Increase in systolic blood pressure and catecholamine level during hyperinsulinemia in a placebo-controlled euglycemic clamp in healthy subjects

Hyperinsulinemia has been shown to induce vasodilation and activation of the sympathetic nervous system. Whether these effects result in changes in blood pressure (BP) is discussed controversially. We measured BP and catecholamine levels in 50 healthy subjects during a 40-min baseline phase and during a 100-min euglycemic clamp phase. In a double-blind, between-subject comparison, 30 subjects were infused with 1.5mU insulin/kg x min, 20subjects were infused with saline solution. Insulin levels increased during insulin infusion from (mean+/-SE) 23.7 0.6 pmol/l to 406.2+/-3.0 pmol/l, but remained unchanged during placebo infusion. Blood glucose levels were identical during both conditions. Systolic BP increased from 116.6+/-1.5 mmHg to 119.8+/-1.8 mmHg during insulin infusion and decreased from 116.6+/-2.3 mmHg to 114.0+/-2.4 mmHg during placebo infusion (p<0.001, for the difference between the effects of insulin vs. placebo). Heart rate was higher during insulin infusion as compared to placebo infusion (63.8+/-1.9 vs. 60.9+/-2.4 beats/min, p<0.05). Norepinephrine levels increased from 1.25+/-0.09 to 1.58+/-0.12 nmol/l during insulin infusion and remained unchanged during placebo infusion (1.24+/-0.09 vs. 1.29+/-0.11 pmol/l; p<0.001). Epinephrine levels were also higher during insulin as compared to placebo infusion (249.8+/-17.4 vs. 212.8+/-21.1 pmol/l, p<0.001). The changes did not depend on whether the subject experienced his first or second clamp. Data demonstrate reproducable increasing effects of hyperinsulinemia within the normal physiological range on catecholamine release and systolic BP in healthy humans.

Rhythms of pituitary-adrenal activity during sleep in patients with Cushing's disease

Previous studies have indicated a dependence of nocturnal pituitary-adrenal secretory activity on central nervous sleep processes in healthy humans: Under normal physiological conditions the release of ACTH/cortisol is inhibited during early sleep and becomes entrained to periods of NonREM sleep during late sleep. Here, we compared nocturnal dynamics in plasma concentrations of ACTH/cortisol in 7 patients with Cushing's disease with those of 7 healthy controls matched in age and sex with the patients. The patients in part were repeatedly tested. The total of 13 nights is composed of 7 nights of hyperpulsatile secretion pattern (5 patients) and 6 nights from hypopulsatile secretion pattern (4 patients). After an adaptation night polysomnographic sleep recordings were obtained and blood was sampled every 15 min between 23.00 and 7.00 h. Controls displayed the typical minimum in ACTH/cortisol concentrations during the early part of the night and maximum concentrations during the late part of the night, whereas ACTH/cortisol levels of Cushing patients indicated a relatively constant elevated pituitary-adrenal activity throughout the night, lacking any circadian variation. Autocorrelation functions revealed the presence of cortisol secretory rhythms with a similar period length in healthy controls (155.6+/-17.4 min) and patients with a hyperpulsatile pattern (142.4+/-6.6 min). In patients displaying hypopulsatility, no significant rhythmicity was observed. However, regardless of the type of secretory pulsatility, adrenal secretory activity started predominantly during periods of NonREM sleep (p<0.01) in healthy controls as well as in patients with Cushing's disease. This data indicates that the normal nocturnal circadian oscillation of pituitary-adrenal activity is absent in Cushing patients, whereas a link between pituitary-adrenal activity and ultradian rhythms of sleep appears to be preserved.

The melanocortin melanocyte-stimulating hormone/adrenocorticotropin(4-10) decreases body fat in humans

The control of body fat is a prominent factor in human health. Animal studies have indicated a homeostatic central nervous system regulation of body fat with particular involvement of the melanocortin receptor pathway. This study provides evidence for a similar role for melanocortins in the long-term control of fat stores in humans. Thirty-six normal weight humans were assigned to one of three experimental groups. After a 4-week baseline, one group was treated with MSH/ACTH(4-10) (MSH/ACTH(4-10)) representing the core sequence of all melanocortins. Another group received desacetyl-alphaMSH, a selective agonist of the brain melanocortin-4 receptor, which shares the 4-10 sequence with MSH/ACTH(4-10). The third group received placebo. Treatments were given intranasally twice daily for 6 weeks, at equimolar doses (MSH/ACTH(4-10), 0.5 mg; desacetyl-alphaMSH, 0.84 mg). Body weight, body composition, and plasma hormone concentrations were measured before and after treatment. MSH/ACTH(4-10) reduced body fat, on the average, by 1.68 kg (P < 0.05) and body weight by 0.79 kg (P < 0.001). Concurrently, plasma leptin levels were decreased by 24% (P < 0.02), and insulin levels were decreased by 20% (P< 0.05) after MSH/ACTH(4-10). Changes after desacetyl-alphaMSH remained nonsignificant. The finding of reduced body adiposity after MSH/ACTH(4-10) confirms and extends to the human the findings of animal models indicating an essential role of the hypothalamic melanocortin system in body weight control.

Postmenopausal estrogen administration suppresses muscle sympathetic nerve activity

The activity of the sympathetic nervous system shows gender-specific differences with lower sympathoneural activity to the muscle vascular bed in women compared with men, with this difference vanishing after menopause. The present study tested the hypothesis that estrogen exerts regulatory influence on the autonomic nervous system in postmenopausal women. Eleven healthy postmenopausal women (age, 58.5 +/- 1.0 yr; mean +/- SEM) were studied in a randomized double-blind crossover protocol with transdermal administration of 100 microgram/day estradiol (E(2)) or placebo (P) for 2 days. Muscle sympathetic activity (MSA), blood pressure, and heart rate were recorded at rest and during sympathoexcitatory maneuvers (apnea, cold pressor test). E(2) administration significantly increased serum E(2) to physiological levels (E(2), 469.5 +/- 51.5; P, 34.8 +/- 2.2 pmol/L; P < 0.05) and significantly lowered MSA (E(2), 30.1 +/- 3.0 vs. P 37.7 +/- 3.1 bursts/min; P < 0.05). At the same time, blood pressure and heart rate were not affected. MSA was significantly enhanced during apnea and the cold pressure test, and this physiological response to the maneuvers was not changed after estrogen supplementation. In conclusion, elevation of low postmenopausal estrogen levels to physiological premenopausal levels by transdermal E(2) administration supresses MSA. This effect is most likely the consequence of a direct E(2) effect on central nervous autonomic centers, which could explain the gender-specific differences in sympathetic outflow to the muscle vascular bed. The sympathoinhibitory estrogen effects could be important for beneficial cardiovascular effects of estrogen replacement therapy in postmenopausal women.

Signs of sexual behaviour are not increased after subchronic treatment with LHRH in young men

Apart from its action as gonadotropin releasing factor, luteinizing hormone-releasing hormone (LHRH) is a potent regulator of sexual behaviour in animals. The present study aimed to assess a similar role of LHRH for sexuality in humans. In a double-blind placebo-controlled and randomized study, effects of human LHRH after acute (400 microg) and subchronic (800 microg/day over 2 weeks) intranasal administration were evaluated in 20 young and healthy men. Sexual desire and activity was assessed by a diary, ratings of women's attractiveness, a modified version of the Stroop colour naming task and a short term memory task. Effects on sexuality were contrasted with those on eating motivation and general neurocognitive functioning, the latter being assessed in addition by tasks of divergent thinking and a motor perseveration test. None of the measures of sexual desire and activity indicated any effect of LHRH, neither after acute nor after subchronic treatment. Unexpectedly, the diary indicated a significant increase in 'food intake' towards the end of the 14-day LHRH treatment. Enhanced colour naming performance on the Stroop task (independently of whether sex, food or neutral stimuli were used) in conjunction with an increased motor perseveration after LHRH points to a general effect on cognitive function towards stronger focussing of cortical processing. While overall the data show discrete central nervous changes after LHRH, a particular influence on sexuality after acute or subchronic intranasal administration in healthy men was not detected.

Changes in direct current (DC) potentials and infra-slow EEG oscillations at the onset of the luteinizing hormone (LH) pulse

An essential function of the neuroendocrine system lies in the coordination of hypothalamo-pituitary secretory activity with neocortical neuronal activity. Cortical direct current (DC) potential shifts and EEG were monitored in conjunction with the circulating concentration of luteinizing hormone (LH) in humans while asleep to assess a hypothalamic-neocortical interaction. The onset of an LH pulse was accompanied (i) at frontocortical locations by a transient positive DC potential shift of approximately 3 min duration and peak amplitude 50 microV; (ii) at frontal and central locations by an increase in power of infra-slow EEG oscillations for periodicities between 64 and 320 s. Results uniquely demonstrate a coupling of hypothalamo-pituitary activity with regulation of neocortical excitability.

The subcutaneous lipolytic response to regional neural stimulation is reduced in obese women

Disturbed fat tissue metabolism with a reduction of the lipolytic rate could be an important pathogenetic factor in obesity. Lipolysis of the subcutaneous tissue of the thigh is partly under neural control and can be increased by intraneural stimulation of the lateral cutaneous femoral nerve in lean women. In the present study, we tested whether the lipolytic response to intraneural stimulation is altered in vivo in obese subjects. Seven obese women were examined and the results were compared with those of seven age-matched lean women. After an overnight fast, the lateral cutaneous femoral nerve was intraneurally stimulated for 10 min, and the local subcutaneous lipolytic response to this procedure was evaluated with microdialytic measurements of interstitial glycerol concentrations in the receptive field of the stimulated nerve fascicle. To exclude unspecific effects of stimulation, lipolysis was also controlled in a corresponding area of the contralateral leg. Intraneural stimulation produced no significant change in subcutaneous lipolysis in obese women (25.7 +/- 9.7%, NS). This finding is in sharp contrast with the marked regional lipolytic response in lean women in which the same stimulation procedure enhanced the regional interstitial glycerol levels by 72 +/- 17% (P < 0.05) compared with the unstimulated corresponding area of the contralateral leg. These in vivo results suggest that human obesity is characterized by a profound unresponsiveness of the subcutaneous adipose tissue to neurally stimulated lipolysis. This could be an important factor in the development and treatment of obesity.

Manipulating neuropeptidergic pathways in humans: a novel approach to neuropharmacology?

Given the tremendous number of neuropeptides, which are synthesized in the central nervous system, the brain can be viewed as one of the most prominent endocrine organs. Elucidation of the functions of these peptides is hampered by the facts that after intravenous administration access to brain receptors is prevented or impaired by the blood-brain barrier. Here, we provide evidence that intranasal administration can be a way to circumvent the blood-brain barrier. Selected experiments will be reported indicating that peptides after intranasal administration in humans can specifically alter a great variety of brain functions. For vasopressin, we demonstrated improving effects of long-term intranasal treatment on sleep in elderly people. Insulin showed improving effects of short-term memory functions. For adrenocorticotropin/melanocyte stimulating hormone, ACTH/MSH-(4-10), a twofold action was isolated: The melanocortin fragment diminished selective attention and, with subchronic administration, reduced body fat. These results could provide the basis for developing a new, specific, and "soft" neuropharmacology.

Insulin activation of insulin receptor kinase in erythrocytes is not altered in non-insulin-dependent diabetes and not influenced by hyperglycemia

Recent studies suggest that high glucose concentrations impair insulin receptor phosphorylation and kinase activation in certain cell models. To examine whether such an effect of glucose can also be demonstrated in vivo, insulin receptor kinase activation was studied in erythrocytes from 11 patients with non-insulin-dependent diabetes (NIDDM), before and after reduction of hyperglycemia (from 14.6+/-1.6 to 6.6+/-0.5 mmol/l fasting plasma glucose within 8.6+/-0.6 days). For the measurement of receptor kinase activation, cells were incubated with insulin (0-400 nmol/l), solubilized and insulin receptors immobilized to microwells coated with anti-insulin receptor antibody. Kinase activity towards insulin receptor substrate-1 and insulin binding were then measured in these wells. Kinase activities (expressed as amol phosphate transferred per min and per fmol insulin binding activity) were similar before (2.4+/-0.4 and 32.2+/-2.0 amol/min per fmol with 0 and 400 nmol/l insulin, respectively) and after improvement of metabolic control (2.4+/-0.5 and 32.0+/-2.3 amol/min per fmol with 0 and 400 nmol/l insulin, respectively). Moreover, activities were also similar in 22 hyperglycemic patients with NIDDM (2.1+/-0.3 and 35.1+/-1.4 amol/min per fmol with 0 and 400 nmol/l insulin, respectively) compared with those in 21 non-diabetic control individuals (2.1+/-0.3 and 34.2+/-1.2 amol/min per fmol with 0 and 400 nmol/l insulin, respectively). We conclude that insulin activation of erythrocyte insulin receptor kinase is not impaired in NIDDM and is not influenced by hyperglycemia.

Adaptation of cognitive function to hypoglycemia in healthy men

OBJECTIVE

Antecedent hypoglycemia reduces hypoglycemic counterregulation and symptoms, thereby provoking the hypoglycemia unawareness syndrome. The effects of antecedent hypoglycemia on hypoglycemia-induced cognitive dysfunction are less well established.

RESEARCH DESIGN AND METHODS

To determine whether antecedent hypoglycemia also reduces hypoglycemic cognitive dysfunction, we performed stepwise hypoglycemic clamp experiments (4.1, 3.6, 3.1, and 2.6 mmol/l) during a 6-h period in 30 young healthy men. A total of 15 subjects additionally received a 2.5-h antecedent hypoglycemic clamp (3.1 mmol/l) on the preceding day (prior-hypo group), whereas the other 15 subjects did not (control group). Cognitive function was assessed by auditory-evoked brain potentials (AEBPs) and reaction time during a vigilance task and short-term memory recall. Tests were performed during the stepwise hypoglycemic clamp at baseline and at each hypoglycemic plateau.

RESULTS

In both groups, performance on all measures of cognitive function deteriorated during stepwise hypoglycemia (all P < 0.01). However, after antecedent hypoglycemia, the hypoglycemia-induced decrease in the amplitude of the P3 of the AEBP was distinctly reduced compared with the control condition (P < 0.05). Also, short-term memory performance was less impaired in the prior-hypo group than in the control group (P < 0.005), and a minor hypoglycemic impairment of reaction time (P < 0.05) was evident in the prior-hypo group.

CONCLUSIONS

Data provide evidence that a single episode of mild antecedent hypoglycemia (3.1 mmol/l) attenuates several aspects of cognitive dysfunction during subsequent hypoglycemia 18-24 h later.

Event-related brain potentials and working memory function in healthy humans after single-dose and prolonged intranasal administration of adrenocorticotropin 4-10 and desacetyl-alpha-melanocyte stimulating hormone

Neuropeptides of the adrenocorticotropin/melanocorticotropin (ACTH/MSH) family are most potent modulators of cognitive function. Their neurobehavioral activity is principally encoded in the 4-10 fragment of the ACTH/MSH molecule; in humans, it has been shown to pertain primarily to functions of attentive stimulus/response processing. The aims of this study were (1) to examine the effects of ACTH 4-10 on event-related brain potentials (ERPs) and behavioral indicators of stimulus encoding within the working memory; (2) to compare the effects after a single dose and after prolonged treatment with ACTH 4-10; and (3) to compare the effects of ACTH 4-10 with those of desacetyl-alpha-MSH (i.e., ACTH 1-13 amide), which, like ACTH 4-10, binds to the known brain melanocortin receptors (MC-Rs) but with distinctly higher affinity. Double-blind, placebo-controlled experiments were performed in 60 healthy control subjects. The authors monitored ERPs and reaction times while these subjects performed an auditory vigilance task ("oddball"). Recall was tested on a verbal short-term memory task including different word categories (neutral, rare, food, sex). After a single (1 mg) as well as prolonged intranasal administration (1 mg/day over a period of 6 weeks), ACTH 4-10 enhanced the positive slow wave in ERPs to target stimuli of the vigilance task (p < 0.05), but left classic P3 unaffected. Moreover, single-dose and prolonged administration of ACTH 4-10 increased the rate of false responses during vigilance (p < 0.01). In the short term, ACTH 4-10 also impaired recall of neutral words (p < 0.05). Equimolar doses of desacetyl-alpha-MSH did not influence ERPs, neither after a single dose nor after prolonged treatment. Similar to ACTH 4-10, desacetyl-alpha-MSH increased the error rate during vigilance and acutely impaired the recall of neutral words. The increase in ERP slow-wave positivity, in conjunction with behavioral impairments after treatment with ACTH 4-10, complemented previous results of inferior focusing of attention and a less concise structure of thought after administration of ACTH 4-10. The changes indicated an impairment in differential processing of relevant versus irrelevant contents within the working memory, and, in this regard, might mimic aspects of psychopathologic disturbances of attention and thought processes. Their persistence after prolonged treatment with ACTH 4-10 suggests an activation of mechanisms subserving the consolidation of the peptide's effects. The poor efficacy of desacetyl-alpha-MSH suggests that the known MC-Rs may be irrelevant for mediating cognitive effects of this neuropeptide family.

Excess triiodothyronine as a risk factor of coronary events

BACKGROUND

Abnormalities in cardiac function, eg, arrhythmias and congestive heart failure, often accompany thyrotoxicosis. A relationship between thyroid hormone excess and the cardiac complications of angina pectoris and myocardial infarction (MI) remains largely speculative.

METHODS

The results of thyroid function studies on blood samples drawn from a total of 1049 patients (aged 40 years or older) immediately on emergency medical admission were related to frequencies of angina pectoris and myocardial infarction as determined according to current diagnostic algorithms. After 3 years, those patients who had initially presented with angina pectoris or acute MI were observed for subsequent coronary events; of these (n=185), 98% of the subjects (n=181) could be reevaluated.

RESULTS

On hospital admission, the relative rate of angina pectoris and MI was markedly high (odds ratio, 2.6; 95% confidence interval, 1.3-5.2; P=.007) in patients with elevated serum free and total triiodothyronine (T(3)) levels. An initially elevated free T(3) level was a risk factor for subsequent coronary events during the 3-year follow-up (adjusted odds ratio, 4.8; 95% confidence interval, 1.3-17.4; P=.02).

CONCLUSIONS

An elevation of serum free T(3) levels at hospital admission is associated with a 2.6-fold greater likelihood of the presence of a coronary event. Moreover, an initially elevated T(3) level is associated with a 3-fold higher risk of developing a subsequent coronary event during the next 3 years. Excess T(3) seemed to be a factor associated with the development and progression of acute myocardial ischemia.

Comparison of the inhibitory effect of insulin and hypoglycemia on insulin secretion in humans

Although both insulin and hypoglycemia are known to inhibit endogenous insulin secretion, their potency to suppress insulin secretion has not been directly compared thus far. The serum C-peptide concentration was measured during 28 euglycemic and 28 stepwise hypoglycemic (4.1,3.6, 3.1, and 2.6 mmol/L) clamp experiments using either a low-rate (1.5 mU x min(-1) x kg(-1)) or high-rate (15.0 mU x mU(-1) x kg(-1)) insulin infusion. The experiments lasted 6 hours and were performed in 28 lean healthy men. During both the euglycemic and hypoglycemic clamps, serum insulin was approximately 40-fold higher during the high-rates versus low-rate insulin infusion (euglycemia, 24,029 +/- 1,595 v 543 +/- 34 pmol/L; hypoglycemia, 23,624 +/- 1,587 v 622 +/- 32 pmol/L). Under euglycemic conditions, serum C-peptide decreased from 0.54 +/- 0.04 to 0.41 +/- 0.05 nmol/L during the low-rate insulin infusion (P < .05) and from 0.55 +/- 0.07 to 0.27 +/- 0.09 nmol/L during the high-rate insulin infusion (P < .001). Under hypoglycemic conditions, serum C-peptide decreased from 0.50 +/- 0.03 to 0.02 +/- 0.01 nmol/L during the low-rate insulin infusion (P< .001) and from 0.46 +/- 0.07 to 0.02 +/- 0.01 nmol/L during the high-rate insulin infusion (P< .001). In the euglycemic clamp condition, the high-rate insulin infusion reduced the C-peptide concentration more than the low-rate insulin infusion (P < .05). Independent of the rate of insulin infusion, the decrease in C-peptide was distinctly more pronounced during hypoglycemia versus euglycemia (P < .001). These data indicate that insulin inhibits insulin/C-peptide secretion in a dose-dependent manner. Hypoglycemia is a much stronger inhibitor of insulin secretion than insulin itself.

Preserved hypothermic response to hypoglycemia after antecedent hypoglycemia

Hypoglycemia is known to decrease the body temperature and to stimulate counterregulatory hormone secretion. Although it is well established that antecedent hypoglycemia reduces the hormonal response to subsequent hypoglycemia, the effects of antecedent hypoglycemia on the subsequent hypothermic response are obscure. In the present study, body temperature was measured orally during a total of 90 glucose clamp experiments in 45 healthy men. The clamps lasted 6 hours and were performed under 6 different experimental conditions: a euglycemic clamp with a low rate of insulin infusion, 1.5 mU/kg x min (low insulin-eu), a euglycemic clamp with a high rate of insulin infusion, 15.0 mU/kg x min (high insulin-eu), a hypoglycemic clamp with a low rate of insulin infusion, 1.5 mU/kg x min (low insulin-hypo), a hypoglycemic clamp with a high rate of insulin infusion, 15.0 mU/kg x min (high insulin-hypo), and 2 hypoglycemic clamps following an antecedent 2.5-hour hypoglycemia (56 mg/dL) induced by either a low (1.5 mU/kg x min, low insulin-ante-hypo) or a high (15.0 mU/kg x min, high insulin-ante-hypo) rate of insulin infusion. Plasma glucose was maintained normal during the euglycemic clamps and was decreased stepwise during the hypoglycemic clamps (76 --> 66 --> 56 --> 46 mg/dL). During the hypoglycemic clamps, body temperature decreased by 0.26 degrees +/- 0.09 degrees C in low insulin-hypo, 0.28 degrees +/- 0.09 degrees C in high insulin-hypo, 0.29 degrees +/- 0.09 degrees C in low insulin-ante-hypo, and 0.41 + 0.11 degrees C in high insulin-ante-hypo (all P < .01). There were no differences in the hypothermic response to hypoglycemia among the different hypoglycemic conditions (P > .1 for all comparisons). In contrast, body temperature remained unchanged during the euglycemic clamps, so the changes in body temperature differed significantly during the euglycemic clamps versus the hypoglycemic clamps (P < .05 for all comparisons). The data show that the body temperature decreases during hypoglycemia and this decrease is influenced neither by antecedent hypoglycemia nor by circulating insulin levels.

Interferon-alpha acutely impairs sleep in healthy humans

We investigated the effects of two low doses of interferon-alpha (IFN-alpha) on nocturnal sleep in 18 healthy men by means of polysomnographic sleep recordings. At 1900h, human recombinant IFN-alpha (1000 or 10000 U/kg body weight) or placebo was administered subcutaneously. Between 2300h and 0700h subjects were allowed to sleep. In general effects were stronger at the dose of 10000 than 1000 U/kg body weight of IFN-alpha. Although, after IFN-alpha subjects experienced increased fatigue, the cytokine impaired the quality of nocturnal sleep. The higher dose of IFN-alpha suppressed slow wave sleep (17.8 +/- 2.0% vs 25.2 +/- 2.6% following placebo, P<0.003) but increased time spent in shallow sleep (P<0.05) during the first half of sleep time. Rapid eye movement (REM) sleep latency was postponed (P<0.02) and time spent in REM sleep was significantly decreased after IFN-alpha (P<0.04). The impairing influence of IFN-alpha on sleep in humans is in contrast with findings of sleep promoting effects of this cytokine in animals. Our data suggest that endogenous IFN-alpha may be a factor responsible for alterations of sleep, e.g. in the course of viral infections.

Glucose metabolism rather than insulin is a main determinant of leptin secretion in humans

Circulating plasma insulin and glucose levels are thought to be major regulators of leptin secretion. There is evidence from in vitro and animal experiments that glucose metabolism rather than insulin alone is a main determinant of leptin expression. Here, we tested the hypothesis that in humans also leptin secretion is primarily regulated by glucose uptake and only secondarily by plasma insulin and glucose. In 30 lean and healthy men we induced 4 experimental conditions by using the blood glucose clamp technique. A total of 60 hypoglycemic and euglycemic clamps, lasting 6 h each, were performed. During these clamps insulin was infused at either high (15.0 mU/min x kg) or low (1.5 mU/min x kg) rates, resulting in low-insulin-hypo, high-insulin-hypo, low-insulin-eu, and high-insulin-eu conditions. Serum leptin increased from 0-360 min by 20.5 +/- 4.1% in the low-insulin-hypo, 33.6 +/- 7.6% in the high-insulin-hypo, 39.6 +/- 6.0% in the low-insulin-eu, and 60.4 +/- 7.6% in the high-insulin-eu condition. Multiple regression analysis revealed a significant effect of circulating insulin (low vs. high insulin; P = 0.001) and blood glucose (hypoglycemia vs. euglycemia; P = 0.001) on the rise of serum leptin. However, when the total amount of dextrose infused during the clamp (grams of dextrose per kg BW) was included into the regression model, this variable was significantly related to the changes in serum leptin (P = 0.001), whereas circulating insulin and glucose had no additional effect. These findings in humans support previous in vitro data that leptin secretion is mainly related to glucose metabolism.

Acute suppression of muscle sympathetic nerve activity by hydrocortisone in humans

In the present study, we examined the acute influence of hydrocortisone on human sympathetic nerve activity and cardiovascular parameters. Muscle sympathetic nerve activity (MSA), heart rate, and blood pressure were monitored in 8 healthy subjects (20 to 37 years old) before and after a bolus injection of 50 mg hydrocortisone followed by a continuous infusion at 50 mg/h during a period of 3 hours in a placebo-controlled, double-blind, crossover protocol. Recordings were performed at rest and during repeated transient sympathoexcitation induced by voluntary apneas. Resting MSA and endogenous serum cortisol concentrations were also measured in a larger study group (49 experiments, 25 subjects). During the experimental period, MSA burst number increased by 56% from the control level in the placebo group. In contrast, MSA was suppressed by 25% at the end of the hydrocortisone infusion, resulting in a significant treatment effect (P<0.05). In addition, sympathoexcitation during apnea was significantly reduced with hydrocortisone after 180 minutes. In parallel with the sympathetic outflow, blood pressure decreased in the hydrocortisone-treated group, whereas it rose in the placebo group (P<0.05 between groups). No correlation was found between basal MSA and basal cortisol levels. Our results indicate that pharmacological doses of hydrocortisone acutely influence MSA responses to short- and long-lasting environmental stimuli, whereas basal native cortisol levels do not appear to be tonically involved in the regulation of resting MSA. The suppressive hydrocortisone effect is most likely induced via supraspinal autonomic centers and cannot be explained by peripheral steroid mechanisms. The effect of elevated corticosteroid levels on sympathetic nerve discharge may be an important mechanism in cardiovascular adaptations to stress.

Selective influence of the menstrual cycle on perception of stimuli with reproductive significance: an event-related potential study

In this study, we examined changes in the event-related potential (ERP) to stimuli with and without reproductive significance occurring during the menstrual cycle. Eleven spontaneously cycling women were tested during three menstrual phases (menses, ovulatory phase, luteal phase) differing in plasma concentrations of gonadal hormones. ERPs were recorded while subjects were presented with slides showing pictures from four different stimulus categories (sexual stimuli, babies, people occupied with body care, ordinary people). Slides were presented randomly in the context of two tasks, requiring either affective processing (i.e., to judge the emotional content of a slide as positive, neutral, or negative) or structural processing (i.e., to estimate the number of parallel thin lines inserted in each picture). Menstrual phase primarily affected a late positive component (LPC) peaking 550-600 ms poststimulus. The effects were as follows: (i) During the ovulatory phase, amplitude of the LPC to sexual stimuli was larger than that evoked by the other stimulus categories. (ii) This relationship was not apparent during the other menstrual phases or (iii) during the ovulatory phase when the task required structural processing. The ovulatory increase in LPC positivity to sexual stimuli suggests a greater valence of these stimuli during a phase of increased sexual desire. The data indicate a specific effect of the menstrual cycle on the processing of sexual stimuli that increases with deeper emotional processing.

Intraneural stimulation elicits an increase in subcutaneous interstitial glycerol levels in humans

1. The effect of intraneural electrical stimulation of the lateral femoral cutaneous nerve on lipolysis in the innervation territory of the stimulated nerve fascicle was studied in seven healthy women. Lipolysis was evaluated by microdialytic measurement of the interstitial glycerol concentration in subcutaneous adipose tissue. 2. Ten minutes of unilateral intraneural stimulation elicited a 22 +/- 8 % (mean +/- s.e.m.) increase in glycerol levels in the stimulated region (P < 0.05), whereas no change was registered in the corresponding area of the contralateral unstimulated leg. 3. Significantly higher glycerol levels in the stimulated vs. contralateral unstimulated region (47 +/- 13 %, P < 0.05) were already observed at baseline (30 min resting period preceding the 10 min stimulation), in all probability as a consequence of the nerve searching procedure and trial stimulations. After the 10 min stimulation, the overall glycerol increase was 72 +/- 17 % compared with the contralateral leg, illustrating the degree of lipolysis induced by the whole experimental procedure. 4. The sympathetic discharge in the lateral femoral nerve (6 recordings) showed typical characteristics of skin sympathetic activity, and the firing pattern was strikingly similar to simultaneously recorded sympathetic discharge in cutaneous nerve fascicles innervating regions without prominent subcutaneous fat stores (2 double nerve recordings). Thus, no component of cutaneous sympathetic outflow specific for the nerve innervating prominent subcutaneous fat stores could be identified. 5. Our findings suggest that sympathetic nerve fibres travelling in cutaneous nerve fascicles exert a regulatory influence on subcutaneous fat tissue in humans. The combination of intraneural recording/stimulation and subcutaneous microdialysis provides a model for evaluating neural control of human fat metabolism.

Sleep and endocrine changes after intranasal administration of growth hormone-releasing hormone in young and aged humans

Systemic administration of growth hormone-releasing hormone (GHRH) has been found to improve human sleep in previous studies. Here we examined effects of GHRH on endocrine function and sleep after intranasal administration, a method which based on previous studies appears to enable a direct effect of peptides on brain function. Also, it was hypothesized that elderly humans displaying deficient GH release and sleep, benefit from GHRH administration more than young subjects. A study was performed according to a double-blind cross-over design. Each of 12 young and 11 old healthy men were intranasally administered with 300 micrograms GHRH (vs. placebo) 30 min before bedtime at 23:00 h. Sleep was recorded polysomnographically until 07:00 h and blood was collected in 15 min intervals for determination of cortisol and GH. Apart from the well-known age-related changes of hormonal secretion and sleep, intranasal GHRH reduced cortisol nadir concentrations in the beginning of sleep (P < 0.05), and also reduced the sleep-induced elevation in GH concentrations during early sleep. Moreover, results indicated that after intranasal administration GHRH increased rapid-eye-movement (REM) sleep and slow wave sleep (SWS), with this influence concentrating on the second half of sleep time. Effects of GHRH did not depend on the subject's age. We conclude that there is a coordinate influence of intranasal GHRH on the central nervous regulation of sleep processes and of hypothalamic-hypophysiotropic secretory activity in both young and elderly men. The effects may mimic the dual neuronal and endocrine function of hypothalamic GHRH activity.

Supraphysiological hyperinsulinemia acutely increases hypothalamic-pituitary-adrenal secretory activity in humans

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis in association with hyperinsulinemia is frequently found in patients with type 1 and type 2 diabetes mellitus and in subjects with abdominal adiposity. We questioned whether insulin could cause HPA axis activation and, if so, whether this insulin action may arise at the adrenal level or at a central (i.e. hypothalamic-pituitary) level. Experiments lasting for 6 h each were done in 30 lean healthy men. In 15 men, insulin was infused at a rate of 1.5 mU min(-1) kg(-1). Plasma glucose concentration was held constant during an euglycemic clamp session and was decreased stepwise in a hypoglycemic clamp session. The sequence of the 2 clamp sessions was random, and a 4-weeks recovery period was allowed between the two sessions. The protocol was essentially the same in another 15 men, with the exception that insulin was infused at a rate of 15.0 mU min(-1) kg(-1). During the euglycemic clamp sessions, we found plasma ACTH levels to increase only in the high-, but not in the low-insulin group (group by time interaction, P < 0.01); serum cortisol levels were greater in the high than in the low-insulin group (P < 0.02). In the hypoglycemic clamp sessions, plasma ACTH levels increased in the same pattern in the 2 groups; serum cortisol was greater in the high than in the low-insulin group at the beginning of the clamp (plasma glucose approximately 4.1 mmol/L; P < 0.05). Our results demonstrate that insulin acutely stimulates the HPA secretory activity in humans. The pattern suggests an effect of insulin at both peripheral and central levels of the HPA axis.

Brain potentials and attention after acute and subchronic intranasal administration ofACTH 4-10 and desacetyl-alpha-MSH in humans

Neuropeptides related to adrenocorticotropin (ACTH) are potent regulators of neurobehavioral functions. In humans, ACTH and its behaviorally active fragment ACTH 4-10 have been consistently found to diminish event-related brain potential (ERP) signs of focussing attention. This study aimed at (1) evaluating effects of ACTH 4-10 on ERP indicators of attention in healthy controls after intranasal administration of the peptide. This route of administration has been proposed to provide a more direct access to the brain than the intravenous administration of the peptide, (2) comparing acute effects and effects of a subchronic treatment with ACTH 4-10, and (3) comparing effects of ACTH 4-10 with those of desacetyl-alpha-MSH (corresponding to ACTH 1-13 amide) which like ACTH 4-10 binds to subgroups of the melanocortin receptor family. Double-blind placebo-controlled experiments were completed in 54 healthy young subjects. ERPs were recorded while the subject performed an auditory selective attention task. Moreover, a modified Stroop interference test including motivational (food, sex) and nonmotivational words was performed. Acute intranasal administration of ACTH 4-10 (1 mg) reduced the processing negativity (PN) of the ERP over frontal and central cortical areas (p < 0.05) indicating diminished focussing of attention. Moreover, on this condition subjects were more prone to interference on the Stroop task especially with motivational words (p < 0.05). Subchronic administration of ACTH 4-10 (1 mg/day over 6 weeks) did not affect PN and Stroop performance. Acute intranasal administration of desacetyl-alpha-MSH at equimolar doses (1.68 mg) also remained ineffective. However, some measures of Stroop performance appeared to improve after subchronic desacetyl-alpha-MSH treatment. Results confirm an acute decrease in focussing of attention after ACTH 4-10. These effects of intranasal administration are likely to reflect a direct action of the peptide on respective brain functions. Moreover, they were specific to ACTH 4-10 and were not obtained after equimolar doses of desacetyl-alpha-MSH, thus excluding a mediation via the known melanocortin receptors.

[Glucocorticoid-induced diabetes mellitus in gastrointestinal diseases]

Glucocorticoid excess causes insulin resistance i.e. a reduced effectiveness of insulin to suppress hepatic glucose production and to increase glucose uptake in muscle and fat tissue. Persons who cannot compensate for the resulting additional insulin need develop overt diabetes during glucocorticoid therapy. In the field of gastroenterology, glucocorticoids are mainly employed for the therapy of chronic inflammatory bowel diseases, alcoholic and autoimmune hepatitis, and after liver transplantation. The risk of developing steroid diabetes depends among other things on the genetic predisposition, the body composition, the underlying gastrointestinal disease, the age, and the steroid dose. The treatment of glucocorticoid-induced diabetes resembles essentially the treatment of type 2-diabetes. In addition to dietary measures, oral antihypoglycemic drugs and/or insulin are applied. If oral antihypoglycemic drugs are used, specific problems that might result from the gastrointestinal diseases need to be observed. In the short and medium term, the prognosis of glucocorticoid-induced diabetes is good since it is well treatable. If glucocorticoid treatment is continued for a long time, the alterations of glucose metabolism and the resulting hyperinsulinemia may lead to increased cardiovascular risk.

Protective effect of insulin against hypoglycemia-associated counterregulatory failure

Antecedent hypoglycemic episodes reduce the counterregulatory neuroendocrine response to hypoglycemia. The role of insulin in the mechanism responsible for the antecedent hypoglycemia causing subsequent counterregulatory failure has not been elucidated. We performed antecedent hypoglycemic clamps (56 mg/dL) lasting 2 h with differing degrees of hyperinsulinemia, which were followed by 6-h stepwise hypoglycemic clamps (76-66-56-46 mg/dL) on the next day. Experiments were carried out in 30 young, healthy men. Fifteen of these subjects were tested on 2 occasions. On 1 occasion the antecedent hypoglycemia was induced by insulin infusion at a rate of 1.5 mU/min x kg (low insulin-ante-hypo); on the other occasion the insulin infusion rate was 15.0 mU/min x kg (high insulin-ante-hypo). Both sessions were separated by at least 4 weeks, and their order was balanced across subjects. The remaining 15 subjects (control group) received the same stepwise hypoglycemic clamp as the other subjects, but without antecedent hypoglycemia. During the stepwise hypoglycemic clamp, the counterregulatory increases in ACTH, cortisol, and norepinephrine were significantly blunted after the low insulin-ante-hypo (P < 0.01, P < 0.05, and P < 0.05, respectively) but not after the high insulin-ante-hypo (P = 0.12, P = 0.92, and P = 0.19, respectively) compared to that in the control group. The cortisol, norepinephrine, and glucagon responses were greater after the high than after the low insulin-ante-hypo (all P < 0.05). In conclusion, the present study clearly demonstrates that even a single episode of mild hypoglycemia reduces neuroendocrine counterregulation 18-24 h later. Insulin has a moderate protective effect on subsequent counterregulation.

A determinant factor in the efficacy of GHRH administration in promoting sleep: high peak concentration versus recurrent increasing slopes

A previous experiment indicated a greater efficacy of episodic than continuous growth hormone (GH)-releasing hormone (GHRH) administration in enhancing sleep. The greater efficacy of episodic administration could principally result from two factors, i.e. the greater peak concentration reached after episodic administration or the recurrence of increasing slopes in GHRH concentration. In order to investigate which factor essentially determines the pharmacodynamics of sleep promotion after GHRH, effects after a transient high peak in GHRH concentration were compared with those of repetitive increases in GHRH concentration. Sleep, plasma concentrations of GH, and GHRH were examined in healthy subjects after evening administration of a 'single' i.v. bolus of 50 micrograms GHRH, after five 'repetitive' boluses of 10 micrograms GHRH, and after placebo. Compared with placebo, single GHRH significantly increased time spent in stage 4 sleep (p < .01) and in stage 2 sleep, reduced time spent in wakefulness and onset latency of stage 4 sleep (p < .05, for each), while repetitive GHRH remained without effects. GH secretory activity also tended to be higher after single than repetitive GHRH. Thus, results suggest the relevance of a transiently high concentration of GHRH in blood as an essential factor in enhancing the central nervous sleep process.