Pharmacokinetic Studies in the Rat on a O-Raffinose Polymerized Human Hemoglobin

Abstract

We have studied the plasma half-life (T_1/2), oxygen-binding affinity (P₅₀), organ distribution, and excretion of the individual molecular weight (MW) components of human hemoglobin polymerized with periodate-oxidized, ring-opened rafflnose (oR poly-Hb), following transfusion in the rat. The model was an isovolemic 50% exchange transfusion in the conscious, chronically catheterized rat. Total plasma Hb levels yielded a (T_1/2) of 10 to 11 hr for oR poly-Hb. The T_1/2 values of individual MW components of the poly-Hb as determined by size-exclusion HPLC were approximately: 4 hr for the monomeric fraction (Hb)₁, 9 hr for the dimer (Hb)₂, and 15 hr for the fraction representing trimers to nanomers (Hb)_3–9. The P₅₀, values of plasma samples containing oR poly-Hb (collected from 0–24 hr after exchange) remained unchanged at 28 ± 3 mmHg. oR stabilized and polymerized Hb were not excreted via the kidneys. Hepatic and renal distribution as well as plasma and renal clearance were determined by liquid scintillation counting using individual tritium [³H] labelled MW components purified from [³H]-oR poly-Hb: (Hb)_1/2, (Hb)₁, (Hb)₂, (Hb)_3&4, and (Hb)₉. In kidney, uptake (determined by the relative concentration of radioactivity) decreased with increasing MW of the labelled component. Conversely, in liver, uptake increased with increasing MW. Plasma and renal clearance results were consistent with those obtained by HPLC analysis. Hematocrit levels returned from a 20% post-transfusion level to normal pre-transfusion levels (44%) within 10 days after the exchange.