Methoscopolamine inhibition of sleep-related growth hormone secretion. Evidence for a cholinergic secretory mechanism

Reciprocal interactions between the GH axis and sleep

For more than 30 years, growth hormone (GH) has been observed to be preferentially secreted during deep, slow-wave sleep (SWS). However, the mechanisms that underlie this robust relationship that links anabolic processes in the body with behavioral rest and decreased cerebral metabolism remain to be elucidated. Current evidence indicates that GH secretion during the beginning of sleep appears to be primarily regulated by GH-releasing hormone (GHRH) stimulation occurring during a period of relative somatostatin withdrawal, which also is associated with elevated levels of circulating ghrelin. Apparently, two populations of GHRH neurons need to be simultaneously active to stimulate, in a coordinated fashion, SWS and pituitary GH release. Pharmacological interventions that are capable of increasing the duration and/or the intensity of SWS such as oral administration of gamma-hydroxybutyrate (GHB), also increase the rate of GH release. Because the normal negative feedback exerted by GH on central GHRH is inoperative in patients with GH deficiency, it is possible that the decreased energy levels and fatigue often reported by GH-deficient adults partly reflect an alteration in sleep-wake regulation. Preliminary data from a sleep study of adults with GH deficiency using wrist actigraphy for 6 nights at home and polysomnography in the laboratory indeed show decreased total sleep time and increased sleep fragmentation in GH-deficient patients as compared with normal controls.

Neuroendocrine control of growth hormone secretion

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.

Sleep electroencephalographic response to muscarinic and serotonin1A receptor probes in patients with major depression and in normal controls

BACKGROUND

To test the hypothesis that depression is associated with an increased ratio of cholinergic to serotonergic neurotransmission, we compared the effects of pilocarpine, a muscarinic agonist, and ipsapirone, a serotonin (5-HT)1A agonist, on electroencephalographic (EEG) sleep in depressed and healthy subjects. We hypothesized, adopting the reciprocal interaction model, that the effects on REM sleep of these probes within the same individuals are negatively correlated and unmask neurobiological changes in depression.

METHODS

Polysomnographic recordings were obtained in 12 unmedicated patients with a current major depression and 12 normal controls. They received placebo, pilocarpine 25 mg, or ipsapirone 10 mg (orally, 15 min before bedtime, after premedication with the peripheral anticholinergic probanthine 30 mg, double blind, counterbalanced) on three occasions.

RESULTS

Pilocarpine shortened and ipsapirone prolonged REM latency equally in both groups. These effects were not correlated. Pilocarpine decreased slow-wave sleep and EEG delta power during the first nonREM episode more in controls than in patients, and enhanced EEG sigma power equally in both groups. Ipsapirone had no significant effects on EEG power.

CONCLUSION

These data do not support the postulate of muscarinic receptor up-regulation and 5-HT1A receptor down-regulation in depression. The significance of blunted delta power suppression in patients following pilocarpine warrants further investigations.

Involvement of brain catecholamines and acetylcholine in growth hormone hypersecretory states. Pathophysiological, diagnostic and therapeutic implications

Secretion of growth hormone (GH) is excessive in acromegaly, but also in a number of other pathological states such as anorexia nervosa, insulin-dependent diabetes mellitus (IDDM), liver cirrhosis, depression, renal failure and GH-insensitivity syndrome. Abnormalities in the neuroendocrine control of GH secretion and/or a state of insensitivity to GH contribute to hypersecretion of GH in these states, with the possible exception of acromegaly, which appears to be a primary pituitary disease. GH hypersecretion may also occur in neonates or adolescents with tall stature, thus reflecting particular physiological or paraphysiological conditions. In the cohort of brain neurotransmitters, catecholamines and acetylcholine reportedly play a major role in the control of neurosecretory GH-releasing hormone (GHRH) and somatostatin (SS)-producing neurons, and hence GH secretion. Activation of alpha 2-adrenoceptors or of muscarinic cholinergic receptors in the hypothalamus stimulates GH release, probably through stimulation of GHRH and inhibition of SS release, respectively. Activation of dopamine receptors likewise stimulates GH release, while activation of beta-receptors inhibits GH release through stimulation of hypothalamic SS function. This review discusses the involvement of brain catecholamines and acetylcholine in GH hypersecretory states, including anorexia nervosa, acromegaly, IDDM, liver cirrhosis, depression, renal failure and GH insensitivity syndrome, with a view to providing a fuller understanding of their pathophysiology and, whenever possible, diagnostic and therapeutic implications.

Effects of ritanserin, a specific serotonin-S2 receptor antagonist, on the release of anterior pituitary hormones during insulin-induced hypoglycemia in normal humans

The role of serotonin in the insulin hypoglycemia (IH) stimulated secretion of prolactin (PRL), growth hormone (GH), adrenocorticotropin (ACTH) and cortisol (F) was studied in a group of 12 normal subjects during the control period after placebo and a consecutive six-day treatment with 20 mg ritanserin (RIT) per day. RIT failed to affect the baseline levels of all the four hormones as well as the PRL response to IH (p > 0.5). The serum GH response to IH was moderately diminished after RIT, the reduction of integrated trapezoidal area under hormone curves (nAUC) being 50.7% +/- 6.9% (p < 0.005). Furthermore, RIT was found to slightly decrease the plasma ACTH response to IH, the reduction of nAUC being 36.3% +/- 2.6% (p < 0.005). Decrease in the corresponding plasma F response to IH was accompanied by 29.1% +/- 2.4% reduction of nAUC (p < 0.005). According to our results, serotonin-S2 receptors appeared to be moderately involved in IH-induced release of GH, but slightly in that of ACTH, leaving unaffected that of PRL.

Serum hormonal concentrations following transcendental meditation--potential role of gamma aminobutyric acid

Transcendental mediation (TM) is a stylized form of physical and mental relaxation which is associated with changes in the secretion and release of several pituitary hormones. The hormonal changes induced by TM mimic the effects of the inhibitory neurotransmitter gamma aminobutyric acid (GABA). It is hypothesized that TM produces changes in pituitary hormone secretion by enhancing hypothalamic GABAergic tone, and its anxiolytic effects by promoting GABAergic tone in specific areas of the brain. This mechanism is similar to the effects of synthetic anxiolytic and tranquilizing agents such as benzodiazepines that bind to components of the GABA-A (GABAA) receptor. TM, therefore, may produce relaxation by enhancing the effects of an endogenous neurotransmitter analogous to the effects of endorphins in runners who reportedly experience a 'runner's high'.

Neuroendocrine responses to intravenous infusion of arecoline in patients with Alzheimer's disease

We have reported that arecoline, a muscarinic receptor agonist replicably enhanced verbal memory in five of nine subjects with Alzheimer's disease (AD). To investigate the mechanism of cognitive improvement, circulating hormone measurements were made during high-dose acute and low-dose chronic intravenous (i.v.) arecoline administration to AD patients. Acute hormone responses were measured during, and for 6 h after, infusion of arecoline 5 mg i.v. over 30 min. Chronic responses were measured in cognitive responders during continuous i.v. infusion of arecoline escalating over 2 weeks (0.5-40 mg/day) and then during a 1 week infusion of the dose optimizing cognition (4-16 mg/day). Acute arecoline administered to 14 subjects produced unpleasant side-effects (e.g. nausea, vomiting), mean adrenocorticotrophic hormone (p = .0006), cortisol (p = .0001) and beta-endorphin (p = .0001) levels were elevated. During chronic arecoline treatment, no side-effects occurred and plasma cortisol, adrenocorticotrophic hormone and beta-endorphin levels were unchanged in nine subjects overall and in five cognitive responders. Thus, high-dose arecoline activates the hypothalamic-pituitary-adrenal (HPA) axis and may increase other anterior pituitary hormone levels, likely representing a 'stress response', but cognition-enhancing, low doses of arecoline do not produce a glucocorticoid response. Hence, arecoline-induced memory improvement is not due to the induction of 'stress' nor to the elevation of peripheral corticosteroid levels.

Radiation and neuroregulatory control of growth hormone secretion

OBJECTIVE

Cranial irradiation frequently results in growth hormone (GH) deficiency. Patients with radiation-induced GH deficiency usually remain responsive to exogenous growth hormone releasing hormone, implying radiation damages the hypothalamus rather than the pituitary. Little is known about the effect of cranial irradiation on the neuroendocrine control of GH secretion. This study was to determine the effect of cranial irradiation on somatostatin tone.

DESIGN

Somatostatin tone was examined by manipulating cholinergic tone in young adults with radiation-induced GH deficiency and a control population. Each individual underwent three separate studies: the GH response to 100 micrograms GHRH-(1-29)-NH2 was assessed alone, and 60 minutes after pyridostigmine or pirenzepine.

PATIENTS

Eight young male adults with radiation induced GH deficiency following treatment in childhood for a brain tumour or acute lymphoblastic leukaemia, and ten healthy adult men were studied.

MEASUREMENTS

Serum growth hormone was measured at 15-minute intervals throughout each of the three study periods.

RESULTS

One of 10 controls and four of eight irradiated subjects had a peak GH level to GHRH analogue of less than 20 mU/l. After pretreatment with pyridostigmine, all subjects except one irradiated subject had a peak GH level of greater than 20 mU/l. Pretreatment with pyridostigmine and pirenzepine significantly modified the GH response to GHRH analogue within both groups (P < 0.0005). Pretreatment with pyridostigmine significantly enhanced the GH response to GHRH analogue (median (range) area under the curve, 9029 (1956-20940) mU/l/min in controls vs 1970 (628-3608) mU/l/min in the irradiated group) compared with GHRH analogue alone (1953 (512-16140) mU/l/min in control group vs 997 (266-3488) mU/l/min in the irradiated group). Pretreatment with pirenzepine significantly attenuated the GH response to GHRH analogue (552 (64-1274) mU/l/min in controls vs 305 (134-2726) mU/l/min in irradiated group). Between the groups there was no significant difference in GH area under the curve (AUC) after GHRH analogue alone. There was a significantly (P = 0.0014) greater increment of GH secretion after pyridostigmine and GHRH analogue compared with GHRH analogue alone (difference in AUC of pyridostigmine+GHRH analogue and GHRH analogue alone 6348 (696-12856) mU/l controls vs 542 (120-1340) mU/l in the irradiated group) and significantly (P = 0.033) greater suppression of GH secretion after pirenzepine and GHRH analogue compared with GHRH analogue alone (difference in AUC of GHRH analogue alone and pirenzepine+GHRH analogue 1644 (222-15205) mU/l in controls vs 479 (469-1623) mU/l in the irradiated group) in the control population compared with those who had received cranial irradiation in childhood.

CONCLUSIONS

These data suggest that cranial irradiation reduces but does not abolish somatostatin (SRIH) tone and also reduces endogenous GHRH secretion. Although SRIH tone is reduced, it can be increased by cholinergic manipulation and is therefore not irreversibly fixed. This has possible implications if GHRH analogues were used to treat children with radiation induced GH deficiency.

Lack of involvement of the cholinergic mechanism in vasoactive intestinal peptide- and peptide-histidine methionine-induced growth hormone (GH) responses in acromegaly: comparison with the GH responses to thyrotropin-releasing hormone and GH-releasing hormone

We examined whether the cholinergic mechanism is involved in the paradoxical GH responses to vasoactive intestinal peptide (VIP) and peptide histidine methionine (PHM) in acromegaly. 28 patients with active acromegaly underwent i.v. bolus injections of thyrotropin-releasing hormone (TRH, 500 micrograms), GH-releasing hormone (GHRH, 100 micrograms), VIP (100 micrograms), and PHM (100 micrograms) with or without a prior atropine treatment (1 mg, i.m., 30 min before). Blood samples were collected before and at intervals up to 120 min after the injection, and plasma GH levels were measured. In response to TRH, GHRH, VIP and PHM, 23 (82%), 24 (86%), 13 (46%) and 7 (25%) patients, respectively, responded with a significant GH increase (> 50% and 6 micrograms/l above the basal level). The effect of atropine pretreatment was examined in only these responders to the respective peptides. When the GH responses were estimated by the area under the response curve, the atropine pretreatment was able to significantly suppress the GH response to GHRH, but not to TRH, VIP, or PHM. Although the lack of cholinergic involvement in the TRH-induced GH release in acromegaly is confirmatory to previous reports, the same results with the VIP- and PHM-induced GH release are novel. The present study may suggest that in acromegaly the physiological GH response is mediated by the cholinergic mechanism, but the paradoxical ones are not.

Influence of partial sleep deprivation on the secretion of thyrotropin, thyroid hormones, growth hormone, prolactin, luteinizing hormone, follicle stimulating hormone, and estradiol in healthy young women

The influence of partial sleep deprivation during the second half of the night on the secretion of thyroid stimulating hormone (TSH), thyroxin (T4), free T4 (fT4), triiodothyronine (T3), prolactin (PRL), growth hormone (GH), luteinizing hormone (LH), follicle stimulating hormone (FSH), and estradiol (E2) was investigated in 10 healthy young women. Blood samples were drawn at hourly intervals over a 64-hour period (i.e., 3 consecutive days and nights). During night 2, all subjects were awakened at 1:30 a.m. During partial sleep deprivation, TSH concentrations increased significantly and remained elevated throughout the following day. Levels of T4, fT4, and T3 were enhanced during the partial sleep deprivation hours only, and changes in these hormones seemed to be independent of TSH. PRL levels decreased, LH and E2 concentrations increased, and GH and FSH secretion remained unchanged during partial sleep deprivation. This pattern of change of different endocrine axes during partial sleep deprivation resembles those seen after total sleep deprivation, suggesting that similar neurochemical changes are induced by both forms of antidepressant therapy. The late evening GH peak occurred almost exclusively before the onset of sleep. Partial sleep deprivation did not influence the chronobiological profiles of any of the hormones investigated. The chemical changes underlying these alterations are speculated to involve enhancement of central norepinephrine and dopamine activity with a concomitant increase in the activity of the sympathetic nervous system.

Eptastigmine augments basal and GHRH-stimulated growth hormone release in young and old dogs

The aim of the present work was to evaluate the effect on the growth hormone (GH) secretion of eptastigmine, a new long-acting cholinesterase inhibitor, in unanesthetized beagle dogs. In a first study, 5 young dogs were given single doses (0.5, 1.0, and 2.0 mg/kg, i.m.) of the drug or saline in a randomized cross-over manner. Blood samples were collected immediately before and, at regular intervals, until 150 min after drug injection. GH plasma concentrations were determined by radioimmunoassay. Plasma cholinesterase activity was measured with a potentiometric method. There was a significant logistic relationship (r = 0.601, P < 0.01) between the administered dose of eptastigmine and the log-transformed areas under the GH plasma concentration-time curve (AUC) with a calculated ED50 for eptastigmine of 0.63 +/- 0.36 mg/kg. There was also a significant linear relationship (r = 0.630, P < 0.01) between log-transformed AUC of GH levels and AUC of plasma cholinesterase activity. In a second study we evaluate the ability of eptastigmine (2.0 mg/kg, i.m.) to potentiate the GH-releasing effect of the GH-releasing hormone (GHRH, 2.0 micrograms/kg, i.v.) in young and old dogs. Eptastigmine was administered 45 min before GHRH and blood collected every 15 min until 90 min after GHRH injection. In young dogs, maximum GH plasma levels (Cmax) were 6.1 +/- 1.0 ng/ml after GHRH compared to 22.5 +/- 2.3 ng/ml after GHRH preceded by eptastigmine (P < 0.01). In old animals, Cmax were 4.6 +/- 1.4 ng/ml after GHRH vs 13.2 +/- 7.4 ng/ml after combined administration of GHRH and eptastigmine (P < 0.05). These data indicate that eptastigmine is very effective in augmenting basal and stimulated GH secretion in old dog. The good activity also shown in old animals suggests a potential use of this drug to reverse the age-dependent decline in GH secretion responsible for many involutional changes of aging.

Nocturnal cortisol, thyroid stimulating hormone, and growth hormone secretory profiles in depressed adolescents

Twelve depressed adolescents and 12 controls matched for age, sex, Tanner stage, time of menstrual cycle (females), weight, and time of year assessed were studied over 3 nights. Measurements for cortisol, thyroid stimulating hormone, and growth hormone were made on serum collected at 10 P.M., 12 midnight, 1 A.M., 2 A.M., 3 A.M., 4 A.M., and 6 A.M. in eight pairs and every 20 minutes from 8 P.M. to 7 A.M. in four pairs. Cortisol secretion did not significantly differentiate the groups. Thyroid stimulating hormone secretion was significantly elevated in the depressed group at one time point. Growth hormone secretion significantly differentiated the two groups at most time points, and the depressed adolescents significantly hypersecreted growth hormone (area under the curve). Implications for the diagnosis, etiology, and treatment of adolescent depression are discussed.

Diagnostic and pharmacological approaches in Alzheimer's disease

Alzheimer's disease is a chronic progressive disease affecting higher intellectual functioning. The clinical diagnosis is made when the onset of illness is insidious, the course slowly progressive and all the treatable causes of dementia have been ruled out. The use of more stringent criteria has improved clinical diagnosis, but at best only 80% of patients are accurately diagnosed. Ultimately the diagnosis depends upon pathological confirmation. The neuritic plaques and neurofibrillary tangles described by Alzheimer, although not pathognomonic for the disease, continue to be the basis for pathological diagnosis. The aetiology and pathophysiology of Alzheimer's disease are presently unknown. Epidemiological studies have suggested a genetic basis for the disorder, and many biochemical studies have linked it to degeneration of central cholinergic neurons, and possibly to abnormalities of other neurotransmitter systems. A marker which would permit accurate diagnosis early in the course of disease would be of major importance to researchers and clinicians alike. No marker has been found to date, although recent research results are promising. Various pharmacological strategies have been employed in the treatment of Alzheimer's disease. More recently attempts have focused on enhancing central cholinergic transmission. Despite the well-founded rationale for these studies, results have been modest.

Nocturnal growth hormone secretion does not affect diurnal variations in arginine and glucose-stimulated insulin secretion

There is a diurnal variation in insulin secretion, with higher values in the morning (AM) than in the afternoon (PM). This study tested the hypothesis that nocturnal human growth hormone (hGH) secretion might be the mechanism producing this diurnal variation in insulin secretion. Six healthy normal-weight men were studied on four occasions: twice in the early morning (AM) and twice in the afternoon (PM). Oral methscopolamine (Pamine), an anticholinergic agent that blocks hGH release, was administered at bedtime prior to the AM study or before breakfast for the PM study. An index of insulin secretion in all four tests was obtained from measurement of the acute release of insulin in response to two intravenous (IV) boluses of arginine, one given basally and the other given after raising glucose levels to approximately 150 mg/dL above the baseline. Insulin secretion was significantly greater in the morning than in the afternoon in both control and methscopolamine-pretreated subjects. The mean peak hGH was reduced in subjects pretreated with oral methscopolamine. Drug treatment reduced insulin secretion proportionally in the morning and afternoon. These results suggest that the diurnal insulin response to stimulation with arginine during a hyperglycemic clamp persists despite complete suppression of hGH by anticholinergic blockade, and that the diurnal insulin secretion is not caused by sleep- or meal-induced GH secretion.

Neuroendocrinological investigations during sleep deprivation in depression. II. Longitudinal measurement of thyrotropin, TH, cortisol, prolactin, GH, and LH during sleep and sleep deprivation

Thyrotropin (TSH), thyroxin (T4), triiodothyronine (T3), free T3 (fT3), cortisol, prolactin, and human growth hormone (HGH) were measured every 2 hr during a night of sleep, the following day, and a night of sleep deprivation (SD) in 14 patients with major depressive disorder. In subgroups fT4 (n = 5), reverse T3 (rT3), and luteinizing hormone (LH) (n = 6) were also investigated. Significant increases in TSH, T4, fT4, T3, fT3, rT3, and cortisol and decreases in prolactin levels occurred during the night of SD, compared to the pattern during the night of sleep. The pre-SD T4 and T3 levels of the responders to SD were already higher than in the nonresponders, and increased less during SD. The cortisol and HGH concentrations of the responders rose higher during SD than those of the nonresponders. Changes in TSH and prolactin were not correlated to clinical response. Analysis of possible neurochemical mechanisms underlying this "pattern" of changes in different endocrine profiles suggests that enhanced noradrenergic activity might play a role in the changes in TSH, cortisol, thyroid hormones, and possibly HGH secretion during SD, and increased dopaminergic tone probably induced the decline in prolactin levels. Additional effects of the serotonergic system cannot be excluded at present. In conclusion, the data suggest that enhanced noradrenergic activity of the locus coeruleus stimulates alpha and/or beta adrenergic receptors in depressed patients during SD. This mechanism could well be involved in the antidepressant effect of this therapy.

A reexamination of the relationship between growth hormone secretion and slow wave sleep using delta wave analysis

Sleep onset growth hormone secretion is a reliable and reproducible finding in young adults and children. Secretion typically occurs during the first non-REM period of sleep and, despite some evidence to the contrary, growth hormone secretion has frequently been associated with the first period of slow wave sleep. By measuring delta wave activity (0.5-2 Hz) instead of slow wave sleep and, accounting for the within subject variability, it has not been possible to demonstrate a consistent or statistically significant linear relationship between delta wave activity and sleep-related growth hormone secretion. This suggests the presence of more complex mediating factors and the possibility that sleep onset and growth hormone secretion are two separate processes which are independently stimulated by events associated with sleep onset.

Muscarinic receptor activity change after prolonged treatment with growth hormone and somatostatin

1. The effect of 10-day treatment with growth hormone (GH) (1 mg/kg body weight day) and somatostatin (SRIF) (0.25 mg/kg body weight day) subcutaneously on the activity of muscarinic (M) receptors in rat hypothalamic, pituitary and cerebral cortical membrane fractions was studied using (3H)quinuclidinyl benzylate [(3H)QNB] as radioligand. 2. The administration of GH and SRIF significantly decreased the M-receptor binding affinity in the hypothalamus. 3. In the pituitary the M-receptor affinity was increased after both GH and SRIF treatment. 4. In the hypothalamus and the pituitary the binding capacity of muscarinic receptors was unchanged. 5. In the cerebral cortex the chronical GH injection induced an increase in the number of antagonist binding sites and a decrease of their affinity, while the similar SRIF treatment led to an increase of the binding affinity without any change of M-receptor capacity. 6. These results indicate that GH and SRIF selectively and region-specifically modulate muscarinic receptor binding affinity and capacity and provide new insight into the feedback regulatory mechanisms of GH secretion.

The paradoxical response of growth hormone (GH) to thyrotropin-releasing hormone (TRH) in constitutionally tall children involves a cholinergic pathway

To investigate whether or not a cholinergic pathway is involved in the paradoxical response of GH to TRH in constitutionally tall children, we studied 8 healthy prepubertal children aged 4 2/12-7 10/12 yr, whose heights were over the 95th percentile of the NCHS tables. We defined as "paradoxical" a GH increment greater than 5 ng/ml in response to TRH. Five out of 8 children showed a paradoxical response of GH to TRH (mean GH peak after TRH of 10.7 +/- 1.1 ng/ml). Pretreatment with atropine (0.01 mg/kg IM 30 min prior to the TRH administration) abolished the TRH induced GH rise (peak GH after TRH of 1.5 +/- 1.0 ng/ml, p less than 0.01) but did not modify the TSH response (peak TSH after TRH: basal conditions 8.7 +/- 0.8 microU/ml, post atropine: 9.5 +/- 1.4 microU/ml, p greater than 0.05). Our results demonstrate that a cholinergic pathway is involved in the paradoxical response of GH to TRH in constitutionally tall children.

Clonidine-induced growth hormone secretion in elderly patients with senile dementia of the Alzheimer type and major depressive disorder

This study was undertaken to assess the value of growth hormone (GH) response to clonidine as a tool in the differential diagnosis between depression and dementia. This response is known to be blunted in depression, and neurochemical changes observed in senile dementia of the Alzheimer type (SDAT) could lead to an up-regulation of GH secretion. No difference was observed between GH response in depressed and demented patients. Together with studies on GH basal secretion in Alzheimer's disease, this finding suggests that the final consequence of SDAT-related changes in an accentuation of the effects of aging on GH reactivity.

Cholinergic muscarinic blockade produces short-term suppression of growth hormone secretion in children with tall stature

We have studied the effects of oral pirenzepine (50 mg twice daily) on growth and growth hormone (GH) secretion in 10 children with tall stature (9F, 1M). Suppression of GH secretion was observed in all children for 2-3 h after drug administration but was followed by rebound secretion of GH after 4-6 h. Consequently there was little overall change in GH secretion. In the dose regimen used the disruption of normal pulsatile GH secretion was not sufficiently significant to change final or predicted heights.

Cholinergic muscarinic receptor blockade with pirenzepine abolishes slow wave sleep-related growth hormone release in young patients with insulin-dependent diabetes mellitus

Cholinergic receptor blockade has been shown to abolish GH secretion in a variety of physiological and pharmacological situations in normal subjects. We have investigated the effect of pirenzepine on nocturnal GH secretion in young adult patients with Type I insulin-dependent diabetes mellitus. Five patients (three male, two female; aged 20-27 years) were studied in a randomized order on two days separated by at least 1 week. All patients showed episodes of slow wave sleep on each occasion and this was followed by peaks of GH release when placebo alone was administered (range of GH peaks 6-115 mU/l). In contrast, cholinergic muscarinic receptor blockade with pirenzepine (100 mg orally at 2200 and 2400 h) completely abolished nocturnal GH release in each individual without altering the occurrence of slow wave sleep itself. Mean plasma glucose levels at each sampling time between each study did not differ significantly. The ability to abolish nocturnal GH secretion may be important in the field of diabetes, since excess GH secretion is implicated in several acute metabolic and chronic microvascular complications of the disease.

Antemortem markers of Alzheimer's disease

This review examines various approaches to the development of antemortem markers of Alzheimer's disease. Among the procedures discussed are: neurochemical and histopathologic studies of the cholinergic system, concentrating on CSF and blood plasma; genetic studies; imaging and electrophysiological studies; and neuroendocrine studies.

Atropine selectively blocks GHRH-induced GH secretion without altering LH, FSH, TSH, PRL and ACTH/cortisol secretion elicited by their specific hypothalamic releasing factors

The role of acetylcholine in the regulation of the hypothalamo-pituitary system in man was assessed using atropine, which selectively blocks cholinergic muscarinic receptors. Paired tests were performed in 10 normal men using either GHRH (1 microgram/kg i.v.), or TRH (300 micrograms i.v.) plus LHRH (100 micrograms i.v.) plus corticotrophin releasing hormone (CRH) (1 microgram/kg i.v.) with or without atropine given 30 min previously (1 mg i.m.). The GHRH-induced GH secretory peak (17.8 +/- 3.0 ng/ml) was completely blocked by atropine administration (2.8 +/- 0.6 ng/ml) (P less than 0.05). Atropine did not, however, modify TRH-induced TSH and PRL secretion, nor FSH and LH release induced by the LHRH pulse. ACTH/cortisol secretion elicited by CRH was also unaffected by atropine. These results suggest that atropine blockade of GHRH-induced GH secretion is highly specific, and constitutes an indication of the importance of cholinergic control of GH function. Furthermore, atropine's lack of action on the other pituitary hormones rules out the possibility that it acts non-specifically, i.e. via blood flow changes or toxic effects.

Cholinergic muscarinic receptor blockade with pirenzepine abolishes slow wave sleep-related growth hormone release in normal adult males

Cholinergic pathways play an important role in the regulation of GH secretion from the anterior pituitary gland, and in this study we have investigated whether cholinergic muscarinic receptor blockade with pirenzepine displayed any inhibitory action on slow wave sleep-related GH release in normal subjects. Six adult males (ages 24-37 years) were studied in a randomized order and fasted from 1800 h on each study day. All subjects showed episodes of slow wave sleep on each occasion and this was followed by peaks of GH release when placebo alone was administered (range of GH peaks 4-50 mU/l). In contrast, pirenzepine treatment (100 mg p.o. at 2200 and 2400 h) completely abolished nocturnal GH release in each individual without altering the occurrence of slow wave sleep itself. These data demonstrate clearly that cholinergic muscarinic receptor blockade completely abolishes slow wave sleep-related GH release in normal adult subjects. Because of the striking effects it is reasonable to conclude that acetylcholine plays an important stimulatory role in mediating slow wave sleep-related GH release. This finding may have investigational and therapeutic applications in young patients with Type 1 diabetes mellitus since GH is implicated in some acute metabolic and chronic microvascular complications of this disease.

Growth hormone neurosecretory dysfunction

The basis for understanding clinical disorders in the neuroregulation of GH secretion is derived from the complexity of the CNS-hypothalamic-pituitary axis. Studies in animals and humans demonstrate an anatomic, physiological and pharmacological evidence for neurosecretory control over GH secretion including neurohormones (GRH, somatostatin), neurotransmitters (dopaminergic, adrenergic, cholinergic, serotonergic, histaminergic, GABAergic), and neuropeptides (gut hormones, opioids, CRH, TRH, etc). The observation of a defect in the neuroregulatory control of GH secretion in CNS-irradiated humans and animals led to the hypothesis of a disorder in neurosecretion, GHND, as a cause for short stature. We speculate that in this heterogeneous group of children a disruption in the neurotransmitter-neurohormonal functional pathway could modify secretion ultimately expressed as poor growth velocity and short stature.

Nicotinic-cholinergic involvement in arginine-vasopressin response to insulin-induced hypoglycemia in normal men

In order to establish whether arginine-vasopressin (AVP) release in response to insulin-induced hypoglycemia is mediated by a muscarinic and/or nicotinic cholinergic pathway, 12 normal men had an insulin tolerance test (ITT) in basal conditions and after treatment with the muscarinic receptor blocker pirenzepine (40 mg IV (intravenously) ten minutes before ITT in six subjects) or the nicotinic receptor antagonist trimethaphan (0.3 mg/min X 30 min IV before ITT in six subjects). The drugs did not modify arterial blood pressure nor produce side effects capable of altering AVP secretion. Pirenzepine administration did not change AVP response to hypoglycemia, whereas trimethaphan significantly reduced AVP increase by about 50% during the ITT. These data suggest the involvement of a cholinergic-nicotinic mechanism in regulation of AVP response to hypoglycemia.

Lack of effect of muscarinic cholinergic blockade on the GH responses to GRF 1-29 and TRH in acromegalic subjects

It is well known that muscarinic cholinergic blockade either reduces or abolishes stimulated GH release in normal subjects. In this study we have investigated whether cholinergic muscarinic blockade could reduce the GH responses to GRF 1-29 and TRH in acromegalic subjects. Eight acromegalic subjects underwent two GRF tests (GRF 1-29, 1 microgram/kg i.v.) with and without pirenzepine (0.6 mg/kg, i.v.). A further four of these patients received TRH (200 micrograms/kg, i.v.) on separate occasions with and without pirenzepine (0.6 mg/kg, i.v.). Cholinergic muscarinic blockade did not alter the GH responses to GRF and TRH in patients with acromegaly. These findings are in contrast with previous data reported on the effects of cholinergic blockade on stimulated GH levels in normal subjects and in patients with type I diabetes mellitus and are compatible with the view that somatotroph adenomas are functionally disconnected from hypothalamic control mechanisms.

Cholinergic but not serotonergic mediation of exercise-induced growth hormone secretion

In order to clarify the roles of cholinergic and serotonergic neurotransmission in the mediation of exercise-induced growth hormone (GH) release, normal young volunteers of both sexes were studied. Exercise was for 20 minutes at 800 kpm for the men and 500 kpm for the women. Pretreatment with 0.4 mg atropine 1 hour prior to exercise, or with methysergide 2 mg po q 6 h for 48 hours prior to exercise, were used to evaluate the influence of cholinergic and serotonergic blockade, respectively. Five of the ten men studied failed to raise GH values with exercise, perhaps because the exercise was not vigorous enough for their high degree of fitness. Of three non-responders restudied, at the same workload, one responded on the second occasion. The mean peak GH with exercise 13.4 +/- 3.27 ng/ml, was reduced to 2.4 +/- 1.28 ng/ml (p less than 0.01) after atropine, but was unaffected by methysergide (15.2 +/- 6.58 ng/ml, p greater than 0.5). Prolactin did not rise with exercise, and was not affected by atropine, but lowered by methysergide as expected. Cholinergic neurotransmission therefore represents a key link in exercise-induced GH secretion, but serotonergic influences are probably not involved.

Clinical studies of the cholinergic deficit in Alzheimer's disease. I. Neurochemical and neuroendocrine studies

Autopsy studies indicating that cholinergic neurons are selectively lost in patients with Alzheimer's disease (AD) and senile dementia of the Alzheimer type (SDAT) suggest that peripheral markers for central cholinergic activity would be useful in diagnosis. The present studies found that cerebrospinal fluid (CSF) concentrations of acetylcholine (ACh) correlated with the degree of cognitive impairment (r = .70) in a sample of carefully diagnosed patients with AD/SDAT, but metabolites of other neurotransmitters were not related to cognitive state; this suggests that CSF ACh may be a valid measure of cholinergic degeneration. Cortisol and growth hormone were measured in plasma samples drawn from patients and controls every 30 minutes from 2100 to 1100 hours the next day. Mean plasma cortisol concentrations were higher in patients with AD/SDAT than in controls and correlated inversely with CSF methoxy-hydroxyphenylglycol (MHPG) (r = .61) and positively with degree of cognitive impairment (r = +.53); as anticholinergic drugs suppress cortisol this finding indicates that cortisol dysregulation may be a marker for abnormalities in other neurotransmitter systems, particularly the noradrenergic system. Growth hormone secretion was not different in patients and controls but was positively correlated with CSF MHPG (r = +.63).

The effects of cholinergic blockade on the growth hormone and prolactin response to insulin hypoglycaemia

The effect of cholinergic blockade on growth hormone (GH) and prolactin (PRL) secretion during insulin-induced hypoglycaemia was assessed in six normal male volunteers (mean age 23, age range 21-25). Each subject underwent two insulin tolerance tests with and without atropine. GH responses were significantly lower 45 min after insulin administration with atropine (17.5 +/- 2.5 mU/l (mean +/- SEM) than with placebo (37.6 +/- 3.6 mU/l, P less than 0.0006). In contrast PRL responses were higher (P less than 0.01) at 45 and 90 min after insulin during treatment with atropine. These data demonstrate that cholinergic mechanisms are involved in stimulatory and inhibitory pathways in the medication of the respective GH and PRL responses to insulin induced hypoglycaemia in man.

Inhibition of physiological growth hormone secretion by atropine

We have investigated the effects of atropine (specific muscarinic cholinergic inhibition) on the nocturnal secretion of GH during the first cycle of stage IV sleep in six normal volunteers and three tall adolescents. Atropine was administered orally in a dose of 0.6 mg (n = 8) or 1.8 mg (n = 4) 30 min before expected sleep and the sampling repeated. Peak GH level without atropine was 45.3 mU/l (range 5.7 to 92.0): both doses of atropine abolished sleep associated GH secretion. Spontaneous daytime GH secretion was demonstrated during five 6 h sampling periods in three normal adults. There was a significant decrease in spontaneous daytime GH secretion when the sampling was repeated after atropine 0.6 mg or 1.8 mg. We conclude that inhibition of GH secretion using anticholinergic drugs should be further investigated in the management of excessive growth hormone secretion.

Gonadotropin, prolactin and TSH secretion in patients with myasthenia gravis

Hypothalamic pituitary function was studied in 13 patients with myasthenia gravis. Gonadotropin, TSH, and prolactin dynamics were investigated using conventional provocative stimuli. No consistent abnormality was found in either gonadotropin or prolactin release. Abnormal TSH responses to TRH administration was present in six of the 13 patients in association with normal free thyroxine indices and the absence of antithyroid antibodies. This latter observation is relevant when the association of myasthenia gravis with hyperthyroidism, thyroiditis and hypothyroidism is considered.

A role for somatostatin in the control of hamster growth

Concentrations of somatostatin-like immunoreactivity (SRIF-LI) were measured in cerebral cortex, hippocampus, septum-POA, median eminence, gastric antrum, fundus and pancreas in adult female hamsters to determine whether changes in somatostatin could be related to increased growth hormone (GH) secretion and somatic growth that follow bilateral transections of hippocampus (n = 18; 17 controls). In addition, choline acetyltransferase (CAT) activity was measured in the four brain regions in hippocampectomized (n = 10) and control hamsters (n = 10) to gain insight into the relationship between these two neurotransmitters. Hippocampal transections induced: significant acceleration of somatic growth; increased serum GH concentrations; increased concentrations of SRIF-LI in septum-POA and gastric antrum; reduced concentrations of SRIF-LI in hippocampus and pancreas; and reduced CAT activity in the hippocampus. These results suggest that somatostatinergic and cholinergic projections to hippocampus via fornix suppress GH and somatic growth in adult hamsters and that reduced release of SRIF-LI in the gastric antrum may contribute to the acceleration of somatic growth through facilitated nutrient digestion and entry.

Motion sickness: a modulatory role for the central cholinergic nervous system

The present review has extended the general theory of motion sickness proposed by Wood and Graybiel [135, 136] by identifying specific neurophysiological mechanisms that are involved in motion sickness and by interpreting the actions of both scopolamine and amphetamine as effective anti-motion sickness drugs within this neurophysiological context. The neurochemical and neurophysiological effects of scopolamine have been reviewed in relationship to central cholinergic pathways. Cholinergic pathways have been associated with both the perception and expression of normal and excessive levels of motion stimuli. New approaches to the problem of the prevention of motion sickness have been considered. Efferent nicotinic innervation at the primary sensory hair cells and the medial vestibular nucleus were identified as sites where modulation by cholinergic drugs might exert a beneficial influence. However, it was generally conceded that the complexity of the cholinergic system and the interaction of scopolamine with that system left open the possibility that pharmacological doses of drugs specific to the cholinergic system might exert significant modulatory influences at alternative sites, as well.

Effects of propantheline bromide on basal growth hormone, cortisol and prolactin levels

Propantheline bromide, a peripheral anticholinergic drug with muscarinic and nicotinic blocking properties, was given by mouth to normal young men. Propantheline (45 mg) significantly lowered basal growth hormone concentrations at 0800 hr, 12 hr after administration. Propantheline (30 mg) tended (p = 0.08) to lower growth hormone concentrations at 1200 hr, 16 hr after administration. Cortisol and prolactin levels were not changed 12, 16 and 20 hr after propantheline (30 mg) nor 12 hr after propantheline (45 mg).

Growth hormone release after acute amitriptyline administration to normal human subjects

Single doses of the antidepressant amitriptyline were given to 12 normal males. After parenteral or oral dose of the drug, the concentration of growth hormone in plasma rose in one third of the subjects. Amitriptyline could have multiple and potentially opposite pharmacological actions on growth hormone. Antidepressants appear to be poor pharmacological tools for assessing the regulation of growth hormone release.

Muscarinic receptor blockade by pirenzepine: effect on prolactin secretion in man

The effect of pirenzepine, a muscarinic receptor blocker which does not cross the blood brain barrier, on basal and TRH-stimulated prolactin (PRL) secretion in normal subjects was studied. Administration of 75 mg oral pirenzepine had no effects on prolactin levels in male subjects whereas it significantly reduced prolactin in females. No effect on TRH induced prolactin secretion was observed.