Cholinergic potentiation of the meal-related rise in ACTH and cortisol concentrations in men

The present study examined the influence of physostigmine, an acetylcholine esterase inhibitor, on the secretory activity of the hypothalamo-pituitary-adrenocortical (HPA)--axis under basal (experiment I) and stimulated (experiment II) conditions in young healthy men. In a third experiment, the effect of scopolamine, a muscarinic acetylcholine receptor antagonist, on HPA secretory activity after physiological stimulation was tested. The experiments started between 09.00 and 10.00 a.m.. After a resting period of 1.5 h, either physostigmine (0.0125 mg per kg body weight soluted in isotonic saline) or placebo (saline) was infused within 15 min. In experiment I subjects (n = 7) remained fasting while in experiment II (n = 18) a standardized lunch was offered after the infusion. Experiment III (n = 7) was designed as experiment II but instead of physostigmine, scopolamine or placebo (0.5 mg) was subcutaneously injected 105 min before the meal. Blood for the determination of ACTH and cortisol was drawn in regular intervals during the experiments. Physostigmine did not change basal ACTH and cortisol secretion per se, excluding activation of basal HPA secretion due to acetylcholineesterase inhibition and its non specific side effects. Meal intake stimulated ACTH and cortisol secretion which was significantly enhanced when physostigmine was administered (p < 0.05). Scopolamine did not influence the meal related ACTH and cortisol secretion. These findings demonstrate that cholinergic neurotransmission is able to increase ACTH and cortisol concentrations in humans. This effect seems to be complementary to other stimulatory neurotransmitter systems, and is functional during stimulated HPA secretory activity and not under basal conditions.

Entrainment of nocturnal pituitary-adrenocortical activity to sleep processes in man--a hypothesis

The 24 hr patterns of plasma ACTH and cortisol concentrations are characterized by prominent circadian and ultradian oscillations. Usually both, nadir and acrophase of the circadian rhythm occur during sleep. This led us to re-evaluated the temporal relationship between sleep processes and nocturnal plasma ACTH and cortisol levels and the impact of several types of sleep manipulation (sleep delay, sleep disruption, sleep prolongation, sleep deprivation, and reversal of the sleep-wake cycle). Pituitary-adrenocortical activity appeared to be linked to the cyclic process of nocturnal sleep with inhibitory influences present during the first two sleep cycles. After initiation of the third sleep cycle stimulatory effects of sleep prevailed, lasting until awakening. The sleep associated influences appeared to act in concert with influences of circadian oscillators and resulted in an amplification of the circadian rhythm of pituitary-adrenal activity; they were strong enough to entrain the circadian rhythm of the pituitary-adrenal system to the sleep-wake cycle, as long as phase delays were moderate. However, with acute sleep-wake reversals the sleep associated influences were masked by the dominant effects of the circadian clock. In contrast, GH secretion appeared to be controlled primarily be sleep-associated mechanism with only minor circadian influences.

Blocking AMPA receptor signalling by caroverine infusion does not affect counter-regulation of hypoglycaemia in healthy men

AIMS/HYPOTHESIS

Glutamatergic pathways are assumed to play a critical role in the hormonal stress response to hypoglycaemia. In rats, glutamate signalling at the amino-3-hydroxy-5-methyl-4-isoxazol propionate (AMPA) receptor contributes to hormone release induced by behavioural stressors. We hypothesised that blocking the AMPA receptor by caroverine in healthy men would impair their perception of neuroglycopenia and thereby diminish hormonal counter-regulation as well as symptoms of hypoglycaemia, as a model of stress.

METHODS

In a balanced double-blind study, two hypoglycaemic clamp sessions (mean blood glucose 2.4 mmol/l for 50 min) were performed in ten healthy men during intravenous administration of 80 mg caroverine or placebo. We assessed concentrations of counter-regulatory hormones as well as subjective symptoms related to hypoglycaemia.

RESULTS

AMPA receptor antagonisation by caroverine did not influence the perception of neuroglycopenic and autonomic hypoglycaemia-associated symptoms (p > 0.39 for all). Notwithstanding, caroverine did increase basal and counter-regulatory glucagon secretion (p < 0.002) and slightly enhanced counter-regulatory growth hormone concentrations (p = 0.07). Counter-regulatory release of ACTH, cortisol, adrenaline (epinephrine) and noradrenaline (norepinephrine) did not differ between conditions (p > 0.11 for all).

CONCLUSIONS/INTERPRETATION

Antagonising AMPA receptor signalling by caroverine infusion failed to diminish and even slightly amplified counter-regulatory hormone release during hypoglycaemia in healthy men. The discrepancy with previous findings in rats may be due to different dosages or administration routes and calls for further investigations on the role of AMPA receptor signalling in hypoglycaemia counter-regulation in humans.

Short-term nocturnal hypoglycaemia increases morning food intake in healthy humans

AIMS

Hypoglycaemia during wakefulness increases hunger and food intake. Patients with Type 1 diabetes mellitus are at high risk of recurrent hypoglycaemia and weight gain. Given the background of frequent hypoglycaemic episodes during night-time sleep in diabetic patients, we investigated morning food intake after nocturnal hypoglycaemia.

METHODS

We tested 16 healthy normal-weight subjects (eight women) on three nights. A linear fall in plasma glucose to a nadir of 2.2 mmol/l within 60 min was induced by insulin infusion immediately after sleep onset ('early hypo') or after about 3.5 h of sleep ('late hypo'). On a control night, no hypoglycaemia was induced. Spontaneous food intake at a breakfast buffet was registered on the subsequent morning.

RESULTS

Compared with the control condition (700 +/- 93 kcal), subjects ate more after 'late hypo' (867 +/- 108 kcal; P = 0.041), but not after 'early hypo' (852 +/- 111 kcal; P = 0.130). Analyses of macronutrient fractions revealed that in comparison with the control condition, subjects ate significantly more carbohydrates after both 'late hypo' (277 +/- 25 kcal vs. 206 +/- 23 kcal, P < 0.001) and 'early hypo' (245 +/- 23 kcal, P = 0.048), with this effect being more pronounced after late than early nocturnal hypoglycaemia (P = 0.026).

CONCLUSIONS

In healthy subjects, nocturnal hypoglycaemia during sleep stimulates spontaneous food intake the following morning, with carbohydrate intake being especially affected. Effects were more pronounced after 'late hypo', suggesting the influence of temporal dynamics. Although healthy non-diabetic subjects were studied, similar mechanisms may contribute to the frequently observed body weight gain in insulin-treated diabetic patients.

Obese men respond to cognitive but not to catabolic brain insulin signaling

CONTEXT AND OBJECTIVE

Insulin acts in the brain to reduce food intake and body weight and is considered a major adiposity signal in energy homeostasis. In normal-weight men, intranasal insulin administration reduces body fat and improves declarative memory. The present experiments aimed to generalize these findings to obese patients, with a view to evaluate the therapeutic potential of the compound.

DESIGN, SUBJECTS AND MEASUREMENTS

Insulin and placebo, respectively, were intranasally administered four times a day (amounting to 160 IU day(-1)) over 8 weeks to two groups of 15 obese men each.

RESULTS

Contrasting with the catabolic effects in normal-weight men, insulin treatment did not induce any significant reduction of body weight (P>0.50) and body fat (P>0.44) in the obese subjects. However, in accordance with the effects in normal-weight men, declarative memory and mood were improved (P<0.05) and hypothalamic-pituitary-adrenal axis activity as assessed by circulating ACTH (P<0.01) and cortisol levels (P<0.04) was reduced.

CONCLUSIONS

Our results indicate that in obese men, intranasal insulin is functionally active in the central nervous system but fails to affect the neuronal networks critically involved in body weight regulation. We conclude that obesity in men is associated with central nervous resistance to the adiposity signal insulin. This defect likely contributes to the persistence of obesity in spite of elevated levels of circulating insulin in obese patients.

PreproTRH(158-183) fails to affect pituitary-adrenal response to CRH/vasopressin in man: a pilot study

Non-glucocorticoid inhibitors of the HPA-system are of utmost interest in the treatment of diseases with impaired regulation of this system, like the metabolic syndrome and depression. In rats, a fragment of the thyreotropin-releasing hormone (TRH) preprohormone, preproTRH((178-199)), has been demonstrated to inhibit basal and stimulated secretion of cortisol. Our pilot study aimed to explore the first time similar effects of the homologue peptide preproTRH((158-183)) in healthy humans. In a double-blind within-subject comparison, eight healthy young men were infused intravenously with placebo and preproTRH((158-183)) at varying doses of 5, 10, 25 and 50 mg/kg of body weight. After 15 min of infusion a corticotropin-releasing hormone (CRH)/vasopressin-test was performed. Plasma concentrations of pituitary hormones and free thyroxine, blood pressure, heart rate and feelings of activation and mood were assessed repeatedly at close intervals. Individual hormone profiles and collapsed data across all doses did not reveal any effects of preproTRH((158-183)) on HPA-activity, although it increased TSH and fT4, stimulated the release of GH and increased systolic blood pressure in the course of the experiment (p<0.05, for all effects). Self-reports indicated enhanced feelings of activation and general well-being following preproTRH (p<0.05). Our data exclude a substantial inhibitory effect of preproTRH((158-183)) on HPA secretory activity and, thus, contrast with findings in rats. In humans, the peptide appears to even exert an albeit weak stimulatory effect on autonomic stress systems as indicated by increased cardiovascular activity in combination with enhanced subjective arousal.

Plasma glucagon decreases during night-time sleep in Type 1 diabetic patients and healthy control subjects

AIMS

In Type 1 diabetes mellitus (T1DM), the glucagon response to hypoglycaemia is known to disappear within a few months after the onset of the disease, whereas the response to other stimuli remains intact. The dynamics of spontaneous glucagon release have rarely been assessed. We monitored spontaneous glucagon release in T1DM patients and healthy subjects during a 7-h period of night-time sleep.

METHODS

Measurements were made in 14 T1DM patients and 14 control subjects matched for age, gender and body mass index after one night's adaptation in our laboratory. Circulating glucose, insulin and glucagon concentrations were measured at 30-min intervals. In diabetic patients, hypoglycaemia (< 3.9 mmol/l) was avoided by infusion of glucose whenever necessary.

RESULTS

During the entire night, plasma glucose and serum insulin levels were higher in T1DM patients than in healthy subjects (P < 0.03 and P < 0.001, respectively). Plasma glucagon concentrations decreased throughout the night in both groups (P < 0.001). Glucagon levels were similar in T1DM patients and healthy subjects (P > 0.87). The duration of diabetes (less and more than 5 years) did not affect glucagon secretion (P > 0.87).

CONCLUSIONS

Plasma glucagon levels decrease significantly during night-time sleep in healthy control subjects. This nocturnal decrease is preserved in T1DM patients regardless of the duration of diabetes. These observations point to distinct nocturnal regulation of spontaneous glucagon release that does not depend on circulating glucose and insulin levels and is unaltered in T1DM patients.

Mood and Cognitive Functions During Acute Euglycaemia and Mild Hyperglycaemia in Type 2 Diabetic Patients

INTRODUCTION

Hyperglycaemia at levels above 15 mmol/l has been shown to impair cognitive functions in type 2 diabetic patients, while effects of mild hyperglycaemia and acute euglycaemia on mood and cognition have rarely been compared. We examined mood and cognitive functions in patients with T2DM during acute euglycaemia in comparison with moderate hyperglycaemia.

METHODS

One euglycaemic (5 mmol/l) and one hyperglycaemic clamp (10.5 mmol/l) of 90 min each were performed in 15 T2DM patients in a balanced, single-blind, within-subject comparison. Mood, cognitive functions (assessed via short-term memory and attention tests) and symptoms related to glycaemic changes were assessed during a baseline period and during both glycaemic plateaus. In addition, patients estimated their blood glucose level and counterregulatory hormones were measured.

RESULTS

None of the assessed aspects of cognitive functions differed between conditions (all p > or = 0.2). Patients rated higher on the well-being scale (p=0.04) and tended to feel less anger (p=0.08) during hyperglycaemia. Self-estimated blood glucose levels were higher during the hyper- than euglycaemic condition (8.6 +/- 2.5 vs 7.2 +/- 1.2 mmol/l; p<0.05) although most individual estimations did not match the actual glucose levels. Counterregulatory hormone levels did not differ (all p>0.25).

CONCLUSIONS

Data indicate that T2DM patients are not cognitively impaired by moderate hyperglycaemia (10.5 mmol/l), pointing to the possibility of a glycaemic threshold for cognitive impairments at higher glycaemic levels.

Causes of obesity: looking beyond the hypothalamus

The brain takes a primary position in the organism. We present the novel view that the brain gives priority to controlling its own adenosine triphosphate (ATP) concentration. It fulfils this tenet by orchestrating metabolism in the organism. The brain activates an energy-on-request system that directly couples cerebral supply with cerebral need. The request system is hierarchically organized among the cerebral hemispheres, the hypothalamus, and peripheral somatomotor, autonomic-visceromotor, and the neuroendocrine-secretomotor neurons. The system initiates allocative behavior (i.e. allocation of energy from body to brain), ingestive behavior (intake of energy from the immediate environment), or exploratory behavior (foraging in the distant environment). Cerebral projections coordinate all three behavioral strategies in such a way that the brain's energy supply is guaranteed continuously. In an ongoing learning process, the brain's request system adapts to various environmental conditions and stressful challenges. Disruption of a cerebral energy-request pathway is critical to the development of obesity: if the brain fails to receive sufficient energy from the peripheral body, it compensates for the undersupply by increasing energy intake from the immediate environment, leaving the body with a surplus. Obesity develops in the long term.