients and control women underwent 24-h blood sampling at 20-min intervals. Cortisol concentrations were measured with a sensitive assay. Data were analyzed with a new deconvolution program, approximate entropy, and cosinor regression.nnnOUTCOMEnBasal, pulsatile, and total cortisol production expressed per liter distribution volume, per square meter body surface, and as absolute amount per 24 h was similar in PCOS patients and matched healthy control women. In addition, the regularity of cortisol secretion and the diurnal properties were identical. Compared with 10 lean control women, mean cortisol production per liter distribution volume was similar in the three groups, but the total 24-h cortisol production was increased in obese control women and PCOS women.nnnCONCLUSIONnThis study demonstrates equally increased cortisol production in PCOS women and obese healthy control women.

Disordered and increased adrenocorticotropin secretion with diminished adrenocorticotropin potency in obese in premenopausal women.

CONTEXTnThe pituitary-adrenal ensemble of obese humans is marked by increased urinary excretion of cortisol and its metabolites in the face of normal circulating cortisol levels. For better understanding of the (patho) physiological meaning of these changes, the mechanistic underpinnings need to be clarified.nnnINTERVENTION AND METHODSnWe investigated 17 obese women [body mass index (BMI) 30-39.4 kg/m(2)] and 14 normal women (BMI, 18.3-24.8 kg/m(2)) who underwent 24-h blood sampling at 10-min intervals, and plasma ACTH and cortisol concentrations were measured with sensitive assays. Data were analyzed with a new deconvolution program, approximate entropy (ApEn) analyses, and cosinor regression.nnnOUTCOMEnACTH and cortisol production rates were higher in obese women than in controls and correlated with BMI. Secretion of ACTH correlated with leptin (R = 0.63; P = 0.0001) and insulin (R = 0.67; P = 0.0001). ACTH ApEn and forward ACTH-cortisol cross-ApEn were diminished in obese women. The half-maximal effective concentration (ED(50)) of ACTH pulses vs. cortisol pulses was higher in obese women (38.3 +/- 4.9 vs. 25.1 +/- 3.7 ng/liter; P = 0.03), indicating decreased potency of ACTH. The diurnal properties of ACTH and cortisol secretion were unchanged in obese females.nnnCONCLUSIONnObese women exhibit enhanced ACTH and cortisol 24-h production compared with lean controls. The amplified ACTH drive is accompanied by decreased secretory regularity and diminished forward coupling between ACTH and cortisol. In addition, the potency of ACTH is decreased in obesity.

Bromocriptine Reduces Augmented Thyrotropin Secretion in Obese Premenopausal Women

CONTEXTnDiurnal TSH secretion is enhanced in obese premenopausal women. Dopamine inhibits TSH secretion through activation of dopamine D(2) receptors (D(2)R). Dopamine D(2)R availability in the brain is reduced in obese humans in proportion to body adiposity. We hypothesized that deficient dopamine D(2)R signaling is involved in the enhanced TSH secretion associated with obesity.nnnOBJECTIVEnThe effect of short-term bromocriptine treatment on spontaneous TSH secretion in obese women was studied while body weight and caloric intake remained constant.nnnDESIGN AND SETTINGnWe conducted a prospective, fixed-order, crossover study in a Clinical Research Center.nnnPARTICIPANTSnSeventeen obese women (body mass index, 33.2 +/- 0.6 kg/m(2)) were studied twice in the early follicular phase of their menstrual cycle.nnnINTERVENTIONnSubjects were treated for 8 d with placebo and bromocriptine.nnnMAIN OUTCOME MEASURE(S)nBlood was collected for 24 h at 10-min intervals, and TSH and leptin were analyzed with deconvolution and correlation techniques, approximate entropy, and cosine regression.nnnRESULTSnBromocriptine reduced 24-h TSH secretion (placebo, 29.8 +/- 4.6 mU/liter . 24 h, vs. bromocriptine, 22.4 +/- 3.7 mU/liter . 24 h; P = 0.001), whereas free T(4) and total T(3) concentrations did not change. Bromocriptine administration reduced the mesor and amplitude of the 24-h rhythm without resetting the phase. The regularity of the subordinate TSH pattern and synchrony between leptin and TSH were unaffected by bromocriptine.nnnCONCLUSIONnActivation of dopamine D(2)R by bromocriptine reverses enhanced diurnal TSH secretion in obese women. Thus, reduced dopaminergic neuronal signaling might be involved in the perturbation of the thyrotrope hormonal axis in obese premenopausal women.

Short-Term Treatment with Bromocriptine Improves Impaired Circadian Growth Hormone Secretion in Obese Premenopausal Women

CONTEXTnA profound reduction of spontaneous as well as stimulated GH secretion has been consistently observed in obesity. Dopamine promotes GH release through activation of dopamine D2 receptors (D2Rs). Dopamine D2R availability in the brain is reduced in obese humans in proportion to body adiposity. We hypothesized that impaired dopamine D2R signaling is mechanistically involved in the deficient GH secretion associated with obesity.nnnOBJECTIVEnTo test this hypothesis, we studied the effect of short-term bromocriptine (B) (a D2R agonist) treatment on spontaneous 24-h GH secretion in obese women, while body weight and caloric intake remained constant.nnnDESIGNnThis was a prospective, fixed order, cross-over study.nnnSETTINGnThe study was performed in the Clinical Research Center at Leiden University Medical Center.nnnPARTICIPANTSnThere were 18 healthy obese women (body mass index 33.2 +/- 0.6 kg/m2) studied twice in the early follicular phase of their menstrual cycle.nnnINTERVENTION(S)nEight days of treatment with B and placebo (Pl) was performed.nnnMAIN OUTCOME MEASURE(S)nBlood was collected during 24 h at 10-min intervals for determination of GH concentrations. GH secretion parameters were calculated using deconvolution analysis.nnnRESULTSnShort-term treatment with B significantly enhanced diurnal GH secretion (Pl 121.4 +/- 16.4 vs. B 155.4 +/- 15.2 microg/liter(volume of distribution).24 h; P = 0.01), whereas IGF-I concentrations remained constant (Pl 22.4 +/- 2.4 vs. B 21.8 +/- 1.6 nmol/liter; P = 0.928).nnnCONCLUSIONSnActivation of dopamine D2Rs by B favorably affects impaired nyctohemeral GH secretion in obese women. Reduced dopaminergic neuronal signaling might be involved in the pathogenesis of obesity associated hyposomatotropism.

Increased basal and pulsatile secretion of FSH and LH in young men with 47,XXY or 46,XX karyotypes.

OBJECTIVEnThe regulation of normal sexual maturation and reproductive function is dependent on a precise hormonal regulation at hypothalamic, pituitary, and gonadal levels. The aim of this study was to investigate the neuroendocrine integrity of the pituitary-gonadal axis in patients with primary testicular failure due to supernumerary X chromosomes.nnnDESIGNnCross-sectional study.nnnMETHODSnIn this study, 7 untreated patients with primary gonadal insufficiency due to SRY-positive 46,XX (n=4) and 46,XXY karyotypes (n=3) aged 18.8 years and 25 age-matched healthy controls participated. Reproductive hormones, testicular size, and overnight LH and FSH serum profiles and overnight urine LH and FSH excretion were determined.nnnRESULTSnBasal LH and FSH secretion was elevated 6.3- and 25.4-fold respectively in the patients and the amount of LH and FSH secreted per burst were 2.0- and 6.6-fold elevated. We found significantly more LH but not FSH peaks per 24 h, as estimated by the Weibull lambda analysis. There was no difference between approximate entropy ratios or Weibull gamma analyses indicating comparable orderliness and regularity of LH and FSH secretion. Overnight urinary LH and FSH excretion was significantly elevated in patients compared with controls and correlated significantly with calculated total overnight LH and FSH secretion respectively, thus validating deconvolution.nnnCONCLUSIONnIn this group of patients with severe hypergonadotropic hypogonadism due to a supernumerary X chromosome, higher basal, pulsatile, and total LH and FSH secretion were associated with significantly more LH peaks per 24 h in comparison with healthy controls. Thus, our data indicate that in patients with Klinefelter syndrome and XX male karyotypes the entire hypothalamic-pituitary-gonadal axis has undergone functional changes.

Thyrotropin Secretion in Healthy Subjects Is Robust and Independent of Age and Gender, and Only Weakly Dependent on Body Mass Index

CONTEXTnStudies of the influence of sex, age, and body weight on TSH secretion are not unanimous. Most reports are based on a single TSH measurement; studies using frequent blood sampling are scarce and include a limited number of selected subjects.nnnOBJECTIVEnThe goal was to investigate TSH dynamics in 117 healthy adults.nnnMETHODSnTSH was measured by a sensitive immunofluorometric assay. Secretion parameters were quantified by automated deconvolution, approximate entropy [ApEn], spikiness, and diurnal properties.nnnRESULTSnMean age was 43 years (range, 22-77 y). Mean body mass index (BMI) was 26.8 kg/m(2) (range, 18.3-39.4 kg/m(2)). Daily TSH secretion was 45.4 mU/L (range, 8.0-207 mU/L). There were no sex differences in secretion parameters, including pulse frequency; basal, pulsatile, and total secretion; pulse mode; half life; pulse regularity; ApEn; spikiness; and nycthemeral properties. BMI was positively related to basal secretion. Total secretion correlated negatively with free T₄ (R = 0.225; P = .018). The onset of the nocturnal surge was delayed by increasing BMI and advanced by increasing age. ApEn and spikiness correlated positively with age, especially in men. The 9 am sample correlated strongly with the total 24-hour secretion, explaining two-thirds of the variability.nnnCONCLUSIONnThis study shows that the 24-hour TSH secretion in healthy volunteers is stable and robust and not influenced by sex, BMI, and age. ApEn in the elderly, especially men, is increased, pointing to a less tight feedback control. Furthermore, aging is associated with advance shifting of the TSH rhythm, which is a phenomenon also observed in other biological rhythms.

Pituitary-hormone secretion by thyrotropinomas

Hormone secretion by somatotropinomas, corticotropinomas and prolactinomas exhibits increased pulse frequency, basal and pulsatile secretion, accompanied by greater disorderliness. Increased concentrations of growth hormone (GH) or prolactin (PRL) are observed in about 30% of thyrotropinomas leading to acromegaly or disturbed sexual functions beyond thyrotropin (TSH)-induced hyperthyroidism. Regulation of non-TSH pituitary hormones in this context is not well understood. We there therefore evaluated TSH, GH and PRL secretion in 6 patients with up-to-date analytical and mathematical tools by 24-h blood sampling at 10-min intervals in a clinical research laboratory. The profiles were analyzed with a new deconvolution method, approximate entropy, cross-approximate entropy, cross-correlation and cosinor regression. TSH burst frequency and basal and pulsatile secretion were increased in patients compared with controls. TSH secretion patterns in patients were more irregular, but the diurnal rhythm was preserved at a higher mean with a 2.5xa0h phase delay. Although only one patient had clinical acromegaly, GH secretion and IGF-I levels were increased in two other patients and all three had a significant cross-correlation between the GH and TSH. PRL secretion was increased in one patient, but all patients had a significant cross-correlation with TSH and showed decreased PRL regularity. Cross-ApEn synchrony between TSH and GH did not differ between patients and controls, but TSH and PRL synchrony was reduced in patients. We conclude that TSH secretion by thyrotropinomas shares many characteristics of other pituitary hormone-secreting adenomas. In addition, abnormalities in GH and PRL secretion exist ranging from decreased (joint) regularity to overt hypersecretion, although not always clinically obvious, suggesting tumoral transformation of thyrotrope lineage cells.