Choline as an agonist: determination of its agonistic potency on cholinergic receptors

Antihypertensive Mechanism of Orally Administered Acetylcholine in Spontaneously Hypertensive Rats

Acetylcholine (ACh) acts as a neurotransmitter and neuromodulator. A small dose of eggplant powder rich in ACh (equivalent to 22 g fresh eggplant/d) has been shown to reduce blood pressure (BP) in individuals with higher BP. Here, we investigated the mechanisms underlying the antihypertensive effects of low-dose orally administered ACh in spontaneously hypertensive rats (SHRs). The effects of ACh on BP and sympathetic nervous activity (SNA), including lumbar SNA (LSNA) and renal SNA (RSNA), were evaluated by subjecting conscious SHRs to a telemetry method. Single oral administration of ACh decreased LSNA and lowered BP. Repeated oral administration of ACh for 30 d decreased RSNA and suppressed the elevated BP. Noradrenaline levels in the urine also decreased. However, vagotomy and co-administration of M3 muscarinic ACh receptor antagonist reversed the BP-lowering effect; the dynamics of non-absorbable orally administered ACh was revealed using stable isotope-labeled ACh. In conclusion, ACh acts on the gastrointestinal M3 muscarinic ACh receptor to increase afferent vagal nerve activity, which decreases SNA by autonomic reflex, suppressing noradrenaline release and lowering BP. This study suggests the use of exogenous ACh as an antihypertensive food supplement for controlling the autonomic nervous system, without absorption into the blood.

Effects of prenatal ethanol exposure on choline-induced long-term depression in the hippocampus

Choline is an essential nutrient under evaluation as a cognitive enhancing treatment for fetal alcohol spectrum disorders (FASD) in clinical trials. As a result, there is increased pressure to identify therapeutic mechanism(s) of action. Choline is not only a precursor for several essential cell membrane components and signaling molecules but also has the potential to directly affect synaptic mechanisms that are believed important for cognitive processes. In the current work, we study how the direct application of choline can affect synaptic transmission in the dentate gyrus (DG) of hippocampal slices obtained from adolescent (postnatal days 21-28) Sprague-Dawley rats (Rattus norvegicus). The acute administration of choline chloride (2 mM) reliably induced a long-term depression (LTD) of field excitatory postsynaptic potentials (fEPSPs) in the DG in vitro. The depression required the involvement of M1 receptors, and the magnitude of the effect was similar in slices obtained from male and female animals. To further study the impact of choline in an animal model of FASD, we examined offspring from dams fed an ethanol-containing diet (35.5% ethanol-derived calories) throughout gestation. In slices from the adolescent animals that experienced prenatal ethanol exposure (PNEE), we found that the choline induced an LTD that uniquely involved the activation of N-methyl-d-aspartate (NMDA) and M1 receptors. This study provides a novel insight into how choline can modulate hippocampal transmission at the level of the synapse and that it can have unique effects following PNEE.NEW & NOTEWORTHY Choline supplementation is a nutraceutical therapy with significant potential for a variety of developmental disorders; however, the mechanisms involved in its therapeutic effects remain poorly understood. Our research shows that choline directly impacts synaptic communication in the brain, inducing a long-term depression of synaptic efficacy in brain slices. The depression is equivalent in male and female animals, involves M1 receptors in control animals, but uniquely involves NMDA receptors in a model of FASD.

Choline or CDP-choline restores hypotension and improves myocardial and respiratory functions in dogs with experimentally - Induced endotoxic shock

Endotoxin shock is associated with severe impairments in cardiovascular and respiratory functions. We showed previously that choline or cytidine-5'-diphosphocholine (CDP-choline) provides beneficial effects in experimental endotoxin shock in dogs. The objective of the present study was to determine the effects of choline or CDP-choline on endotoxin-induced cardiovascular and respiratory dysfunctions. Dogs were treated intravenously (i.v.) with saline or endotoxin (LPS, 0.1 mg/kg) 5 min before i.v. infusion of saline, choline (20 mg/kg) or CDP-choline (70 mg/kg). Blood pressure, cardiac rate, myocardial and left ventricular functions, respiratory rate, blood gases, serum electrolytes and cardiac injury markers were determined before and at 0.5-48 h after endotoxin. Plasma tumor necrosis factor alpha (TNF-α), high mobility group box-1 (HMGB1), catecholamine and nitric oxide (NO) levels were measured 2 h and 24 h after the treatments. Endotoxin caused immediate and sustained reductions in blood pressure, cardiac output, pO₂ and pH; changes in left ventricular functions, structure and volume parameters; and elevations in heart rate, respiratory rate, pCO2 and serum electrolytes (Na, K, Cl, Ca and P). Endotoxin also resulted in elevations in blood levels of cardiac injury markers, TNF-α, HMGB1, catecholamine and NO. In choline- or CDP-choline-treated dogs, all endotoxin effects were much smaller in magnitude and shorter in duration than observed values in controls. These data show that treatment with choline or CDP-choline improves functions of cardiovascular and respiratory systems in experimental endotoxemia and suggest that they may be useful in treatment of endotoxin shock in clinical setting.

Efficacy of Long-Term Feeding of α-Glycerophosphocholine for Aging-Related Phenomena in Old Mice

α-Glycerophosphocholine (GPC) is a natural source of choline. It reportedly prevents aging-related decline in cognitive function, but the underlying mechanism remains unclear. Although it is understood that aging influences taste sensitivity and energy regulation, whether GPC exerts antiaging effects on such phenomena requires further elucidation. Here, we used old C57BL/6J mice that were fed a GPC-containing diet, to investigate the molecular mechanisms underlying the prevention of a decline in cognitive function associated with aging and examine the beneficial effects of GPC intake on aging-related phenomena, such as taste sensitivity and energy regulation. We confirmed that GPC intake reduces the aging-related decline in the expression levels of genes related to long-term potentiation. Although we did not observe an improvement in aging-related decline in taste sensitivity, there was a notable improvement in the expression levels of β-oxidation-associated genes in old mice. Our results suggest that the prevention of aging-related decline in cognitive function by GPC intake may be associated with the improvement of gene expression levels of long-term potentiation. Furthermore, GPC intake may positively influence lipid metabolism.

Choline and Choline alphoscerate Do Not Modulate Inflammatory Processes in the Rat Brain

Choline is involved in relevant neurochemical processes. In particular, it is the precursor and metabolite of acetylcholine (ACh). Choline is an essential component of different membrane phospholipids that are involved in intraneuronal signal transduction. On the other hand, cholinergic precursors are involved in ACh release and carry out a neuroprotective effect based on an anti-inflammatory action. Based on these findings, the present study was designed to evaluate the effects of choline and choline precursor (Choline alphoscerate, GPC) in the modulation of inflammatory processes in the rat brain. Male Wistar rats were intraperitoneally treated with 87 mg of choline chloride/kg/day (65 mg/kg/day of choline), and at choline-equivalent doses of GPC (150 mg/kg/day) and vehicle for two weeks. The brains were dissected and used for immunochemical and immunohistochemical analysis. Inflammatory cytokines (Interleukin-1β, IL-1β; Interleukin-6 , IL-6 and Tumor Necrosis Factor-α, TNF-α) and endothelial adhesion molecules (Intercellular Adhesion Molecule, ICAM-1 and Vascular cell Adhesion Molecule, VCAM-1) were studied in the frontal cortex, hippocampus, and cerebellum. The results clearly demonstrated that treatment with choline or GPC did not affect the expression of the inflammatory markers in the different cerebral areas evaluated. Therefore, choline and GPC did not stimulate the inflammatory processes that we assessed in this study.

Influence of Cdp-Choline Administration on Early Burn Edema in Rats

PURPOSE

The cholinergic anti-inflammatory pathway may play an important role in early burn edema. Therefore, we evaluated the influence of cdp-choline on early systemic burn edema and leukocyte activation in shock in rat mesenteries after burn plasma transfer.

METHODS

Burn plasma harvested from donor rats 4 hours after thermal injury (30% total body surface area, 100°C water, 12 seconds) was administered intravenously to healthy animals during 2 hours of intravital microscopy. Shamburn plasma (same procedure but water at 37°C) was transferred for negative controls. In the study group, bolus injection of 100 mg/kg body weight cdp-choline was undertaken 15 minutes before examination. Intravital microscopy was performed in the ileal portion of rat mesenteries at 0, 60, and 120 minutes. Capillary leakage was assessed by fluorescein isothiocyanate-albumin extravasation and leukocyte-endothelial interaction were observed via transillumination microscopy. To assure comparable hemodynamic conditions, microhemodynamic parameters, foremost venular wall shear rate, were assessed.

RESULTS

Capillary leakage increased significantly after burn plasma transfer when compared to the shamburn group. Additional intravenous administration of cdp-choline attenuates macromolecular efflux to shamburn levels. Leukocyte activation is reduced after cdp-choline treatment.

CONCLUSIONS

The significant increase of albumin efflux in rat mesenteries after burn plasma transfer is decreased by additional cdp-choline bolus administration. Further investigations for proof of the relevance of the cholinergic anti-inflammatory pathway in early burn trauma are strongly required.

Intravenous CDP-choline activates neurons in supraoptic and paraventricular nuclei and induces hormone secretion

The aim of the present study was to assess the effects of intravenous (i.v.) cytidine-5'-diphosphate (CDP)-choline administration on the activation of oxytocin and vasopressin neurons in the supraoptic (SON) and paraventricular nuclei (PVN), using the immunohistochemical identification of c-Fos expression as a marker of neuronal activation and to correlate this with the plasma hormone levels. Rats were catheterized under sevofluorane anesthesia and experiments were conducted 24h later. Blood samples were withdrawn from arterial catheter at 2, 5, 10, 20, 40 and 60 min after CDP-choline (0.5, 1.0 and 2.0 g/kg; i.v.) or saline (1.0 ml/kg; i.v.) for the measurement of plasma oxytocin and vasopressin levels by radioimmunoassay. Animals were sacrificed 90 min after CDP-choline administration for dual immunohistochemistry which was performed on paraformaldehyde-fixed vibratome sections. Dual immunohistochemistry for c-Fos and oxytocin or vasopressin revealed that CDP-choline activates these neurons in a dose-dependent manner. Light microscopic analyses showed that, about 41%, 75% or 87% of the oxytocin neurons and about 18%, 46% or 82% of the vasopressin neurons in SON express c-Fos, thus activated, by the dosages of 0.5, 1.0 or 2.0 g/kg CDP-choline, respectively. Increases in c-Fos expression were about 29%, 62% or 81% for the oxytocin neurons and about 38%, 70% or 78% for the vasopressin neurons in PVN with the dosages of 0.5, 1.0 or 2.0 g/kg CDP-choline, respectively. When compared to the control groups (8% and 7% oxytocin or 2% and 5% vasopressin neuronal activation in SON or PVN, respectively), these increases were found to be statistically significant (p<0.05). In the PVN most of the magnocellular neurons were activated while less number of parvocellular neurons expressed c-Fos in response to CDP-choline challenge. In correlation with c-Fos data, CDP-choline increased plasma oxytocin and vasopressin levels both dose- and time-dependently. Results of the present study suggested that peripheral administration of CDP-choline is able to increase plasma oxytocin and vasopressin levels while activating the respective neurons.

CDP-choline-induced contractions in the mouse gastric fundus through purinoceptors and Rho/Rho-kinase signalling

AIMS

This study aimed to investigate the effects of cytidine-5'-diphosphocholine (CDP-choline), an endogenous lipid precursor, on the reactivity of the mouse gastric fundus and to determine the mechanism(s) mediating its effects.

MAIN METHODS

Possible contractile effect of CDP-choline (10(-5)-10(-2)M) was investigated in the absence and presence of a muscarinic receptor antagonist, atropine (3 × 10(-6)M), an acetylcholine esterase inhibitor, physostigmine (10(-6)M), a Na(+) channel blocker, tetrodotoxin (TTX, 3 × 10(-6)M), a Rho-kinase inhibitor, Y-27632 (10(-5) M), a purinoceptor antagonist, suramin (2 × 10(-4)M), a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine (L-NA, 3 × 10(-4)M), a Ca(2+) channel blocker, nifedipine (10(-6)M), an α(7) nicotinic receptor antagonist, methyllycaconitine citrate (MLA, 10(-6)M) and a G protein (G(i/o)) inhibitor, pertussis toxin (PTX, 2 μg/ml). The metabolites of CDP-choline, namely choline (10(-4)-10(-2)M), cytidine 5'-triphosphate (CTP, 10(-5)-10(-2)M), cytidine (10(-5)-10(-2)M) and cytidine monophosphate (CMP, 10(-3)-10(-2)M) were also tested. Besides, phosphorylation of MYPT1, which indicates Rho-kinase activity, was also detected.

KEY FINDINGS

CDP-choline produced contractions in a concentration-dependent manner. The contractions were not affected by atropine, physostigmine, TTX, PTX, MLA or L-NA. However, Y-27632, suramin or nifedipine partly reduced these contractions. CDP-choline increased phosphorylation of MYPT1. Among CDP-choline metabolites, cytidine had no contractile effects. However, choline induced considerable contractions, which were sensitive to atropine. CMP and CTP had also contractile activity, comparable to that of CDP-choline.

SIGNIFICANCE

These results suggest that CDP-choline produced contraction through, at least in part, purinoceptors and Rho/Rho-kinase signalling in the mouse gastric fundus.

Choline or CDP-choline attenuates coagulation abnormalities and prevents the development of acute disseminated intravascular coagulation in dogs during endotoxemia

Sepsis/endotoxemia causes platelet dysfunctions, abnormalities in coagulation and hemostatic mechanisms leading to organ dysfunctions and mortality. Choline prevents organ injury and improves survival during endotoxemia. The main objective of the present study was to determine the effects of choline or cytidine-5'-diphosphocholine (CDP-choline) on endotoxin-induced activation of coagulation and development of disseminated intravascular coagulation (DIC). Dogs were treated intravenously (i.v.) with saline, choline (20 mg/kg), or CDP-choline (70 mg/kg) three times with 4-h intervals starting 5 min before i.v. injection of endotoxin (1 mg/kg). Platelet counts and functions, prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, coagulation factors, D-dimer and antithrombin (AT) were measured before and at 0.5-96 h after endotoxin. Circulating platelet, fibrinogen, coagulation factors and AT were decreased, whereas PT and aPTT were prolonged and serum D-dimer levels were elevated after endotoxin. Endotoxin-induced reductions in platelet counts and functions, fibrinogen, coagulation factors and AT were attenuated or blocked by choline or CDP-choline. Choline or CDP-choline blocked endotoxin-induced prolongation in PT and aPTT and enhancement in D-dimer. Elevated DIC scores were attenuated by choline and blocked by CDP-choline. Choline administration increased serum choline concentrations and caused bradycardia. Choline also increased choline and acetylcholine contents of circulating mononuclear cells and inhibited radioligand binding to their cholinergic receptors. These data show that choline administration, as choline chloride or CDP-choline, restores the abnormalities in the primary, secondary, and tertiary hemostasis and prevents the development of DIC during experimental endotoxemia in dogs probably by increasing both neuronal and non-neuronal cholinergic activity.

Transient central cholinergic activation enhances sympathetic nervous system activity but does not improve hemorrhage-induced hypotension in alcohol-intoxicated rodents

Morbidity and mortality after traumatic injury and hemorrhagic shock (HS) are exacerbated in the alcohol-intoxicated individual. The level of hypotension at the time of admittance into the emergency department is a critical indicator of outcome from injury. Previously, we have demonstrated that acute alcohol intoxication (AAI) decreases basal mean arterial blood pressure (MABP), exaggerates hypotension throughout HS, and attenuates the pressor response to fluid resuscitation in male rodents. This AAI-induced impaired hemodynamic counter-regulation to blood loss is associated with dampened neuroendocrine activation (i.e., epinephrine, norepinephrine, and arginine vasopressin [AVP] release). We hypothesize that the blunted neuroendocrine response is the principal mechanism involved in hemodynamic instability during and after HS in AAI. The present study investigates whether enhancing central cholinergic activity via intracerebroventricular (ICV) choline, a precursor of acetylcholine, would restore the neuroendocrine response and, as a result, improve hemodynamic compensation after HS. Chronically catheterized, conscious, male Sprague-Dawley rats (225-250 g) received a primed 15-h alcohol infusion (30% wt/vol; total approximately 8 g x kg(-1)) before ICV choline (150 microg) injection and were subsequently subjected to fixed-volume HS (50%) and fluid resuscitation with lactated Ringer's solution (2x volume removed). There were a total of eight experimental groups (n = 5-12 rats per group): alcohol-treated not hemorrhaged (alcohol/sham), dextrose-treated not hemorrhaged (dextrose/sham), alcohol-treated hemorrhaged (alcohol/hemorrhage), and dextrose-treated hemorrhaged (dextrose/hemorrhage), with ICV choline or water injection. Intracerebroventricular choline immediately increased basal MABP in both control (16%) and AAI animals (12%), but did not alter MABP after HS in either group. Intracerebroventricular choline increased basal plasma epinephrine (196%), norepinephrine (96%), and AVP (145%) and enhanced the HS-induced increase in epinephrine and AVP, without altering norepinephrine responses to HS, in control animals. Acute alcohol intoxication blunted choline-induced neuroendocrine activation and prevented the HS-induced increase in norepinephrine, without affecting post-HS epinephrine and AVP levels. Intracerebroventricular choline administration to AAI animals enhanced the HS-induced increase in epinephrine without affecting post-HS norepinephrine or AVP. These results indicate that ICV choline produced immediate neuroendocrine activation and elevation in MABP that was not sustained sufficiently to improve hemodynamic counter-regulation in alcohol-treated animals.

Choline or CDP-choline alters serum lipid responses to endotoxin in dogs and rats: involvement of the peripheral nicotinic acetylcholine receptors

We showed previously that choline administration protects dogs from endotoxin-induced multiple organ injury and platelet dysfunctions. Because sepsis/endotoxemia is associated with alterations in lipid metabolism, we have investigated whether choline or cytidine-5'-diphosphate choline, a choline donor, alters serum lipid responses to endotoxin in dogs and rats. In response to endotoxin, serum concentrations of triglycerides, choline-containing phospholipids, total cholesterol, and high-density lipoprotein cholesterol increased in a dose- and time-related manner. Administration of choline (20 mg/kg i.v. in dogs or 90 mg/kg i.p. in rats) or cytidine-5'-diphosphate choline (70 mg/kg i.v. in dogs) 5 min before and 4 and 8 h after endotoxin blocked or attenuated the increases in serum triglycerides, total cholesterol, and nonesterified fatty acids. Endotoxin-induced elevations in serum phospholipid levels did not change in rats and were enhanced in dogs by choline. In rats, serum lipid response to endotoxin was accompanied by severalfold elevations in serum levels of hepatorenal injury markers; their elevations were also blocked by choline. Pretreatment with hexamethonium blocked choline's effects on serum lipids and hepatorenal injury markers. Pretreatment with atropine blocked endotoxin-induced elevations in serum lipid and hepatorenal injury markers, but failed to alter choline's actions on these parameters. Choline treatment improved survival rate of rats in lethal endotoxin shock. In conclusion, these data show that choline treatment alters serum lipid responses to endotoxin and prevents hepatorenal injury during endotoxemia through a nicotinic acetylcholine receptor-mediated mechanism. Hence, choline and choline-containing compounds may have a therapeutic potential in the treatment of endotoxemia/sepsis.

Central choline suppresses plasma renin response to graded haemorrhage in rats

Central administration of choline increases blood pressure in normotensive and hypotensive states by increasing plasma concentrations of vasopressin and catecholamines. We hypothesized that choline could also modulate the renin-angiotensin pathway, the third main pressor system in the body. Plasma renin activity (PRA), which serves as an index of the function of the peripheral renin-angiotensin system, was determined in rats subjected to graded haemorrhage following central choline administration. Intracerebroventricular (i.c.v.) injection of choline (12.5-150 microg), a precursor of the neurotransmitter acetylcholine (ACh), inhibited the increase in PRA in rats subjected to graded haemorrhage by sequential removal of 0.55 mL blood/100 g bodyweight. Choline, in the range 50-150 microg, increased blood pressure. Intraperitoneal (i.p.) administration of 150 microg choline failed to alter blood pressure and plasma renin responses to graded haemorrhage. Administration of a higher dose (90 mg/kg, i.p.) of choline decreased blood pressure and enhanced PRA in the first two blood samples obtained during the graded haemorrhage. Physostigmine (10 microg, i.c.v.), ACh (10 microg, i.c.v.), carbamylcholine (10 microg, i.c.v.) and cytidine 5'-diphosphocholine (CDP-choline; 250 microg, i.c.v.) increased blood pressure and attenuated plasma renin responses to graded haemorrhage. Inhibition of PRA by i.c.v. choline was abolished by i.c.v. pretreatment with mecamylamine (50 microg), but not atropine (10 microg). Blood pressure responses to choline (150 microg) were attenuated by pretreatment with both mecamylamine and atropine. Inhibition of PRA in response to central choline administration was associated with enhanced plasma vasopressin and catecholamine responses to graded haemorrhage. Pretreatment of rats with a vasopressin antagonist reversed central choline-induced inhibition of plasma renin responses to graded haemorrhage without altering the blood pressure response. In conclusion, central administration of choline inhibits the plasma renin response to graded haemorrhage. Nicotinic receptor activation and an increase in plasma vasopressin appear to be involved in this effect.

Choline, CDP-choline or phosphocholine increases plasma glucagon in rats: involvement of the peripheral autonomic nervous system

The present study was designed to test the effects of choline, cytidine-5'-diphosphocholine (CDP-choline) and phosphocholine on plasma glucagon concentrations in rats. Intraperitoneal (i.p.) injection of 200-600 micromol/kg of choline, CDP-choline or phosphocholine produced a dose-dependent increase in plasma glucagon and choline concentrations. Pretreatment with hexamethonium (15 mg/kg; i.p.), a peripherally-acting ganglionic nicotinic acetylcholine receptor antagonist, entirely blocked the increases in plasma glucagon by 600 micromol/kg of choline, CDP-choline or phosphocholine. The increases in plasma glucagon by these choline compounds was reduced significantly (P<0.01) by about 25% by pretreatment with atropine methylnitrate (2 mg/kg), a peripherally-acting muscarinic acetylcholine receptor antagonist. Blockade of central acetylcholine receptors did not alter the increase in plasma glucagon induced by i.p. choline (600 micromol/kg). While alpha(2)-adrenoceptor blockade or bilateral adrenalectomy attenuated the increase in plasma glucagon evoked by choline compounds, blockade of alpha(1)- or beta-adrenoceptors or chemical sympathectomy failed to alter this increase. Intracerebroventricular (i.c.v.) choline (1.5 micromol) administration also increased plasma glucagon; the effect was blocked by central pretreatment with a neuronal type nicotinic acetylcholine receptor antagonist, mecamylamine (50 microg; i.c.v.) or the neuronal choline uptake inhibitor, hemicholinium-3 (20 microg; i.c.v.). These data show that choline, CDP-choline or phosphocholine increases plasma glucagon concentrations by increasing peripheral nicotinic and muscarinic cholinergic neurotransmissions. Central choline also increases plasma glucagon by augmenting central nicotinic cholinergic neurotransmission by acting presynaptically. Stimulation of adrenal medullary catecholamine release and subsequent activation of alpha(2)-adrenoceptors are mainly involved in the increase in plasma glucagon induced by choline, CDP-choline or phosphocholine.

Peripheral administration of CDP-choline, phosphocholine or choline increases plasma adrenaline and noradrenaline concentrations

1 Intraperitoneal (i.p.) injection of 200-600 mumol/kg of cytidine-5'-diphosphocholine (CDP-choline) increased plasma adrenaline and noradrenaline concentrations dose- and time-dependently. 2 CDP-choline treatment caused several-fold increases in plasma concentrations of CDP-choline and its metabolites phosphocholine, choline, cytidine monophosphate (CMP) and cytidine. 3 Equivalent doses (200-600 mumol/kg; i.p.) of phosphocholine or choline, but not CMP or cytidine, increased plasma adrenaline and noradrenaline dose-dependently. 4 CDP-choline, phosphocholine and choline (600 mumol/kg; i.p.) augmented the increases in plasma adrenaline and noradrenaline in response to graded haemorrhage. 5 The increases in plasma adrenaline and noradrenaline induced by i.p. 600 mumol/kg of CDP-choline, phosphocholine or choline were abolished by pre-treatment with hexamethonium (15 mg/kg; i.p.), but not atropine (2 mg/kg; i.p.). 6 At 320-32 000 mum concentrations, choline, but not CDP-choline or phosphocholine, evoked catecholamine secretion from perfused adrenal gland. Choline (3200 mum)-induced catecholamine secretion was attenuated by the presence of 1 mum of hexamethonium or mecamylamine, but not atropine, in the perfusion medium. 7 Intracerebroventricular (i.c.v.) injection of choline (0.5-1.5 mumol) also increased plasma adrenaline and noradrenaline dose- and time-dependently. Pre-treatment with mecamylamine (50 mug; i.c.v.) or hexamethonium (15 mg/kg; i.p.), but not atropine (10 mug; i.c.v.), prevented i.c.v. choline (1.5 mumol)-induced elevations in plasma adrenaline and noradrenaline. 8 It is concluded that i.p. administration of CDP-choline or its cholinergic metabolites phosphocholine and choline increases plasma adrenaline and noradrenaline concentrations by enhancing nicotinic cholinergic neurotransmission in the sympatho-adrenal system. Central choline also activates the sympatho-adrenal system by increasing central nicotinic cholinergic neurotransmission.

Intraperitoneal administration of CDP-choline and its cholinergic and pyrimidinergic metabolites induce hyperglycemia in rats: involvement of the sympathoadrenal system

CDP-choline is an endogenous metabolite in phosphatidylcholine biosynthesis. Exogenous administration of CDP-choline has been shown to affect brain metabolism and to exhibit neuroprotective actions. On the other hand, little is known regarding its peripheral actions. Intraperitoneal administration of CDP-choline (200-600 micromol/kg) induced a dose- and time-dependent hyperglycemia in rats. Hyperglycemic response to CDP-choline was associated with several-fold elevations in serum concentrations of CDP-choline and its metabolites. Intraperitoneal administration of phosphocholine, choline, cytidine, cytidine monophosphate, cytidine diphosphate, cytidine triphosphate, uridine, uridine monophosphate, uridine diphosphate and uridine triphosphate also produced significant hyperglycemia. Pretreatment with atropine methyl nitrate failed to alter the hyperglycemic responses to CDP-choline and its metabolites whereas hexamethonium, the ganglionic nicotinic receptor antagonist which blocks nicotinic cholinergic neurotransmission at the autonomic ganglionic level, blocked completely the hyperglycemia induced by CDP-choline, phosphocholine and choline, and attenuated the hyperglycemic response to cytidine monophosphate and cytidine. Increased blood glucose following CDP-choline, phosphocholine and choline was accompanied by elevated plasma catecholamine concentrations. Hyperglycemia elicited by CDP-choline and its metabolites was entirely blocked either by pretreatment with a nonselective -adrenoceptor antagonist phentolamine or by the 2-adrenoceptor antagonist, yohimbine. Hyperglycemic responses to CDP-choline, choline, cytidine monophosphate and cytidine were not affected by chemical sympathectomy, but were prevented by bilateral adrenalectomy. Phosphocholine-induced hyperglycemia was attenuated by bilateral adrenalectomy or by chemical sympathectomy. These data show that CDP-choline and its metabolites induce hyperglycemia which is mediated by activation of ganglionic nicotinic receptors and stimulation of catecholamine release that subsequently activates 2-adrenoceptors.

Cardiovascular effects of CDP-choline and its metabolites: involvement of peripheral autonomic nervous system

Intraperitoneal administration of CDP-choline (200-900 micromol/kg) increased blood pressure and decreased heart rate of rats in a dose- and time-dependent manner. These responses were accompanied by elevated serum concentrations of CDP-choline and its metabolites phosphocholine, choline, cytidine monophosphate and cytidine. Blood pressure increased by intraperitoneal phosphocholine (200-900 micromol/kg), while it decreased by choline (200-600 micromol/kg) administration; phosphocholine or choline administration (up to 600 micromol/kg) decreased heart rate. Intraperitoneal cytidine monophosphate (200-600 micromol/kg) or cytidine (200-600 micromol/kg) increased blood pressure without affecting heart rate. Pressor responses to CDP-choline, phosphocholine, cytidine monophosphate or cytidine were not altered by pretreatment with atropine methyl nitrate or hexamethonium while hypotensive effect of choline was reversed to pressor effect by these pretreatments. Pretreatment with atropine plus hexamethonium attenuated or blocked pressor response to CDP-choline or phosphocholine, respectively. Heart rate responses to CDP-choline, phosphocholine and choline were blocked by atropine and reversed by hexamethonium. Cardiovascular responses to CDP-choline, phosphocholine and choline, but not cytidine monophosphate or cytidine, were associated with elevated plasma catecholamines concentrations. Blockade of alpha-adrenoceptors by prazosin or yohimbine attenuated pressor response to CDP-choline while these antagonists blocked pressor responses to phosphocholine or choline. Neither bilateral adrenalectomy nor chemical sympathectomy altered cardiovascular responses to CDP-choline, choline, cytidine monophosphate or cytidine. Sympathectomy attenuated pressor response to phosphocholine. Results show that intraperitoneal administration of CDP-choline and its metabolites alter cardiovascular parameters and suggest that peripheral cholinergic and adrenergic receptors are involved in these responses.

Intravenous administration of choline or cdp-choline improves platelet count and platelet closure times in endotoxin-treated dogs

This study was performed to assess the effects of intravenous choline chloride and cytidine-5'-diphosphate choline (CDP-choline) treatments on circulating platelet, white blood cell, and red blood cell counts and platelet functions in response to endotoxin. Saline (0.2 mL/kg), choline chloride (20 mg/kg), or CDP-choline (70 mg/kg) were given intravenously three times at 4-h intervals, and endotoxemia was induced by endotoxin (E. coli 055:B5, 20 microg/kg) infusion, 5 min after the first treatment. Blood samples were collected before and at multiple time points after the challenge, for a panel of hematologic parameters and platelet closure times measured by PFA-100. In saline-treated dogs, circulating platelet counts decreased by 85% (P < 0.001) at 0.5 h and remained low by 36%-80% (P < 0.5-0.001) 1-12 h after endotoxin. Circulating WBC counts decreased by 80%-90% (P < 0.001) at 0.5-2 h, and increased (P < 0.001) by 190% 12 h after the endotoxin. In response to endotoxin, RBCs increased by 10%-13% (P < 0.05) at 1-12 h. Endotoxin-induced decline in circulating platelets was attenuated at 0.5 h (P < 0.05-0.01) and reversed at 1-12 h (P < 0.05-0.001) by choline. Platelet closure times were shortened from 81 +/- 10 s and 135 +/- 10 s to 29 +/- 5 s (P < 0.001) and 60 +/- 3 s (P < 0.001) at 0.5 h, and prolonged (P < 0.001) at 1-8 h after endotoxin induction. Endotoxin-induced shortening in platelet closure times was attenuated (P < 0.05) and blocked (P < 0.01) by choline and CDP-choline, respectively. These results showed that choline and CDP-choline treatments improved circulating platelet counts and platelet function during endotoxemia in dogs.

Cortical choline transporter function measured in vivo using choline-sensitive microelectrodes: clearance of endogenous and exogenous choline and effects of removal of cholinergic terminals

The capacity of the high-affinity choline transporter (CHT) to import choline into presynaptic terminals is essential for acetylcholine synthesis. Ceramic-based microelectrodes, coated at recording sites with choline oxidase to detect extracellular choline concentration changes, were attached to multibarrel glass micropipettes and implanted into the rat frontoparietal cortex. Pressure ejections of hemicholinium-3 (HC-3), a selective CHT blocker, dose-dependently reduced the uptake rate of exogenous choline as well as that of choline generated in response to terminal depolarization. Following the removal of CHTs, choline signal recordings confirmed that the demonstration of potassium-induced choline signals and HC-3-induced decreases in choline clearance require the presence of cholinergic terminals. The results obtained from lesioned animals also confirmed the selectivity of the effects of HC-3 on choline clearance in intact animals. Residual cortical choline clearance correlated significantly with CHT-immunoreactivity in lesioned and intact animals. Finally, synaptosomal choline uptake assays were conducted under conditions reflecting in vivo basal extracellular choline concentrations. Results from these assays confirmed the capacity of CHTs measured in vivo and indicated that diffusion of substrate away from the electrode did not confound the in vivo findings. Collectively, these results indicate that increases in extracellular choline concentrations, irrespective of source, are rapidly cleared by CHTs.

Antinociceptive effects of choline against acute and inflammatory pain

We used the hot plate test and the formalin test to evaluate the antinociception of choline after i.c.v. or i.v. administration. The analgesic mechanism of choline was also studied. The response latency of mice was significantly prolonged in the hot plate test after choline (90-120 mug/animals) i.c.v. administration in a dose-dependent manner. Pretreatment with methyllycaconitine citrate (MLA), alpha-bungarotoxin, or atropine blocked the antinociception of choline in the hot plate test. In contrast, mecamylamine and naloxone had no effect. No antinociceptive action of choline was found in the hot plate test, but it did have an effect in the late phase of the formalin test after i.v. administration. The effect of choline on anti-inflammatory pain was blocked by MLA, but not by mecamylamine, naloxone and atropine, which is indicative of the involvement of alpha7 receptors in peripheral sites. When choline (2 mg/kg) was coadministered with aspirin (9.4 mg/kg), the licking/biting times in the late phase significantly decreased, although no effects were shown when these doses of drugs were used alone. Similarly, coadministration of choline (2 mg/kg) with morphine (0.165 mg/kg) significantly increased the antinociception of morphine in the late phase, but had no effect in the early phase. These results demonstrate that activation of alpha7 nicotinic receptors by choline elicits antinociceptive effects both in an acute thermal pain model and in an inflammatory pain model. Choline holds promise for development as a non-addictive analgesic drug and in reducing the regular dose of aspirin or morphine in inflammatory pain.

New approaches to the treatment of pemphigus

In pemphigus vulgaris, treatment with systemic glucocorticosteroids is life saving; it may, however, cause severe side effects, including death. A patient with pemphigus vulgaris and myasthenia gravis was treated for approximately five years with the cholinomimetic Mestinon (pyridostigmine bromide), Imuran (azathioprine), and a topical corticosteroid gel before the need to introduce systemic glucocorticosteroids. Because activation of keratinocyte acetylcholine receptors also has been shown to abolish pemphigus IgG-induced acantholysis in cultured keratinocyte monolayers, a clinical trial of Mestinon was initiated in patients with active pemphigus vulgaris, pemphigus foliaceus, and paraneoplastic autoimmune multiorgan syndrome (also known as paraneoplastic pemphigus). First results indicate that nonsteroidal treatment of pemphigus is possible. Mestinon may be used to slow down progression of the disease and to treat mild cases with chronic lesions on limited areas. Stimulation of the keratinocyte- acetylcholine axis may lead to a therapeutic effect through any of the following mechanisms: (1) stimulating keratinocyte cell-to-cell attachment; (2) accelerating reepithelialization; and (3) competing with the disease-causing pemphigus antibodies, preventing them from attachment to keratinocytes. Glucocorticosteroids and various types of steroid-sparing drugs used to treat pemphigus exhibit cholinergic side effects, including effects on expression and function of keratinocyte adhesion molecules, that are very similar to those produced by the cholinomimetic drugs. Further elucidation of the mechanisms underlying therapeutic efficacy of antiacantholytics may shed light on the immunopharmacological mechanisms of pemphigus antibody-induced acantholysis.

Choline increases serum insulin in rat when injected intraperitoneally and augments basal and stimulated aceylcholine release from the rat minced pancreas in vitro

Intraperitoneal injection of choline (30-90 mg.kg-1) produced a dose-dependent increase in serum insulin, glucose and choline levels in rats. The increase in serum insulin induced by choline (90 mg.kg-1) was blocked by pretreatment with the muscarinic acetylcholine receptor antagonists, atropine (2 mg.kg-1), pirenzepine (2 mg.kg-1) and 4-diphenylacetoxy-N-methylpiperidine (2 mg.kg-1) or the ganglionic nicotinic receptor antagonist, hexamethonium (15 mg.kg-1). The effect of choline on serum insulin and glucose was enhanced by oral glucose administration (3 g.kg-1). Choline administration was associated with a significant (P < 0.001) increase in the acetylcholine content of pancreatic tissue. Choline (10-130 microm) increased basal and stimulated acetylcholine release but failed to evoke insulin release from the minced pancreas at considerably higher concentrations (0.1-10 mm). Hemicholium-3, a choline uptake inhibitor, attenuated the increase in acetylcholine release induced by choline augmentation. Choline (1-32 mm) inhibited [3H]quinuclidinyl benzilate binding to the muscarinic receptors in the pancreatic homogenates. These data show that choline, a precursor of the neurotransmitter acetylcholine, increases serum insulin by indirectly stimulating peripheral acetylcholine receptors through the enhancement of acetylcholine synthesis and release.

Intracerebroventricular choline increases plasma vasopressin and augments plasma vasopressin response to osmotic stimulation and hemorrhage

Intracerebroventricular (i.c.v.) injection of choline (50-150 microg), a precursor of the neurotransmitter acetylcholine, produced a time-and dose-dependent increase in plasma vasopressin levels in conscious, freely moving rats. The increase in plasma vasopressin in response to i.c.v. choline (150 microg) was inhibited by pretreatment with the nicotinic receptor antagonist, mecamylamine (50 microg; i.c.v.), but not by the muscarinic receptor antagonist, atropine (10 microg; i.c.v). The choline-induced rise in plasma vasopressin levels was greatly attenuated by hemicholinium-3 (HC-3; 20 microg; i.c.v.), a neuronal choline uptake inhibitor. Choline (50 or 150 microg; i.c.v.) produced a much greater increase in plasma vasopressin levels in osmotically stimulated or hemorrhaged rats than in normal rats. Choline (150 microg; i.c.v.) also enhanced plasma vasopressin response to graded hemorrhage; the enhancing effect of choline was also attenuated by HC-3 (20 microg; i.c.v.). Choline and acetylcholine concentrations in hypothalamic dialysates increased significantly following i.c.v. injection of choline (150 microg). It is concluded that choline increases plasma vasopressin levels by stimulating central nicotinic receptors indirectly, through the enhancement of acetylcholine synthesis and release, and augments the ability of osmotic stimulations or hemorrhage to stimulate vasopressin release.

Hyperglycemia induced by intracerebroventricular choline: involvement of the sympatho-adrenal system

Intracerebroventricular (i.c.v.) injection of choline (75-300 microg) produced a dose-dependent increase in blood glucose levels. Pre-treatment with the nicotinic acetylcholine receptor antagonist, mecamylamine (50 microg, i.c.v.) blocked the hyperglycemia induced by choline (150 microg, i.c.v.), but the response was not affected by pre-treatment with the muscarinic acetylcholine receptor antagonist, atropine (10 microg, i.c.v.). Pre-treatment with the neuronal choline uptake inhibitor, hemicholinium-3 (20 microg, i.c.v.), attenuated the hyperglycemia induced by choline. The hyperglycemic response to choline was associated increased plasma levels of adrenaline and noradrenaline. The hyperglycemia elicited by choline was greatly attenuated by bilateral adrenalectomy, and entirely blocked by either surgical transection of the splanchnic nerves or by pre-treatment with the alpha-adrenoceptor antagonist, phentolamine. These data show that choline, a precursor of acetylcholine, increases blood glucose and this effect is mediated by central nicotinic acetylcholine receptor activation. An increase in sympatho-adrenal activity appears to be involved in the hyperglycemic effect of choline.

Pemphigus vulgaris antibody identifies pemphaxin. A novel keratinocyte annexin-like molecule binding acetylcholine

Because pemphigus vulgaris (PV) IgGs adsorbed on the rDsg3-Ig-His baculoprotein induced blisters in neonatal mice, it was proposed that anti-desmoglein 3 (Dsg 3) autoantibody causes PV. However, we found that rDsg3-Ig-His absorbs autoantibodies to different antigens, including a non-Dsg 3 keratinocyte protein of 130 kDa. This prompted our search for novel targets of PV autoimmunity. The PV IgG eluted from a 75-kDa keratinocyte protein band both stained epidermis in a pemphigus-like pattern and induced acantholysis in keratinocyte monolayers. Screening of a keratinocyte lambdagt11 cDNA library with this antibody identified clones carrying cDNA inserts encoding a novel molecule exhibiting approximately 40% similarity with annexin-2, named pemphaxin (PX). Recombinant PX (rPX-His) was produced in Escherichia coli M15 cells, and, because annexins can act as cholinergic receptors, its conformation was tested in a cholinergic radioligand binding assay. rPX-His specifically bound [(3)H]acetylcholine, suggesting that PX is one of the keratinocyte cholinergic receptors known to be targeted by disease-causing PV antibodies. Preabsorption of PV sera with rPX-His eliminated acantholytic activity, and eluted antibody immunoprecipitated native PX. This antibody alone did not cause skin blisters in vivo, but its addition to the preabsorbed PV IgG fraction restored acantholytic activity, indicating that acantholysis in PV results from synergistic action of antibodies to different keratinocyte self-antigens, including both acetylcholine receptors and desmosomal cadherins.

The effects of choline on body temperature in conscious rats

Choline (75-300 microg) produced dose-dependent hypothermia when injected intracerebroventricularly (i.c.v.). Pre-treatment with the muscarinic receptor antagonist, atropine (10 microg, i.c.v.), blocked the hypothermic effect of choline (150 microg), but the response was only partially attenuated by pre-treatment with the nicotinic receptor antagonist, mecamylamine (20 microg, i.c.v.). Pirenzepine (25 microg), a muscarinic M1 receptor antagonist, or hexahydro-siladifenidol (HHSD) (100 microg), a muscarinic M3 receptor antagonist, also blocked choline-induced hypothermia when injected centrally. Unlike the other muscarinic receptor antagonists, M2-selective 11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyri do[2,3-b][1,4]benzodiazepin-6-one (AF-DX116) (10 microg), did not affect choline-induced hypothermia. We also found that choline-induced hypothermia was very sensitive to the ambient temperature. Similar to its effect at room temperature, choline produced dose-dependent hypothermia at 4 degrees C, but this effect was abolished at 32 degrees C. These data suggest that choline produces hypothermia and this effect is mediated by muscarinic receptors.

Brain choline has a typical precursor profile

Choline is product and precursor to both acetylcholine and membrane phospholipids, and, in the brain, is ultimately provided by the circulation. The brain is protected from excess choline and choline deprivation by a refined system of homeostatic mechanisms that maintain a level of extracellular choline that, for its role as precursor, meets saturation criteria under normal conditions. The kinetic and activity profiles of choline are typical for a biosynthetic precursor.

Choline administration reverses hypotension in spinal cord transected rats: the involvement of vasopressin

Intracerebroventricular (i.c.v.) choline (50-150 microg) increased blood pressure and decreased heart rate in spinal cord transected, hypotensive rats. Choline administered intraperitoneally (60 mg/kg), also, increased blood pressure, but to a lesser extent. The pressor response to i.c.v. choline was associated with an increase in plasma vasopressin. Mecamylamine pretreatment (50 microg; i.c.v.) blocked the pressor, bradycardic and vasopressin responses to choline (150 microg). Atropine pretreatment (10 microg; i.c.v.) abolished the bradycardia but failed to alter pressor and vasopressin responses. Hemicholinium-3 [HC-3 (20 microg; i.c.v.)] pretreatment attenuated both bradycardia and pressor responses to choline. The vasopressin V1 receptor antagonist, (beta-mercapto-beta,beta-cyclopenta-methylenepropionyl1, O-Me-Tyr2, Arg8)-vasopressin (10 microg/kg) administered intravenously 5 min after choline abolished the pressor response and attenuated the bradycardia-induced by choline. These data show that choline restores hypotension effectively by activating central nicotinic receptors via presynaptic mechanisms, in spinal shock. Choline-induced bradycardia is mediated by central nicotinic and muscarinic receptors. Increase in plasma vasopressin is involved in cardiovascular effects of choline.

Cardiovascular effects of central choline during endotoxin shock in the rat

The cardiovascular effects of intracerebroventricular (i.c.v.) administration of choline were studied in endotoxin-treated rats. Intravenous (i.v.) endotoxin (20 mg/kg) caused a moderate hypotension and tachycardia within 10 min of treatment. Choline (50, 100, and 150 microg; i.c.v.) increased blood pressure and decreased heart rate in this condition in a dose-dependent manner. Mecamylamine (50 microg; i.c.v.) pretreatment prevented the pressor and bradycardic responses to choline, whereas atropine (10 microg; i.c.v.) failed to alter both responses. Atropine pretreatment, alone, inhibited endotoxin-induced hypotension. The pressor responses to choline in endotoxin-treated rats were attenuated by pretreatment with hemicholinium-3 (20 microg; i.c.v.), a high-affinity neuronal choline-uptake inhibitor. Plasma vasopressin levels of endotoxin-treated rats were severalfold higher than those of control animals, and choline (50-150 microg; i.c.v.) produced further increases in plasma vasopressin in this condition. Mecamylamine abolished vasopressin response to endotoxin as well as to choline. The vasopressin receptor antagonist, (beta-mercapto-beta,beta-cyclopentamethylene-propionyl(1)-O-Me-Tyr2,Arg8 )-vasopressin (10 microg/kg; i.v.) administered 5 min after choline decreased blood pressure from the increased level to the precholine levels but did not alter bradycardia. These results indicate that, in rats treated with endotoxin, choline increases blood pressure and decreases heart rate by a presynaptic mechanism leading to the activation of central nicotinic cholinergic pathways. An increase in plasma vasopressin levels seems to be involved in the pressor, but not in the bradycardic response, to choline.

Centrally administered choline increases plasma prolactin levels in conscious rats

Intracerebroventricular (i.c.v.) administration of choline, a precursor of acetylcholine (ACh) increased plasma prolactin levels in a time and dose-dependent manner in conscious rats. Pretreatment of rats with the cholinergic muscarinic antagonist, atropine (10 microg, i.c.v.), blocked the increase in plasma prolactin level. The increase was not influenced by pretreatment with the cholinergic nicotinic antagonist, mecamylamine (50 microg, i.c.v.). Pretreatment with hemicholinium-3 (HC-3; 20 microg, i.c.v.), a high affinity choline uptake inhibitor, attenuated the choline-induced increase of plasma prolactin levels. These results show that choline increases plasma prolactin levels by activating muscarinic receptors via presynaptic mechanisms.

Central choline reverses hypotension caused by alpha-adrenoceptor or ganglion blockade in rats: the role of vasopressin

The effect of intracerebrovenricularly (i.c.v.) injected choline on blood pressure was investigated in rats made hypotensive by blocking peripheral alpha-adrenoceptors or autonomic ganglionic transmission. Choline (50-150 micrograms; i.c.v.) increased blood pressure in a dose-dependent manner and 150 micrograms of choline restored blood pressure to the resting level. The pressor response to choline was associated with an increase in plasma vasopressin levels. Pretreatment with mecamylamine (50 micrograms; i.c.v.), but not atropine (10 micrograms; i.c.v.), blocked both the pressor and vasopressin responses to i.c.v. choline. The vasopressin receptor antagonist, [beta-mercapto-beta,beta-cyclopenta-methylene-propionyl1,O-Me-T ry2,Arg8] vasopressin (10 micrograms/kg; i.v.), given 5 min after i.c.v. choline (150 micrograms), abolished the pressor effect of choline and blood pressure returned to the pre-choline levels. It is concluded that the precursor of acetylcholine, choline, can increase blood pressure and reverse hypotension in alpha-adrenoceptor or ganglionic transmission blocked rats, by increasing plasma vasopressin.

Effect of intracerebroventricularly injected choline on plasma ACTH and beta-endorphin levels in conscious rats

In the present study, we examined the effect of intracerebroventricularly injected choline on plasma ACTH (adrenocorticotrophin) and beta-endorphin levels in conscious rats. The intracerebroventricularly injection of choline (50-150 micrograms) elevated plasma ACTH levels in a dose-dependent manner. Plasma beta-endorphin levels were also significantly increased. Pretreatment of rats with mecamylamine (50 micrograms; intracerebroventricularly), the nicotinic receptor antagonist, completely inhibited the ACTH and beta-endorphin response to choline (150 micrograms; intracerebroventricularly). An antagonist of the muscarinic receptor, atropine (10 micrograms; intracerebroventricularly), failed to alter these effects. Pretreatment of rats with hemicholinium-3 (20 micrograms; intracerebroventricularly), a drug which inhibits the uptake of choline into cholinergic neurons, abolished the choline-induced increases in both plasma ACTH and beta-endorphin levels. These results indicate that choline can increase plasma concentrations of ACTH and beta-endorphin through the activation of central nicotinic acetylcholine receptors.

Intracerebroventricular injection of choline increases plasma oxytocin levels in conscious rats

In the present study, we examined the effect of intracerebroventricularly (i.c.v.) injected choline on both basal and stimulated oxytocin release in conscious rats. I.c.v. injection of choline (50-150 micrograms) caused time- and dose-dependent increases in plasma oxytocin levels under normal conditions. The increase in plasma oxytocin levels in response to i.c.v. choline (150 micrograms) was greatly attenuated by the pretreatment of rats with atropine (10 micrograms; i.c.v.), muscarinic receptor antagonist. Mecamylamine (50 micrograms; i.c.v.), a nicotinic receptor antagonist, failed to suppress the effect of 150 micrograms choline on oxytocin levels. Pretreatment of rats with 20 micrograms of hemicholinium-3 (HC-3), a specific inhibitor of choline uptake into nerve terminals, greatly attenuated the increase in plasma oxytocin levels in response to i.c.v. choline injection. Osmotic stimuli induced by either oral administration of 1 ml hypertonic saline (3 M) following 24-h dehydration of rats (type 1) or an i.c.v. injection of hypertonic saline (1 M) (type 2) increased plasma oxytocin levels significantly, but hemorrhage did not alter basal oxytocin concentrations. The i.c.v. injection of choline (50, 150 micrograms) under these conditions caused an additional and significant increase in plasma oxytocin concentrations beyond that produced by choline in normal conditions. These data show that choline can increase plasma oxytocin concentrations through the stimulation of central cholinergic muscarinic receptors by presynaptic mechanisms and enhance the stimulated oxytocin release.

Restoration of blood pressure by choline treatment in rats made hypotensive by haemorrhage

1. Intracerebroventricular (i.c.v.) injection of choline (25-150 micrograms) increased blood pressure in rats made acutely hypotensive by haemorrhage. Intraperitoneal administration of choline (60 mg kg-1) also increased blood pressure, but to a lesser extent. Following i.c.v. injection of 25 micrograms or 50 micrograms of choline, heart rate did not change, while 100 micrograms or 150 micrograms i.c.v. choline produced a slight and short lasting bradycardia. Choline (150 micrograms) failed to alter the circulating residual volume of blood in haemorrhaged rats. 2. The pressor response to i.c.v. choline (50 micrograms) in haemorrhaged rats was abolished by pretreatment with mecamylamine (50 micrograms, i.c.v.) but not atropine (10 micrograms, i.c.v.). The pressor response to choline was blocked by pretreatment with hemicholinium-3 (20 micrograms, i.c.v.). 3. The pressor response to i.c.v. choline (150 micrograms) was associated with a several fold increase in plasma levels of vasopressin and adrenaline but not of noradrenaline and plasma renin. 4. The pressor response to i.c.v. choline (150 micrograms) was not altered by bilateral adrenalectomy, but was attenuated by systemic administration of either phentolamine (10 mg kg-1) or the vasopressin antagonist [beta-mercapto-beta,beta-cyclopenta-methylenepropionyl1, O-Me-Tyr2,Arg8]-vasopressin (10 micrograms kg-1). 5. It is concluded that the precursor of acetylcholine, choline, can increase and restore blood pressure in acutely haemorrhaged rats by increasing central cholinergic neurotransmission. Nicotinic receptor activation and an increase in plasma vasopressin and adrenaline level appear to be involved in this effect of choline.

Role of Ca2+ channels in the ability of membrane depolarization to prevent neuronal death induced by trophic-factor deprivation: evidence that levels of internal Ca2+ determine nerve growth factor dependence of sympathetic ganglion cells

Sympathetic neurons depend on nerve growth factor (NGF) for their survival both in vivo and in vitro; these cells die upon acute deprivation of NGF. We studied the effects of agents that cause membrane depolarization on neuronal survival after NGF deprivation. High-K+ medium (greater than or equal to 33 mM) prevented cell death; the effect of K+ was dose-dependent (EC50 = 21 mM). The protection by high K+ was abolished either by withdrawal of extracellular Ca2+ or by preloading the cells with a Ca2+ chelator. The involvement of Ca2+ flux across membranes in high-K+ saving of NGF-deprived neurons was also supported by experiments using Ca2+-channel antagonists and agonists. The Ca2+ antagonists nimodipine and nifedipine effectively blocked the survival-promoting effect of high K+. The Ca2+ agonists Bay K 8644 and (S)-202-791 did not by themselves save neurons from NGF deprivation but did strongly augment the effect of high K+; EC50 was shifted from 21 mM to 13 mM. These data suggest that dihydropyridine-sensitive L-type Ca2+ channels play a major role in the high-K+ saving. The depolarizing agents choline (EC50 = 1 mM) and carbamoylcholine (EC50 = 1 microM), acting through nicotinic cholinergic receptors, also rescued NGF-deprived neurons. The saving effect of nicotinic agonists was not blocked by withdrawal of extracellular Ca2+ but was counteracted by a chelator of intracellular Ca2+, suggesting the possible involvement of Ca2+ release from internal stores. Based on these findings we propose a "Ca2+ set-point hypothesis" for the degree of trophic-factor dependence of sympathetic neurons in vitro.