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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
`
`J Clin Endocrinol Metab. 2011 Sep; 96(9): 2882–2888.
`Published online 2011 Jul 13. doi: 10.1210/jc.2011-0682: 10.1210/jc.2011-0682
`
`PMCID: PMC3167666
`PMID: 21752898
`
`Glucose Ingestion Selectively Amplifies ACTH and Cortisol
`Secretory-Burst Mass and Enhances Their Joint Synchrony in
`Healthy Men
`Ali Iranmanesh, Donna Lawson, Barbara Dunn, and Johannes D. Veldhuis
`
`Endocrine Section (A.I., D.L., B.D.), Medical Service, Salem Veterans Affairs Medical Center, Salem, Virginia
`24153; and Endocrine Research Unit (J.D.V.), Mayo School of Graduate Medical Education, Center for
`Translational Science Activities, Mayo Clinic, Rochester, Minnesota 55905
`Corresponding author.
`Address all correspondence and requests for reprints to: Johannes D. Veldhuis, M.D., Endocrine Research Unit,
`Mayo School of Graduate Medical Education, Mayo Clinic, Rochester, Minnesota 55905. E-mail:
`veldhuis.johannes@mayo.edu.
`
`Received 2011 Mar 22; Accepted 2011 Jun 17.
`Copyright © 2011 by The Endocrine Society
`
`Abstract
`
`Context:
`Glucose intake is associated with a variable increase in adrenal glucocorticoid secretion.
`
`Hypothesis:
`Glucose ingestion elevates cortisol secretion by 1) augmenting pulsatile ACTH release; and/or 2)
`enhancing ACTH-cortisol synchrony or dose-responsiveness.
`
`Subjects:
`Fifty-eight healthy men ages 19–78 yr with computed tomography-estimated abdominal visceral fat
`participated in the study.
`
`Location:
`The study was conducted at the Clinical Translational-Research Center and Veterans Affairs Medical
`Center.
`
`Methods:
`We conducted frequent sampling of plasma ACTH and cortisol concentrations after glucose vs. water
`ingestion in the fasting state, as well as deconvolution, approximate entropy, linear-regression, and dose-
`response analysis.
`
`Outcomes:
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`After water ingestion, age was a negative correlate of the mass of ACTH (P = 0.009; R = 0.119) and of
`2
`cortisol (P < 0.001; R = 0.269) secreted per burst. Glucose ingestion abolished both relationships but
`amplified pulsatile ACTH (P = 0.009) and cortisol (P = 0.001) secretion. Glucose exposure selectively
`augmented the mass of ACTH (P < 0.001) and of cortisol (P = 0.004) secreted per burst without altering
`burst number or basal secretion. The increment in pulsatile ACTH strongly predicted the increment in
`−4
`2
`pulsatile cortisol (P < 10 ; R = 0.325) secretion. Abdominal visceral fat positively forecast the glucose-
`induced increment in cortisol secretory-burst mass (P = 0.019). According to approximate entropy
`analysis, glucose input also enhanced the joint synchrony of ACTH-cortisol secretory patterns (P ≤ 0.001).
`Caloric intake did not affect analytical dose-response estimates of ACTH potency and efficacy or adrenal
`sensitivity.
`
`Conclusion:
`Conjoint augmentation of the mass of ACTH and cortisol secreted per burst and enhancement of ACTH-
`cortisol synchrony underlie glucose-induced glucocorticoid secretion in healthy men. Visceral adiposity is
`a predictor of the glucose-stimulated increment in burst-like cortisol output, suggesting an additional
`possible mechanism for increased cardiovascular risk in abdominal obesity.
`
`Ingestion of glucose, amino acids, protein, or mixed meals tends to increase serum and salivary cortisol
`concentrations in healthy adults (1–8). Gender, time of day, and enteric peptides, such as glucagon-like
`peptide, tachykinins, and glucose-dependent insulinotropic peptide, may modulate such effects (7–10). In
`pathological states like ACTH-independent macronodular adrenal hyperplasia, anomalous or exaggerated
`expression of peptidyl and adrenergic receptors may contribute to excessive cortisol secretion with meals
`(11, 12). However, the precise mechanisms that mediate oral nutrient effects in healthy individuals are not
`known. Indeed, under physiological conditions, both ACTH-dependent and ACTH-independent
`mechanisms of food-induced cortisol secretions have been postulated (3, 13–15). To our knowledge,
`pulsatile ACTH secretion after caloric ingestion has never been quantified adequately by current standards
`(16). This limitation is significant because pivotal meal-triggered mechanisms could include amplification
`of basal (nonpulsatile) or pulsatile ACTH secretion, enhancement of ACTH-cortisol synchrony,
`potentiation of ACTH-cortisol dose-responsiveness, and augmentation of adrenal cortisol secretion
`independently of ACTH.
`The present investigations used a paired within-subject crossover design with frequent (10-min) sampling
`over 6.5 h to measure time-varying ACTH and cortisol concentrations in 58 adults before and after
`ingestion of a fixed glucose load or equivalent volume of water. Deconvolution, approximate entropy
`(ApEn), and ACTH-cortisol dose-response analyses were then applied to test the foregoing hypotheses
`noninvasively.
`
`Subjects and Methods
`
`Subjects
`Fifty-eight healthy men were recruited to participate after providing voluntary written informed consent
`approved by the local Institutional Review Board. The admissible age range was 19–78 yr, with body mass
`2
`index of 20–39 kg/m . Exclusion diagnoses were congestive heart failure, acute or chronic liver or renal
`disease, anemia, hypothalamopituitary disease, neuropsychiatric drug exposure, glucocorticoid use,
`systemic inflammatory disease, malignancy, substance abuse, intracranial disease, sleep apnea, and
`diabetes mellitus. Inclusion criteria were community-dwelling, independently living, consenting adults
`with stable diurnal work habits, body weight (within 2 kg in 3 months), and recreational exercise patterns.
`
`Protocol
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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
`Subjects (n = 58) undertook two 10-min sampling sessions after overnight fasting, beginning at 0800 h. At
`0830 h, glucose (75 g) or the same volume of water (10 ounces) was administered orally. Blood sampling
`continued thereafter for 6 more hours (until 1430 h). Plasma was obtained in chilled tubes containing
`divalent-metal chelators. An abdominal computed tomography (CT) scan was performed at the L3–4
`interspace to estimate abdominal visceral fat (AVF) cross-sectional area, as described (17). In three
`subjects, there was a delay (not exceeding 1 h) in starting the protocol.
`
`Assays
`Circulating concentrations of ACTH, cortisol, and insulin were assayed by Immulite 2000 (Siemens
`Healthcare Diagnostics, Flanders, NJ), using reagents from the Siemens Healthcare Diagnostics. The assay
`for cortisol has a detection range of 0.2–50 μg/dl with intra-and interassay coefficients of variation of 7.2–
`9.4% and 6.3–7.5% at respective concentrations of 3.8–44 and 3.7–41 μg/dl. ACTH assay has a detection
`range of 5–1250 ng/liter, with intra- and interassay coefficients of variation of 6.1–8.2% and 4.4–5.7% at
`respective concentrations of 32–417 and 30–446 ng/liter. Single fasting blood specimens were used for the
`measurements of glucose and insulin. Synchron (Beckman Coulter, Fullerton, CA) and Siemens
`Dimension Vista autoanalyzers were used for the measurement of serum glucose concentrations.
`
`Analyses
`Plasma ACTH and cortisol time series were subjected to automated deconvolution analysis using a
`Matlab-implemented maximum-likelihood methodology (18). The two-component cortisol half-life model
`was 2.4 and 56 min (63% slow decay), and that of ACTH was 3.5 and 18 min (63% slow component) (19,
`20). Outcome variables were basal (nonpulsatile), pulsatile and total (sum of basal plus pulsatile) secretion,
`and the mass (concentration units), number (per 6 h after the ingestion), and shape (mode) of ACTH and
`cortisol secretory bursts.
`ApEn was calculated on the last 5.5 h of sampling (beginning 30 min after glucose ingestion). ApEn
`provides a scale-independent model-free estimate of secretory-pattern reproducibility or regularity,
`wherein higher ApEn corresponds to greater irregularity or higher process randomness (21). ApEn
`provides a surrogate measure of changes in feedback control in interconnected systems with high
`sensitivity and specificity (both >90%) (22). Cross-ApEn is the bivariate counterpart applied to paired time
`series, where higher values identify greater asynchrony (less pattern coordination), and conversely (23).
`Dose-response estimates of ACTH-cortisol drive were performed as recently described (24). The Matlab
`program regresses deconvolved cortisol secretion rates on reconvolved ACTH concentrations via a four-
`parameter logistic dose-response model. Analyses used the paired 6.5-h ACTH-cortisol time series in each
`subject.
`
`Statistics
`A paired Student's t test was used to evaluate the effect of oral glucose compared with water ingestion on
`deconvolution, ApEn, and dose-response parameters. Linear regression analysis was employed to assess
`effects of age and/or AVF on ACTH and cortisol measures (25). Systat 11 (Systat Inc., Richmond, CA)
`was the software platform. Data are expressed as the mean ± SEM.
`
`Results
`Fasting plasma glucose (mg/dl) and insulin (mU/liter) concentrations averaged 94 ± 1.2 and 5.9 ± 0.61,
`2
`respectively. The age range was 19–78 yr, and body mass index range was 20–39 kg/m . Figure 1 gives the
`mean (±SEM) paired profiles of ACTH and cortisol concentrations measured every 10 min for 6.5 h in the
`58 men studied before (0.5 h) and after (6.0 h) water and glucose ingestion. There were visually prominent
`increases in ACTH and cortisol 2.5–4 h after glucose ingestion.
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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
`Deconvolution analysis was used to estimate ACTH and cortisol secretion over the 6-h interval starting
`with glucose or water ingestion. Figure 2A gives mean ± SEM outcomes for ACTH: basal secretion,
`pulsatile secretion, secretory-burst mass, and number on the control (fasting) and glucose-ingestion days.
`Paired statistical comparisons (control vs. glucose) disclosed the following: 1) a 31% increase in pulsatile
`ACTH secretion on the glucose day (P = 0.009), due to commensurately augmented ACTH secretory-burst
`mass (P < 0.001) rather than number (P = 0.055); and 2) no change in basal (nonpulsatile) ACTH secretion
`(P = 0.298). In addition, ACTH secretory-burst shape (modal time in minutes of maximal ACTH secretion
`rate) was similar for control (9.3 ± 0.68) and glucose (9.4 ± 0.73) conditions. Thematically comparable
`outcomes were observed for glucose-induced cortisol secretion, in which pulsatile secretion rose by 27%
`(P = 0.001) (Fig. 2B). Glucose selectively augmented the size (mass) of cortisol secretory bursts (P =
`0.004) and weakly decreased basal cortisol secretion (P = 0.031) with no effect on cortisol pulse number
`(P = 0.890). The mode was invariant of condition (grand mean, 12 ± 0.62 min).
`To assess whether increased pulsatile cortisol secretion reflected increased pulsatile ACTH secretion,
`intraindividual glucose-minus-control incremental values for cortisol were regressed on matching
`2
`incremental values for ACTH (Fig. 3). This yielded Pearson's P < 0.0001 and R = 0.325. If five Systat-
`2
`identified high-leverage values were removed, the regression yielded P = 0.0003, R = 0.227 (Fig. 3,
`inset). The pulsatile ACTH-pulsatile cortisol relationship was equally strong by nonparametric Spearman's
`rank correlation, P = 0.000635, rho=0.435 (n = 58). Regression of incremental cortisol secretory-burst
`mass (dependent variable) on incremental ACTH secretory-burst mass (independent variable) resulted in
`2
`2
`Pearson's P = 0.046 and R = 0.070 (n = 58) (without six extreme values, P was 0.0085, R = 0.130). For
`nonparametric Spearman's rank correlation, P was 0.00998 and rho was 0.336 (n = 58).
`AVF was a positive determinant of cortisol secretory-burst mass increments (glucose minus control value)
`2
`with P = 0.019, R = 0.10 (Fig. 4, top). In addition, AVF was a positive correlate of ACTH secretory-burst
`2
`mode (duration) with P = 0.023, R =0.091 (Fig. 4, bottom).
`
`Univariate ApEn was applied separately to ACTH and cortisol time series as a model-free measure of
`altered feedback control (Subjects and Methods). ApEn was higher for ACTH than cortisol in the control
`and glucose conditions (both P < 0.01), indicating greater process randomness in ACTH than cortisol
`secretory patterns (Fig. 5). Glucose ingestion decreased ApEn of ACTH (P = 0.021) and cortisol (P =
`0.025), signifying reduced process randomness (greater pattern reproducibility). Bivariate cross-ApEn
`estimates unmasked prominent reductions in both forward ACTH-cortisol (P = 0.001) and reverse cortisol-
`ACTH (P < 0.001) cross-ApEn, denoting marked joint-synchrony enhancement after glucose exposure.
`2
`2
`ApEn of ACTH (R = 0.15; P = 0.035), as well as cross-ApEn of ACTH-cortisol (R = 0.086; P = 0.026)
`2
`and cortisol-ACTH (R = 0.83; P = 0.028) increased with age in the control but not the glucose-
`administration session (plots not shown).
`To test the hypothesis that glucose administration enhances ACTH-cortisol feedforward coupling,
`analytical dose-response estimation was carried out using the sensitivity model (Subjects and Methods).
`Adrenal sensitivity (slope term), the one-half maximally effective concentration of ACTH [EC
`50
`(ng/liter)], ACTH efficacy (μg/dl · min cortisol secretion), and basal secretion (same units) were all
`independent of glucose ingestion (Supplemental Table 1, published on The Endocrine Society's Journals
`Online web site at http://jcem.endojournals.org).
`
`Discussion
`The present analyses in 58 healthy men demonstrate concomitant amplification of pulsatile ACTH and
`pulsatile cortisol secretion after 75-g glucose ingestion in the morning. The mechanism entailed selective
`augmentation of ACTH and cortisol secretory-burst mass. Indeed, ACTH and cortisol burst size rose
`2
`comparably by 27–31% after oral glucose administration (R = 0.325; P < 0.0001). Basal (nonpulsatile)
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`ACTH secretion and cortisol secretory-burst number and shape were unaffected at good statistical power
`(β > 0.85 for α = 0.05 and δ = 30%). Model-free ApEn and cross-ApEn analyses further unveiled
`enhancement of joint ACTH-cortisol and cortisol-ACTH secretory synchrony (both P ≤ 0.001). In contrast,
`analytical estimates of endogenous ACTH-cortisol dose-response properties were unaffected by oral
`glucose exposure. In ensemble, these data demonstrate that morning glucose ingestion stimulates pulsatile
`cortisol and ACTH secretion, thereby elevating their mean concentrations; the increase in pulsatile cortisol
`is directly proportionate to the increase in pulsatile ACTH secretion; both increments are due to selective
`augmentation of secretory-burst size; the glucose effect includes enhancement of ACTH-cortisol secretory
`synchrony; and the glucose effect does not require a commensurate change in ACTH-cortisol dose-
`response properties.
`Exploratory regression analyses revealed that CT-estimated AVF positively predicts incremental pulsatile
`cortisol secretion in response to a glucose load. A plausible mechanism is that relative obesity augments
`the release of gut-derived insulinotropic peptides, like glucagon-like peptide-1, gastric inhibitory peptide,
`and glucagon, which amplify secretion of not only insulin but also cortisol and CRH (9, 10, 12, 14). These
`gut peptides were not measured here. In fact, the extent of gut peptide-derived facilitation of cortisol
`secretion in obesity is not known, but any effects might be reduced by the tendency for lower endogenous
`peptide levels, at least in diabetic individuals (e.g. glucagon-like peptide-1) (26). In the present study,
`neither glucose nor insulin was a strong predictor of the incremental rise in pulsatile ACTH or cortisol
`secretion. However, adiponectin was a positive correlate of incremental adrenal sensitivity to ACTH after
`2
`glucose ingestion (P = 0.027; R = 0.084; n = 58 men) (Supplemental Fig. 1). As surrogate measures of
`adverse metabolic risk (27), AVF and omental fat-cell size have been associated in some but not all studies
`with increased activity or expression of 11β-hydroxysteroid dehydrogenase type 1, which promotes
`conversion of inactive cortisone to active cortisol (28–31). If hepatic, splanchnic, or whole-body cortisone
`activation does increase with AVF, this mechanism might amplify conversion of glucose-induced pulsatile
`cortisone to cortisol. Other mechanisms could include modulation of adrenal stimulation by splanchnic
`neurotransmitters (α-2, dopamine, β-adrenergic, GABAergic, nitric oxide), insulin, and nonenteric
`peptides, such as adiponectin, leptin, IGF-II, IGF-I, or TNFα (11, 32–38). Whatever the mechanism(s), an
`underlying pulsatile ACTH input to the adrenal cortex seems required to augment glucocorticoid pulses
`per se (39), as observed here. Moreover, an enteric route of glucose delivery appears critical because
`overnight iv glucose actually blunts the normal early-morning increase in cortisol secretion (40).
`Caveats include the need for further studies to ascertain interactions among age, gender, and glucose
`ingestion; to discriminate ACTH-independent vis-à-vis ACTH-coupled cortisol secretion; and to define
`how glucose-induced ACTH/cortisol pulses are altered in the metabolic syndrome. The delayed ACTH-
`cortisol response to oral glucose suggests that glucose requires uptake and metabolism to initiate the
`activating effect. In particular, glucose may induce a cascade of intermediate responses, e.g. via
`adipocytokines, which take time to evolve sequentially (26). Although only glucose was evaluated here,
`the capability of protein or fat loads to induce similar changes in ACTH-cortisol secretion could be studied
`by the new methodology implemented here. In addition, whether hypothalamic-pituitary-adrenal reactivity
`to other stressors is altered by glucose ingestion is not known at this time.
`In conclusion, glucose ingestion in the morning selectively augments burst-like ACTH and cortisol
`secretion and markedly synchronizes ACTH and cortisol secretory patterns. Glucose exposure does not
`alter analytical estimates of pulsatile ACTH-cortisol dose-responsiveness. Abdominal visceral adiposity
`positively predicts glucose-evoked increments in pulsatile cortisol secretion. Together, these data elucidate
`important interactions among glucose ingestion, body composition, and pulsatile secretion of ACTH and
`cortisol.
`
`Supplementary Material
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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
`Supplemental Data:
`
`Acknowledgments
`We thank Jill Smith for support of manuscript preparation; Ashley Bryant for data analysis and graphics;
`the Salem Veterans Affairs Immunoassay Laboratory for assay assistance; and the Endocrine Clinical
`Research staff at Salem Veterans Affairs Medical Center for implementing the protocol.
`This work was supported in part by Center for Translational Science Activities (CTSA) Grant 1 UL 1
`RR024150 from the National Center for Research Resources (Rockville, MD); Grant DK050456 from the
`Metabolic Studies Core of the Minnesota Obesity Center; and Grant DK073148 from the National
`Institutes of Health (Bethesda, MD). It was also supported by the Salem Veterans Affairs Medical Center
`and Salem Research Institute (Salem, VA). The content is solely the responsibility of the authors and does
`not necessarily represent the official views of the National Institute on Aging or the National Institutes of
`Health. Matlab versions of the deconvolution methodology are available from
`Veldhuis.johannes@mayo.edu.
`Disclosure Summary: The authors have nothing to disclose.
`
`Footnotes
`Abbreviations:
`
`ApEn Approximate entropy
`AVF abdominal visceral fat
`CT computed tomography.
`
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`Figures and Tables
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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
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`Fig. 1.
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`Open in a separate window
`Mean ± SEM plasma cortisol (top) and ACTH (bottom) 10-min time series over 6.5 h in the fasting control setting
`(closed circles) and after glucose ingestion (open circles) in 58 healthy men. Time zero is 0800 h. Glucose (OGT)
`or water was administered orally at 30 min (vertical arrows).
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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
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`Fig. 2.
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`Open in a separate window
`ACTH (A) and cortisol (CORT) (B) deconvolution analysis. Bar graphs with paired comparisons give the mean ±
`SEM (n = 58 men) based upon Student's t test. Deconvolution outcomes apply to the 6-h interval immediately after
`water (fasting) or 75-g glucose (OGT) ingestion (40–390 min, Fig. 1).
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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
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`Fig. 3.
`
`Linear regression analysis of the relationship between incremental pulsatile cortisol (dependent variable) and
`incremental pulsatile ACTH (independent variable) secretion rates (concentration units per 6 h) in 58 men. Each
`datum is an incremental (glucose minus control) pulsatile secretion rate for ACTH (x-axis) and cortisol (y-axis).
`Pearson's parametric correlation estimates are stated numerically. The inset tests the same relationship when five
`high-leverage values are removed.
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`Glucose Ingestion Selectively Amplifies ACTH and Cortisol Secretory-Burst Mass and Enhances Their Joint Synchrony in Healthy Men
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`Fig. 4.
`
`Linear regression of incremental cortisol secretory-burst size (mass) (top) and incremental ACTH secretory-burst
`duration (mode) (bottom) on CT-estimated AVF cross-sectional area. The singl