Brain M3 muscarinic receptors are involved in the ACTH-induced reversal of hemorrhagic shock

Venous Waveform Analysis Correlates With Echocardiography in Detecting Hypovolemia in a Rat Hemorrhage Model

BACKGROUND

Assessing intravascular hypovolemia due to hemorrhage remains a clinical challenge. Central venous pressure (CVP) remains a commonly used monitor in surgical and intensive care settings for evaluating blood loss, despite well-described pitfalls of static pressure measurements. The authors investigated an alternative to CVP, intravenous waveform analysis (IVA) as a method for detecting blood loss and examined its correlation with echocardiography.

METHODS

Seven anesthetized, spontaneously breathing male Sprague Dawley rats with right internal jugular central venous and femoral arterial catheters underwent hemorrhage. Mean arterial pressure (MAP), heart rate, CVP, and IVA were assessed and recorded. Hemorrhage was performed until each rat had 25% estimated blood volume removed. IVA was obtained using fast Fourier transform and the amplitude of the fundamental frequency (f1) was measured. Transthoracic echocardiography was performed utilizing a parasternal short axis image of the left ventricle during hemorrhage. MAP, CVP, and IVA were compared with blood removed and correlated with left ventricular end diastolic area (LVEDA).

RESULTS

All 7 rats underwent successful hemorrhage. MAP and f1 peak amplitude obtained by IVA showed significant changes with hemorrhage. MAP and f1 peak amplitude also significantly correlated with LVEDA during hemorrhage (R = 0.82 and 0.77, respectively). CVP did not significantly change with hemorrhage, and there was no significant correlation between CVP and LVEDA.

CONCLUSIONS

In this study, f1 peak amplitude obtained by IVA was superior to CVP for detecting acute, massive hemorrhage. In addition, f1 peak amplitude correlated well with LVEDA on echocardiography. Translated clinically, IVA might provide a viable alternative to CVP for detecting hemorrhage.

Cardiovascular effects of H3 histamine receptor inverse agonist/ H4 histamine receptor agonist, clobenpropit, in hemorrhage-shocked rats

Hemorrhagic shock has a potential to be life-threatening when it is not treated. The main causes of hemorrhagic shock involve: (1) forces causing injury; and (2) diseases that can cause hemorrhage., Therefore, due to the causes of hemorrhagic shock and the life-threatening potential, the search for new methods of shock treatment is extremely valuable to the modern medicine. The aim of this study was to investigate the influence of clobenpropit in the model of hemorrhagic shock. The experiments were conducted in 110 adult male Wistar rats weighing between 205 and 470g. 1, 2 and 5 μmol/kg of intravenous H₃ receptors reverse agonists, clobentropit, and/or 1, 5 and 10 μmol/kg H₃ receptor agonist, imetit, were used as general anesthetics. Irreversible hemorrhagic shock was induced by the paused bleeding until the mean arterial pressure (MAP) lowered to the level of 20–25 mmHg. It was proved that, in cases of critical hypotension, clobenpropit triggered a dose-dependent increase of: systolic blood pressure (SBP), diastolic blood pressure (DBP), MPA and heart rate (HR) of rats with critical hypotension. The most significant changes in hemodynamic parameters were achieved by administrating dosages of 2 mmol/kg. This resulted in the survival rate increase to up to 100%. However, imetit did not trigger any hemodynamic changes nor an increase in SBP, DBP, MAP or HR. Furthermore, it was found that the premedication with prazosin, yohimbine, 6-hydroxydopamine and the vasopressin V_1a receptor antagonist blocked the effects of clobenpropit. Additionally, premedication with propranolol, captopril and ZD 7155 did not cause any significant changes in the measured hemodynamic parameters. In conclusion, after an intravenous injection clobenpropit, the inverse agonist of H₃ histamine receptors/agonist of histamine receptors H₄, causes a resuscitating effect on rats in hemorrhagic shock. Moreover, such effect is based on the effector mechanisms of sympathetic nervous system and vasopressin.

Endogenous Central Histamine-Induced Reversal of Critical Hemorrhagic Hypotension in Rats: Studies with l-Histidine

Activation of the histaminergic system is characteristic of response to the action of adverse or potentially dangerous stimuli that disturb circulatory homeostasis, such as dehydration and changes in blood pressure. Previous study demonstrates that inhibition of histamine N-methyltransferase, which catabolizes histamine released from neurons, leads to the increase in endogenous central histamine concentrations and to the reversal of critical hemorrhagic hypotension. In the present study, the influence of intraperitoneal loading with histamine precursor L-histidine on central cardiovascular regulation was studied in a model of irreversible pressure-controlled hemorrhagic shock. Experiments were carried out in male Wistar rats anesthetized with ketamine/xylazine subjected to critical hemorrhagic hypotension of 20 to 25 mmHg, which resulted in the death of all control saline-treated animals within 30 min. L-histidine administered in 5 min of critical hypotension produced dose-dependent increases in mean arterial pressure and heart rate (100-500 mg/kg), and a 100% survival rate of 2 h (500 mg/kg), whereas in normotensive animals, it did not influence cardiovascular parameters. The resuscitating effect of L-histidine (500 mg/kg) was associated with increases in histamine concentrations in the cerebral cortex (0.97 +/- 0.11 nmol/g of wet tissue vs. 0.67 +/- 0.22 nmol/g of wet tissue; P<0.05), hypothalamus (4.78 +/- 0.58 nmol/g of wet tissue vs. 4.08 +/- 0.43 nmol/g of wet tissue; P<0.01), and medulla oblongata (0.55 +/- 0.18 nmol/g of wet tissue vs. 0.34 +/- 0.09 nmol/g of wet tissue; P<0.05), as well as with no changes in plasma histamine concentrations in comparison with the saline-treated group 20 min after injection. Pretreatment with (S)-alpha-fluoromethylhistidine (alpha-FMH, 0.5 mg intracerebroventricularly), an irreversible inhibitor of L-histidine decarboxylase, produced a decrease in central histamine concentrations and diminished volumes of blood required to achieve critical hypotension. Moreover, alpha-FMH inhibited L-histidine-induced increases in central histamine concentrations and its resuscitating effect. In conclusion, the increase in central histamine concentrations after loading with L-histidine in rats subjected to critical hemorrhagic hypovolemia leads to the reversal of hypotension and the improvement in the survival rate of 2 h. On the other hand, inhibition of L-histidine decarboxylase activity, and thus histamine synthesis, produces a decrease in hemodynamic stability in hypotension, which suggests the histaminergic system-induced activation of compensatory mechanisms in hemorrhagic shock.

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.

Role of neuronal and vascular Ca(2+)-channels in the ACTH-induced reversal of haemorrhagic shock

1. In a rat model of volume-controlled haemorrhagic shock causing the death of all control (saline-treated) animals within 30 min, the intravenous (i.v.) bolus injection of ACTH-(1-24) at a dose of 160 micrograms kg-1 produced an impressive and sustained restoration of arterial pressure, pulse pressure and respiratory function, with 100% survival at the end of the observation period (2 h). 2. Both intracerebroventricular (i.c.v., 0.015-0.06 microgram kg-1) and i.v. (5 micrograms kg-1) pretreatment with the N-calcium channel blocker, omega-conotoxin GVIA, and i.v. (but not i.c.v.) pretreatment with the L-calcium channel blocker, nicardipine (125-500 micrograms kg-1) dose-dependently prevented the ACTH-induced shock reversal. 3. These results further indicate that the effect of ACTH in haemorrhagic shock may involve a neuronal link and the eventual restoration of vascular tone mediated by N- and L-type calcium channels, respectively.

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.

Nicotine reverses hemorrhagic shock in rats

Cholinergic mechanisms are currently thought to play an essential role in blood pressure homeostasis. Here we show that, in urethane-anaesthetized rats bled to severe hemorrhagic shock, the i.v. administration of nicotine 0.2-50 micrograms/kg causes a prompt, sustained and dose-dependent improvement in cardiovascular and respiratory functions, the animals' survival rate being significantly higher than that of animals treated with saline. These effects are prevented by bilateral cervical vagotomy and by concurrent local anaesthesia of the carotid bodies, which suggests that stimulation of visceral afferents is the main mechanism of action of nicotine in hemorrhagic shock.