The Pharmacokinetics of Hemoglobin-Based Oxygen Carrier Hemoglobin Glutamer-200 Bovine in the Horse

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).

Administration of bovine polymerized haemoglobin before and during coronary occlusion reduces infarct size in rabbits

BACKGROUND

Haemoglobin-based oxygen carriers (HBOC) seem to increase the risk of mortality and myocardial infarction in clinical trials. Therefore, we designed this randomized placebo-controlled animal study to evaluate the effects of prophylactic and therapeutic administration of HBOC in a myocardial ischaemia-reperfusion model with respect to infarct size and areas of impaired perfusion (no reflow, NR).

METHODS

Thirty-two anaesthetized, mechanically ventilated rabbits were randomized to one of the four groups. Group G1 received 0.4 g kg(-1) i.v. HBOC-200 25 min before coronary artery occlusion, G2 received the same dose i.v. 10 min after occlusion, and G3 and 4 received i.v. saline. G1, 2, and 3 were subjected to 30 min occlusion of left coronary artery followed by 240 min of reperfusion. G4 was treated without ischaemia-reperfusion. Measurement included assessment of the area at risk and infarct size using triphenyltetrazolium chloride stain and areas of NR using thioflavin stain. Ischaemia-reperfusion was confirmed by microspheres technique.

RESULTS

Infarct size as a percentage of the area at risk was significantly reduced in G1 [25 (sd 13)%, P=0.026] and G2 [22 (20)%, P=0.009] compared with G3 [48 (17)%]. The areas of NR in percentage of the area at risk [G1, 26 (15)%; G2, 34 (22)%; G3, 36 (12)%; G4, 5 (3)%] did not differ between the groups of animals undergoing coronary occlusion and reperfusion.

CONCLUSIONS

Prophylactic and therapeutic administration of HBOC-200 reduces infarct size in myocardial ischaemia and reperfusion in rabbits. This reduction of infarct size is not accompanied by an improvement of areas of NR.

Pharmacokinetics of methylprednisolone acetate after intra-articular administration and its effect on endogenous hydrocortisone and cortisone secretion in horses

OBJECTIVE

To determine the pharmacokinetics of methylprednisolone (MP) and develop a pharmacokinetic-pharmacodynamic model of the related changes in plasma concentrations of endogenous hydrocortisone (HYD) and cortisone (COR) following intra-articular administration of methylprednisolone acetate (MPA) in horses.

ANIMALS

6 Thoroughbreds.

PROCEDURES

In each horse, 200 mg of MPA was injected intrasynovially into a carpal joint, and plasma MP, HYD, and COR concentrations were determined via liquid chromatography-mass spectrometry.

RESULTS

A 5-compartment pharmacokinetic-pharmacodynamic model was used to describe the concatenated changes in the plasma concentrations of MP, HYD, and COR and to estimate the instantaneous rate of endogenous HYD production. The median transfer half-life (t(1/2t)) of methylprednisolone from the joint to plasma and elimination half-life (t(1/2e)) from plasma were 1.7 and 19.2 hours, respectively. Maximum plasma concentration of methylprednisolone was 7.26 +/- 3.3 ng/mL at 8 hours, which decreased to 0.11 +/- 0.08 ng/mL at 144 hours after injection. At 3 hours after MPA administration, plasma COR and HYD concentrations were significantly decreased from baseline values (from 2.9 +/- 0.28 ng/mL to 2.10 +/- 1.0 ng/mL and from 61.1 +/- 18.9 ng/mL to 25.7 +/- 12.1 ng/mL, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

The sensitivity of the analytic method used allowed complete description of the related kinetics of MP, HYD, and COR following intra-articular administration of MPA. A single intra-articular administration of MPA profoundly affected the secretion of HYD and COR in horses; secretion of endogenous corticosteroids remained suppressed for as long as 240 hours after injection.