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

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.

Severity of locomotor and cardiovascular derangements after experimental high-thoracic spinal cord injury is anesthesia dependent in rats

Anesthetics affect outcomes from central nervous system (CNS) injuries differently. This is the first study to show how two commonly used anesthetics affect continuously recorded hemodynamic parameters and locomotor recovery during a 2-week period after two levels of contusion spinal cord injury (SCI) in rats. We hypothesized that the level of cardiovascular depression and recovery of locomotor function would be dependent upon the anesthetic used during SCI. Thirty-two adult female rats were subjected to a sham, 25-mm or 50-mm SCI at T3-4 under pentobarbital or isoflurane anesthesia. Mean arterial pressure (MAP) and heart rate (HR) were telemetrically recorded before, during, and after SCI. Locomotor function recovered best in the 25-mm-injured isoflurane-anesthetized animals. There was no significant difference in locomotor recovery between the 25-mm-injured pentobarbital-anesthetized animals and the 50-mm-injured isoflurane-anesthetized animals. White matter sparing and extent of intermediolateral cell column loss appeared larger in animals anesthetized with pentobarbital, but this was not significant. There were no differential effects of anesthetics on HR and MAP before SCI, but recovery from anesthesia was significantly slower in pentobarbital-anesthetized animals. At the time of SCI, MAP was acutely elevated in the pentobarbital-anesthetized animals, whereas MAP decreased in the isoflurane-anesthetized animals. Hypotension occurred in the pentobarbital-anesthetized groups and in the 50-mm-injured isoflurane-anesthetized group. In pentobarbital-anesthetized animals, SCI resulted in acute elevation of HR, although HR remained low. Return of HR to baseline was much slower in the pentobarbital-anesthetized animals. Severe SCI at T3 produced significant chronic tachycardia that was injury severity dependent. Although some laboratories monitor blood pressure, HR, and other physiological variables during surgery for SCI, inherently few have monitored cardiovascular function during recovery. This study shows that anesthetics affect hemodynamic parameters differently, which in turn can affect functional outcome measures. This supports the need for a careful evaluation of cardiovascular and other physiological measures in experimental models of SCI. Choice of anesthetic should be an important consideration in experimental designs and data analyses.

Compensatory mechanisms to maintain blood pressure in paraplegic rats: implication of central tachykinin NK-1 and NK-3 receptors?

People with high level spinal cord injury (SCI) suffer from both hypotension and spontaneous hypertension due to loss of supraspinal control of spinal sympathetic outflow. Few reports have addressed whether any changes occur in central regulation of blood pressure (BP) and heart rat (HR) at the supraspinal level. Central tachykinin NK-1 and NK-3 receptors are located in many cardiovascular areas in the brain and are known to modulate BP and HR. This study examined the intracerebroventricular (i.c.v.) effects of the selective NK-1 receptor agonist [Sar(9), Met(O(2))(11)]SP (65pmol, n=6) and NK-3 receptor agonist senktide (650pmol, n=6) on mean arterial pressure (MAP) and HR before and after complete spinal cord transection at thoracic level 4 (T4). [Sar(9), Met(O(2))(11)]SP evoked increases in MAP and HR which were still present 4days after the T4 SCI. Further analysis using the beta(1)-adrenoceptor antagonist atenolol (10mgkg(-1)) revealed an increased contribution of HR in the MAP increase after SCI. For senktide, 2 and 5weeks after T4 SCI, the rise in MAP induced by senktide was significantly increased in magnitude and was similar to a normal response at 8weeks. These effects were accompanied by a bradycardia, which was still present and amplified at 8weeks. Our results reveal a transient potentiation of the senktide-mediated MAP effect and a greater contribution of the HR in MAP increase by [Sar(9), Met(O(2))(11)]SP in T4 transected rats. Although the significance of these changes remains to be established. This suggest a reorganization of supraspinal mechanisms regulating BP and HR after a high level SCI. Central NK-1 and NK-3 receptors might therefore contribute to the maintenance of MAP following high thoracic SCI.

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.

Selective blockade of central m1 muscarinic cholinergic receptors with pirenzepine impairs cardiovascular and respiratory function in rats with acute hemorrhage

Ultrasound studies showed that selective antagonist of central M1 muscarinic cholinergic receptors pirenzepine (50 mg/kg intravenously) causes transitory hypotension and respiratory depression in anesthetized intact rats. The M1 receptor antagonist had no effect on cardiac output and portal blood flow. Pretreatment with pirenzepine increased the sensitivity of rats with acute massive hemorrhage to circulatory hypoxia. After blockade of central M1 muscarinic cholinergic receptors, the posthemorrhagic period was characterized by primary decompensation of blood pressure, portal blood flow, and respiration and development of low cardiac output syndrome. The animals died over the first minutes after bleeding arrest. Our results indicate that central M1 muscarinic cholinergic receptors act as shock-limiting cholinergic structures under conditions of posthemorrhagic changes in systemic and portal blood flow, as well as during respiratory dysfunction.

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.

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.