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

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.

Low serum choline and high serum betaine levels are associated with favorable components of metabolic syndrome in Newfoundland population

BACKGROUND

We investigated the relationships between serum choline and betaine levels with metabolic syndrome-related indices in the general population of Newfoundland.

METHODS

1081 adults were selected from the CODING study. Serum choline and betaine levels were measured. Major confounding factors were controlled in all analyses.

RESULTS

Partial correlation and linear regression analysis showed that serum choline levels were positively associated with systolic blood pressure (r: 0.124), serum TG levels (r: 0.132) and negatively correlated with serum glucose levels (r: -0.121) in males (p < 0.01 for all). In females, serum choline levels were positively correlated with serum TG, TC and HDL levels (r: 0.104 to 0.148, p < 0.05 for all). Serum betaine levels were negatively associated with serum TG, TC, LDL and insulin levels, and with atherogenic index and HOMA-IR index in males (r: -0.081 to -0.179, p < 0.05 for all). In females, serum betaine levels were negatively associated with serum TG, hsCRP and insulin levels, and with HOMA-IR index (r: -0.092 to -0.213, p < 0.05 for all). Moreover, subjects with serum choline levels in the highest tertile showed highest serum TG levels and systolic blood pressure in males, and highest serum lipids levels in females. Subjects with the highest serum betaine levels had the lowest serum lipids levels, atherogenic index, IR severity in males, and the lowest serum TG and hsCRP levels, and IR severity in females.

CONCLUSION

Low serum choline and high serum betaine levels are associated with favorable components of metabolic syndrome in general adults.

Modulation of nesfatin-1-induced cardiovascular effects by the central cholinergic system

Nesfatin-1, a peptide whose receptor is yet to be identified, has been shown to be involved in the modulation of feeding, stress, and metabolic responses. Recently, increasing evidence has supported a modulatory role of nesfatin-1 in cardiovascular activity. We have previously reported that nesfatin-1 causes an increase in blood pressure in normotensive and hypotensive rats by increasing plasma catecholamine, vasopressin, and renin levels. Recent reports suggest that nesfatin-1 may activate the central cholinergic system. However, there is no evidence showing an interaction between central nesfatin-1 and the cholinergic system. Therefore, this study aimed to determine whether the central cholinergic system may have a functional role in the nesfatin-1-induced cardiovascular effect observed in normotensive rats. Intracerebroventricular injection of nesfatin-1 caused short-term increases in mean arterial pressure and heart rate responses including bradycardic/tachycardic phases in normotensive animals. Central injection of nesfatin-1 increased the acetylcholine and choline levels in the posterior hypothalamus, as shown in microdialysis studies. Central pretreatment with the cholinergic muscarinic receptor antagonist atropine and/or nicotinic receptor antagonist mecamylamine blocked nesfatin-1-induced cardiovascular effects. In conclusion, the results show that centrally administered nesfatin-1 produces a pressor effect on blood pressure and heart rate responses including bradycardic/tachycardic phases in normotensive rats. Moreover, according to our findings, the central cholinergic system can modulate nesfatin-1-evoked cardiovascular activity.

Blood borne hormones in a cross-talk between peripheral and brain mechanisms regulating blood pressure, the role of circumventricular organs

Accumulating evidence suggests that blood borne hormones modulate brain mechanisms regulating blood pressure. This appears to be mediated by the circumventricular organs which are located in the walls of the brain ventricular system and lack the blood-brain barrier. Recent evidence shows that neurons of the circumventricular organs express receptors for the majority of cardiovascular hormones. Intracerebroventricular infusions of hormones and their antagonists is one approach to evaluate the influence of blood borne hormones on the neural mechanisms regulating arterial blood pressure. Interestingly, there is no clear correlation between peripheral and central effects of cardiovascular hormones. For example, angiotensin II increases blood pressure acting peripherally and centrally, whereas peripherally acting pressor catecholamines decrease blood pressure when infused intracerebroventricularly. The physiological role of such dual hemodynamic responses has not yet been clarified. In the paper we review studies on hemodynamic effects of catecholamines, neuropeptide Y, angiotensin II, aldosterone, natriuretic peptides, endothelins, histamine and bradykinin in the context of their role in a cross-talk between peripheral and brain mechanisms involved in the regulation of arterial blood pressure.

Alcohol abuse and the injured host: dysregulation of counterregulatory mechanisms review

Traumatic injury ranks as the number one cause of death for the younger than 44 years age group and fifth leading cause of death overall (www.nationaltraumainstitute.org/home/trauma_statistics.html). Although improved resuscitation of trauma patients has dramatically reduced immediate mortality from hemorrhagic shock, long-term morbidity and mortality continue to be unacceptably high during the postresuscitation period particularly as a result of impaired host immune responses to subsequent challenges such as surgery or infection. Acute alcohol intoxication (AAI) is a significant risk factor for traumatic injury, with intoxicating blood alcohol levels present in more than 40% of injured patients. Severity of trauma, hemorrhagic shock, and injury is higher in intoxicated individuals than that of sober victims, resulting in higher mortality rates in this patient population. Necessary invasive procedures (surgery, anesthesia) and subsequent challenges (infection) that intoxicated trauma victims are frequently subjected to are additional stresses to an already compromised inflammatory and neuroendocrine milieu and further contribute to their morbidity and mortality. Thus, dissecting the dynamic imbalance produced by AAI during trauma is of critical relevance for a significant proportion of injured victims. This review outlines how AAI at the time of hemorrhagic shock not only prevents adequate responses to fluid resuscitation but also impairs the ability of the host to overcome a secondary infection. Moreover, it discusses the neuroendocrine mechanisms underlying alcohol-induced hemodynamic dysregulation and its relevance to host defense restoration of homeostasis after injury.

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.

Effect of repeatedly given CDP-choline on cardiovascular and tissue injury in spinal shock conditions: investigation of the acute phase

OBJECTIVES

The protective effect of CDP-choline in spinal cord transection and the mediation of its cardiovascular effects were investigated.

METHODS

Spinal cords of rats were transected at the T1-T2 levels. CDP-choline (250 mg/kg; intravenous) was administered 2 h and/or 24 h after the injury.

KEY FINDINGS

Spinal cord transection caused severe tissue damage, decreased mean arterial pressure, heart rate, plasma adrenaline, and noradrenaline but increased plasma vasopressin levels. Repeated CDP-choline treatment attenuated the degree of tissue injury. Administration of CDP-choline at 2 h after transection transiently increased blood pressure and decreased heart rate, while it produced a small decrease in blood pressure and heart rate when it was given at 24 h. Plasma adrenaline levels were higher in the group where CDP-choline was given repeatedly. Plasma noradrenaline and vasopressin levels did not change additionally after CDP-choline injections in all groups. In order to determine if CDP-choline attenuates the oxidative injury induced by transection, we measured blood superoxide dismutase, glutathione peroxidase activity and malondialdehyde levels. Repeated CDP-choline administration decreased blood superoxide dismutase and glutathione peroxidase activity without any effect on malondialdehyde levels.

CONCLUSIONS

Data indicate that repeated intravenous CDP-choline treatment prevents tissue damage in spinal shock conditions in the acute phase. The cardiovascular effects of the drug do not seem to be responsible for this protection but the drug-induced attenuation of the oxidative stress may play a role.

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.

Cardiovascular effect of peripheral injected melittin in normotensive conscious rats: Mediation of the central cholinergic system

Recently we demonstrated that centrally administrated melittin, a phospholipase A(2) (PLA(2)) activator, caused the pressor effect in normotensive, conscious rats. In the present study, we aimed to determine the cardiovascular effect of peripherally injected melittin and the involvement of the central cholinergic system on these effects in the normotensive conscious rats. For this reason, 250, 500 or 1000microg/kg doses of melittin were injected intraperitoneally to normotensive male Sprague Dawley rats. Melittin produced dose- and time-dependent increases in mean arterial pressure (MAP) and heart rate (HR). Both peripheral (5mg/kg; i.p.) and central (500microg; i.c.v.) pretreatment with indomethacin, nonselective inhibitor of cyclooxygenase (COX) 1 and 2, totally abolished cardiovascular effect of melittin. Intraperitoneal (i.p.) pretreatment with propranolol, a nonselective beta-adrenergic receptor blocker, completely abolished the tachycardic response to melittin. Also, the pressor effect of melittin was partially attenuated in these rats. In order to test the mediation of the central cholinergic system on the pressor and tachycardic effects of melittin, the rats were pretreated with atropine sulfate (10microg; i.c.v.), a cholinergic nonselective muscarinic receptor antagonist, mecamylamine (50microg; i.c.v.), a cholinergic nonselective nicotinic receptor antagonist, methyllycaconitine (10microg; i.c.v.) or alpha-bungarotoxin (10microg; i.c.v.), selective antagonists of alpha7 subtype nicotinic acetylcholine receptors (alpha7nAChRs) 15min prior to melittin (500microg/kg; i.p.) injection. Pretreatment with mecamylamine, methyllycaconitine or alpha-bungarotoxin partially diminished the pressor and tachycardic response to melittin in the normotensive conscious rats whereas pretreatment with atropine sulfate had no effect. In conclusion, our data demonstrate that peripherally administered melittin exerts a clear pressor and tachycardic effect by activating COX pathway. The activation of central cholinergic nicotinic receptors, predominantly alpha7nAChRs, appears to be involved in the pressor and tachycardic effects of the drug.

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.

The involvement of the central cholinergic system in the pressor and bradycardic effects of centrally administrated melittin in normotensive conscious rats

Recently we demonstrated that centrally administrated melittin, a phospholipase A(2) (PLA(2)) activator, caused pressor and bradycardic effect in the normotensive conscious rats. In the current study we aimed to determine the mediation of central cholinergic system in the pressor and bradycardic effect of centrally administrated melittin. Studies were performed in normotensive male Sprague-Dawley rats. 1.5, 3.0 or 6.0microg/5.0microl doses of melittin were injected intracerebroventricularly (i.c.v.). Melittin caused dose- and time-dependent increases in mean arterial pressure (MAP) and decrease in heart rate (HR). In order to test the mediation of central cholinergic system on the pressor and bradycardic effect of melittin, the rats were pretreated with mecamylamine (50microg; i.c.v.), cholinergic nonselective nicotinic receptor antagonist, atropine sulfate (10microg; i.c.v.), a cholinergic nonselective muscarinic receptor antagonist, hemicholinium-3 (20microg; i.c.v.), a high affinity neuronal choline uptake inhibitor, methyllycaconitine (10 and 25microg; i.c.v.) or alpha-bungarotoxin (10 and 25microg; i.c.v.), selective antagonists of alpha-7 subtype nicotinic acetylcholine receptors (alpha7nAChRs), 15min prior to melittin (3.0microg) injection. Pretreatment with mecamylamine, hemicholinium-3, methyllycaconitine or alpha-bungarotoxin partially attenuated the pressor and bradicardia effect of elicited by melittin in the normotensive conscious rats whereas pretreatment with atropine had no effect. In conclusion, i.c.v. administration of melittin increases MAP and decreases HR in conscious rats. The activation of central nicotinic cholinergic receptors, predominantly alpha7nAChRs, partially acts as a mediator in the pressor responses to i.c.v. injection of melittin in the normotensive conscious rats. Moreover, decreased uptake of choline to the cholinergic terminals may consider that melittin activates central choline and acetylcholine release, as well.

Activation of the central cholinergic system mediates the reversal of hypotension by centrally administrated U-46619, a thromboxane A2 analog, in hemorrhaged rats

In the present study, we investigated the role of the central cholinergic system in mediating the pressor effect of intracerebroventricularly administrated U-46619, a thromboxane A2 (TxA2) analog, in hemorrhaged hypotensive rats. Hemorrhage was performed by withdrawing a total volume of 2.1 ml of blood per 100 g body weight over a period of 10 min. Intracerebroventricular (i.c.v.) injection of U-46619 (0.5, 1, 2 micro g) produced a dose- and time-dependent increase in arterial pressure and reversed the hypotension of this condition. Hemorrhage caused small increases in extracellular hypothalamic acetylcholine and choline levels. Intracerebroventricular administration of U-46619 (1 micro g) further increased the levels of extracellular acetylcholine and choline by 57% and 41%, respectively. Pretreatment with SQ-29548 (8 mug; i.c.v.), a selective TxA2 receptor antagonist, completely abrogated the effects of subsequent injection of U-46619 (1 mug; i.c.v.) on arterial pressure and extracellular acetylcholine and choline levels. Pretreatment with mecamylamine (50 micro g; i.c.v.), a cholinergic nonselective nicotinic receptor antagonist, attenuated the pressor effect of U-46619 (1 micro g, i.c.v.) in hemorrhaged rats whereas pretreatment with atropine (10 micro g; i.c.v.), a cholinergic nonselective muscarinic receptor antagonist, had no effect. Interestingly, pretreatment of rats with methyllycaconitine (10 micro g; i.c.v.) or alpha-bungarotoxin (10 micro g; i.c.v.), selective antagonists of alpha-7 subtype nicotinic acetylcholine receptors (alpha7nAChRs), partially abolished the pressor effect of U-46619 (1 micro g; i.c.v.) in the hypotensive condition. Pretreatment with a combination of mecamylamine plus methyllycaconitine or mecamylamine plus alpha-bungarotoxin attenuated the reversal effect of U-46619, but only to the same extent as pretreatment with either antagonist alone. In conclusion, i.c.v. administration of U-46619 restores arterial pressure and increases posterior hypothalamic acetylcholine and choline levels by activating central TxA2 receptors in hemorrhaged hypotensive rats. The activation of central nicotinic cholinergic receptors, predominantly alpha7nAChRs, partially acts as a mediator in the pressor responses to i.c.v. injection of U-46619 under these conditions.

The involvement of central cholinergic system in the pressor effect of intracerebroventricularly injected U-46619, a thromboxane A2 analog, in conscious normotensive rats

The aim of this study was to determine the involvement of the central cholinergic system in the rise in blood pressure evoked by the thromboxane A2 (TxA2) analog, U-46619, given centrally. Intracerebroventricular (i.c.v.) injections of U-46619 (0.5, 1.0 and 2.0 microg) caused dose- and time-related increases in blood pressure and decreased heart rate in awake rats. U-46619 (1 microg; i.c.v.) also produced an approximately 65% increase in posterior hypothalamic extracellular acetylcholine and choline levels. Pretreatment with SQ-29548 (8 microg; i.c.v.), selective TxA2 receptor antagonist, completely inhibited both the cardiovascular responses and the increase in acetylcholine and choline levels to subsequent injection of U-46619 (1 microg; i.c.v.). Atropine (10 microg; i.c.v.), nonselective muscarinic receptor antagonist, pretreatment did not affect the cardiovascular responses observed after U-46619 (1 microg; i.c.v.). Pretreatment with the nonselective nicotinic receptor antagonist, mecamylamine (50 microg; i.c.v.) attenuated the pressor effect of U-46619 (1 microg; i.c.v.). Higher doses of mecamylamine (75 and 100 microg; i.c.v.) pretreatments did not change the magnitude of the blockade of pressor response to U-46619; however, they abolished the bradycardic effect of U-46619 dose-dependently. Interestingly, pretreatment of rats with methyllycaconitine (10 microg; i.c.v.) or alpha-bungarotoxin (10 microg; i.c.v.), selective antagonists of alpha7 subtype of nicotinic acetylcholine receptors (alpha7nAChRs), partially abolished the pressor response to i.c.v. injection of U-46619 (1 microg). Similar to the mecamylamine data, the use of higher doses of methyllycaconitine (25 and 50 microg; i.c.v.) produced the same magnitude of blockade that was observed after the 10 microg methyllycaconitine pretreatment, but it completely abolished the bradycardic effect of U-46619 (1 microg; i.c.v.) at the dose of 25 microg. The present results show that central administration of U-46619 produces pressor and bradycardic effect and increase in hypothalamic acetylcholine and choline levels by activating central TxA2 receptors. The activation of central nicotinic receptors, predominantly alpha7nAChRs, partially mediates the cardiovascular responses to i.c.v. injection of U-46619.

Effects of intracerebroventricularly injected glucagon-like peptide-1 on cardiovascular parameters; role of central cholinergic system and vasopressin

We aimed to investigate the effects of intracerebroventricularly (i.c.v.) injected glucagon-like peptide-1 (GLP-1) on blood pressure and heart rate, and whether central cholinergic system and vasopressinergic system play roles in these effects. Male Wistar albino rats were used throughout the experiments. Blood pressures and heart rates were observed before and for 30 min following drug injections. i.c.v. GLP-1 (100, 500 and 1000 ng/10 microl) caused a dose-dependent increase in both blood pressure and heart rate. Nicotinic receptor antagonist mecamylamine (25 microg/10 microl, i.c.v.) and muscarinic receptor antagonist atropine (5 microg/10 microl, i.c.v.) prevented the stimulating effect of GLP-1 on blood pressure. The effect of GLP-1 on heart rate was blocked only by mecamylamine. The V1 receptor antagonist of vasopressin (B-mercapto B, B-cyclopentamethylenepropionyl, O-Me-Tyr,Arg)-vasopressin (10 microg/kg), that was applied intraarterially, only prevented the effect of GLP-1 on blood pressure, but did not show any effect on heart rate. Our data indicate that i.c.v. GLP-1 increases blood pressure and heart rate, and stimulation of central nicotinic and partially muscarinic receptors and vasopressinergic system play a role in the effects of i.c.v. GLP-1 on blood pressure. The effect of GLP-1 on heart rate may be partially due to stimulation of central nicotinic receptors.

Centrally injected CDP-choline increases plasma vasopressin levels by central cholinergic activation

In the present study, both the effects of intracerebroventricular (i.c.v.) injection of cytidine-5'-diphosphate choline (CDP-choline) on plasma vasopressin levels and the choline involvement of these effects were investigated. I.c.v. administration of CDP-choline (0.5, 1.0 and 2.0 micromol) increased plasma vasopressin levels dose- and time-dependently. I.c.v. injection of equimolar dose of choline (1 micromol) produced similar vasopressin response. However equimolar dose of cytidine (1 micromol; i.c.v.), the other hydrolysis product of CDP-choline, did not affect plasma vasopressin levels. Pretreatment of rats with hemicholinium-3, neuronal high affinity choline uptake inhibitor (20 microg; i.c.v.) blocked the vasopressin response to i.c.v. CDP-choline (1 micromol). Pretreatment of rats with mecamylamine (50 microg; i.c.v.), a nonselective nicotinic receptor antagonist, abolished the increase in plasma vasopressin induced by CDP-choline while atropine (10 microg; i.c.v.), nonselective muscarinic receptor antagonist, failed to change the response. In conclusion, intracerebroventricularly injected CDP-choline can increase plasma vasopressin levels by activating central nicotinic cholinergic receptors through the activation of presynaptic cholinergic mechanisms.

Choline potentiates the pressor response evoked by glycyl-glutamine or naloxone in haemorrhaged rats

1. Severe blood loss initially lowers arterial pressure through a central mechanism that is thought to involve opioid and cholinergic neurons. The present study tested the hypothesis that simultaneous administration of a cholinergic agonist and an opioid receptor antagonist would produce a synergistic effect in the treatment of haemorrhage. Specifically, we tested whether choline, a precursor of acetylcholine, potentiates the pressor effect of the beta-endorphin derived peptide glycyl-glutamine (Gly-Gln) or the opioid receptor antagonist naloxone following acute haemorrhage. 2. Conscious rats were treated intracerebroventricularly (i.c.v.) with choline chloride (180 nmol) alone or combined with Gly-Gln (10 nmol) or naloxone (10 nmol) 2 min after blood withdrawal (2.5 mL/100 g bodyweight over 20 min) was completed; mean arterial pressure and heart rate were monitored for 30 min. 3. Combined treatment with choline and Gly-Gln elevated mean arterial pressure but did not affect heart rate significantly. Choline and Gly-Gln had no effect on cardiovascular function when administered alone to haemorrhaged rats or when given together to normotensive animals. Choline also potentiated the pressor and tachycardic effect of naloxone in haemorrhaged rats. 4. These data show that choline potentiates the pressor effect of Gly-Gln and naloxone in haemorrhaged rats.

Intravenously injected CDP-choline increases blood pressure and reverses hypotension in haemorrhagic shock: effect is mediated by central cholinergic activation

Intravenous (i.v.) administration of cytidine-5'-diphosphate choline (CDP-choline) (100, 250 and 500 mg/kg) increased blood pressure in normal rats and reversed hypotension in haemorrhagic shock. Choline (54 mg/kg; i.v.), at the dose equimolar to 250 mg/kg CDP-choline decreased blood pressure of rats in both conditions and caused the death of all hypotensive animals within 2-5 min. Equimolar dose of cytidine (124 mg/kg; i.v.) did not change cardiovascular parameters. Choline levels in plasma, lateral cerebral ventricle and hypothalamus increased after CDP-choline administration. Intracerebroventricular (i.c.v.) hemicholinium-3 pretreatment (20 microg), greatly attenuated the pressor effect of CDP-choline in both conditions. Atropine pretreatment (10 microg; i.c.v.) did not change the pressor effect of CDP-choline while mecamylamine (50 microg; i.c.v.) abolished the pressor response to drug. Besides, acetylcholine (1 micromol; i.c.v.) produced similar increases in blood pressure in normal and hypotensive conditions to that observed in CDP-choline given rats. CDP-choline (250 mg/kg; i.v.) increased plasma catecholamines and vasopressin levels but not plasma renin activity. Pretreatment of rats with either prazosin (0.5 mg/kg; i.v.) or vasopressin V(1) receptor antagonist, [beta-mercapto,beta,beta-cyclopentamethylenepropionyl(1),O-Me-Tyr(2)-Arg(8)]vasopressin (10 microg/kg; i.v.), attenuated the pressor response to CDP-choline while simultaneous administration of these antagonists before CDP-choline injection completely blocked the pressor effect. Results show that i.v. CDP-choline increases blood pressure and reverses hypotension in haemorrhagic shock. Activation of central nicotinic cholinergic mechanisms by the increases in plasma and brain choline concentrations appears to be involved in the pressor effect of this drug. Moreover, the increases in plasma catecholamines and vasopressin levels mediate these effects.

Hypertonic saline dextran alleviates hepatic injury in hypovolemic rats undergoing porta hepatis occlusion

To monitor the ischemic and/or reperfusion injury after porta hepatis occlusion (Pringle maneuver) in livers subjected to hypotension, serum alanine amino transferase (ALT), liver malondialdehyde (MDA), and liver glutathione (GSH) levels were measured. MDA is a by-product of oxidant-induced lipid peroxidation, and GSH is an endogenous antioxidant. The effects of lactated Ringer's (LR) and hypertonic saline (7.5%)/Dextran (6%; HSD) resuscitation on liver injury, if any, was investigated. Rats in sham (S, n = 8) and five other groups (n = 8) underwent femoral artery and vein catheterization and laparotomy. The hemorrhage and ischemia (HI) group was bled 30% of their blood volume and had their porta hepatis occluded for 30 min. The HI, LR, and HSD groups underwent both hemorrhage and occlusion. Thirty minutes after hemorrhage, the LR and HSD groups received either LR (equivalent to three times the shed blood) or HSD (10 mL/kg) resuscitation over 30 min. Both LR and HSD resuscitation lowered the increased ALT and liver tissue MDA seen in the HI group. ALT was decreased from 348 +/- 93 IU/L in the HI group to 200 +/- 98 IU/L in the LR and 139 +/- 74 IU/L in the HSD groups. Liver tissue MDA was 353 +/- 22 nmol/g/tissue in the HI group and LR decreased it to 261 +/- 17 nmol/g/tissue, whereas HSD decreased it to 273 +/- 20 nmol/g/tissue. The decrease in ALT and the increase in liver GSH were more pronounced with HSD resuscitation (P < 0.05). HSD seems to be more effective than LR in decreasing the liver tissue damage produced by total hepatic inflow occlusion under hypovolemic conditions.

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.

The Effect of RSR13, a Synthetic Allosteric Modifier of Hemoglobin, on Brain Tissue pO2 (Measured by Eproximetry) Following Severe Hemorrhagic Shock in Rats

RSR13 is a synthetic allosteric modifier of hemoglobin that decreases the oxygen binding affinity of hemoglobin, potentially increasing oxygen availability to hypoxic tissues. Using in vivo EPR to directly measure cortical pO2, we examined whether RSR13 would improve brain tissue pO2 following severe hemorrhagic shock in rats. Hemorrhagic shock was induced by withdrawing blood (2.7-2.8 mL/100 g/15 min). Following a 30 min shock period, resuscitation was performed by infusion with Ringer lactate plus RSR13 (150 mg/kg) or saline (control). Following hemorrhage, brain pO2 decreased by about 14 mm Hg in both groups. Following crystalloid resuscitation brain pO2 remained depressed in the control group but returned to the pre-hemorrhage values in the rats that received RSR13. RSR13 immediately increased and maintained the paO2 while controls had a very gradual increase towards pre-hemorrhage values. There was no difference in the blood pressure or heart rate between groups. RSR13 may have useful applications to decrease the effects of acute hemorrhagic hypoxemia by increasing brain oxygenation.

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.

The decline in serum choline concentration in humans during and after surgery is associated with the elevation of cortisol, adrenocorticotropic hormone, prolactin and beta-endorphin concentrations

Serum choline concentrations decrease during and after surgery. We undertook this study to determine whether the decrease of choline is associated with an increase in stress hormones. In 16 patients undergoing abdominal surgery with general anesthesia, circulating choline cortisol, prolactin, adrenocorticotropic hormone (ACTH) and -endorphin levels were measured before, during and after surgery. Choline levels decreased by 41% (P<0.01) during surgery, remained 15-38% decreased for 48 h, and returned to preoperative values 72 h after surgery. The decrease in serum choline was associated and inversely correlated with the increase in serum cortisol (P<0.001; r = -0.642), prolactin (P<0.001; r = -0.756), -endorphin (P<0.001; r = -0.726) and ACTH (P<0.01; r = -0.458). In conclusion, we found that abdominal surgery induces a decline in serum choline associated with an increase in circulating cortisol, prolactin, ACTH and -endorphin.

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.

Central injection of captopril inhibits the blood pressure response to intracerebroventricular choline

In the present study, we investigated the involvement of the brain renin-angiotensin system in the effects of central cholinergic stimulation on blood pressure in conscious, freely moving normotensive rats. In the first step, we determined the effects of intracerebroventricular (icv) choline (50, 100 and 150 microg) on blood pressure. Choline increased blood pressure in a dose-dependent manner. In order to investigate the effects of brain renin-angiotensin system blockade on blood pressure increase induced by choline (150 microg, icv), an angiotensin-converting enzyme inhibitor, captopril (25 and 50 microg, icv), was administered 3 min before choline. Twenty-five microg captopril did not block the pressor effect of choline, while 50 microg captopril blocked it significantly. Our results suggest that the central renin-angiotensin system may participate in the increase in blood pressure induced by icv choline in normotensive rats.

Neural mechanisms in the cardiovascular responses to acute central hypovolaemia

1. The haemodynamic response to acute central hypovolaemia consists of two phases. During phase I, arterial pressure is well maintained in the face of falling cardiac output (CO) by baroreceptor-mediated reflex vasoconstriction and cardio-acceleration. Phase II commences once CO has fallen to a critical level of 50-60% of its resting value, equivalent to loss of approximately 30% of blood volume. 2. During phase II, sympathetic vasoconstrictor and cardiac drive fall abruptly and cardiac vagal drive increases. In humans, this response is invariably associated with fainting and has been termed vasovagal syncope. 3. In both experimental animals and in humans, the responses to acute central hypovolaemia are greatly affected by anaesthetic agents, in that the compensatory responses during phase I (e.g. halothane) or their failure during phase II (e.g. alfentanil) are blunted or abolished. 4. Therefore, our present knowledge of the neurochemical basis of the response to hypovolaemia depends chiefly on the results of experiments in conscious animals. Use of techniques for simulating haemorrhage has greatly enhanced this research effort, by allowing the effects of multiple treatments on the response to acute central hypovolaemia to be tested in the same animal. 5. The results of such experiments indicate that phase II of the response to hypovolaemia is triggered, at least in part, by a signal from cardiac vagal afferents. There is also strong evidence that phase II depends on brainstem delta-opioid receptor and nitrergic mechanisms and can potentially be modulated by circulating or neuronally released adrenocorticotropic hormone, brainstem serotonergic pathways operating through 5-HT1A receptors and opioids acting through mu- and kappa-opioid receptors in the brainstem. 6. Phase II also appears to require input from supramedullary brain centres. Future studies should determine how these neurotransmitter systems interact and their precise neuroanatomical arrangements.

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.

Effect of muscimol on cholinomimetic-induced cardiovascular responses in rats

Brain acetylcholine and gamma-aminobutyric acid (GABA) are both involved in the regulation of central cardiovascular control. Despite data from anatomical and electrophysiological experiments characterizing the interaction between central GABAergic and cholinergic neurotransmission, the potential significance of this interaction in central cardiovascular regulation remains unknown. The purpose of this study was to determine whether activation of GABA(A) receptors by intracerebroventricular or intrahypothalamic administration of muscimol affects the cholinergic agonist-induced cardiovascular responses. All experiments were performed in conscious, Sprague-Dawley rats instrumented with a guide cannula for drug injection and iliac arterial catheters for direct measurement of mean arterial pressure and heart rate. Administration of a cholinergic agonist, carbachol, either intracerebroventricularly or into the dorsomedial hypothalamic nucleus, produced a significant increase in mean arterial pressure, whereas injection of carbachol into the posterior hypothalamic nucleus caused a slight elevation in blood pressure. Pretreatment with muscimol 10 min before administration of carbachol prevented the carbachol-evoked blood pressure changes. On the other hand, carbachol produced variable changes in heart rate, depending on the site of injection. In [3H]quinuclydinyl benzilate binding experiments, muscimol did not displace the muscarinic radioligand from its binding sites, suggesting that it does not exert any direct antagonistic activity at muscarinic receptors. These results suggest that the dorsomedial hypothalamic nucleus is a potential site of action for microinjected carbachol and that the GABAergic system has an inhibitory influence on cholinergic neurons involved in blood pressure regulation.

Pressor and bradycardic effects of tacrine and other acetylcholinesterase inhibitors in the rat

The cardiovascular effects of three different acetylcholinesterase inhibitors: physostigmine, tacrine and rivastigmine injected by intravenous (i.v.) route were compared in freely moving Wistar rats. The three drugs significantly increased both systolic and diastolic blood pressure and decreased heart rate. Compared to physostigmine, a 20-fold higher dose of tacrine and a 40-fold higher dose of rivastigmine was necessary to induce a comparable pressor effect. Tacrine was chosen as a model to study the mechanisms underlying the cardiovascular effects of i.v. cholinesterase inhibitors. Atropine totally abolished while methylatropine did not affect tacrine pressor effects. Conversely, both drugs abolished tacrine-induced bradycardia. The alpha1-adrenoceptor antagonist prazosin or the vasopressin V1 receptor antagonist, [beta-mercapto-beta,beta-cyclopenta-methylenepropionyl1, O-Me-Tyr2, Arg8] vasopressin partially but significantly reduced tacrine pressor effect and mostly abolished it when administered concomitantly. The tacrine pressor response was inhibited in a dose-dependent manner by the i.c.v. administration of the non-selective muscarinic receptor antagonist atropine (ID50 = 1.45 microg), the muscarinic M1 receptor antagonist pirenzepine (ID50 = 4.33 microg), the muscarinic M2 receptor antagonist methoctramine (ID50 = 1.39 microg) and the muscarinic M3 receptor antagonist para-fluoro-hexahydro-sila-difenidol (ID50 = 31.19 microg). Central injection of such muscarinic receptor antagonists did not affect tacrine-induced bradycardia. Our results show that acetylcholinesterase inhibitors induce significant cardiovascular effects with a pressor response mediated mainly by the stimulation of central muscarinic M2 receptors inducing a secondary increase in sympathetic outflow and vasopressin release. Conversely, acetylcholinesterase inhibitor-induced bradycardia appears to be mediated by peripheral muscarinic mechanisms.

The effects of G-CSF treatment and starvation on bacterial translocation in hemorrhagic shock

BACKGROUND

Bacterial translocation is thought to be responsible for infectious complications after hemorrhagic shock. The aim of this study is to investigate the effects of granulocyte colony-stimulating factor (G-CSF) treatment on bacterial translocation in starved or fed animals subjected to hemorrhagic shock.

MATERIALS AND METHODS

Fifty Wistar albino rats (200-275 g) were divided into six groups such as naive control (n = 7), G-CSF treatment (n = 7), hemorrhagic shock in starved rats (n = 9), hemorrhagic shock in fed rats (n = 9), G-CSF treatment 24 h before hemorrhagic shock in starved rats (n = 9), and G-CSF treatment 20 min after hemorrhagic shock in fed rats (n = 9). Hemorrhagic shock was induced by withdrawal of 2.1 ml/100 g blood via a carotid arterial cannulae placed under sodium pentobarbital anesthesia. Twenty-four hours later, mesenteric lymph nodes, liver, spleen, and peripheral blood samples were evaluated by using a quantitative microbiological technique and the numbers of colony-forming units were compared between groups.

RESULTS

No bacteria was detected in samples from naive controls or G-CSF-treated unshocked rats. In animals subjected to hemorrhage, Escherichia coli was the predominant pathogen together with Streptococcus faecalis, Pseudomonas, and Lactobacillus species. In this model, starvation augmented the magnitude of bacterial translocation while G-CSF treatment has virtually abolished it.

CONCLUSION

Under experimental conditions, preshock starvation increases gut-derived bacterial translocation and administration of G-CSF before or after hemorrhagic insult significantly reduces it.

Central cardiovascular effects of tacrine in the conscious dog: a role for catecholamines and vasopressin release

Centrally acting cholinergic agents are currently reported to increase blood pressure in various species through the stimulation of muscarinic cholinoceptors. Moreover, several cardiovascular adverse effects have been reported from clinical studies. The aim of this study was to investigate the effects of tacrine, an acetylcholinesterase inhibitor which has been reported to have therapeutic potential in Alzheimer's disease, on blood pressure and two vasopressor systems (sympathetic and vasopressinergic) in Beagle dogs. Intravenous (i.v.) tacrine (2 mg kg(-1)) induced, in conscious and anesthetized dogs, an increase in systolic and diastolic blood pressure, accompanied by bradycardia. This increase was dose-dependent with a peak effect at 1.5 min following administration. Tacrine also induced an increase in noradrenaline, adrenaline and vasopressin plasma levels. Pretreatment with the muscarinic receptor antagonist, atropine (2 mg kg(-1), i.v.), abolished the pressor response to i.v. injection of tacrine while pretreatment with the peripheral muscarinic receptor antagonist, methylscopolamine (0.2 mg kg(-1), i.v.), did not alter the increase in blood pressure. Similarly, noradrenaline and adrenaline changes in plasma levels were not modified by methylscopolamine but were abolished by atropine pretreatment. A similar tendency although not significant was observed for vasopressin plasma levels. The present results demonstrate that in dogs, tacrine (2 mg kg(-1), i.v.) stimulates central muscarinic cholinoceptors to increase blood pressure through activation of the two components of the sympathetic nervous system (i.e., neuroneuronal noradrenergic and the neurohormonal adrenergic pathways) as well as through increasing noradrenaline, adrenaline and vasopressin plasma levels.

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.

Decreased serum choline concentrations in humans after surgery, childbirth, and traumatic head injury

The serum levels of choline decreased by approximately 50% in patients having a surgery under general as well as epidural anesthesia. The decrease is lasts for two days after surgery. Intravenous administration of succinylcholine, either by a single bolus injection or by a slow continuous infusion, increased the serum choline levels several folds during surgery. In these patients, a significant decrease in the serum choline levels was observed one and two days after surgery. In 16 pregnant women at the term, serum choline levels were higher than the value observed in 19 nonpregnant women. The serum choline levels decreased by about 40% or 60% after having a childbirth either by vaginal delivery or caesarean section, respectively. Serum choline levels in blood obtained from 9 patients with traumatic head injury were significantly lower than the observed levels in blood samples obtained from healthy volunteers. These observations show that serum choline levels increase during pregnancy and decrease during stressful situations in humans.

Cardiovascular effects of centrally injected tetrahydroaminoacridine in conscious normotensive rats

In freely moving rats, intracerebroventricularly (i.c.v.) injected tetrahydroaminoacridine (10, 25, 50 microg) increased blood pressure and decreased heart rate in a dose- and time-dependent manner. Intravenous (i.v.) tetrahydroaminoacridine (1 and 3 mg/kg) also increased blood pressure. Atropine sulphate (10 microg; i.c.v.) pretreatment greatly attenuated the blood pressure response to i.c.v. tetrahydroaminoacridine while mecamylamine (50 microg; i.c.v.) failed to change the pressor effect. Neither atropine sulphate nor mecamylamine pretreatment affected the bradycardia induced by tetrahydroaminoacridine. However, the bradycardic response was completely blocked by atropine methylnitrate (2 mg/kg; i.p.) pretreatment. The pressor response to i.c.v. tetrahydroaminoacridine was associated with a several-fold increase in plasma levels of vasopressin, adrenaline and noradrenaline, but not of plasma renin. Pretreatment with prazosin (0.5 mg/kg; i.v.) attenuated the pressor effect without changing the bradycardia. Vasopressin V1 receptor antagonist [beta-mercapto-beta,beta-cyclopentamethylenepropionyl1,O-Me-Tyr2-A rg8]vasopressin (10 microg/kg; i.v.) pretreatment also partially inhibited the pressor response to i.c.v. tetrahydroaminoacridine and abolished the bradycardia. Tetrahydroaminoacridine's cardiovascular effects were completely blocked when rats were pretreated with prazosin plus vasopressin antagonist. The data show that tetrahydroaminoacridine increases blood pressure in normotensive freely moving rats by activating central muscarinic cholinergic transmission. Increases in plasma catecholamines and vasopressin are both involved in this response. The tetrahydroaminoacridine-induced reduction in heart rate appears to be due to the increase in vagal tone and plasma vasopressin.

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.

Physostigmine has a life-saving effect in rats subjected to prolonged respiratory arrest

We have previously reported that centrally-acting cholinomimetic drugs have a prompt and sustained resuscitating effect in pre-terminal conditions of hemorrhagic shock in rats. Here we have studied the effect of physostigmine in another experimental condition of hypoxia in anesthetized rats, which were endotracheally intubated and subjected to prolonged (5 min) interruption of ventilation. This led to a dramatic fall in mean arterial pressure (MAP), pulse pressure (PP), heart rate (HR), pH, PO2, SO2 and base excess, while PCO2 increased; the electroencephalogram (EEG) became isoelectric, and the electrocardiogram (ECG) showed marked bradycardia, P-wave inversion, partial atrio-ventricular block and S-T segment elevation; all saline-treated rats died of cardiac arrest within 7.01 +/- 0.85 min of ventilation being resumed. When ventilation resumption was associated with the simultaneous intravenous (i.v.) injection of physostigmine (70 microg/kg) there was an almost immediate and impressive increase in MAP, PP and HR, with normalization of ECG within 4 min and full recovery of EEG after 30-50 min. This was associated with a normalization of blood gases and pH. Fifteen days later 40% of treated animals were still alive and apparently in normal health, the mean survival time of the remaining 60% animals being 22.67 +/- 10.19 h. Pretreatment with atropine sulfate or hemicholinium-3 did not modify the response to physostigmine, which, however, was strongly antagonized by the intracerebroventricular injection of mecamylamine. These results suggest that centrally-acting cholinomimetic agents may have a resuscitating effect in pre-terminal conditions produced by prolonged asphyxia, probably through the direct activation of nicotinic receptors in the central nervous system.

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.