Venodilator action of an organotransition-metal nitrosyl complex

The individual survival benefits of tumor necrosis factor soluble receptor and fluid administration are not additive in a rat sepsis model

BACKGROUND

Tumor necrosis factor (TNF) antagonists [e.g., TNF soluble receptor (TNFsr)] improved survival in preclinical but not clinical sepsis trials. However fluid support-itself beneficial-is standard clinically but rarely employed in preclinical sepsis models. We hypothesized that these therapies may not have additive benefit.

METHODS AND RESULTS

Antibiotic-treated rats (n = 156) were randomized to intratracheal or intravenous Escherichia coli challenges (>LD50) and either placebo or TNFsr and 24 h fluid treatments alone or together. The survival effects of these therapies did not differ significantly comparing challenge routes. When averaged across route, while TNFsr or fluid alone decreased the hazard ratio of death significantly [ln ± standard error (SE): -0.65 ± 0.30 and -0.62 ± 0.30, respectively, p ≤ 0.05], together they did not (p = 0.16). Furthermore, the observed effect of TNFsr and fluid together on reducing the hazard ratio was significantly less than estimated (-0.37 ± 0.29 versus -1.27 ± 0.43, respectively, p = 0.027) based on TNFsr and fluid alone. While each treatment increased central venous pressure at 6 and 24 h, the observed effects of the combination were also less than estimated ones (p ≤ 0.0005).

CONCLUSIONS

The individual survival benefits of TNFsr and fluids were not additive in this rat sepsis model. Investigating new sepsis therapies together with conventional ones during preclinical testing may be informative.

Effect of intermedin/adrenomedullin-2 on venous tone in conscious rats

We investigated the effect of intermedin/adrenomedullin-2 (3 and 10 nmol/kg, i.v.), a member of the calcitonin gene-related peptide family, relative to the vehicle (0.9% NaCl) on mean circulatory filling pressure (index of venous tone) in conscious rats: intact (unblocked) or ganglionic blocked through treatment with mecamylamine (10 mg/kg, i.v.) and noradrenaline (4 microg/kg/min, i.v.). In intact rats, both doses of intermedin/adrenomedullin-2 reduced mean arterial pressure (-14+/-3, -30+/-3 mmHg), but did not alter mean circulatory filling pressure; the high dose also increased heart rate. In ganglionic-blocked rats, both doses decreased mean arterial pressure (-22+/-3, -46+/-5 mmHg) and the high dose also decreased mean circulatory filling pressure (-2.81+/-0.82 mmHg), but neither dose affected heart rate. The vehicle did not have any effects in any of the groups. In addition, intermedin/adrenomedullin-2 did not have any effect on blood volume in both intact and ganglion-blocked rats. The results show that intermedin/adrenomedullin-2 is a dilator of arterial resistance and capacitance vessels.

Static filling pressure in patients during induced ventricular fibrillation

The static pressure resulting after the cessation of flow is thought to reflect the filling of the cardiovascular system. In the past, static filling pressures or mean circulatory filling pressures have only been reported in experimental animals and in human corpses, respectively. We investigated arterial and central venous pressures in supine, anesthetized humans with longer fibrillation/defibrillation sequences (FDSs) during cardioverter/defibrillator implantation. In 82 patients, the average number of FDSs was 4 +/- 2 (mean +/- SD), and their duration was 13 +/- 2 s. In a total of 323 FDSs, arterial blood pressure decreased with a time constant of 2.9 +/- 1.0 s from 77.5 +/- 34.4 to 24.2 +/- 5.3 mmHg. Central venous pressure increased with a time constant of 3.6 +/- 1.3 s from 7.5 +/- 5.2 to 11.0 +/- 5.4 mmHg (36 points, 141 FDS). The average arteriocentral venous blood pressure difference remained at 13.2 +/- 6.2 mmHg. Although it slowly decreased, the pressure difference persisted even with FDSs lasting 20 s. Lack of true equilibrium pressure could possibly be due to a waterfall mechanism. However, waterfalls were identified neither between the left ventricle and large arteries nor at the level of the diaphragm in supine patients. We therefore suggest that static filling pressures/mean circulatory pressures can only be directly assessed if the time after termination of cardiac pumping is adequate, i.e., >20 s. For humans, such times are beyond ethical options.

Venous dilator effect of apelin, an endogenous peptide ligand for the orphan APJ receptor, in conscious rats

Apelin is an endogenous depressor peptide for the G protein-coupled APJ receptor. Our hypothesis is that apelin is a venodilator, and it reduces mean circulatory filling pressure (MCFP; index of venous tone). Dose-response curves of apelin (10, 20 and 40 nmol/kg) or vehicle (0.9% NaCl) were constructed in two groups each of conscious, unrestrained rats: unblocked rats and rats pretreated with mecamylamine (Mec; ganglionic blocker) and noradrenaline (NA; to restore vascular tone). The vehicle had no effects in the unblocked or ganglionic-blocked rats. Apelin decreased mean arterial pressure (MAP) and increased heart rate (HR), but it did not alter mean circulatory filling pressure in the unblocked rats. In the ganglionic-blocked rats, apelin did not alter heart rate but decreased mean arterial pressure and mean circulatory filling pressure. These results show that apelin is an arterial and venous dilator in vivo. The depressor effect of apelin is accompanied by tachycardia which is abolished by ganglion blockade.

Effect of nociceptin/orphanin FQ on venous tone in conscious rats

Nociceptin (orphanin FQ) is an endogenous agonist for the opioid receptor-like1 (ORL1) receptor. We investigated the effects of nociceptin on mean circulatory filling pressure, an index of venous tone. The effects of nociceptin (10, 30 nmol/kg, i.v.) and the vehicle (0.9% NaCl) on mean arterial pressure, heart rate and mean circulatory filling pressure were examined in two groups each of conscious rats: rats with, or without, ganglionic blockade through pretreatment with mecamylamine (1 mg/kg, i.v.) and noradrenaline (2 microg/kg min, i.v.). In the unblocked rats, both doses of nociceptin decreased mean arterial pressure and heart rate, and the high dose also decreased mean circulatory filling pressure. In the ganglionic-blocked rats, nociceptin did not alter heart rate but caused greater reductions of mean arterial pressure and mean circulatory filling pressure. The vehicle had no effects in any group. Therefore, nociceptin is a depressor agent with prominent direct venodilator and bradycardic action.