W. Ferrari

α-MSH and other ACTH fragments improve cardiovascular function and survival in experimental hemorrhagic shock

Hypovolemic shock was produced in rats by withdrawing about 50% of the estimated total blood volume. Following mean arterial pressure stabilization in the range of 15–25 mm Hg, with a pulse pressure of 7–12 mm Hg, the rats were given intravenous bolus injections either of ACTH fragments or of saline. The following ACTH fragments or analogs were used: ACTH-(4–10), α-MSH, ACTH-(1–16), ACTH-(1–17), ACTH(1–18), [Nle4, D-Phe7]α-MSH, [β-Ala1,Lys17]ACTH-(1–17)-4-amino-n-butilamide (alsactide). ACTH-(1–24) and human synthetic ACTH-(1–39) were used for comparison. All animals treated with saline died in 22.51 ± 3.62 min. Treatment with ACTH fragments (160 μg/kg i.v.) increased blood pressure and pulse amplitude, the effect starting within a few minutes, gradually increasing, and reaching a maximum in 15–30 min. The blood and pulse pressure increases were sustained, remaining almost stable until the end of the 2 h recording. Two out of nine rats treated with alsactide, which was the least active, died within 2 h after treatment, while all rats treated with the other ACTH fragments or analogs were still surviving at that time. Both on a weight and on a molar basis, the most active was ACTH-(1–24), followed by ACTH-(1–16), by the α-MSH analog [Nle4,D-Phe7]ACTH-(1–13), by ACTH-(1–18) and by ACTH-(1–17). The present results show that melanocortins reverse otherwise fatal hypovolemic shock, and suggest a new therapeutic approach for shock treatment. Since endogenous opioids play a key role in the pathophysiology of shock, these data provide further experimental support to the hypothesis of a melanocortin-opioid homeostatic system, involved in many important body functions.

Adrenocorticotropin reversal of experimental hemorrhagic shock is antagonized by morphine

ACTH-(1-24) dose-dependently improved cardiovascular function in rats and dogs subjected to experimental hemorrhagic shock, and intravenous dose of 160 and 100/microgram/kg, respectively, completely restoring arterial blood pressure and pulse amplitude. All saline-treated animals died within 30 min of bleeding, while all ACTH-treated animals were still alive at the end of the observation period (2 hr). The injection of ACTH-(1-24) also dramatically improved the respiratory function. Morphine, i.v. injected into rats at the dose of 2.5 mg/kg, antagonised the effect of ACTH-(1-24) to a greater or lesser degree, depending on the dose of peptide employed: at 160/microgram/kg, antagonism was complete, at 320/microgram/kg antagonism was only partial, while at 480/microgram/kg antagonism was almost completely overcome. These data further support the idea that melanocortins are physiological antagonists of opioids, and suggest that melanocortin peptides may prove to be rational and effective drugs in the treatment of hypovolemic shock.

Reversal of haemorrhagic shock in rats by cholinomimetic drugs.

1 In an experimental model of haemorrhagic shock resulting in the death of all rats within 20–30 min, the intravenous (i.v.) injection of the tertiary amine cholinesterase inhibitor physostigmine (17–70 μgkg−1) induced a prompt, sustained and dose‐dependent improvement of cardiovascular and respiratory function, with marked increase in the volume of circulating blood and survival of all treated animals, at least for the 2 h of observation. 2 Similar results were obtained with the i.v. injection of the cholinoceptor agonist oxotremorine (5–25 μg kg−1), while neostigmine (54 or 70 μgkg−1), a quaternary cholinesterase inhibitor which cannot cross the blood‐brain barrier, had negligible effects. 3 The anti‐shock activities of oxotremorine and physostigmine were blocked by the intracerebroventricular injection of either of the combined nicotinic and M2‐muscarinic receptor antagonists gallamine and pancuronium, or of the nicotinic antagonist mecamylamine. They were also blocked by intraperitoneal injection of the adrenergic neurone blocking agent guanethidine, but they were not antagonized by either the combined M1‐ and M2‐muscarinic receptor antagonist atropine, the M1‐muscarinic receptor antagonist pirenzepine, or the M2‐muscarinic receptor antagonist 4‐diphenylacetoxy‐N‐methylpiperidine methobromide. 4 It is concluded that cholinomimetic drugs can reverse hypovolaemic shock through central activation (seemingly mediated by nicotinic receptors) of sympathetic tone, with mobilization and redistribution of the residual blood.

The adrenocorticotropic hormone (ACTH)-induced reversal of hemorrhagic shock.

Adrenocorticotropic hormone (ACTH), while having negligible effects on cardiovascular function in the intact animal, induces a potent and sustained reversal of an otherwise invariably, rapidly fatal condition of hemorrhage-induced hypovolemic shock, in rats and dogs. The main site(s) of action are at the peripheral level; however, subsidiary site(s) of action in the CNS cannot be excluded. The studies on the mechanism of action indicate that the ACTH-induced reversal of hemorrhagic shock (a) is an extra-hormonal, adrenal-independent effect, because it is not affected by adrenalectomy and is shared by many ACTH-fragments practically devoid of corticotropic activity; (b) is antagonized by morphine in a surmontable way; (c) needs the functional integrity of the sympathetic nervous system (it is prevented by guanethidine, reserpine, and clonidine) and the availability of peripheral alpha-adrenoceptors (it is antagonized by dibenamine, prazosin and yohimbine, but not by practolol); (d) requires the integrity of afferent vagal fibers (it is almost completely abolished by vagotomy); (e) involves central cholinergic networks (it is antagonized by atropine sulphate, but not by atropine methyl bromide; and it is prevented by the intracerebroventricular injection of hemicholinium-3); (f) is associated with a massive increase in the volume of circulating blood, likely due to a mobilization from peripheral pooling sites (it is largely prevented by splenectomy or by suprahepatic veins ligature, and is associated with a restoration of the venous blood flow in peripheral vascular beds and with a normalization of venous PO2); (g) is associated with a restoration of heart and spleen adrenoceptors, whose number is significantly decreased during hemorrhagic shock. The survival time of hemorrhage-shocked animals, which is 26 +/- 3 min in controls, is greatly prolonged (44 +/- 18 h) by ACTH, provided that the treatment is made within 5-10 min after bleeding. Finally, in animals treated with ACTH within 5-10 min after bleeding, blood reinfusion retains its effectiveness and reverse shock even if performed 2-5 h later.

ACTH-(1–24) restores blood pressure in acute hypovolaemia and haemorrhagic shock in humans

Although the rote of opioids in autonomic regulation of cardiovascular function and blood pressure is controversial [1], many recent data suggest that endogenous opioid systems play a key role in the pathophysiology of circulatory :shock [2]. There is evidence that the opioid antagonist naloxone improves cardiovascular function and survival in many animal models of shock [2] and, albeit less consistently [3], in shock states in man [4]. There is also increasing evidence of reciprocal functional antagonism between opioid peptides and melanopeptides, the neuropeptides of the ACTH-MSH family [5]. The intravenous injection of ACTH and of shorter melanopeptides [ACTH-(1-24),-(I-18),-(1-17), -(I16)<(1 13) and-(4I 0)] in doses of 40-160 ~g/kg, has recently been shown to produce a prompt and sustained improvement in blood pressure, pulse amplitude and respiratory function, and to prevent death, in dogs and rats (intact or adrenalectomized) bled to otherwise fatal haemorrhagic shock [6-8]. Since ACTH-(1-24) is known to be devoid of acute toxicity and it is reported to be well tolerated by humans up to 100 mg i.v. [9], it has now been administered to patients with acute hypovolaemic hypotension, and in a single case of haemorrhagic shock.

Early treatment with ACTH-(1-24) in a rat model of hemorrhagic shock prolongs survival and extends the time-limit for blood reinfusion to be effective.

The ability of ACTH-(1-24) to prolong survival and to extend the deadline for effective blood reinfusion has been studied in a model of lethal hypovolemic shock in the rat. Anesthetized rats were bled to a mean arterial pressure of 18 to 25 mm Hg and then subjected to one of the following iv treatments: a) saline; b) ACTH-(1-24), 160 micrograms/kg; c) blood reinfusion; d) ACTH-(1-24), 160 micrograms/kg; c) blood reinfusion; d) ACTH-(1-24), with saline 5 min after bleeding died within 0.05 h. On the other hand, the treatment with ACTH-(1-24) induced an almost complete and sustained recovery of cardiovascular and respiratory functions associated with a survival time of 44 +/- 18 h, while four of six rats reinfused with the withdrawn blood were still alive 15 days later. The time-lapse between bleeding and treatment was of crucial importance, and neither ACTH-(1-24) injection nor blood reinfusion had any effect if performed 25 min after bleeding. However, treatment with ACTH-(1-24) shortly after bleeding (5 min) greatly improved the effect of a later blood reinfusion. These data indicate that ACTH-(1-24) can prolong survival and permit the time-lapse between blood loss and blood reinfusion to be extended.

Involvement of the sympathetic nervous system in the cardiovascular effects of ACTH-(1-24) during hemorrhagic shock in rats

SummaryIn urethane-anesthetized rats, removal of about 50% of the total blood volume over a period of 25 – 30 min caused hypovolemic shock, with extreme hypotension (MAP = 18–25 mmHg and death of all animals within 22±5 min. The i.v. injection of ACTH-(1-24) in the dose range of 40–160 μg/kg induced a sustained, dose-dependent, and, at the highest dose used, an almost complete recovery of blood pressure, and 100% survival, at least for 2 h after treatment. The effect of ACTH-(1–24) was completely prevented by reserpine (5 mg/kg) and clonidine (0.1 mg/kg), significantly reduced by prazosin (0.1 mg/kg), dibenamine (15 mg/kg) and i.v. yohimbine (1 mg/kg) and unaffected by i.c.v. yohimbine (0.2 mg/kg) and i.v. practolol (15 mg/kg). These data suggest that the effect of ACTH-(1–24) in hypovolemic shock depends on the functional integrity of the sympathetic nervous system and is mediated through an activation of peripheral alpha-adrenoceptors.

Caerulein and cholecystokinin reverse experimental hemorrhagic shock

Intravenously injected cholecystokinin octapeptide (CCK-8) (5-20/micrograms/kg) and caerulein (1.25-10/micrograms/kg) caused a prompt, dose-dependent and sustained improvement in blood pressure, pulse amplitude and survival in rats subjected to otherwise invariably fatal hemorrhagic shock.

Influence of vagotomy and of atropine on the anti-shock effect of adrenocorticotropin

ACTH-(1-24), intravenously injected at the dose of 160 micrograms/kg to rats bled to the point of otherwise irreversible hypovolemic shock, causes a prompt and sustained increase in blood pressure and pulse amplitude, all treated rats surviving at the end of the experiment (2 hr). Bilateral vagotomy, as well as atropine sulphate (2 mg/kg i.p. immediately before bleeding), almost completely abolishes the anti-shock activity of ACTH. These data indicate that a central cholinergic pathway and vagal afferent (but not efferent) fibers play an important role in the anti-shock effect of ACTH.

Sodium deoxycholate promotes the absorption of heparin administered orally, probably by acting on gastrointestinal mucosa, in rats

Sodium deoxycholate (DOC), selected as a promoter of gastrointestinal absorption of heparin, was administered orally to rats, followed, at increasing intervals, by heparin. Maximal plasma clearing activity (PC) was obtained with a 60-min interval, though PC was still elicited after 24 h, suggesting that DOC acts on the gastrointestinal mucosa. Inhibition of blood coagulation was also observed after oral heparin. The suggestion that DOC increases heparin absorptions is supported by increased plasma levels of heparin. No signs of several gastrointestinal damage were seen.