Cannabinoid CB(1) receptor blockade enhances the protective effect of melanocortins in hemorrhagic shock in the rat.

Activation of peripheral cannabinoid CB(1) receptors contributes to hemorrhagic hypotension, and endocannabinoids produced by macrophages and platelets may be mediators of this effect. A number of studies have provided evidence that functional links exist in the mechanisms of action of cannabinoids and opioid peptides; and opioids too play an important role in the pathophysiology of hemorrhagic hypotension and shock. On the other hand, melanocortin peptides, which are the main endogenous functional antagonists of opioid peptides, have an antishock effect in animals and humans. Thus, we investigated whether an interaction exists between endocannabinoids and the endogenous opioid/antiopioid system also in a condition of hemorrhagic shock and, particularly, whether the blockade of cannabinoid CB(1) receptors potentiates the antishock effect of melanocortins. Urethane-anesthetized rats were stepwise bled until mean arterial pressure decreased to, and stabilized at, 21-23 mm Hg. In this model of hemorrhagic shock, which caused the death of all control rats within 30 min after vehicle (tween 80, 5% in saline) injection, the intravenous (i.v.) bolus injection of the cannabinoid CB(1) receptor antagonist N-piperidino-5-[4-chlorophenyl]-1-[2,4 dichlorophenyl]-4-methyl-3-pyrazolecarboxamide (SR141716A) increased mean arterial pressure, pulse pressure, respiratory rate and survival rate in a dose-related manner (0.1-3 mg/kg), an almost complete recovery of mean arterial pressure, pulse pressure and respiratory rate, and 100% survival at the end of the observation period (2 h), occurring with the dose of 3 mg/kg. The melanocortin ACTH-(1-24) (adrenocorticotropin) also produced in a dose-related manner (0.02-0.16 mg/kg i.v.) a restoration of cardiovascular and respiratory functions, and increased survival rate, an almost complete recovery and 100% survival at the end of the observation period (2 h) occurring with the dose of 0.16 mg/kg. When a subactive dose of SR141716A (0.2 mg/kg; 30% survival) was associated with a subactive dose of ACTH-(1-24) (0.02 mg/kg; 12% survival), a complete reversal of the shock condition was obtained with 100% survival at the end of the 2-h observation period. The present results show that the concurrent inhibition of both endogenous opioid and cannabinoid systems produces a reversal of hemorrhagic shock more effective than that produced by the inhibition of either of them. These data suggest that functional interactions between endocannabinoids and opioid/antiopioid are at work also in the pathophysiology of hemorrhagic shock.

MC(3) receptors are involved in the protective effect of melanocortins in myocardial ischemia/reperfusion-induced arrhythmias.

Myocardial ischemia/reperfusion induces ventricular tachycardia (VT), ventricular fibrillation (VF) and a high degree of lethality. Since ACTH-(1-24) (adrenocorticotropin) protects against such injuries in rats, we investigated which melanocortin MC receptor is involved. Ischemia was produced in anesthetized rats by ligature of the left anterior descending coronary artery (5 min), and reperfusion-induced VT, VF, lethality and time-course of arterial blood pressure within the 5 min following reperfusion were evaluated. I.v. administration of the selective MC(3) receptor agonist gamma(1)-melanocyte-stimulating hormone (gamma(1)-MSH), as well as of an equimolar dose (162 nmol/kg) of both the non-selective agonist ACTH-(1-24) and alpha-MSH, significantly prevented VT and VF, and increased survival. Coronary reperfusion was followed by an abrupt and massive fall in mean arterial pressure and pulse pressure, in saline-treated rats. Treatment either with ACTH-(1-24) or gamma(1)-MSH completely prevented such fall. The protective effect of ACTH-(1-24) against the occurrence of VT, VF and lethality was neither affected by adrenalectomy, nor by i.v. pretreatment with the selective MC(4) receptor antagonist HS014 and the MC(4)-MC(5) antagonist HS059. On the other hand, the MC(3)-MC(4) receptor antagonist SHU 9119 prevented such protective effect. Moreover, the selective MC(1) receptor agonist MS05 (162 nmol/kg i.v.) failed to reduce the incidence of arrhythmias and lethality. These data demonstrate that MC(3) receptors mediate the protective effect of melanocortins in myocardial ischemia/reperfusion-induced arrhythmias, in rats.

Involvement of the central nervous system in the protective effect of melanocortins in myocardial ischaemia/reperfusion injury.

Melanocortin peptides exert, in rats, a protective effect in myocardial ischaemia followed by reperfusion, or permanent occlusion of a coronary artery. Moreover, melanocortins have an anti-shock effect. Since the mechanism of the life-saving effect of these peptides in haemorrhagic shock includes an essential brain loop, we aimed to determine whether the central nervous system (CNS) is also involved in the protective effect against the outcome of short-term myocardial ischaemia followed by reperfusion. Ischaemia was produced in anaesthetized rats by ligature of the left anterior descending coronary artery for 5 min. Reperfusion-induced ventricular tachycardia (VT), ventricular fibrillation (VF) and lethality, and the time-course of arterial blood pressure over 5 min following reperfusion were evaluated. Groups of 8-14 rats were used. Intravenous (i.v.) injection of ACTH-(1-24) (0.16-0.48 mg/kg) during the ischaemic period dose dependently reduced the incidence of VT, VF and of lethality. In saline-treated rats, coronary reperfusion caused VT in 100% animals, VF in 86%, and death in 86%. The highest dose of ACTH-(1-24) (0.48 mg/kg) completely prevented the occurrence of VT, VF and death in all rats (P<0.005). Moreover, the melanocortin peptide prevented the fall in mean arterial pressure (MAP) occurring during reperfusion. Treatment with ACTH-(1-24) by the intracerebroventricular (i.c.v.) route also reduced the incidence of VT, VF and lethality, and prevented the fall in MAP in a dose dependent manner. Complete (100%) protection occurred with an i.c.v. dose (0.048 mg/kg) 10 times less than that needed by the i.v. route. The present data show that in the protective effect of melanocortin peptides against the injury after myocardial ischaemia/reperfusion, the i.c.v. route of administration is more effective than the i.v. route. They suggest that a CNS mechanism, not yet identified, may be involved.