Nicotine reverses hemorrhagic shock in rats

Melanocortins and the cholinergic anti-inflammatory pathway

Experimental evidence indicates that small concentrations of inflammatory molecules produced by damaged tissues activate afferent signals through ascending vagus nerve fibers, that act as the sensory arm of an "inflammatory reflex". The subsequent activation of vagal efferent fibers, which represent the motor arm of the inflammatory reflex, rapidly leads to acetylcholine release in organs of the reticuloendothelial system. Acetylcholine interacts with α7 subunit-containing nicotinic receptors in tissue macrophages and other immune cells and rapidly inhibits the synthesis/release of tumor necrosis factor-α and other inflammatory cytokines. This neural anti-inflammatory response called "cholinergic anti-inflammatory pathway" is fast and integrated through the central nervous system. Preclinical studies are in progress, with the aim to develop therapeutic agents able to activate the cholinergic anti-inflammatory pathway. Melanocortin peptides bearing the adrenocorticotropin/α-melanocyte-stimulating hormone sequences exert a protective and life-saving effect in animals and humans in conditions of circulatory shock. These neuropeptides are likewise protective in other severe hypoxic conditions, such as prolonged respiratory arrest, myocardial ischemia, renal ischemia and ischemic stroke, as well as in experimental heart transplantation. Moreover, experimental evidence indicates that melanocortins reverse circulatory shock, prevent myocardial ischemia/reperfusion damage and exert neuroprotection against ischemic stroke through activation of the cholinergic anti-inflammatory pathway. This action occurs via stimulation of brain melanocortin MC3/MC4 receptors. Investigations that determine the molecular mechanisms of the cholinergic anti-inflammatory pathway activation could help design of superselective activators of this pathway.

Melanocortins as potential therapeutic agents in severe hypoxic conditions

Melanocortin peptides with the adrenocorticotropin/melanocyte-stimulating hormone (ACTH/MSH) sequences and synthetic analogs have protective and life-saving effects in experimental conditions of circulatory shock, myocardial ischemia, ischemic stroke, traumatic brain injury, respiratory arrest, renal ischemia, intestinal ischemia and testicular ischemia, as well as in experimental heart transplantation. Moreover, melanocortins improve functional recovery and stimulate neurogenesis in experimental models of cerebral ischemia. These beneficial effects of ACTH/MSH-like peptides are mostly mediated by brain melanocortin MC(3)/MC(4) receptors, whose activation triggers protective pathways that counteract the main ischemia/reperfusion-related mechanisms of damage. Induction of signaling pathways and other molecular regulators of neural stem/progenitor cell proliferation, differentiation and integration seems to be the key mechanism of neurogenesis stimulation. Synthesis of stable and highly selective agonists at MC(3) and MC(4) receptors could provide the potential for development of a new class of drugs for a novel approach to management of severe ischemic diseases.

Drug-induced activation of the nervous control of inflammation: a novel possibility for the treatment of hypoxic damage

Together with undernutrition and, on the opposite, overeating and obesity, sudden tissue hypoperfusion is the most important cause of mortality and disability worldwide. Tissue hypoperfusion/hypoxia rapidly triggers an unrestrained inflammatory cascade that is the main responsible for the severity of the eventual outcome. The brain plays a key role in inflammation, either through activation of the hypothalamic-pituitary-adrenal humoral response or through activation of the vagal "cholinergic anti-inflammatory pathway". Both humoral and nervous brain responses to inflammation are under the regulatory control of melanocortins, which have moreover a direct anti-inflammatory effect on inflammatory cells. Abundant experimental and clinical evidence indicates that MC(3)/MC(4) melanocortin receptor agonists and cholinergic receptor agonists (mainly at the α7-nicotinic subtype) should by now be considered as completely innovative, effective drugs for the treatment of hypoxic conditions; melanocortin agonists being practically devoid of harmful side effects.

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.

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.

The reversal of experimental hemorrhagic shock induced by nicotine and dimethylphenylpiperazinium is adrenal-dependent

In a rat model of volume-controlled hemorrhagic shock causing the death of all control animals within 30 min, the intravenous injection of either nicotine (50 micrograms/kg) or dimethylphenylpiperazinium (DMPP) (0.5 micrograms/kg) produced a rapid and sustained reversal of the shock condition, with 100% survival 2 h after treatment. Bilateral adrenalectomy completely prevented the anti-shock effect of the two drugs, even though administered at higher doses (150 micrograms/kg in the case of nicotine; 10 micrograms/kg in the case of DMPP). It is concluded that stimulation of adrenaline release plays a fundamental role in the mechanism of action of nicotine- and DMPP-induced shock reversal.

The opioid/anti-opioid balance in shock: a new target for therapy in resuscitation

Teleologically, pain is of paramount importance for survival and induces the organism to cope in an active way with aggressions from a basically hostile environment. While the activation of endogenous analgesic (opioid) systems typically occurs in conditions of surrender (pre-terminal conditions, sustained tortures, etc.), the activation of endogenous anti-analgesic systems triggers mechanisms of active or passive defence (such as camouflage) aimed at survival. The distinctive features of the main anti-analgesic systems (melanocortinergic, cholecystokininergic, thyroliberinergic) and the dramatic results obtained in experimental pre-terminal conditions (hemorrhagic shock, prolonged respiratory arrest) with the administration of their neuropeptide transmitters (ACTH and several ACTH-fragments, including alpha-MSH, CCK peptides and thyrotropin-releasing hormone) are here reviewed. The study of the mechanisms underlying the resuscitating effects of these neuropeptides has led to the discovery of the (often extremely potent) resuscitating effect of other drugs (protoveratrines, nicotine, centrally-acting cholinergic agents, ganglion-stimulating drugs). It is particularly remarkable that in pre-terminal conditions these neuropeptides and drugs have highly impressive effects on cardiocirculatory parameters at doses that are almost or actually inactive under normal conditions, and that their resuscitating effect is obtained without the need for any other supportive treatment and at dose-levels well below toxic ranges. Finally, in hemorrhage-shocked animals, the treatment with anti-analgesic neuropeptides shortly after bleeding considerably extends the time-limit for an effective and definitively curing blood reinfusion. This would be of self-evident importance in clinical practice, because an extremely simple, non-toxic first-aid treatment in the field, shortly after a massive hemorrhage, could resuscitate the patient for a period sufficient to effectively set up the most appropriate in-hospital treatment.

Reversal of hemorrhagic shock in rats by oxotremorine: the role of muscarinic and nicotinic receptors, and AV3V region

In an experimental model of hemorrhagic shock resulting in the death of almost all rats within 20-30 min, centrally active cholinomimetic drugs are reported to induce a prompt, sustained and dose-dependent improvement in blood pressure and survival rate claimed to be due to nicotinic, but not muscarinic actions. In the present study, cholinergic receptor agonist, oxotremorine (50 micrograms/kg, i.v.) increased mean arterial pressure (from 22 +/- 1 to 123 +/- 3 mm Hg) and 60 min-survival rate (from 0% to 92%) in rats bled to hypovolemic shock. Atropine (2 mg/kg, i.v.) pretreatment inhibited the pressor effect of oxotremorine significantly, but did not modify its effect on survival rate. On the other hand, pretreatment with mecamylamine (50 micrograms, i.c.v.) almost abolished the reduction in mortality rate, but inhibited the pressor effect of oxotremorine, partially. These results indicate that oxotremorine-induced pressor response and decrease in mortality in rats with severe hemorrhagic shock are primarily mediated via central muscarinic and nicotinic receptors, respectively. AV3V region was previously reported to be involved in pressor and natriuretic effects of i.c.v. carbachol in normotensive rats. In the present study, the electrolytic lesions of AV3V region significantly inhibited oxotremorine-induced increases in both blood pressure and survival rate in rats subjected to hemorrhagic shock. These findings indicate that AV3V region plays a major role in cholinergic cardiovascular control in hypotensive animals as well as normotensives.

Reversal of experimental hemorrhagic shock by dimethylphenylpiperazinium (DMPP)

In a rat model of hemorrhagic shock which caused the death of all control rats within 30 min, i.v. injection of the ganglion-stimulating drug dimethylphenylpiperazinium (DMPP) caused a dose-dependent reversal of the shock condition--without the need for reinfusion of the shed blood--starting from the dose of 4 ng/kg i.v. Shock reversal was associated with the mobilization of residual blood and improvement in blood flow, particularly at the carotid level. These results could influence our thinking on pathophysiology and first-aid management of shock.

Influence of ACTH-(1-24) on metabolic acidosis and hypoxemia induced by massive hemorrhage in rats

In anesthetized rats, step-wise bleeding to a severe condition of hemorrhagic shock causes a decrease in arterial and venous pH and in venous PO2 and SO2 and an increase in arterial PO2 and in venous PCO2 and lactic acid. The intravenous bolus injection of ACTH-(1-24) (160 micrograms/kg)--which causes a rapid and sustained reversal of the shock condition--produces a gradual and almost complete recovery (within 60 min) of venous PO2, PCO2 and SO2; on the other hand, the normalization of blood pH and lactate is preceded by a further worsening during the first minutes after treatment. On the whole, these data are compatible with the ACTH-(1-24)-induced mobilization of the residual blood--which is pooled in poorly oxygenated tissues--and with the improved circulatory and respiratory functions.