Endothelin plays a role in contractions of isolated pig pulmonary vessels induced by diaspirin cross-linked hemoglobin

Investigation of the effects of a polymerised bovine haemoglobin solution on tension in isolated canine saphenous artery

OBJECTIVES

To investigate the vasoconstriction induced by a polymerised bovine haemoglobin solution, Hb-200, in isolated canine arteries.

METHODS

Rings of canine saphenous artery, from euthanatized dogs, were mounted between stainless steel wires in Krebs' solution (95% O2 , 5% CO2 , 37°C) for isometric tension recording. Following incubation with Hb-200, cumulative concentration response curves to phenylephrine (vasoconstrictor) and acetylcholine (vasodilator) were investigated. Responses to acute addition of Hb-200 were also examined in pre-constricted or pre-dilated arteries. Responses were further studied in the presence or absence of the endothelium, inhibitors of endothelium-dependent vasodilation (L-NAME, charybdotoxin and apamin), an endothelin antagonist (BQ-788) and the antioxidant superoxide dismutase.

RESULTS

Incubation with Hb-200 (0·2 or 2 g/L) significantly enhanced phenylephrine-induced contraction (decreasing half maximal effective concentration, EC50 , P=0·0035) and inhibited acetylcholine-induced relaxation (increasing EC50 , P<0·0001). Acute addition of Hb-200 (0·2 or 2 g/L) significantly increased tension in pre-constricted arteries (P=0·0059) and reversed relaxation in pre-dilated arteries (P=0·0005). These acute responses were abolished in endothelium-denuded arteries and arteries incubated with L-NAME. Responses to Hb-200 were unaffected by incubation with charybdotoxin and apamin, BQ-788, or superoxide dismutase.

CLINICAL SIGNIFICANCE

Low concentrations of Hb-200 enhance vasoconstriction in isolated canine saphenous artery, primarily by antagonism of nitric oxide. This effect may be detrimental in some dogs (e.g. those at risk of volume overload) but beneficial in others (e.g. those in septic shock).

Hemodynamic response and oxygen transport in pigs resuscitated with maleimide-polyethylene glycol-modified hemoglobin (MP4)

Cell-free Hb increases systemic and pulmonary pressure and resistance and reduces cardiac output and heart rate in animals and humans, effects that have limited their clinical development as “blood substitutes.” The primary aim of this study was to evaluate the hemodynamic response to infusion of several formulations of a new polyethylene glycol (PEG)-modified human Hb [maleimide PEG Hb (MalPEGHb)] in swine, an animal known to be sensitive to Hb-induced vasoconstriction. Anesthetized animals underwent controlled hemorrhage (50% of blood volume), followed by resuscitation (70% of shed volume) with 10% pentastarch (PS), 4% MalPEG-Hb in lactated Ringer (MP4), 4% MalPEG-Hb in pentastarch (HS4), 2% MalPEG-Hb in pentastarch (HS2), or 4% stroma-free Hb in lactated Ringer solution (SFH). Compared with baseline, restoration of blood volume after resuscitation was similar and not significantly different for the PS (103%), HS2 (99%), HS4 (106%), and MP4 (87%) animals but significantly less for the SFH animals (66%) ( P < 0.05). All solutions that contained MalPEG-Hb restored mean arterial and pulmonary pressure and cardiac output. Systemic vascular resistance was unchanged, and pulmonary arterial pressure and resistance were increased slightly. Both systemic and pulmonary vascular resistance increased significantly in animals that received SFH, despite less adequate blood volume restoration. Oxygen consumption was maintained in all animals that received MalPEG-Hb, but not PS. Base excess improved only with MalPEG-Hb and PS, but not SFH. Red blood cell O2extraction was significantly increased in animals that received Hb, regardless of formulation. These data demonstrate resuscitation with MalPEG-human Hb without increasing systemic vascular resistance and support our previous observations in animals suggesting that the efficacy of low concentrations of PEG-Hb in the plasma results from reduced vasoconstriction.